全文获取类型
收费全文 | 23314篇 |
免费 | 1381篇 |
国内免费 | 893篇 |
出版年
2023年 | 355篇 |
2022年 | 538篇 |
2021年 | 658篇 |
2020年 | 651篇 |
2019年 | 911篇 |
2018年 | 920篇 |
2017年 | 583篇 |
2016年 | 582篇 |
2015年 | 687篇 |
2014年 | 1420篇 |
2013年 | 1820篇 |
2012年 | 1071篇 |
2011年 | 1436篇 |
2010年 | 1024篇 |
2009年 | 1106篇 |
2008年 | 1127篇 |
2007年 | 1144篇 |
2006年 | 979篇 |
2005年 | 870篇 |
2004年 | 740篇 |
2003年 | 652篇 |
2002年 | 533篇 |
2001年 | 345篇 |
2000年 | 325篇 |
1999年 | 325篇 |
1998年 | 291篇 |
1997年 | 249篇 |
1996年 | 245篇 |
1995年 | 212篇 |
1994年 | 204篇 |
1993年 | 205篇 |
1992年 | 176篇 |
1991年 | 170篇 |
1990年 | 139篇 |
1989年 | 121篇 |
1988年 | 105篇 |
1987年 | 99篇 |
1986年 | 99篇 |
1985年 | 197篇 |
1984年 | 365篇 |
1983年 | 295篇 |
1982年 | 283篇 |
1981年 | 215篇 |
1980年 | 189篇 |
1979年 | 165篇 |
1978年 | 133篇 |
1977年 | 134篇 |
1976年 | 122篇 |
1975年 | 101篇 |
1973年 | 105篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Monika Primon Peter C. Huszthy Helena Motaln Krishna M. Talasila Ana Torkar Rolf Bjerkvig Tamara Lah Turnšek 《Experimental cell research》2013
Despite improved treatment options, glioblastoma multiforme (GBM) remains the most aggressive brain tumour with the shortest post-diagnostic survival. Arsenite (As2O3) is already being used in the treatment of acute promyelocytic leukaemia (APL), yet its effects on GBM have not been evaluated in detail. In U87MG cell monolayers, we have previously shown that arsenite cytotoxicity significantly increases upon transient inhibition of lysosomal protease Cathepsin L (CatL). As multicellular spheroids more closely represent in vivo tumours, we aimed to evaluate the impact of permanent CatL silencing on arsenite treatment in U87MG spheroids. CatL was stably silenced using shRNA expression plasmid packed lentiviruses. By using metabolic- and cell viability assays, we demonstrated that long-term CatL silencing significantly increased arsenite cytotoxicity in U87MG spheroids. Silenced CatL also increased arsenite-mediated apoptosis in spheroids via elevated p53 expression, Bax/Bcl2 ratio and caspase 3/7 activity, though with lower efficacy than in monolayers. Arsenite cytotoxicity was enhanced by lower CatL activity, since similar cytotoxicity increase was also observed using the novel CatL inhibitor AT094. The results have significant translational impact, since stable CatL silencing would enable the application of lower systemic doses of arsenite to achieve the desired cytotoxic effects on GBMs in vivo. 相似文献
992.
María Eugenia Sabatino Liliana del Valle Sosa Juan Pablo Petiti Jorge Humberto Mukdsi Iván Darío Mascanfroni Claudia Gabriela Pellizas Silvina Gutiérrez Alicia Inés Torres Ana Lucía De Paul 《Experimental cell research》2013
Toll like receptor 4 (TLR4) has been characterized for its ability to recognize bacterial endotoxin lipopolysaccharide (LPS). Considering that infections or inflammatory processes might contribute to the progression of pituitary tumors, we analyzed the TLR4 functional role by evaluating the LPS effect on lactotroph proliferation in primary cultures from experimental pituitary tumors, and examined the involvement of PI3K-Akt and NF-κB activation in this effect. In addition, the role of 17β-estradiol as a possible modulator of LPS-induced PRL cell proliferation was further investigated. In estrogen-induced hyperplasic pituitaries, LPS triggered lactotroph cell proliferation. However, endotoxin failed to increase the number of lactotrophs taking up BrdU in normal pituitaries. Moreover, incubation with anti-TLR4 antibody significantly reduced LPS-induced lactotroph proliferation, suggesting a functional role of this receptor. As a sign of TLR4 activation, an LPS challenge increased IL-6 release in normal and tumoral cells. By flow cytometry, TLR4 baseline expression was revealed at the plasma membrane of tumoral lactotrophs, without changes noted in the percentage of double PRL/TLR4 positive cells after LPS stimulus. Increases in TLR4 intracellular expression were detected as well as rises in CD14, p-Akt and NF-κB after an LPS challenge, as assessed by western blotting. The TLR4/PRL and PRL/NF-κB co-localization was also corroborated by immunofluorescence and the involvement of PI3K/Akt signaling in lactotroph proliferation and IL-6 release was revealed through the PI3K inhibitor Ly-294002. In addition, 17β-estradiol attenuated the LPS-evoked increase in tumoral lactotroph proliferation and IL-6 release. Collectively these results demonstrate the presence of functional TLR4 in lactotrophs from estrogen-induced hyperplasic pituitaries, which responded to the proliferative stimulation and IL-6 release induced by LPS through TLR4/CD14, with a contribution of the PI3K-Akt and NF-κB signaling pathways. 相似文献
993.
