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   31304篇
  免费   2761篇
  国内免费   22篇
  2023年   143篇
  2022年   323篇
  2021年   776篇
  2020年   415篇
  2019年   549篇
  2018年   654篇
  2017年   537篇
  2016年   965篇
  2015年   1631篇
  2014年   1709篇
  2013年   1999篇
  2012年   2632篇
  2011年   2679篇
  2010年   1632篇
  2009年   1353篇
  2008年   2009篇
  2007年   1985篇
  2006年   1930篇
  2005年   1655篇
  2004年   1679篇
  2003年   1476篇
  2002年   1440篇
  2001年   275篇
  2000年   202篇
  1999年   264篇
  1998年   299篇
  1997年   214篇
  1996年   197篇
  1995年   168篇
  1994年   149篇
  1993年   143篇
  1992年   116篇
  1991年   141篇
  1990年   103篇
  1989年   94篇
  1988年   84篇
  1987年   66篇
  1986年   84篇
  1985年   93篇
  1984年   92篇
  1983年   92篇
  1982年   111篇
  1981年   110篇
  1980年   88篇
  1979年   60篇
  1978年   45篇
  1977年   45篇
  1976年   47篇
  1975年   46篇
  1974年   46篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
172.
173.
Birefringence in endosperm mitosis   总被引:10,自引:0,他引:10  
  相似文献   
174.
175.
176.
177.
Postcoital (pc) cervical mucus was collected in 73 menstrual cycles of cynomolgus monkeys and in 43 cycles of rhesus monkeys at 2,6,10,30 hr pc. Videomicrography was used to analyze sperm numbers and movement in the mucus. Both cynomolgus and rhesus monkeys had comparable populations of motile sperm in the mucus at 2 hr pc. However, by 6 hr pc, cervical mucus from cynomolgus monkeys contained twice as many total sperm and motile sperm as mucus from rhesus monkeys (P <.05). Mean swimming speeds of the free-swimming cervical sperm were similar for the two species at this time. No motile sperm were recovered in mucus from rhesus monkeys at 30 hr pc. In cynomolgus monkeys, however, 14 of the 26 animals examined at 30 hr pc had motile sperm in their mucus. These sperm exhibited lower percent molility, percent free-swimming sperm, and swimming speed than those sperm observed at 6 hr pc. Uterine sperm were collected by transcervical or transuterine aspiration from cynomolgus monkeys. In the transcervical technique, sperm were successfully obtained in four of nine animals examined at 6 hr and in four of five animals at 30 hr pc. The percentage of motile sperm in the uterine fluid was high, 82% ± 4%, and the swimming speeds (86 ± 2μm/sec) were higher than those observed in cervical mucus. Approximately 5–10% of the uterine sperm exhibited swimming motions similar to the hyperactivated motility seen in most mammals. These findings indicate that the sperm cervical mucus interaction in vivo in cynomolgus monkeys has more similarities to the human situation than does the interaction in rhesus monkeys.  相似文献   
178.
The disamed Ti-binary vector pBIN 6 in Agrobacterium tumefaciens has been used in leaf disc transfomations to produce transgenic apple (Malus pumila Mill.) plants with a nomal phenotype except for a somewhat reduced capacity to root. The presence of the genes for nopaline synthase and neomycin phosphotrans ferase (conferring kanamycin resistance), inserted into the host genome by the vector, was confirmed by Southern blot analysis, the detection of nopaline synthase activity and rooting in the presence of the antibiotic.The nopaline synthase gene continued to be expressed in glasshouse-grown plants several months after removal from in vitro growth conditions.  相似文献   
179.
180.
The glycoprotein VP7, the major serotype antigen of rotaviruses, is localized to the endoplasmic reticulum (ER) of the cell, where it is retained as a membrane-associated protein before assembly into mature virus particles. Wild-type VP7 expressed by a recombinant vaccinia virus was also located internally and was poorly antigenic. Using recombinant techniques, a correctly processed, secreted form of VP7 (S.C. Stirzaker and G.W. Both, Cell 56:741-747, 1989) was modified by addition to its C terminus of the membrane anchor and cytoplasmic domains from the influenza virus hemagglutinin. The hybrid protein was directed to the surface of cells, where it was anchored in the plasma membrane. When expressed in mice and rabbits by a recombinant vaccinia virus, the surface-anchored antigen stimulated a level of rotavirus-specific antibodies that was greater than 100-fold above the level induced by wild-type VP7. T-cell responses to the novel antigen were also elevated in comparison with the wild-type, intracellular protein. Cell surface anchoring may provide a strategy to increase the immunogenicity of intracellular antigens from other parasites and viruses.  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