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   784612篇
  免费   95294篇
  国内免费   421篇
  2016年   8785篇
  2015年   13144篇
  2014年   15207篇
  2013年   21217篇
  2012年   24066篇
  2011年   24149篇
  2010年   16297篇
  2009年   15419篇
  2008年   22044篇
  2007年   22676篇
  2006年   21275篇
  2005年   20471篇
  2004年   20238篇
  2003年   19641篇
  2002年   18990篇
  2001年   34399篇
  2000年   34834篇
  1999年   28064篇
  1998年   10768篇
  1997年   11372篇
  1996年   10572篇
  1995年   10327篇
  1994年   10181篇
  1993年   10006篇
  1992年   23578篇
  1991年   22848篇
  1990年   22471篇
  1989年   21803篇
  1988年   20080篇
  1987年   19741篇
  1986年   18106篇
  1985年   18201篇
  1984年   15128篇
  1983年   13201篇
  1982年   10561篇
  1981年   9393篇
  1980年   8951篇
  1979年   14553篇
  1978年   11693篇
  1977年   10570篇
  1976年   9956篇
  1975年   10802篇
  1974年   11627篇
  1973年   11410篇
  1972年   10216篇
  1971年   9476篇
  1970年   8105篇
  1969年   7661篇
  1968年   6843篇
  1967年   6171篇
排序方式: 共有10000条查询结果,搜索用时 828 毫秒
51.
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   
52.
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   
53.
54.
55.
56.
57.
Four myeloid cell lines (M1, WEHI-3B D+, FDC-P1, and 32D) were screened for the presence of J11d antigen. One of these cell lines, the myeloid leukemia M1, was found to express a high level of J11d antigen on the cell surface. Recombinant mouse leukemic inhibitory factor (rm-LIF), recombinant human LIF (rh-LIF), and steroids (hydrocortisone and dexamethasone) could induce M1 cells to undergo monocytic differentiation. The level of J11d antigen was greatly reduced after treatment of the cells with LIF or steroids. Western blotting revealed that the apparent molecular weight of the J11d antigen on M1 cells was 45-48 kDa. Furthermore, the level of J11d mRNA was also reduced during LIF-induced differentiation of M1 cells.  相似文献   
58.
59.
H Katsumi  T Tomita  J Kaneko  Y Kamio 《FEBS letters》1999,460(3):451-456
Staphylococcal gamma-hemolysin and leukocidin are bi-component cytolysins, consisting of LukF (or Hlg1)/Hlg2 and LukF/LukS, respectively. Here, we purified serum inhibitors of gamma-hemolysin and leukocidin from human plasma. Protein sequencing showed that the purified inhibitors of 62, 57, 50 and 38 kDa were the vitronectin fragments with truncation(s) of the C-terminal or both N- and C-terminal regions. The purified vitronectin fragments specifically bound to the Hlg2 component of gamma-hemolysin and the LukS component of leukocidin to form high-molecular-weight complexes with them, leading to inhibition of the toxin-induced lysis of human erythrocytes and human polymorphonuclear leukocytes, respectively. Intact vitronectin also showed inhibitory activity to the toxins. The ability of gamma-hemolysin and leukocidin to bind vitronectin and its fragments is a novel function of the pore-forming cytolysins.  相似文献   
60.
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