全文获取类型
收费全文 | 8313篇 |
免费 | 450篇 |
国内免费 | 24篇 |
专业分类
8787篇 |
出版年
2024年 | 11篇 |
2023年 | 106篇 |
2022年 | 278篇 |
2021年 | 398篇 |
2020年 | 373篇 |
2019年 | 520篇 |
2018年 | 412篇 |
2017年 | 300篇 |
2016年 | 407篇 |
2015年 | 446篇 |
2014年 | 538篇 |
2013年 | 689篇 |
2012年 | 681篇 |
2011年 | 687篇 |
2010年 | 353篇 |
2009年 | 311篇 |
2008年 | 338篇 |
2007年 | 353篇 |
2006年 | 308篇 |
2005年 | 259篇 |
2004年 | 200篇 |
2003年 | 155篇 |
2002年 | 144篇 |
2001年 | 39篇 |
2000年 | 33篇 |
1999年 | 35篇 |
1998年 | 27篇 |
1997年 | 24篇 |
1996年 | 21篇 |
1995年 | 11篇 |
1994年 | 17篇 |
1993年 | 19篇 |
1992年 | 20篇 |
1991年 | 23篇 |
1990年 | 19篇 |
1989年 | 18篇 |
1988年 | 13篇 |
1987年 | 15篇 |
1986年 | 19篇 |
1985年 | 21篇 |
1984年 | 17篇 |
1983年 | 10篇 |
1982年 | 15篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 10篇 |
1978年 | 14篇 |
1977年 | 11篇 |
1976年 | 10篇 |
1974年 | 10篇 |
排序方式: 共有8787条查询结果,搜索用时 15 毫秒
21.
Showket Hussain Vilas Nasare Malasha Kumari Shashi Sharma Mohammad Aijaz Khan Bhudev C. Das Mausumi Bharadwaj 《PloS one》2014,9(11)
Background
Human Papillomavirus (HPV) -associated cervical cancer is the second-most common cancer in women worldwide but it is the most frequent gynaecological cancer and cancer associated death in India women. The objective of this study was to assess knowledge about cervical cancer, HPV, HPV vaccine, HPV vaccine acceptance among school and undergraduates students and their parent’s perception about acceptance of HPV vaccine in Northern part of India (Delhi and NCR regions).Materials and Methods
A qualitative questionnaire based survey among 2500 urban/rural students aged 12–22 years was conducted.Results
Overall, a low frequency (15%) of HPV and cervical cancer awareness was observed in students and their parents. However, the awareness was much higher in females belonging to urban setup compared to boys with a perception that HPV causes cervical cancer in women only. Additionally, only (13%) participants who were aware of cervical cancer and HPV) were willing to accept HPV vaccination. Apparently, parents of female students were two times more willing to accept HPV vaccination for their ward than male students (p<0.001; OR 95%CI = 2.09 (1.58–2.76).Conclusion
Cervical cancer and HPV awareness among school, undergraduate students and also to their parents was found to be very low in this part of India. The level of awareness and education appears to be insignificant determinants in rural compared to urban setup. Better health education will be needed to maximize public awareness for cervical cancer prevention. 相似文献22.
Didem Turgut Coşan Faruk Saydam Cansu Özbayer Fulya Doğaner Ahu Soyocak Hasan Veysi Güneş İrfan Değirmenci Hülyam Kurt Mehmet Cengiz Üstüner Cengiz Bal 《Cytotechnology》2015,67(1):97-105
Hypertension is a major health problem with increasing prevalence around the world. Tannic acid is water-soluble polyphenol that is present in tea, green tea, coffee, red wine, nuts, fruits and many plant foods. It has been reported to serve as an antioxidant or a pro-oxidant depending on the type of cells and its concentration. The purpose of our study was to evaluate the effect of tannic acid on systolic blood pressure, oxidative stress and some urinary parameters in the rat model of essential hypertension. Blood pressures of all rats were measured using the tail-cuff method. The nitric oxide synthase inhibitor N (omega)-nitro-L-arginine was administered orally at a dose of 0.5 g/l/day for 15 days to rats in order to create an animal model of hypertension. Tannic acid was intraperitoneally injected at a dose of 50 mg/kg for 15 days. Superoxide dismutase, catalase activity and the concentration of malondialdehyde (MDA) were determined in blood plasma and homogenates of heart, liver and kidney. In order to evaluate renal functions, urine pH, urine volume, urine creatine, uric acid, and urea nitrogen values were measured. Compared with the hypertension group, a decrease in MDA concentrations of heart tissue (p < 0.01), urea nitrogen values (p < 0.01) and urine volumes (p < 0.001) were established in hypertension + tannic acid group. There was also a decrease in blood pressure values (20th and 30th days) of this group, but there was no a statistical difference according to hypertension group. The findings of our research show the effect of tannic acid in lowering blood pressure in hypertensive rats. 相似文献
23.
