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   276351篇
  免费   30270篇
  国内免费   258篇
  306879篇
  2016年   3089篇
  2015年   4312篇
  2014年   4865篇
  2013年   7401篇
  2012年   7960篇
  2011年   8230篇
  2010年   5447篇
  2009年   5010篇
  2008年   7430篇
  2007年   7546篇
  2006年   7175篇
  2005年   6918篇
  2004年   6830篇
  2003年   6619篇
  2002年   6410篇
  2001年   11759篇
  2000年   11793篇
  1999年   9330篇
  1998年   3389篇
  1997年   3626篇
  1996年   3522篇
  1995年   3129篇
  1994年   3111篇
  1993年   3105篇
  1992年   7869篇
  1991年   7852篇
  1990年   7518篇
  1989年   7475篇
  1988年   6856篇
  1987年   6603篇
  1986年   6024篇
  1985年   6211篇
  1984年   5147篇
  1983年   4340篇
  1982年   3375篇
  1981年   3145篇
  1980年   2944篇
  1979年   4950篇
  1978年   3811篇
  1977年   3724篇
  1976年   3433篇
  1975年   3787篇
  1974年   4177篇
  1973年   4092篇
  1972年   3666篇
  1971年   3435篇
  1970年   3086篇
  1969年   2996篇
  1968年   2745篇
  1967年   2370篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
DdeI polymorphism in the HLA-DRA regulatory region   总被引:1,自引:0,他引:1       下载免费PDF全文
  相似文献   
992.
Clinicians rely heavily on expert based systems-consultation with colleagues, journal reviews and textbooks, and continuing education activities-to obtain new information. The usefulness of sources such as these depends on the relevance and validity of the information and the work it takes to obtain it. Useful information can be distinguished from the useless by asking three questions: Does the information focus on an outcome that my patients care about? Is the issue common to my practice, and is the intervention feasible? If the information is true, will it require me to change my practice? If the answer to all three questions is yes, then the information is a common POEM (patient oriented evidence that matters), capable of improving the lives of your patients and must be evaluated for validity. Conclusions based on results of well designed clinical trials are more likely to be valid than those drawn from observations based on experience in clinical practice. Both members of the team, clinicians and experts, must take responsibility for their respective roles.  相似文献   
993.
The synthesis, translocation, and decarboxylation of phosphatidylserine can occur in a cell-free system (Voelker, D. R. (1989) J. Biol. Chem. 264, 8019-8025). We made use of the spatial separation of the site of biosynthesis and the site of decarboxylation of phosphatidylserine to demonstrate that mitochondrial contact sites are intimately involved in the translocation of phosphatidylserine prior to decarboxylation. In that sense, the inhibition of phosphatidylserine decarboxylase leads to an accumulation of this phospholipid in the contact site-enriched fractions without mixing the inner membrane phospholipid pool. On the other hand, newly synthesized phosphatidylethanolamine can be exported very rapidly to the mitochondrial surface in the same way, i.e. via contact sites. These data provide further evidence for the existence of a structural and functional microcompartmentation at the inner mitochondrial membrane surface.  相似文献   
994.
The rate of proteolysis is an important determinant of the intracellular protein content. Part of the degradation of intracellular proteins occurs in the lysosomes and is mediated by macroautophagy. In liver, macroautophagy is very active and almost completely accounts for starvation-induced proteolysis. Factors inhibiting this process include amino acids, cell swelling and insulin. In the mechanisms controlling macroautophagy, protein phosphorylation plays an important role. Activation of a signal transduction pathway, ultimately leading to phosphorylation of ribosomal protein S6, accompanies inhibition of macroautophagy. Components of this pathway may include a heterotrimeric Gi3-protein, phosphatidylinositol 3- kinase and p70S6 kinase. Recent evidence indicates that lysosomal protein degradation can be selective and occurs via ubiquitin- dependent and -independent pathways. This revised version was published online in November 2006 with corrections to the Cover Date.  相似文献   
995.
996.
The foam collapse and foam formation properties of four different simulated fermentation media were compared in the presence and absence of natural oils. It was found that optimum effective natural oil concentration resulting in optimum foam suppression did not always correspond with the optimum for foam collapse, nor the optimum for maximum foam collapse rate.  相似文献   
997.
Detection of Infectious Astroviruses in Water   总被引:3,自引:2,他引:1       下载免费PDF全文
A method based on the infection of CaCo-2 cells and molecular hybridization with a specific cDNA probe has been developed for the detection of infectious astroviruses in environmental samples. By this procedure wild-type astroviruses have been detected in water from an area where a concurrent gastroenteritis outbreak was reported.  相似文献   
998.
999.
The European Beaver Castor fiber once occurred throughout Europe, but in many countries was exterminated or greatly reduced by over-hunting. In the UK, Beavers were last recorded in Scotland in the sixteenth century. Thirteen countries have carried out reintroduction programmes to restore the range of the Beaver in Europe, We provide a basis for discussing the feasibility and desirability of reintroducing the Beaver to Britain. The basic biology of the Beaver is described, followed by summaries of reintroductions in Europe and an evaluation of their successes and failures. We address the fundamental questions of propagule size, habitat requirements, habitat size and provenance of Beavers to be released, before examining in theory whether reintroducing Beavers to Britain is likely to fulfil UKCINC and IUCN criteria relating to environmental impact, socioeconomics and conservation. We then make suggestions as to how a reintroduction to Britain could proceed. Essential work outstanding includes site assessment and public consultation. The restoration of the Beaver to Britain could be a fitting start to the millennium.  相似文献   
1000.
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