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   595743篇
  免费   72837篇
  国内免费   213篇
  2018年   5280篇
  2016年   7249篇
  2015年   10757篇
  2014年   12633篇
  2013年   17197篇
  2012年   20035篇
  2011年   20020篇
  2010年   13225篇
  2009年   12424篇
  2008年   17728篇
  2007年   18472篇
  2006年   17326篇
  2005年   16774篇
  2004年   16625篇
  2003年   16018篇
  2002年   15372篇
  2001年   23410篇
  2000年   23717篇
  1999年   19406篇
  1998年   7683篇
  1997年   7721篇
  1996年   7460篇
  1995年   7114篇
  1994年   7072篇
  1993年   7031篇
  1992年   16721篇
  1991年   16546篇
  1990年   16192篇
  1989年   15707篇
  1988年   14723篇
  1987年   14093篇
  1986年   13188篇
  1985年   13413篇
  1984年   11409篇
  1983年   10028篇
  1982年   7901篇
  1981年   7424篇
  1980年   6925篇
  1979年   11213篇
  1978年   8780篇
  1977年   8077篇
  1976年   7664篇
  1975年   8420篇
  1974年   8754篇
  1973年   8527篇
  1972年   8034篇
  1971年   6998篇
  1970年   6113篇
  1969年   5780篇
  1968年   5248篇
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
51.
52.
Over the past 10 years the AIDS crisis has produced a large volume of writing. Much of this is documentary. Dozens of studies of AIDS from various clinical and political perspectives have been complemented by just as many published diaries, autobiographies, novels, plays, and poems. A few of these works have risen to the surface not only as extraordinarily valuable testimonies to the changes AIDS has wrought in individual and collective life but also as first-rate literary works, worth reading because beyond their immediate purposes they articulate with extraordinary lucidity and compassion some deep truths about the human--and the modern--condition. Paul Monette's Borrowed Time is among the most distinctive of those. It speaks not only for the community of people with AIDS and those who support them but for a generation.  相似文献   
53.
54.
55.
56.
57.
Isopropanol administered in a large (6 g/kg, orally) as well as in a lower dose (1 g/kg, I.P.) is slowly oxidized into acetone by the intact rat. Using two inhibitors, 3 amino-1,2,4-triazole and pyrazole, investigations on the hepatic enzymatic system involved in the oxidation of isopropanol show that catalase does not play an important part in this pathway, contrary to alcohol dehydrogenase which is the major enzyme responsible for this oxidation. Although isopropanol oxidation is mainly catalysed in the liver through alcohol dehydrogenase, no alteration of the hepatic extramitochondrial redox state occurs after the administration of a large as well as of a lower dose of isopropanol. From these experiments it may be concluded that alterations of the liver NAD+/NADH ratio, which seem to play an important part in the ethanol induced fatty liver, are not involved in the isopropanol induced one.  相似文献   
58.
59.
An agar-degrading marine bacterium identified as a Microscilla species was isolated from coastal California marine sediment. This organism harbored a single 101-kb circular DNA plasmid designated pSD15. The complete nucleotide sequence of pSD15 was obtained, and sequence analysis indicated a number of genes putatively encoding a variety of enzymes involved in polysaccharide utilization. The most striking feature was the occurrence of five putative agarase genes. Loss of the plasmid, which occurred at a surprisingly high frequency, was associated with loss of agarase activity, supporting the sequence analysis results.  相似文献   
60.
Expression of the glycoprotein clusterin is markedly increased following tissue injury. One function of clusterin is to promote cell interactions which are perturbed in these pathologic settings. Clusterin causes cell aggregation and adhesion in vitro yet the molecular mechanism for this effect is not known. In order to identify the active site(s) of clusterin, 34 peptides, each 15 amino acid residues in length, were synthesized from hydrophilic regions of human clusterin. When studied individually, none of the peptides caused aggregation of LLC-PK1 cells, a porcine renal epithelial cell line. However, two out of the 34 peptides inhibited clusterin-induced cell aggregation in a dose-dependent manner. Scrambled versions of these two 'active' peptides did not inhibit cell aggregation. Seven peptides promoted cell adhesion. In conclusion, these findings provide evidence for novel amino acid sequences mediating clusterin-induced renal cell interactions.  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