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   748157篇
  免费   82449篇
  国内免费   560篇
  831166篇
  2018年   6863篇
  2017年   6626篇
  2016年   9246篇
  2015年   12011篇
  2014年   14150篇
  2013年   20851篇
  2012年   22919篇
  2011年   23484篇
  2010年   15887篇
  2009年   14586篇
  2008年   20856篇
  2007年   21465篇
  2006年   20252篇
  2005年   19457篇
  2004年   19246篇
  2003年   18426篇
  2002年   17819篇
  2001年   36157篇
  2000年   36171篇
  1999年   28344篇
  1998年   9338篇
  1997年   10080篇
  1996年   9402篇
  1995年   8610篇
  1994年   8355篇
  1993年   8391篇
  1992年   22849篇
  1991年   22162篇
  1990年   21323篇
  1989年   20827篇
  1988年   19149篇
  1987年   17957篇
  1986年   16739篇
  1985年   16717篇
  1984年   13685篇
  1983年   11562篇
  1982年   8757篇
  1981年   7956篇
  1980年   7523篇
  1979年   13003篇
  1978年   9962篇
  1977年   9367篇
  1976年   8504篇
  1975年   9404篇
  1974年   10264篇
  1973年   10004篇
  1972年   9114篇
  1971年   8384篇
  1970年   7314篇
  1969年   6970篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
A new gas-liquid chromatographic method was developed for the determination of diethylether in whole blood. Ether was quantitated by peak area ratio analysis with n-propanol as the internal standard using a flame ionization detector. Blood ether concentrations were determined in cats undergoing inhalational anesthesia by ether in oxygen. In normal spontaneously breathing cats, anesthesia began at ether concentrations of about 0.6 g/l, and respiratory arrest occurred at 2.4 g/l and above. Mean arterial blood pressure was well maintained throughout the entire anesthetic range. In spinal artificially respired animals, mean arterial blood pressure correlated inversely with blood ether concentration. The data suggest that decline in blood pressure may be a useful sign of ether toxicity in spinal cats.  相似文献   
153.
154.
155.
From three Fouquieria sp. 12 iridoid glucosides were isolated and identified. Eight of these were structurally related to galioside (monotropein methylester), while four were hydroxy substitution products of deoxyloganin. In three cases the glucoside occurred together with the corresponding 10-O-acetate.  相似文献   
156.
A computer-assisted analysis of the spatial distribution of neurons having homogeneous characteristics is described in this paper. The camera lucida drawings of sections of a brain nucleus and the points representing the neurons labeled on the basis of a specific behavior of discharge rates were digitized on a personal computer Amiga 2000 or IBM compatible. Our software provided: a) the computerized, stereotaxically oriented reconstruction of the stored sections and of the plotted neurons; b) the identification within each section of the mass center (MC) of the units sharing a given behavior and of the area where the density of such neurons was maximal (MDA). The routine was tested on the spatial distribution of neuronal responses to serotonin in the lateral vestibular nucleus.  相似文献   
157.
An indwelling nasal suction tampon is described that effectively controls both intraoperative and postoperative nasal hemorrhage. The significant benefits of this device are better intraoperative control for the surgeon and less complicated postoperative recovery. I do not have any financial involvement in this device, but I would like other nasal surgeons to benefit from its particular advantages. The device is available under the trade name Instant and may be obtained from Innovations by Westmed, 3351 E. Hemisphere Loop, Tucson, Ariz. 85706; (602) 294-7987.  相似文献   
158.
In many species of actinomycetes, carotenogenesis can be photoinduced. The capacity to respond to photoinduction is, however unstable and, in various strains of Streptomyces, is lost at a relatively high frequency. In Streptomyces setonii ISP5395, which normally produces no carotenoids, carotenoid-producing mutants can be obtained following protoplast regeneration. We report here the characterization of a gene, crtS, which was isolated from one such mutant and can confer on wild-type S. setonii ISP5395 cells the capacity to synthesize carotenoids. Sequence analysis of crtS reveals an open reading frame, which shows homology to genes that encode alternative sigma factors in Bacillus subtilis. We propose that crtS encodes a sigma factor which is necessary for the expression of a cryptic gene(s) for carotenoid biosynthesis in S. setonii ISP5395.  相似文献   
159.
160.
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