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   1438571篇
  免费   137608篇
  国内免费   1430篇
  1577609篇
  2021年   17978篇
  2019年   16250篇
  2018年   17831篇
  2017年   16529篇
  2016年   28229篇
  2015年   42583篇
  2014年   50607篇
  2013年   76857篇
  2012年   38796篇
  2011年   27497篇
  2010年   43858篇
  2009年   45232篇
  2008年   26101篇
  2007年   24384篇
  2006年   29311篇
  2005年   30322篇
  2004年   29572篇
  2003年   27103篇
  2002年   25073篇
  2001年   38430篇
  2000年   36203篇
  1999年   35057篇
  1998年   25989篇
  1997年   25988篇
  1996年   25468篇
  1995年   23640篇
  1994年   23450篇
  1993年   22663篇
  1992年   30844篇
  1991年   29492篇
  1990年   28157篇
  1989年   28581篇
  1988年   26464篇
  1987年   25215篇
  1986年   24061篇
  1985年   25912篇
  1984年   25037篇
  1983年   22163篇
  1982年   21923篇
  1981年   21207篇
  1980年   19751篇
  1979年   21723篇
  1978年   19808篇
  1977年   18872篇
  1976年   17974篇
  1975年   17821篇
  1974年   18263篇
  1973年   18554篇
  1972年   16127篇
  1971年   14508篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
Zooplankton data collected during September 1995 in the NorthWest Atlantic at 4139'N, 4958'W (the location of the siteof the ‘Titanic’ wreck) were analysed. The regioninvestigated was characterized by a very sharp frontal zonebetween the Gulf Stream and the main stream of the LabradorCurrent. The total plankton biomass in the water column wasvery high. The macroplankton biomass values below the 600 mlayer were significantly higher as compared with the similarvalues measured before in other productive boreal regions ofthe Atlantic and Pacific oceans. A lot of dead mesoplanktonanimals occurred in the deep layers. The reason was that thecold-water mesoplankton advected by the Labrador Current diedoff intensively within the deep layers of the frontal zone andwere used as a food resource by the macroplankton carnivoresand scavengers that were very abundant there.  相似文献   
112.
113.
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   
114.
115.
116.
117.
Besides vobtusine and vobtusine-lactone, deoxyvobtusine was isolated from the leaves of Voacanga grandifolia (Miq. Rolfe. Spectral and chemical evi  相似文献   
118.
119.
120.
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   
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