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   565108篇
  免费   54882篇
  国内免费   626篇
  2018年   9705篇
  2017年   9484篇
  2016年   9204篇
  2015年   7480篇
  2014年   8717篇
  2013年   12723篇
  2012年   15982篇
  2011年   20743篇
  2010年   14985篇
  2009年   14068篇
  2008年   17805篇
  2007年   19822篇
  2006年   12727篇
  2005年   12969篇
  2004年   12599篇
  2003年   12662篇
  2002年   12352篇
  2001年   25527篇
  2000年   25571篇
  1999年   20130篇
  1998年   6336篇
  1997年   6846篇
  1996年   6351篇
  1995年   5930篇
  1994年   5751篇
  1993年   5728篇
  1992年   16467篇
  1991年   16031篇
  1990年   15626篇
  1989年   15395篇
  1988年   14274篇
  1987年   13218篇
  1986年   12301篇
  1985年   12607篇
  1984年   10198篇
  1983年   8842篇
  1982年   6725篇
  1981年   5895篇
  1980年   5505篇
  1979年   9672篇
  1978年   7533篇
  1977年   7023篇
  1976年   6603篇
  1975年   7188篇
  1974年   7751篇
  1973年   7629篇
  1972年   7539篇
  1971年   6833篇
  1970年   5533篇
  1969年   5458篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
It is known that skin releases volatile organic compounds to the environment, and also that its emission pattern changes with aging of the skin. It could be considered, that these compounds are intermediaries in cell metabolism, since many intermediaries of metabolic pathways have a volatile potential. In this work, a simple and non-destructive method consisting of SPME sampling and GC/MS analysis was developed to identify volatile organic emanations from cell cultures. This technique, applied to skin cells culture, indicates that the cells or cell metabolism produce several skin emissions. Chemometric analysis was performed in order to explore the relationship between a volatile profile and the senescence of cell cultures. Volatile profiles were different for cell cultures in different degrees of senescence, indicating that volatile compound patterns could be used to provide information about the age of skin cells.  相似文献   
32.
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   
33.
The literature relating to chemical, biochemical and biological aspects of the steroidal glycoalkaloid, α-tomatine, is reviewed. The alkaloid, which can be used as a starting compound for the synthesis of steroidal hormones, is toxic to a wide range of living organisms. The significance of tomatine to plants which elaborate it is discussed and some possible uses of the compound are mentioned.  相似文献   
34.
35.
36.
37.
38.
39.
40.
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