Background
Continuing efforts in development of non-invasive prenatal genetic tests have focused on the isolation of fetal nucleated red blood cells (NRBCs) from maternal blood for decades. Because no fetal cell-specific antibody has been described so far, the present study focused on the development of monoclonal antibodies (mAbs) to antigens that are expressed exclusively on fetal NRBCs.Methods: Mice were immunized with fetal erythroid cell membranes and hybridomas screened for Abs using a multi-parameter fluorescence-activated cell sorting (FACS). Selected mAbs were evaluated by comparative FACS analysis involving Abs known to bind erythroid cell surface markers (CD71, CD36, CD34), antigen-i, galactose, or glycophorin-A (GPA). Specificity was further confirmed by extensive immunohistological and immunocytological analyses of NRBCs from umbilical cord blood and fetal and adult cells from liver, bone marrow, peripheral blood, and lymphoid tissues.Results: Screening of 690 hybridomas yielded three clones of which Abs from 4B8 and 4B9 clones demonstrated the desired specificity for a novel antigenic structure expressed on fetal erythroblast cell membranes. The antigenic structure identified is different from known surface markers (CD36, CD71, GPA, antigen-i, and galactose), and is not present on circulating adult erythroid cells, except for occasional detectability in adult bone marrow cells.Conclusions:The new mAbs specifically bind the same or highly overlapping epitopes of a surface antigen that is almost exclusively expressed on fetal erythroid cells. The high specificity of the mAbs should facilitate development of simple methods for reliable isolation of fetal NRBCs and their use in non-invasive prenatal diagnosis of fetal genetic status. 相似文献994.
Yu Liu Feiya Du Wei Chen Minya Yao Kezhen Lv Peifen Fu 《Experimental cell research》2013,319(20):3140-3149
BackgroundBreast cancer is the major cause of cancer-related deaths in females world-wide. Doxorubicin-based therapy has limited efficacy in breast cancer due to drug resistance, which has been shown to be associated with the epithelial-to-mesenchymal transition (EMT). However, the molecular mechanisms linking the EMT and drug resistance in breast cancer cells remain unclear. Dual specificity phosphatase 4 (DUSP4), a member of the dual specificity phosphatase family, is associated with cellular proliferation and differentiation; however, its role in breast cancer progression is controversial.MethodsWe used cell viability assays, Western blotting and immunofluorescent staining, combined with siRNA interference, to evaluate chemoresistance and the EMT in MCF-7 and adriamycin-resistant MCF-7/ADR breast cancer cells, and investigate the underlying mechanisms.ResultsKnockdown of DUSP4 significantly increased the chemosensitivity of MCF-7 and MCF-7/ADR breast cancer cells to doxorubicin, and MCF-7/ADR cells which expressed high levels of DUSP4 had a mesenchymal phenotype. Furthermore, knockdown of DUSP4 reversed the EMT in MCF-7/ADR cells, as demonstrated by upregulation of epithelial biomarkers and downregulation of mesenchymal biomarkers, and also increased the chemosensitivity of MCF-7/ADR cells to doxorubicin.ConclusionsDUSP4 might represent a potential drug target for inhibiting drug resistance and regulating the process of the EMT during the treatment of breast cancer. 相似文献
995.
The methylerythritol phosphate (MEP) pathway of Plasmodium falciparum (P. falciparum) has become an attractive target for anti-malarial drug discovery. This study describes a kinetic model of this pathway, its use in validating 1-deoxy-d-xylulose 5-phosphate reductoisomerase (DXR) as drug target from the systemic perspective, and additional target identification, using metabolic control analysis and in silico inhibition studies. In addition to DXR, 1-deoxy-d-xylulose 5-phosphate synthase (DXS) can be targeted because it is the first enzyme of the pathway and has the highest flux control coefficient followed by that of DXR. In silico inhibition of both enzymes caused large decrement in the pathway flux. An added advantage of targeting DXS is its influence on vitamin B1 and B6 biosynthesis. Two more potential targets, 2-C-methyl-d-erythritol 2,4-cyclodiphosphate synthase and 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate synthase, were also identified. Their inhibition caused large accumulation of their substrates causing instability of the system. 相似文献
996.
M. Skrzypski M. Kakkassery S. Mergler C. Grötzinger N. Khajavi M. Sassek D. Szczepankiewicz B. Wiedenmann K.W. Nowak M.Z. Strowski 《FEBS letters》2013
Transient receptor potential channel vanilloid type 4 (TRPV4) is a Ca2+- and Mg2+-permeable cation channel that influences oxidative metabolism and insulin sensitivity. The role of TRPV4 in pancreatic beta cells is largely unknown. Here, we characterize the role of TRPV4 in controlling intracellular Ca2+ and insulin secretion in INS-1E beta cells. Osmotic, thermal or pharmacological activation of TRPV4 caused a rapid rise of intracellular Ca2+ and enhanced glucose-stimulated insulin secretion. In the presence of the TRPV channel blocker ruthenium red (RuR) or after suppression of TRPV4 protein production, TRPV4 activators failed to increase [Ca2+]i and insulin secretion in INS-1E cells. 相似文献
997.
