全文获取类型
收费全文 | 3407篇 |
免费 | 198篇 |
国内免费 | 9篇 |
专业分类
3614篇 |
出版年
2023年 | 50篇 |
2022年 | 129篇 |
2021年 | 164篇 |
2020年 | 100篇 |
2019年 | 127篇 |
2018年 | 125篇 |
2017年 | 86篇 |
2016年 | 133篇 |
2015年 | 169篇 |
2014年 | 190篇 |
2013年 | 276篇 |
2012年 | 230篇 |
2011年 | 269篇 |
2010年 | 135篇 |
2009年 | 130篇 |
2008年 | 133篇 |
2007年 | 149篇 |
2006年 | 124篇 |
2005年 | 109篇 |
2004年 | 102篇 |
2003年 | 86篇 |
2002年 | 90篇 |
2001年 | 48篇 |
2000年 | 30篇 |
1999年 | 38篇 |
1998年 | 25篇 |
1997年 | 23篇 |
1996年 | 13篇 |
1995年 | 11篇 |
1994年 | 22篇 |
1993年 | 13篇 |
1992年 | 17篇 |
1991年 | 17篇 |
1990年 | 13篇 |
1989年 | 14篇 |
1988年 | 24篇 |
1987年 | 13篇 |
1986年 | 18篇 |
1985年 | 17篇 |
1984年 | 9篇 |
1983年 | 14篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 13篇 |
1977年 | 12篇 |
1976年 | 10篇 |
1974年 | 6篇 |
1973年 | 10篇 |
1971年 | 7篇 |
排序方式: 共有3614条查询结果,搜索用时 15 毫秒
91.
92.
Liu Y Sainz IM Wu Y Pixley R Espinola RG Hassan S Khan MM Colman RW 《Experimental cell research》2008,314(4):774-788
Cleaved high molecular weight kininogen (HKa), as well as its domain 5 (D5), inhibits migration and proliferation induced by angiogenic factors and induces apoptosis in vitro. To study its effect on tube formation we utilized a collagen-fibrinogen, three-dimensional gel, an in vitro model of angiogenesis. HKa, GST-D5 and D5 had a similar inhibitory effect of tube length by 90+/-4.5%, 86+/-5.5% and 77+/-12.9%, respectively. D5-derived synthetic peptides: G440-H455 H475-H485 and G486-K502 inhibited tube length by 51+/-3.7%, 54+/-3.8% and 77+/-1.7%, respectively. By a comparison of its inhibitory potency and its sequences, a functional sequence of HKa was defined to G486-G496. PP2, a Src family kinase inhibitor, prevented tube formation in a dose-dependent manner (100-400 nM), but PP3 at 5 microM, an inactive analogue of PP2, did not. HKa and D5 inhibited Src 416 phosphorylation by 62+/-12.3% and 83+/-6.1%, respectively. The C-terminal Src kinase (Csk) inhibits Src kinase activity. Using a siRNA to Csk, expression of Csk was down-regulated by 86+/-7.0%, which significantly increased tube length by 27+/-5.8%. The addition of HKa and D5 completely blocked this effect. We further showed that HKa inhibited Src family kinase activity by disrupting the complex of uPAR, alphavbeta3 integrin and Src. Our results indicate that the anti-angiogenic effect of HKa and D5 is mediated at least in part through Src family kinases and identify a potential novel target for therapeutic inhibition of neovascularization in cancer and inflammatory arthritis. 相似文献
93.
Omeje Edwin Ogechukwu Osadebe Patience Ogoamaka Nworu Chukwuemeka Sylvester Amal Hassan Abdessamad Debbab Esimone Charles Okechukwu Akira Kawamura Proksch Peter 《Phytochemistry letters》2011,4(3):357-362
In search of immunomodulatory constituents from the Eastern Nigeria mistletoe, Loranthus micranthus Linn, two new stigmastane steroids: stigmast-7,20 (21)-diene-3β-hydroxy-6-one (1) and 3β-hydroxy-stigmast-23-ene (2); three (two new and one known) lupeol-based triterpenoid esters: 7β,15α-dihydroxyl-lup-20(29)-ene-3β-palmitate (3), 7β,15α-dihydroxyl-lup-20(29)-ene-3β-stearate (4) and 7β,15α-dihydroxyl-lup-20(29)-ene-3β-eicosanoate (5) were isolated and characterized following bioactivity-guided fractionation. The new compounds, 1, 2, 4 and 5 at concentrations of 10, 25 and 100 μg/ml were subjected to cell proliferation and early activation marker (CD69) expression studies in C57Bl/6 mice splenocytes using flow cytometry techniques against Lipopolysaccharide (LPS; 10 μg/ml) and Concanavalin A (ConA; 2 μg/ml) standards. The stigmastane steroids (1 and 2) at the highest concentration of 100 μg/ml showed statistically significantly (p < 0.05) stimulatory activity on the C57B1/6 splenocytes compared to the controls with values of 46 ± 0.76% and 43 ± 0.46% compared to 7.69 ± 0.41% recorded for the negative control. The novel lupeol esters, 4 and 5 at same concentration of 100 μg/ml exhibited lower stimulations of 30 ± 0.41% and 29 ± 0.17% respectively compared to the controls above. The CD69 expression assay at the above doses showed that all the compounds have minimal stimulation. The present study supports the observed immunomodulatory property of the Eastern Nigeria mistletoe and thus confirms the efficacy of this plant in mitigating against wide array of disease conditions orchestrated by immunodeficiency. 相似文献
94.
