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   47185篇
  免费   3845篇
  国内免费   4篇
  2023年   236篇
  2021年   353篇
  2020年   304篇
  2019年   301篇
  2018年   941篇
  2017年   965篇
  2016年   1054篇
  2015年   944篇
  2014年   1111篇
  2013年   1963篇
  2012年   3280篇
  2011年   3610篇
  2010年   1836篇
  2009年   1185篇
  2008年   2939篇
  2007年   3018篇
  2006年   2828篇
  2005年   2502篇
  2004年   2374篇
  2003年   2251篇
  2002年   2216篇
  2001年   1570篇
  2000年   1813篇
  1999年   989篇
  1998年   430篇
  1997年   352篇
  1996年   410篇
  1995年   364篇
  1994年   393篇
  1993年   345篇
  1992年   411篇
  1991年   328篇
  1990年   309篇
  1989年   289篇
  1988年   265篇
  1987年   282篇
  1986年   235篇
  1985年   337篇
  1984年   404篇
  1983年   351篇
  1982年   330篇
  1981年   311篇
  1980年   273篇
  1979年   283篇
  1978年   291篇
  1977年   266篇
  1976年   259篇
  1975年   305篇
  1974年   231篇
  1973年   218篇
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
61.
62.
63.
Summary 6-methyl-5-hepten-2-one was reduced to sulcatol ((+)-6-methyl-5-hepten-2-ol) by using alcohol dehydrogenase fromThermoanaerobium brockii in a continuous process. The cofactor NADP(H) was retained by a charged UF-membrane and regenerated by oxidation of isopropanol to acetone. Use of native NADP in a charged UF-membrane reactor proved to be superior to use of PEG coupled NADP in a uncharged UF-membrane reactor.  相似文献   
64.
65.
66.
Summary Saruplase — a recombinant single-chain urokinase-type plasminogen activator was identified immunohistochemically in normal rat tissue after intravenous administration by means of a polyclonal antibody. For this purpose, rat tissues were fixed in various ways (liquid nitrogen, ethanol, formaldehyd solution). Saruplase could be detected by the PAP method, streptavidinbiotin system and indirect immunofluorescence in the kidney (proximal tubule), liver (hepatocytes, Kupffer cells) and spleen (reticular cells). Saruplase was not localized in the rat endothelium. It is discussed that the ratspecific receptors for urokinase-type plasminogen activator on endothelial cells cannot bind Saruplase due to the extreme species specificity.  相似文献   
67.
1. Ecosystem processes depend on the biomass of the involved organisms, but their functional diversity may play an additional role. In particular, the exclusion of key functional groups through habitat disturbance may lead to the breakdown of ecosystem functions. Dung removal is an important process contributing to nutrient cycling and thus productivity in grazed ecosystems. 2. This study investigated the role of different functional groups of dung beetles in dung removal in different habitats within a wood-pasture in two different seasons. An experimental setting with 12 blocks and 108 dung pads was used to investigate short-term dung removal over 1 week of exposure. 3. Dung removal was most strongly affected by habitat type, with almost 40% lower levels in grassland than in adjacent forest and forest gaps. Of all assemblage characteristics, total biomass of tunneller species was the strongest predictor of dung removal, whereas functional diversity showed no significant effect. In accordance with the dung removal pattern at habitat type level, densities of large tunnellers were suppressed in grassland compared with forest. 4. It is concluded that dung removal is habitat-specific and large tunnellers play a disproportionate role in this important ecosystem function in temperate forests.  相似文献   
68.
69.
70.
Hahne  Bettina  Lörz  Horst  Hahne  Günther 《Plant cell reports》1990,8(10):590-593
Oat (Avena sativa L.) mesophyll protoplasts were recently demonstrated to be capable of dedifferentiation, repeated divisions, and colony formation. Since the development of oat mesophyll protoplasts is decisively influenced by the nature of the used feeder culture (species, variety and concentration), we conducted a systematic study of this parameter. Generally, graminaceous feeders promoted protoplast proliferation, while dicot species repressed protoplast divisions. The beneficial effect of those feeders that promote divisions was counterbalanced by a factor that causes necrosis. The correct balance between promotion of divisions or necrosis depended on the nature of the feeder and its plating density.  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