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   242837篇
  免费   13115篇
  国内免费   876篇
  2022年   1006篇
  2021年   2185篇
  2020年   1573篇
  2019年   1729篇
  2018年   13933篇
  2017年   12575篇
  2016年   10745篇
  2015年   5992篇
  2014年   5929篇
  2013年   8121篇
  2012年   14312篇
  2011年   22413篇
  2010年   17384篇
  2009年   12958篇
  2008年   17414篇
  2007年   18904篇
  2006年   8123篇
  2005年   8370篇
  2004年   8654篇
  2003年   7989篇
  2002年   7343篇
  2001年   3903篇
  2000年   3812篇
  1999年   2902篇
  1998年   1834篇
  1997年   1479篇
  1996年   1591篇
  1995年   1381篇
  1994年   1385篇
  1993年   1339篇
  1992年   1854篇
  1991年   1657篇
  1990年   1444篇
  1989年   1433篇
  1988年   1429篇
  1987年   1297篇
  1986年   1215篇
  1985年   1310篇
  1984年   1395篇
  1983年   1150篇
  1982年   1084篇
  1981年   1034篇
  1980年   927篇
  1979年   937篇
  1978年   918篇
  1977年   831篇
  1975年   826篇
  1974年   753篇
  1973年   732篇
  1971年   750篇
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
11.
Hostile intercommunity relations, including attacking and killing extra-community infants of both sexes have occurred at most wild chimpanzee sites. We describe three recent cases of intercommunity attacks on infants committed by members of the Ngogo chimpanzee community in Kibale National Park, Uganda. Two of the attacks resulted in confirmed infanticides while a third attack probably resulted in the infant's death. In common with previous accounts of chimpanzee infanticides, the attacks described here occurred during boundary patrols outside the Ngogo community's usual range, adult and adolescent males were the main participants, one infant was cannibalized after being killed, and the victims’ mothers did not accompany the attacking party back to the Ngogo range. However, the patrol parties during each infanticide were larger than before and included females from the Ngogo community. Our observations indirectly support both the range expansion and imbalance of power hypotheses, which address why and under which conditions chimpanzee intercommunity encounters lead to aggression. These cases of intercommunity infanticide add to the growing database of the phenomenon in wild chimpanzees.  相似文献   
12.
13.
14.
With DNA sequencing now getting cheaper more quickly than data storage or computation, the time may have come for genome informatics to migrate to the cloud.  相似文献   
15.
Rice fields are an alternative habitat for waterbirds and provide food and shelter for many avian species, but there is a lack of information about how the use of rice fields translates into population level effects. The aim of this study was to test the relationship between the use of rice fields by European waterbirds and trends in their populations. We tested this relationship during the autumn migration season and during the breeding season. Based on counts conducted over the last 23 years in natural marshes and areas of rice fields in Doñana (SW Spain), an index of rice field use was constructed for 76 bird species, which was then compared to these species’ European population trends obtained from the literature. A positive relationship was found between waterbird population trends and the use of rice fields during autumn migration season. Our study suggests that changes in the Common Agriculture Policy in Europe leading to reductions in areas of rice cultivation may have important effects on waterbirds. The restoration of former marsh areas and the maintenance of rice cultivation would seem to be more environmentally friendly approaches than the use of these areas to grow alternative crops or solar farms.  相似文献   
16.
The linkage of the Phi, Pgd, Po2, S, H and halothane sensitivity loci was followed in a Belgian Landrace family, heterozygous for these systems over 6 generations. Recombination next to the S locus occurred mainly in pigs belonging to this particular family. From this investigation the position of the S locus is proved to be outwith the Phi-Pgd region, next to Phi . Therefore the gene sequence S - Phi - Hal -H- Po2 -Pgd is proposed. Higher recombination rates were observed in the female parental line of the multiheterozygous family when compared to the male parental line. Additional data from animals, unrelated to this strain, confirm the evidence of close linkage of the S system to the nearest marker loci.  相似文献   
17.
18.
19.
20.

Background  

Recent studies point to a great diversity of non-ribosomal peptide synthesis systems with major roles in amino acid and co-factor biosynthesis, secondary metabolism, and post-translational modifications of proteins by peptide tags. The least studied of these systems are those utilizing tRNAs or aminoacyl-tRNA synthetases (AAtRS) in non-ribosomal peptide ligation.  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