Adi L. Tarca Edgar Hernandez-Andrade Hyunyoung Ahn Maynor Garcia Zhonghui Xu Steven J. Korzeniewski Homam Saker Tinnakorn Chaiworapongsa Sonia S. Hassan Lami Yeo Roberto Romero 《PloS one》2016,11(11)
ObjectivesTo assess the value of single and serial fetal biometry for the prediction of small- (SGA) and large-for-gestational-age (LGA) neonates delivered preterm or at term.MethodsA cohort study of 3,971 women with singleton pregnancies was conducted from the first trimester until delivery with 3,440 pregnancies (17,334 scans) meeting the following inclusion criteria: 1) delivery of a live neonate after 33 gestational weeks and 2) two or more ultrasound examinations with fetal biometry parameters obtained at ≤36 weeks. Primary outcomes were SGA (<5th centile) and LGA (>95th centile) at birth based on INTERGROWTH-21st gender-specific standards. Fetus-specific estimated fetal weight (EFW) trajectories were calculated by linear mixed-effects models using data up to a fixed gestational age (GA) cutoff (28, 32, or 36 weeks) for fetuses having two or more measurements before the GA cutoff and not already delivered. A screen test positive for single biometry was based on Z-scores of EFW at the last scan before each GA cut-off so that the false positive rate (FPR) was 10%. Similarly, a screen test positive for the longitudinal analysis was based on the projected (extrapolated) EFW at 40 weeks from all available measurements before each cutoff for each fetus.ResultsFetal abdominal and head circumference measurements, as well as birth weights in the Detroit population, matched well to the INTERGROWTH-21st standards, yet this was not the case for biparietal diameter (BPD) and femur length (FL) (up to 9% and 10% discrepancy for mean and confidence intervals, respectively), mainly due to differences in the measurement technique. Single biometry based on EFW at the last scan at ≤32 weeks (GA IQR: 27.4–30.9 weeks) had a sensitivity of 50% and 53% (FPR = 10%) to detect preterm and term SGA and LGA neonates, respectively (AUC of 82% both). For the detection of LGA using data up to 32- and 36-week cutoffs, single biometry analysis had higher sensitivity than longitudinal analysis (52% vs 46% and 62% vs 52%, respectively; both p<0.05). Restricting the analysis to subjects with the last observation taken within two weeks from the cutoff, the sensitivity for detection of LGA, but not SGA, increased to 65% and 72% for single biometry at the 32- and 36-week cutoffs, respectively. SGA screening performance was higher for preterm (<37 weeks) than for term cases (73% vs 46% sensitivity; p<0.05) for single biometry at ≤32 weeks.ConclusionsWhen growth abnormalities are defined based on birth weight, growth velocity (captured in the longitudinal analysis) does not provide additional information when compared to the last measurement for predicting SGA and LGA neonates, with both approaches detecting one-half of the neonates (FPR = 10%) from data collected at ≤32 weeks. Unlike for SGA, LGA detection can be improved if ultrasound scans are scheduled as close as possible to the gestational-age cutoff when a decision regarding the clinical management of the patient needs to be made. Screening performance for SGA is higher for neonates that will be delivered preterm. 相似文献
95.
96.
