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   709632篇
  免费   76145篇
  国内免费   567篇
  2018年   6952篇
  2017年   6791篇
  2016年   9276篇
  2015年   11478篇
  2014年   13834篇
  2013年   20026篇
  2012年   22152篇
  2011年   23012篇
  2010年   15589篇
  2009年   14217篇
  2008年   20166篇
  2007年   20767篇
  2006年   19546篇
  2005年   18754篇
  2004年   18425篇
  2003年   17698篇
  2002年   17142篇
  2001年   36022篇
  2000年   35862篇
  1999年   27853篇
  1998年   8690篇
  1997年   9264篇
  1996年   8700篇
  1995年   8054篇
  1994年   7720篇
  1993年   7647篇
  1992年   21965篇
  1991年   21098篇
  1990年   20591篇
  1989年   20047篇
  1988年   18417篇
  1987年   17252篇
  1986年   15932篇
  1985年   15975篇
  1984年   13003篇
  1983年   11012篇
  1982年   8042篇
  1981年   7318篇
  1980年   6867篇
  1979年   12044篇
  1978年   9243篇
  1977年   8524篇
  1976年   7885篇
  1975年   8787篇
  1974年   9467篇
  1973年   9334篇
  1972年   8398篇
  1971年   7683篇
  1970年   6729篇
  1969年   6263篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
161.
162.
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   
163.
164.
Studies on the ecology of microbial parasites and their hosts are predicated on understanding the assemblage of and relationship among the species present. Changes in organismal morphology and physiology can have profound effects on host–parasite interactions and associated microbial community structure. The marine rickettsial organism, “Candidatus Xenohaliotis californiensis” (WS-RLO), that causes withering syndrome of abalones has had a consistent morphology based on light and electron microscopy. However, a morphological variant of the WS-RLO has recently been observed infecting red abalone from California. We used light and electron microscopy, in situ hybridization and16S rDNA sequence analysis to compare the WS-RLO and the morphologically distinct RLO variant (RLOv). The WS-RLO forms oblong inclusions within the abalone posterior esophagus (PE) and digestive gland (DG) tissues that contain small rod-shaped bacteria; individual bacteria within the light purple inclusions upon hematoxylin and eosin staining cannot be discerned by light microscopy. Like the WS-RLO, the RLOv forms oblong inclusions in the PE and DG but contain large, pleomorphic bacteria that stain dark navy blue with hematoxylin and eosin. Transmission electron microscopy (TEM) examination revealed that the large pleomorphic bacteria within RLOv inclusions were infected with a spherical to icosahedral-shaped putative phage hyperparasite. TEM also revealed the presence of rod-shaped bacteria along the periphery of the RLOv inclusions that were morphologically indistinguishable from the WS-RLO. Binding of the WS-RLO-specific in situ hybridization probe to the RLOv inclusions demonstrated sequence similarity between these RLOs. In addition, sequence analysis revealed 98.9–99.4 % similarity between 16S rDNA sequences of the WS-RLO and RLOv. Collectively, these data suggest that both of these RLOs infecting California abalone are “Candidatus Xenohaliotis californiensis,” and that the novel variant is infected by a putative phage hyperparasite that induced morphological variation of its RLO host.  相似文献   
165.
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   
166.
Galactose- and inositol-binding proteins with lectin activity (GL-GAL and GL-I, respectively) were isolated from membranes enriched with cells of chicken brain fractions. Both lectins are glycoproteins of molecular mass 13.5 and 11.5 kDa, respectively; they show a high affinity to EDTA (GL-I) and EGTA (GL-GAL, GL-I), which indicates an important role of Ca+2 in molecular organization of these lectins. In brain glial cells of chick embryos, unlike adult chickens, a soluble form of lectins has been revealed; it is easily extracted with 2 mM EDTA and shows sensitivity to L-lactose, D-galactose, and N-acetyl-D-galactosamine. It is suggested that in the course of embryonal and postembryonal development of the chicken brain, a transformation and qualitative changes of the lectin spectrum occur due to a change of function of glial cells.  相似文献   
167.
168.
169.
170.
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