首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1486篇
  免费   197篇
  国内免费   10篇
  2022年   11篇
  2021年   18篇
  2020年   15篇
  2019年   27篇
  2018年   30篇
  2017年   23篇
  2016年   46篇
  2015年   66篇
  2014年   80篇
  2013年   98篇
  2012年   122篇
  2011年   81篇
  2010年   60篇
  2009年   57篇
  2008年   78篇
  2007年   73篇
  2006年   76篇
  2005年   50篇
  2004年   63篇
  2003年   56篇
  2002年   65篇
  2001年   46篇
  2000年   35篇
  1999年   39篇
  1998年   13篇
  1997年   16篇
  1996年   12篇
  1995年   14篇
  1994年   7篇
  1993年   7篇
  1992年   17篇
  1991年   25篇
  1990年   22篇
  1989年   16篇
  1988年   11篇
  1987年   10篇
  1986年   16篇
  1985年   9篇
  1984年   17篇
  1983年   11篇
  1982年   8篇
  1980年   13篇
  1979年   10篇
  1978年   16篇
  1977年   10篇
  1975年   21篇
  1974年   13篇
  1973年   18篇
  1972年   9篇
  1965年   5篇
排序方式: 共有1693条查询结果,搜索用时 31 毫秒
991.
One novel dimeric coumarin analog, fatouapilosin ( 1 ), together with 18 known compounds, have been isolated from the whole plants of Fatoua pilosa. The structures of these isolates were elucidated by means of spectroscopic techniques (UV, IR, MS, 1H‐ and 13C‐NMR, DEPT, COSY, NOESY, HSQC, HMBC, and MS analyses). Among the tested compounds 2 – 14 , scopoletin ( 3 ), isobavachalcone ( 12 ), and (E)‐1‐[2,4‐dihydroxy‐3‐(3‐methylbut‐2‐enyl)phenyl]‐3‐(2,2‐dimethyl‐8‐hydroxy‐2H‐benzopyran‐6‐yl)prop‐2‐en‐1‐one ( 14 ) exhibited the strongest antimycobacterial activities against Mycobacterium tuberculosis H37Rv, with MIC values of 42, 18, and 30 μg/ml, respectively.  相似文献   
992.
The hepatocyte growth factor (HGF)/c‐Met signalling pathway is deregulated in most cancers and associated with a poor prognosis in breast cancer. Cardiotoxin III (CTX III), a basic polypeptide isolated from Naja naja atra venom, has been shown to exhibit anticancer activity. In this study, we use HGF as an invasive inducer to investigate the effect of CTX III on MDA‐MB‐231 cells. When cells were treated with non‐toxic doses of CTX III, CTX III inhibited the HGF‐promoted cell migration and invasion. CTX III significantly suppressed the HGF‐induced c‐Met phosphorylation and downstream activation of phosphatidylinositol 3‐kinase (PI3k)/Akt and extracellular signal‐regulated kinase (ERK) 1/2. Additionally, CTX III similar to wortmannin (a PI3K inhibitor) and U0126 (an upstream kinase regulating ERK1/2 inhibitor) attenuated cell migration and invasion induced by HGF. This effect was paralleled by a significant reduction in phosphorylation of IκBα kinase and IκBα and nuclear translocation of nuclear factor κB (NF‐κB) as well as a reduction of matrix metalloproteinase‐9 (MMP‐9) activity. Furthermore, the c‐Met inhibitor PHA665752 inhibited HGF‐induced MMP‐9 expression, cell migration and invasion, as well as the activation of ERK1/2 and PI3K/Akt, suggesting that ERK1/2 and PI3K/Akt activation occurs downstream of c‐Met activation. Taken together, these findings suggest that CTX III inhibits the HGF‐induced invasion and migration of MDA‐MB‐231 cells via HGF/c‐Met‐dependent PI3K/Akt, ERK1/2 and NF‐κB signalling pathways, leading to the downregulation of MMP‐9 expression. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
993.
994.
995.
996.
Wu KW  Chien CY  Li SW  King CC  Chang CH 《Genomics》2012,100(2):102-109
This study focused on identifying the conserved epitopes in a single subtype A (H3N2)-as candidates for vaccine targets. We identified a total of 32 conserved epitopes in four viral proteins [22 HA, 4PB1, 3 NA, 3 NP]. Evaluation of conserved epitopes in coverage during 1968-2010 revealed that (1) 12 HA conserved epitopes were highly present in the circulating viruses; (2) the remaining 10 HA conserved epitopes appeared with lower percentage but a significantly increasing trend after 1989 [p<0.001]; and (3) the conserved epitopes in NA, NP and PB1 are also highly frequent in wild-type viruses. These conserved epitopes also covered an extremely high percentage of the 16 vaccine strains during the 42 year period. The identification of highly conserved epitopes using our approach can also be applied to develop broad-spectrum vaccines.  相似文献   
997.
H Chien  RD Dix 《Journal of virology》2012,86(20):10961-10978
AIDS-related human cytomegalovirus (HCMV) retinitis remains a major ophthalmologic problem worldwide. Although this sight-threatening disease is well characterized clinically, many pathogenic issues remain unresolved, among them a basic understanding of the relative roles of cell death pathways during development of retinal tissue destruction. Using an established model of experimental murine cytomegalovirus (MCMV) retinitis in mice with retrovirus-induced immunosuppression (MAIDS), we initially investigated MCMV-infected eyes for evidence of apoptosis-associated molecules in mice with MAIDS of 4 weeks' (MAIDS-4) and 10 weeks' (MAIDS-10) duration, which were resistant and susceptible to retinal disease, respectively, but which harbored equivalent amounts of infectious MCMV. Whereas MCMV-infected eyes of MAIDS-4 mice showed little evidence of apoptosis-associated molecules, MCMV-infected eyes of MAIDS-10 mice showed significant amounts of tumor necrosis factor alpha (TNF-α), TNF receptors 1 and 2, active caspase 8, active caspase 3, TNF-related apoptosis-inducing ligand (TRAIL), TRAIL-R(DR5), Fas, and Fas ligand mRNAs and/or proteins, all detected at peak amounts prior to development of most severe retinal disease. Immunohistochemical staining showed macrophages, granulocytes (neutrophils), Müller cells, and microglial cells as TNF-α sources. Remarkably, quantification of apoptosis by terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) assay suggested that apoptosis contributed minimally to retinal disease in MCMV-infected eyes of MAIDS-10 mice. Subsequent studies demonstrated that MCMV-infected eyes of MAIDS-10 mice, but not MAIDS-4 mice, showed evidence of significant increases in molecules associated with two additional cell death pathways, necroptosis (receptor-interacting protein 1 [RIP1] and RIP3 mRNAs) and pyroptosis (caspase 1, interleukin 1β [IL-1β], and IL-18 mRNAs). We conclude that apoptosis, necroptosis, and pyroptosis participate simultaneously during MAIDS-related MCMV retinitis, and all may play a role during AIDS-related HCMV retinitis.  相似文献   
998.
999.
Exacerbated oxidative stress and inflammation may induce three types of programmed cell death, autophagy, apoptosis and pyroptosis in unilateral ureteral obstruction (UUO) kidney. Sulforaphane activating NF-E2-related nuclear factor erythroid-2 (Nrf-2) signaling may ameliorate UUO-induced renal damage. UUO was induced in the left kidney of female Wistar rats. The level of renal blood flow, cortical and medullary oxygen tension and reactive oxygen species (ROS) was evaluated. Fibrosis, ED-1 (macrophage/monocyte) infiltration, oxidative stress, autophagy, apoptosis and pyroptosis were evaluated by immunohistochemistry and Western blot in UUO kidneys. Effects of sulforaphane, an Nrf-2 activator, on Nrf-2- and mitochondrial stress-related proteins and renal injury were examined. UUO decreased renal blood flow and oxygen tension and increased renal ROS, 3-nitrotyrosine stain, ED-1 infiltration and fibrosis. Enhanced renal tubular Beclin-1 expression started at 4 h UUO and further enhanced at 3d UUO, whereas increased Atg-5-Atg12 and LC3-II expression were found at 3d UUO. Increased renal Bax/Bcl-2 ratio, caspase 3 and PARP fragments, apoptosis formation associated with increased caspase 1 and IL-1β expression for pyroptosis formation were started from 3d UUO. UUO reduced nuclear Nrf-2 translocation, increased cytosolic and inhibitory Nrf-2 expression, increased cytosolic Bax translocation to mitochondrial and enhanced mitochondrial Cytochrome c release into cytosol of the UUO kidneys. Sulforaphane significantly increased nuclear Nrf-2 translocation and decreased mitochondrial Bax translocation and Cytochrome c release into cytosol resulting in decreased renal injury. In conclusion, sulforaphane via activating Nrf-2 signaling preserved mitochondrial function and suppressed UUO-induced renal oxidative stress, inflammation, fibrosis, autophagy, apoptosis and pyroptosis.  相似文献   
1000.