Marwan Osman Dima El Safadi Sadia Benamrouz Karine Guyot Eduardo Dei-Cas El Moukhtar Aliouat Colette Creusy Hassan Mallat Monzer Hamze Fouad Dabboussi Eric Viscogliosi Gabriela Certad 《PloS one》2015,10(5)
Cryptosporidium spp. represent a major public health problem worldwide and infect the gastrointestinal tract of both immunocompetent and immunocompromised persons. The prevalence of these parasites varies by geographic region, and no data are currently available in Lebanon. To promote an understanding of the epidemiology of cryptosporidiosisin this country, the main aim of this study was to determine the prevalence Cryptosporidium in symptomatic hospitalized patients, and to analyze the genetic diversity of the corresponding isolates. Fecal specimens were collected in four hospitals in North Lebanon from 163 patients (77 males and 86 females, ranging in age from 1 to 88 years, with a mean age of 22 years) presenting gastrointestinal disorders during the period July to December 2013. The overall prevalence of Cryptosporidium spp. infection obtained by modified Ziehl-Neelsen staining and/or nested PCR was 11%, and children <5 years old showed a higher rate of Cryptosporidium spp. The PCR products of the 15 positive samples were successfully sequenced. Among them, 10 isolates (66.7%) were identified as C. hominis, while the remaining 5 (33.3%) were identified as C. parvum. After analysis of the gp60 locus, C. hominis IdA19, a rare subtype, was found to be predominant. Two C. parvum subtypes were found: IIaA15G1R1 and IIaA15G2R1. The molecular characterization of Cryptosporidium isolates is an important step in improving our understanding of the epidemiology and transmission of the infection. 相似文献
97.
Osamu Kaneko Lucy Gong Jingli Zhang Johanna K. Hansen Raffit Hassan Byungkook Lee Mitchell Ho 《The Journal of biological chemistry》2009,284(6):3739-3749
Ovarian cancer and malignant mesothelioma frequently express both
mesothelin and CA125 (also known as MUC16) at high levels on the cell surface.
The interaction between mesothelin and CA125 may facilitate the implantation
and peritoneal spread of tumors by cell adhesion, whereas the detailed nature
of this interaction is still unknown. Here, we used truncated mutagenesis and
alanine replacement techniques to identify a binding site on mesothelin for
CA125. We examined the molecular interaction by Western blot overlay assays
and further quantitatively analyzed by enzyme-linked immunosorbent assay. We
also evaluated the binding on cancer cells by flow cytometry. We identified
the region (296–359) consisting of 64 amino acids at the N-terminal of
cell surface mesothelin as the minimum fragment for complete binding activity
to CA125. We found that substitution of tyrosine 318 with an alanine abolished
CA125 binding. Replacement of tryptophan 321 and glutamic acid 324 with
alanine could partially decrease binding to CA125, whereas mutation of
histidine 354 had no effect. These results indicate that a
conformation-sensitive structure of the region (296–359) is required and
sufficient for the binding of mesothelin to CA125. In addition, we have shown
that a single chain monoclonal antibody (SS1) recognizes this CA125-binding
domain and blocks the mesothelin-CA125 interaction on cancer cells. The
identified CA125-binding domain significantly inhibits cancer cell adhesion
and merits evaluation as a new therapeutic agent for preventing or treating
peritoneal malignant tumors.Ovarian cancer largely is confined to the peritoneal cavity for much of its
natural history (1). Peritoneal
mesothelioma is a highly invasive tumor originating from the mesothelial
linings of the peritoneum (2).
The development of effective drug regimens against ovarian cancer and
mesothelioma has proven extremely difficult.Mesothelin was first identified in 1992 by the monoclonal antibody
(mAb)2 K1 that was
generated by the immunization of mice with human ovarian carcinoma (OVCAR-3)
cells (3). The mesothelin gene
encodes a 71-kDa precursor protein that is processed to a 40-kDa protein
termed mesothelin, which is a glycosylphosphatidylinositol (GPI)-anchored
glycoprotein present on the cell surface
(4). Mesothelin is a
differentiation antigen that is present on a restricted set of normal adult
tissues such as the mesothelium. In contrast, it is overexpressed in a variety
of cancers including mesothelioma, ovarian cancer, and pancreatic cancer
(5). In addition, mesothelin is
also expressed on the surface of non-small cell lung cancer cells
(6,
7), especially most lung
adenocarcinomas (8).We and others have shown that mesothelin is shed from tumor cells
(9,
10), and antibodies specific
for mesothelin are elevated in the sera of patients with mesothelioma and
ovarian cancer (11). Shed
serum mesothelin has been approved by the United States Food and Drug
Administration (FDA) as a new diagnostic biomarker in mesothelioma. In a Phase
I clinical study of an intrapleural interferon-β gene transfer using an
adenoviral vector in patients with mesotheliomas, we found that antitumor
immune responses targeting mesothelin were elicited in several patients
(12). A recent study indicated
that anti-mesothelin antibodies and circulating mesothelin relate to the
clinical state in ovarian cancer patients
(13). Pastan and colleagues
(14) developed an immunotoxin
(SS1P) with a Fv for mesothelin. Two Phase I clinical trials were completed at
the National Cancer Institute (National Institutes of Health, Bethesda, MD)
and there was sufficient antitumor activity of SS1P to justify a Phase II
trial. A chimeric antibody containing the mouse SS1 Fv for mesothelin was also
developed and is currently examined in a Phase I clinical trial for ovarian
cancer, mesothelioma, pancreatic cancer, and non-small cell lung cancer
(15).Mucins are heavily glycosylated proteins found in the mucus layer or at the
cell surface of many epitheliums
(16). There are two
structurally distinct families of mucins, secreted and membrane-bound forms.
