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   663261篇
  免费   75818篇
  国内免费   468篇
  739547篇
  2016年   6818篇
  2015年   9737篇
  2014年   11448篇
  2013年   16526篇
  2012年   18211篇
  2011年   18440篇
  2010年   12404篇
  2009年   11407篇
  2008年   16308篇
  2007年   17173篇
  2006年   16165篇
  2005年   15695篇
  2004年   15676篇
  2003年   15097篇
  2002年   15038篇
  2001年   29369篇
  2000年   29911篇
  1999年   23990篇
  1998年   8269篇
  1997年   8525篇
  1996年   8011篇
  1995年   7740篇
  1994年   7663篇
  1993年   7581篇
  1992年   20027篇
  1991年   19282篇
  1990年   18870篇
  1989年   18308篇
  1988年   17207篇
  1987年   16403篇
  1986年   15356篇
  1985年   15522篇
  1984年   12896篇
  1983年   11186篇
  1982年   8864篇
  1981年   8076篇
  1980年   7510篇
  1979年   12806篇
  1978年   9965篇
  1977年   9273篇
  1976年   8662篇
  1975年   9624篇
  1974年   10529篇
  1973年   10536篇
  1972年   9722篇
  1971年   8940篇
  1970年   7672篇
  1969年   7559篇
  1968年   6802篇
  1967年   5859篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
In 1990 and 1994, two males of Golden Eagles were found with small lead particles in their stomachs. Both individuals died soon after they had been taken sitting on the soil in bad condition. There are some findings of dead eagles in the same area which showed no sign of having been injured. The two cases of presumed lead poisoning coincide with intense efforts to reduce the number of ChamoixRupicapra rupicapra by hunting. The bullets used contain a nucleus of lead and eagles were seen taking the entrails of the shot chamoix.  相似文献   
112.
113.
114.
115.
116.
117.
Synaptonemal complexes and meiosis in myxomycetes   总被引:4,自引:0,他引:4  
Synaptonemal complexes (SC) have been observed in spores 18–24 hr past cleavage in natural fruitings of Physarum cinereum, P. bogoriense, Hemitrichia stipitata, Tubifera ferruginosa, and Arcyria incarnata. Laboratory fruitings of Arcyria cinerea, Stemonitis herbatica, and a homothallic isolate of Physarum pusillum also have SC's present in spores during the same postcleavage period. The presence of these paired chromosomes of meiotic prophase in spores of species collected in nature and in a diversity of taxa suggests that the usual position of meiosis in Myxomycetes is inside the postcleavage spore. Criteria are proposed for evaluating the validity of the SC as an indicator of meiosis.  相似文献   
118.
Systematic analysis of the long-chain components of Eubacterium lentum   总被引:1,自引:0,他引:1  
The cellular long-chain component patterns of 33 strains of Eubacterium lentum were determined by gas chromatography. Two main types of long-chain component patterns were distinguished. The first (26 strains) was characterized by saturated branched-chain fatty acids (br14:0, br15:0, br16:0 and br17:0). The second (7 strains) did not contain branched-chain fatty acids and was characterized by saturated straight-chain fatty acids (11:0, 12:0, 14:0 and 16:0). Both types contained fatty aldehydes and their respective dimethyl acetals (14ald and 14dma, 16ald and 16dma). br16dma was only found in the first type. The G + C content of the DNA (Tm) of the 33 strains varied between 63.7 and 69.1 mol %. Canonical correlation analysis distinguished three subtypes within the first main type.  相似文献   
119.
W D Davies  J Pittard  B E Davidson 《Gene》1985,33(3):323-331
Defective transducing phages carrying aroG, the structural gene for phenylalanine (phe)-inhibitable phospho-2-keto-heptonate aldolase (EC 4.1.2.15; previously known as 3-deoxy-D-arabinoheptulosonate-7-phosphate synthetase[phe]), have been isolated, and DNA from two of these phages has been used to construct a restriction map of the region from att lambda to aroG. A 7.6-kb PstI-HindIII fragment from one of these phages was cloned into pBR322 and shown to contain aroG. The location of aroG within the 7.6 kb was established by subcloning and Tn3 transpositional mutagenesis. A fragment carrying the aroG promoter and operator has been cloned into a high copy number promoter-cloning vector (pMC489), and the resulting aroGpo-LacZ' (alpha) fusion subcloned in a low copy number vector. Strains with this fusion on the low copy number vector exhibit negative regulation of beta-galactosidase expression by both phenylalanine and tryptophan and positive regulation by tyrosine in a tyrR+ background.  相似文献   
120.
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