The electro-oxidation of epinephrine (EP), uric acid (UA), folic acid (FA), and their mixture has been studied by modified carbon nanotube paste electrode of 2,2'-[1,2-ethanediylbis(nitriloethylidyne)]-bis-hydroquinone using cyclic voltammetry, chronoamperometry and differential pulse voltammetry. This modified electrode exhibited potent and persistent electron mediating behavior followed by well-separated oxidation peaks towards EP, UA and FA with activation overpotential. For the ternary mixture containing EP, UA and FA the three compounds can be well separated from each other at the scan rate of 20mVs(-1). The obtained catalytic peak current, was linearly dependent on the EP, UA and FA concentrations in the range of 0.7-1200muM, 25-750muM and 15-800muM and the detection limits for EP, UA and FA were 0.216+/-0.004, 8.8+/-0.2 and 11.0+/-0.3muM, respectively. The diffusion coefficient (D), and the kinetic parameters such as electron transfer coefficient, (alpha) and heterogeneous rate constant, (k') for EP were also determined using electrochemical approaches. The modified electrode showed good sensitivity, selectivity and stability, and was employed for the determination of EP, UA and FA in the real samples. 相似文献
24.
Water buffalo lactoperoxidase (WBLP) was purified with Amberlite CG 50 H+ resin, CM Sephadex C-50 ion-exchange chromatography, and Sephadex G-100 gel filtration chromatography from skim milk. All purification steps of the WBLP were shown with SDS-PAGE and Rz (A412/A280) controlled the purification degree of the enzyme. Rz value for the purified WBLP was 0.8. To determine purification steps and kinetic properties, the activity of enzyme was measured by using 2,2-azino-bis-(3-ethylbenzthiazoline-6 sulfonic acid) diammonium salt (ABTS) as a choromogenic substrate at pH=6. Km, Vmax, optimum pH, and optimum temperature for the WBLP were found by means of graphics for ABTS as substrates. Optimum pH and optimum temperature of the WBLP were 6 and 60 degrees C, respectively. Km value at optimum pH and optimum temperature for the WBLP was 0.82 mM. Vmax value at optimum pH and optimum temperature was 13.7 micromol/mL x min. Km value at optimum pH and 25 degrees C for the WBLP was 0.77 mM. Vmax value at optimum pH and 25 degrees C was 4.83 micromol/mL x min. The purified WBLP was found to have high antibacterial activity in a thiocynate-H2O2 medium for some pathogenic bacteria, such as Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginose, Shigella sonnei, Staphylococcus saphrophyticus, Staphylococcus epidermidis, and Shigella dysenteriae and compared with well known antibacterial substances such as tetracycline, penicillin, and netilmicine. 相似文献
25.
Hakimelahi GH Shia KS Pasdar M Hakimelahi S Khalafi-Nezhad A Soltani MN Mei NW Mei HC Saboury AA Rezaei-Tavirani M Moosavi-Movahedi AA 《Bioorganic & medicinal chemistry》2002,10(9):2927-2932
A novel cephalosporin derivative of monohydroguaiaretic acid (cephem-M(3)N, 7) was synthesized and found to possess anticancer activity against human leukemia (K562), breast carcinoma (MCF7), human lung cancer (A549), human colon cancer (Colo205) and pancreatic cancer cells (Capan2 and MiaPaCa2). A tumor targeting fusion protein (dsFv3-beta-lactamase) was also used in conjunction with cephem-based M(3)N 7 and its potency toward K562, MCF7, A549, Colo205, Capan2, and MiaPaCa2 was found to approach that of the free M(3)N (4). In the presence of dsFv3-beta-lactamase, tumor cells were found to be much more susceptible to conjugate 7 than normal human embryonic lung (HEL) cells and normal fibroblasts (Hef522). These notions provide a new approach to the use of nordihydroguaiaretic acid (NDGA) and its derivatives for antitumor therapy. 相似文献
26.
Mohammad Abdel-Halim Adam B. Keeton Evrim Gurpinar Bernard D. Gary Simon M. Vogel Matthias Engel Gary A. Piazza Frank M. Boeckler Rolf W. Hartmann Ashraf H. Abadi 《Bioorganic & medicinal chemistry》2013,21(23):7343-7356
Derivatives with scaffolds of 1,3,5-tri-substituted pyrazoline and 1,3,4,5-tetra-substituted pyrazoline were synthesized and tested for their inhibitory effects versus the p53+/+ HCT116 and p53?/? H1299 human tumor cell lines. Several compounds were active against the two cell lines displaying IC50 values in the low micromolar range with a clearly more pronounced effect on the p53+/+ HCT116 cells. The compound class shows excellent developability due to the modular synthesis, allowing independent optimization of all three to four key substituents to improve the properties of the molecules. 相似文献
27.
