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   60326篇
  免费   4933篇
  国内免费   31篇
  65290篇
  2022年   413篇
  2021年   854篇
  2020年   528篇
  2019年   638篇
  2018年   831篇
  2017年   771篇
  2016年   1357篇
  2015年   2392篇
  2014年   2512篇
  2013年   3335篇
  2012年   4236篇
  2011年   4243篇
  2010年   2755篇
  2009年   2440篇
  2008年   3531篇
  2007年   3590篇
  2006年   3391篇
  2005年   3418篇
  2004年   3355篇
  2003年   3148篇
  2002年   3116篇
  2001年   711篇
  2000年   531篇
  1999年   729篇
  1998年   865篇
  1997年   597篇
  1996年   602篇
  1995年   591篇
  1994年   572篇
  1993年   596篇
  1992年   535篇
  1991年   463篇
  1990年   389篇
  1989年   405篇
  1988年   402篇
  1987年   338篇
  1986年   340篇
  1985年   395篇
  1984年   444篇
  1983年   374篇
  1982年   459篇
  1981年   409篇
  1980年   363篇
  1979年   240篇
  1978年   293篇
  1977年   284篇
  1976年   231篇
  1975年   216篇
  1974年   236篇
  1973年   219篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Aquatic environmental impact associated with stream-crossing by a pipeline was monitored at Archibald Creek, B.C. for two years. Water chemistry and benthic macroinvertebrates were used as monitoring tools. Results indicated that impacts arising from stream-crossing were short-term and non-residual.Funded by a contract from Canadian Arctic Gas Study Limited, calgary, to Aquatic Environments Limited, Calgary.Aquatic Environments Limited, Calgary.Aquatic Environments Limited, Calgary.  相似文献   
52.
53.
The uptake of free and liposome-entrapped 125I-labelled poly(vinylpyrrolidone) was measured in an intestinal sac preparation from adult rats. An an equal concentration of 125I-labelled poly(vinylpyrrolidone), the rate of uptake of the liposome-entrapped material was four times that of the free macromolecule.  相似文献   
54.
Peter hman 《Acta zoologica》1971,52(2):287-297
The outer segment of long and short photoreceptors in the retina of the river lamprey, Lampetra fluviatilis, were studied by light- and fluorescence microscopy together with some different electron microscopic methods. The outer segments show characteristics of both rods and cones and are suggested to represent intermediate kinds of photoreceptors.  相似文献   
55.
Summary A cell line derived from a human ovarian carcinosarcoma was established in tissue culture and in nude mice. Two sublines, LDF and HDF, separated by discontinuous density centrifugation were also established from the parent line JoN. The cloning efficiency of the JoN line was 21%. Morphologic features of adenocarcinoma cells characteristic of the parent JoN cells were retained in the sublines and clones; all lines showed the same karyotype and DNA content (pseudodiploid and pseudotetraploid). Keratin, as demonstrated immunohistochemically, was strongly expressed in the parent line JoN and the xenograft tumor, but not at all in the LDF sublines and only moderately in the HDF sublines. Vimentin, however, was expressed in neither the parent line JoN nor the xenograft tumor, but was present in both sublines. Transglutaminase and plasminogen activator activity was high in the parent line JoN. Neither, sublines nor clones showed the same high enzyme activity as the parent line. It is concluded that this human tumor line JoN is comprised of epithelial cells, capable of multidirectional differentiation.  相似文献   
56.
57.
Small-Sized Mutants of SACCHAROMYCES CEREVISIAE   总被引:5,自引:0,他引:5       下载免费PDF全文
The isolation of mutants of Saccharomyces cerevisiae that divide at approximately half the size of the wild type is described. Three mutants have been isolated in which the small size at bud initiation is due to a mutation in a single nuclear gene.  相似文献   
58.
59.
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