Background

A case-control study was conducted to evaluate the role of adult diet on nasopharyngeal carcinoma (NPC) in Taiwan.

Methods

A total of 375 incident NPC cases and 327 controls matched to the cases on sex, age, and residence were recruited between July 1991 and December 1994. A structured questionnaire inquiring complete dietary history, socio-demographic characteristics, and other potential confounding factors was used in the personal interview. Unconditional logistic regression analysis was used to estimate multivariate-adjusted odds ratio (ORadj) with 95% confidence interval (CI) after accounting for known risk factors.

Results

Fresh fish (ORadj, 0.56; 95% CI, 0.38–0.83 for the highest vs. lowest tertile of intake), green tea (ORadj, 0.61; 95% CI, 0.40–0.91 for drinking ≥1 times/week vs. never) and coffee (ORadj, 0.56; 95% CI, 0.37–0.85 for drinking ≥0.5 times/week vs. never) were inversely associated with the NPC risk. No association with NPC risk was observed for the intake of meats, salted fish, fresh vegetables, fruits and milk. Intake of vitamin A from plant sources was associated with a decreased NPC risk (ORadj, 0.62; 95% CI, 0.41–0.94 for the highest vs. lowest tertile).

Conclusion

The study findings suggest that certain adult dietary patterns might protect against the development of NPC.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号