A bioartifical pancreas (BAP) remains a promising approach for treating insulin‐dependent diabetes. Several obstacles to the clinical implementation of a BAP remain, including hypoxia following implantation. Within native pancreatic islets, CXCL12 and glucagon‐like peptide‐1 (GLP‐1) act in a paracrine fashion to promote the survival, function, and proliferation of β‐cells. This work sought to investigate if the presentation of CXCL12 and delivery of a GLP‐1 receptor analog, Exendin‐4 (Ex‐4), alone and in combination, conferred pro‐survival and insulinotropic effects on an encapsulated β‐cell line, βTC‐tet, cultured under hypoxic conditions of 7.6 mmHg O2. Our findings indicate that presentation of CXCL12 in the encapsulation matrix completely abrogated apoptosis under hypoxic conditions. Delivery of Ex‐4 increased insulin secretion rate under both normoxic and hypoxic conditions, and additionally reduced apoptosis under hypoxic conditions. Furthermore, presentation of CXCL12 combined with Ex‐4 delivery significantly increased insulin secretion rate under hypoxic conditions compared to delivery of Ex‐4 alone. These findings demonstrate that the presentation of CXCL12 combined with the delivery of Ex‐4 may constitute a promising strategy for supporting β‐cell function and survival following transplantation. Biotechnol. Bioeng. 2013; 110: 2292–2300. © 2013 Wiley Periodicals, Inc. 相似文献
998.
Yongjun Du Ping Li Zhiqun Chen Yanru Lin Yahong Wang Yuanxia Qin 《Entomologia Experimentalis et Applicata》2013,146(3):357-363
The sex pheromone of Phyllonorycter ringoniella (Matsumura) (Lepidoptera: Gracillariidae) has been identified to be a blend of (Z)‐10‐tetradecenyl acetate (Z10‐14:OAc) and E4,Z10‐tetradecadienyl acetate (E4,Z10‐14:OAc) in Japan, Korea, and China. However, the commercial product based on previous results is not attractive enough to be used for monitoring and controlling apple leafminer populations in the field. We re‐investigated the attractiveness of the two pheromone components, singly and in blends, in apple orchards in Shangdong and Shaanxi, the main apple‐growing provinces in China. Our results revealed that Z10‐14:OAc alone was not attractive to P. ringoniella male moths in the field, but E4,Z10‐14:OAc alone not only was strongly attractive but caught more males than any of the blends of Z10‐14:OAc and E4,Z10‐14:OAc tested. The most attractive blend ratios differed slightly for the two locations. No clear dose–response relationship was obtained for the 2:8 blend of Z10‐14:OAc and E4,Z10‐14:OAc. However, the dose–response field study of E4,Z10‐14:OAc alone showed that 1 mg per lure achieved the highest moth catch. These findings differ from the previous report of the best pheromone blend in China. Our data showed that E4,Z10‐14:OAc is the major component of the pheromone of P. ringoniella. 相似文献
999.
Chie Tomikawa Takayuki Ohira Yasushi Inoue Takuya Kawamura Akihiko Yamagishi Tsutomu Suzuki Hiroyuki Hori 《FEBS letters》2013
Thermoplasma acidophilum is a thermo-acidophilic archaeon. We purified tRNALeu (UAG) from T. acidophilum using a solid-phase DNA probe method and determined the RNA sequence after determining via nucleoside analysis and m7G-specific aniline cleavage because it has been reported that T. acidophilum tRNA contains m7G, which is generally not found in archaeal tRNAs. RNA sequencing and liquid chromatography–mass spectrometry revealed that the m7G modification exists at a novel position 49. Furthermore, we found several distinct modifications, which have not previously been found in archaeal tRNA, such as 4-thiouridine9, archaeosine13 and 5-carbamoylmethyuridine34. The related tRNA modification enzymes and their genes are discussed. 相似文献
1000.
Avery L. McIntosh Anca D. Petrescu Heather A. Hostetler Ann B. Kier Friedhelm Schroeder 《FEBS letters》2013
Hepatocyte nuclear factor 4α (HNF4α) regulates liver type fatty acid binding protein (L-FABP) gene expression. Conversely as shown herein, L-FABP structurally and functionally also interacts with HNF4α. Fluorescence resonance energy transfer (FRET) between Cy3-HNF4α (donor) and Cy5-L-FABP (acceptor) as well as FRET microscopy detected L-FABP in close proximity (∼80 Å) to HNF4α, binding with high affinity Kd ∼250–300 nM. Circular dichroism (CD) determined that the HNF4α/L-FABP interaction altered protein secondary structure. Finally, L-FABP potentiated transactivation of HNF4α in COS7 cells. Taken together, these data suggest that L-FABP provides a signaling path to HNF4α activation in the nucleus. 相似文献