CA125 (also known as MUC16) was first identified in 1981 by OC125, a mAb that
had been developed from mice immunized with human ovarian cancer cells
(17). The first cDNA clones
were reported in 2001 (18,
19). CA125 is a very large
membrane-bound cell surface mucin, with an average molecular mass between 2.5
and 5 million daltons. It is also heavily glycosylated with both
O-linked and N-linked oligosaccharides
(20). The peptide backbone of
CA125 is composed of the N-terminal region, extensive Ser/Thr/Pro-rich tandem
repeats (TR) with 156 amino acids each with both N- and
O-glycosylations, a SEA domain with high levels of
O-glycosylation and a C-terminal region with a short cytoplasmic tail
(19). The SEA domain was first
identified as a module commonly found in sea urchin sperm protein,
enterokinase and agrin (21,
22). The significance of the
SEA domain in CA125 is not clear.CA125 was originally used as a biomarker in ovarian cancer due to its high
expression in ovarian carcinomas and that it is shed into the serum
(23). A majority (88%) of
mesotheliomas are also CA125 positive on the cell membrane
(24). It was shown that 25% of
peritoneal mesotheliomas have high CA125 expression
(25). The intensity of CA125
membranous expression is indistinguishable between ovarian carcinomas and
peritoneal mesotheliomas. Gene expression analysis using the SAGE tag data
base has shown that mesothelioma has the second highest co-expression of CA125
and mesothelin after ovarian cancer
(26). Rump and colleagues
(26) have shown that
mesothelin binds to CA125 and that this interaction may mediate cell adhesion.
Scholler et al. (27)
recently showed that CA125/mesothelin-dependent cell attachment could be
blocked with anti-CA125 antibodies. Because mesothelin is present on
peritoneal mesothelium, there may be an important role for the
mesothelin-CA125 interaction in the tumorigenesis of ovarian cancer and
mesothelioma in the peritoneal cavity. The mesothelin binding site on CA125
may lie within the 156-amino acid TR units, indicating multimeric binding of
mesothelin to CA125. It has been found that the extraordinarily abundant
N-glycans on CA125, presumably in the TR region, are required for
binding to both glycosylated and non-glycosylated mesothelin
(28).Here, we identified the binding site of CA125 on mesothelin by use of
truncated mutagenesis and alanine replacement approaches. We measured binding
qualitatively by Western blot overlay assays and quantitatively by
enzyme-linked immunosorbent assay (ELISA). We also evaluated the interaction
of CA125 and mesothelin on cancer cells by flow cytometry. Furthermore, we
have shown that a single chain mAb (SS1) recognized the CA125-binding domain
and blocked the mesothelin-CA125 interaction on cancer cells. The identified
CA125-binding domain-Fc fusion protein also significantly inhibited cancer
cell adhesion. Our results suggest that conformation-sensitive structures of
the region (296–359) are required and sufficient for specific binding of
mesothelin to CA125. The domain proteins or the antibodies that block the
mesothelin-CA125 interaction merit evaluation as new therapeutic agents in
treating peritoneal malignant tumors. 相似文献
98.