Kazim Sahin Mehmet Tuzcu Cemal Orhan Hasan Gencoglu Mustafa Ulas Mustafa Atalay Nurhan Sahin Armagan Hayirli James R. Komorowski 《Biological trace element research》2012,150(1-3):291-296
The objective of this experiment was to investigate the effects of supplemental chromium picolinate (CrPic) and chromium histidinate (CrHis) on nuclear factor-kappa B (NF-??B p65) and nuclear factor (erythroid-derived 2)-like 2 (Nrf2) signaling pathway in diabetic rat brain. Nondiabetic (n?=?45) and diabetic (n?=?45) male Wistar rats were either not supplemented or supplemented with CrPic or CrHis via drinking water to consume 8???g elemental chromium (Cr) per day for 12?weeks. Diabetes was induced by streptozotocin injection (40?mg/kg i.p., for 2?weeks) and maintained by high-fat feeding (40?%). Diabetes was associated with increases in cerebral NF-??B and 4-hydroxynonenal (4-HNE) protein adducts and decreased in cerebral nuclear factor of kappa light polypeptide gene enhancer in B cells inhibitor, alpha (I??B??) and Nrf2 levels. Both Cr chelates were effective to decrease levels of NF-??B and 4-HNE protein adducts and to increase levels of I??B?? and Nrf2 in the brain of diabetic rats. However, responses of these increases and decreases were more notable when Cr was supplemented as CrHis than as CrPic. In conclusion, Cr may play a protective role in cerebral antioxidant defense system in diabetic subjects via the Nrf2 pathway by reducing inflammation through NF-??B p65 inhibition. Histidinate form of Cr was superior to picolinate form of Cr in reducing NF-??B expression and increasing Nrf2 expression in the brain of diabetic rats. 相似文献
28.
29.
This study determined the full-length sequence of CYP2E1, one of six cytochrome P450 genes previously examined in camel tissues by western blotting and semi-quantitative PCR. The Camelus dromedarius CYP2E1 has an open reading frame of 1,473 bp, and the cDNA encodes a protein of 490 amino acid residues with a molecular weight of 54.8 kDa. The deduced amino acid sequence showed the highest identity with Bos taurus (88%), Sus scrofa (87%), and Homo sapiens (83%). In a phylogenetic analysis, the C. dromedarius CYP2E1 isoform was located beside cattle and pigs. The deduced amino acid sequence of camel CYP2E1 showed the conserved proline-rich amino terminus and the heme-binding signature localized near the carboxy terminus of the protein. 相似文献
30.
Vif counteracts a cyclophilin A-imposed inhibition of simian immunodeficiency viruses in human cells 下载免费PDF全文
Takeuchi H Buckler-White A Goila-Gaur R Miyagi E Khan MA Opi S Kao S Sokolskaja E Pertel T Luban J Strebel K 《Journal of virology》2007,81(15):8080-8090
Vif is a primate lentiviral accessory protein that is crucial for viral infectivity. Vif counteracts the antiviral activity of host deaminases such as APOBEC3G and APOBEC3F. We now report a novel function of African green monkey simian immunodeficiency virus (SIVagm) Vif that promotes replication of SIVagm in human cells lacking detectable deaminase activity. We found that cyclophilin A (CypA) was excluded from wild-type SIV particles but was efficiently packaged into vif-deficient SIVagm virions. The presence of CypA in vif-defective SIVagm was correlated with reduced viral replication. Infection of CypA knockout Jurkat cells or treatment of Jurkat cells with cyclosporine A eliminated the Vif-sensitive inhibition and resulted in replication profiles that were similar for wild-type and vif-deficient SIVagm. Importantly, the inhibitory effect of CypA was restricted to virus-producing cells and was TRIM5alpha independent. The abilities of SIVagm Vif to inhibit encapsidation of CypA and to increase viral infectivity were shared by rhesus macaque SIV Vif and thus seem to be general properties of SIV Vif proteins. Exclusion of CypA from SIVagm particles was not associated with intracellular degradation, suggesting a mode of Vif action distinct from that proposed for APOBEC3G. This is the first report of a novel vif-sensitive antiviral activity of human CypA that may limit zoonotic transmission of SIV and the first demonstration of CypA encapsidation into a virus other than human immunodeficiency virus type 1. 相似文献