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   22243篇
  免费   2057篇
  国内免费   12篇
  2021年   220篇
  2020年   127篇
  2019年   188篇
  2018年   255篇
  2017年   218篇
  2016年   359篇
  2015年   586篇
  2014年   689篇
  2013年   934篇
  2012年   1200篇
  2011年   1292篇
  2010年   857篇
  2009年   765篇
  2008年   1097篇
  2007年   1164篇
  2006年   1154篇
  2005年   1159篇
  2004年   1164篇
  2003年   1058篇
  2002年   1108篇
  2001年   268篇
  2000年   219篇
  1999年   323篇
  1998年   331篇
  1997年   243篇
  1996年   245篇
  1995年   225篇
  1994年   286篇
  1993年   265篇
  1992年   235篇
  1991年   220篇
  1990年   211篇
  1989年   235篇
  1988年   201篇
  1987年   203篇
  1986年   179篇
  1985年   242篇
  1984年   257篇
  1983年   246篇
  1982年   302篇
  1981年   309篇
  1980年   305篇
  1979年   204篇
  1978年   210篇
  1977年   211篇
  1976年   183篇
  1975年   164篇
  1974年   200篇
  1973年   172篇
  1972年   131篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
33.
Proteinase inhibitors I and II were purified to electrophoretic homogeneity from leaves of tomato plants induced by either wounding intact plants or by supplying excised plants with the proteinase inhibitor inducing factor. Affinity chromatography with chymotrypsin-Sepharose was employed as a final purification step for each inhibitor. The tomato leaf inhibitors are very similar to potato tuber inhibitors I and II in subunit molecular weight, composition, and inhibitory activities against chymotrypsin, trypsin, and subtilisin. However, unlike the potato tuber which contains multiple isoinhibitors by isoelectric focusing, the tomato leaf exhibits only two isoinhibitor forms of inhibitor I and a single form of inhibitor II. The molecular weight of native potato inhibitor I was reevaluated by rigorous ultracentrifugal analysis and compared with data from previous analyses. The data confirm that native inhibitor I has a native Mr of about 41,000 and is a pentamer. Inhibitor II has a molecular weight of near 23,000 and is a dimer.  相似文献   
34.
35.
Small-Sized Mutants of SACCHAROMYCES CEREVISIAE   总被引:5,自引:0,他引:5       下载免费PDF全文
The isolation of mutants of Saccharomyces cerevisiae that divide at approximately half the size of the wild type is described. Three mutants have been isolated in which the small size at bud initiation is due to a mutation in a single nuclear gene.  相似文献   
36.
37.
38.

Background  

Ontario provincial abattoirs have the potential to be important sources of syndromic surveillance data for emerging diseases of concern to animal health, public health and food safety. The objectives of this study were to: (1) describe provincially inspected abattoirs processing cattle in Ontario in terms of the number of abattoirs, the number of weeks abattoirs process cattle, geographical distribution, types of whole carcass condemnations reported, and the distance animals are shipped for slaughter; and (2) identify various seasonal, secular, disease and non-disease factors that might bias the results of quantitative methods, such as cluster detection methods, used for food animal syndromic surveillance.  相似文献   
39.
Adiponectin is an adipokine whose plasma levels are inversely correlated to metabolic syndrome components. Adiponectin protects against atherosclerosis and decreases risks in myocardial infarction. Endothelial progenitor cells (EPCs) are a heterogeneous population of circulating cells involved in vascular repair and neovascularization. EPCs number is reduced in patients with cardiovascular disease. We hypothesize that the positive effects of adiponectin against atherosclerosis are explained in part by its interactions with EPCs. Cells were obtained from healthy volunteers' blood by mononuclear cell isolation and plating on collagen‐coated dishes. Three sub‐populations of EPCs were identified and characterized using flow cytometry. EPCs' expression of adiponectin receptors, AdipoR1, and AdipoR2 was evaluated by quantitative PCR. The effects of recombinant adiponectin on EPCs' susceptibility to apoptosis were assessed. Finally, expression of neutrophil elastase by EPCs and activity of this enzyme on adiponectin processing were assessed. Quantitative PCR analysis of EPCs mRNAs showed that AdipoR1 mRNA is expressed at higher levels than AdipoR2. Expression of AdipoR1 protein was confirmed by western blot. Adiponectin significantly increased survival of two sub‐populations of EPCs in conditions of serum deprivation. Such effect could not be demonstrated in the third EPCs sub‐population. We also demonstrated that EPCs, particularly one sub‐population, express neutrophil elastase. Neutrophil elastase activity was confirmed in EPCs' conditioned media. Adiponectin protects some EPCs sub‐populations against apoptosis and therefore could modulate EPCs ability to induce repair of vascular damage. Neutrophil elastase activity of EPCs could locally modulate adiponectin activity by its involvement in the generation of the globular form of adiponectin.  相似文献   
40.
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