Syed Mohammed Basheeruddin Asdaq Naira Nayeem Abida Md. Tauquir Alam Saleh I. Alaqel Mohd. Imran El-Waleed Elamin Hassan Syed Imam Rabbani 《Saudi Journal of Biological Sciences》2022,29(3):1456-1464
Tectona grandis L.f is a timber plant that is commonly referred to as teak. Its wide use as a medicine in the various indigenous systems makes it a plant of importance. A wide gamut of phytoconstituents like alkaloids, phenolic glycosides, steroids, etc. has been reported. A renewed interest in this plant has resulted in scientific investigations by various researchers towards the isolation and identification of active constituents along with scientific proof of its biological activities. The different parts of the plant have been scientifically evaluated for their antioxidant, antipyretic, analgesic, hypoglycemic, wound healing, cytotoxic, and many more biological activities. Documentation of this scientific knowledge is of importance to have consolidated precise information encompassing the various aspects of this plant, which could provide a base for future studies. This review is a compilation of the salient reports on these investigations concerning phytochemistry, the methods used to identify and quantify the constituents, the evaluation methods of the biological activity, toxicological studies, allergies and the patent/patent applications. This will further help researchers to find an area of the gap for future studies. 相似文献
99.
Devina Lobine Bryan Pairyanen Gokhan Zengin Mustafa Abdullah Yılmaz Rayene Ouelbani Souheir Bensari Gunes Ak Hassan H. Abdallah Muhammad Imran Mohamad Fawzi Mahomoodally 《化学与生物多样性》2021,18(4):e2000999
Toddalia asiatica (L.) Lam. is extensively used in traditional medicinal systems by various cultures. Despite its frequent use in traditional medicine, there is still a paucity of scientific information on T. asiatica growing on the tropical island of Mauritius. Therefore, the present study was designed to appraise the pharmacological and phytochemical profile of extracts (methanol, ethyl acetate and water) and essential oil obtained from aerial parts of T. asiatica. Biological investigation involved the evaluation of in vitro antioxidant and enzyme inhibitory potentials. The chemical profile of the EO was determined using gas chromatography coupled to mass spectrometry (GC/MS) analysis, while for the extracts, the total phenolic (TPC) and flavonoid content were quantified as well as their individual phenolic compounds by LC/MS/MS. Quinic acid, fumaric acid, chlorogenic acid, quercitrin and isoquercitrin were the main compounds in the extracts. Highest total phenolic (82.5±0.94 mg gallic acid equivalent (GAE/g)) and flavonoid (43.8±0.31 mg rutin equivalent (RE/g)) content were observed for the methanol extract. The GC/MS analysis has shown the presence of 26 compounds with linalool (30.9 %), linalyl acetate (20.9 %) and β-phellandrene (7.9 %) being most abundant components in the EO. The extracts and EO showed notable antioxidant properties, with the methanol extract proved to be superior source of antioxidant compounds. Noteworthy anti-acetylcholinesterase (AChE) and anti-butyrylcholinesterase (BChE) effects were recorded for the tested samples, while only the methanol and ethyl acetate extracts were active against tyrosinase. With respect to antidiabetic effects, the extracts and EO were potent inhibitors of α-glucosidase, while modest activity was recorded against α-amylase. Docking results showed that linalyl acetate has the highest affinity to interact with the active site of BChE with docking score of −6.25 kcal/mol. The findings amassed herein act as a stimulus for further investigations of this plant as a potential source of bioactive compounds which can be exploited as phyto-therapeutics. 相似文献
100.
Aklima Nasrin Mahbub Hassan Ping Ye 《Biochemical and biophysical research communications》2018,495(3):2118-2124
How to effectively delivering therapeutic agents, including γ-secretase inhibitors (GSIs), into live cells, remains a significant challenge. This study assessed the effect of Notch signaling inhibition by examining levels of the Notch1 intracellular domain (N1ICD) in cultured oral cancer cells analyzed with random stitched images (2D) and 3D visualizations using confocal microscopy and quantitative gene analysis. Substantially, we have developed a novel method to assist the delivery of γ-secretase inhibitor, DAPT, into live cells in the presence of an effective minimum concentration of Triton-X100 (0.001%) without damaging cell activity and membrane integrity assessed with cell proliferation assays. The images obtained in this study showed that DAPT alone could not block the γ-secretase inhibitor despite inhibiting cell growth. Further analysis of quantitative gene expressions of Notch signaling canonical pathway to verify the effectiveness of the novel method for delivering inhibitor into live cells, displayed deregulation of Notch1, Delta-like ligand 1 (DLL1) and hairy and enhancer of split 1 (Hes1). Our data suggest that Notch1/Hes1 signaling pathway is deactivated using DAPT with a low dose of Triton-X100 in this cancer cells. And the finding also suggests that Notch1 could be engaged by DLL1 to promote differentiation in oral cancer cells. Using this approach, we demonstrate that Triton-X100 is a promising and effective permeabilization agent to deliver γ-secretase inhibitor DAPT into live oral epithelial cells. This strategy has the potential to implicate in the treatment of cancer diseases. 相似文献