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   2119篇
  免费   287篇
  2021年   32篇
  2020年   17篇
  2019年   21篇
  2018年   24篇
  2017年   22篇
  2016年   46篇
  2015年   53篇
  2014年   54篇
  2013年   104篇
  2012年   90篇
  2011年   91篇
  2010年   59篇
  2009年   52篇
  2008年   86篇
  2007年   98篇
  2006年   80篇
  2005年   71篇
  2004年   65篇
  2003年   59篇
  2002年   55篇
  2001年   68篇
  2000年   50篇
  1999年   45篇
  1998年   29篇
  1997年   20篇
  1996年   26篇
  1995年   32篇
  1994年   28篇
  1993年   21篇
  1992年   54篇
  1991年   41篇
  1990年   43篇
  1989年   50篇
  1988年   41篇
  1987年   53篇
  1986年   35篇
  1985年   51篇
  1984年   29篇
  1983年   43篇
  1982年   29篇
  1980年   21篇
  1979年   21篇
  1978年   16篇
  1977年   23篇
  1975年   22篇
  1973年   13篇
  1972年   16篇
  1971年   18篇
  1969年   15篇
  1967年   15篇
排序方式: 共有2406条查询结果,搜索用时 15 毫秒
1.
3H-labeled Acholeplasma DNA probes were generated in vitro by the nick-translation method and used to determine the nucleotide sequence homology among the type strains of the eight currently recognized species of Acholeplasma. Very little nucleotide sequence homology (less than or equal to 18%) was found among the eight species, with heteroduplexes showing at least 12% or more mismatching as determined by thermal elution midpoints. The small amount of nucleotide sequence homology among the eight species indicates that these species are quite distinct and are not closely related to each other genomically.  相似文献   
2.
3.
4.
Food sharing: a model of manipulation by harassment   总被引:3,自引:1,他引:2  
Most analyses of food-sharing behavior invoke complex explanationssuch as indirect and delayed benefits for sharing via kin selectionand reciprocal altruism. However, food sharing can be a moregeneral phenomenon accounted for by more parsimonious, mutualisticexplanations. We propose a game theoretical model of a generalsharing situation in which food owners share because it is in their own self-interest—they avoid high costs associatedwith beggar harassment. When beggars harass, owners may benefitfrom sharing part of the food if their consumption rate islow relative to the rate of cost accrual. Our model predictsthat harassment can be a profitable strategy for beggars if they reap some direct benefits from harassing other than sharedfood (such as picking up scraps). Therefore, beggars may manipulatethe owner's fitness payoffs in such a way as to make sharingmutualistic.  相似文献   
5.
Ultrastructural data are presented on time-course changes in isolated rat hepatocyte suspensions exposed either to 1.2 or 1.8 mM CCl4 for up to 1 h. The subcellular changes at the lower concentration, but not the higher, are shown to closely parallel those reported to occur in rat hepatocytes following ingestion of CCl4.  相似文献   
6.
On 11 May 1985 the main stand of Bradford City Football Club caught fire. Within four minutes the stand was alight from end to end. Fifty three people were burnt to death and about 250 injured; 83 required admission to hospital, and 55 of these were treated by primary excision of their burns and skin grafting. In such disasters the help of staff from other hospitals and areas is essential. Patients should be assessed to see whether they have burns that will ultimately be fatal; if they have they should not be sent to regional burns units, where they would take up beds that could be used for patients with treatable burns. All districts should ensure that their plans for accidents in which burns injuries predominate are adequate.  相似文献   
7.
8.
9.
10.
Significant morbidity and mortality of South African clawed frogs, Xenopus laevis, can be caused by parasitism of the epidermis by a capillarid nematode. These worms produce an erosive dermatitis that is complicated by infection with gram-negative microorganisms. The nematode apparently has a direct life cycle that can be completed within the epidermis of the frog. These characteristics are suggested by the lack of an intermediate host and failure to detect visceral migration. Another unique feature of the parasite was the presence of larvated eggs, in utero. Some have named the parasite Capillaria xenopodis, whereas others called it Pseudocapillaroides xenopi to distinguish it form the typical members of the genus Capillaria.  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