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   765600篇
  免费   86791篇
  国内免费   428篇
  2018年   7052篇
  2016年   9297篇
  2015年   11735篇
  2014年   14141篇
  2013年   20550篇
  2012年   23487篇
  2011年   24483篇
  2010年   15920篇
  2009年   14434篇
  2008年   21557篇
  2007年   22477篇
  2006年   21051篇
  2005年   20207篇
  2004年   19956篇
  2003年   19252篇
  2002年   18700篇
  2001年   32881篇
  2000年   33402篇
  1999年   26273篇
  1998年   9133篇
  1997年   9506篇
  1996年   9277篇
  1995年   8813篇
  1994年   8773篇
  1993年   8571篇
  1992年   22184篇
  1991年   21852篇
  1990年   21633篇
  1989年   20996篇
  1988年   19625篇
  1987年   18835篇
  1986年   17420篇
  1985年   17909篇
  1984年   14908篇
  1983年   13020篇
  1982年   9890篇
  1981年   9188篇
  1980年   8635篇
  1979年   14427篇
  1978年   11272篇
  1977年   10377篇
  1976年   9921篇
  1975年   11182篇
  1974年   11617篇
  1973年   11467篇
  1972年   10579篇
  1971年   9420篇
  1970年   8252篇
  1969年   7715篇
  1968年   7165篇
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
61.
62.
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   
63.
64.
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   
65.
66.
67.
68.
Besides vobtusine and vobtusine-lactone, deoxyvobtusine was isolated from the leaves of Voacanga grandifolia (Miq. Rolfe. Spectral and chemical evi  相似文献   
69.
70.
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