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   623507篇
  免费   65773篇
  国内免费   371篇
  2021年   4836篇
  2018年   7397篇
  2017年   7059篇
  2016年   9731篇
  2015年   12858篇
  2014年   14661篇
  2013年   20843篇
  2012年   23745篇
  2011年   23747篇
  2010年   15774篇
  2009年   13796篇
  2008年   20396篇
  2007年   20956篇
  2006年   19438篇
  2005年   18582篇
  2004年   18205篇
  2003年   17256篇
  2002年   16419篇
  2001年   29905篇
  2000年   29736篇
  1999年   23323篇
  1998年   7375篇
  1997年   7813篇
  1996年   7174篇
  1995年   6714篇
  1994年   6472篇
  1993年   6342篇
  1992年   18032篇
  1991年   17251篇
  1990年   16546篇
  1989年   16009篇
  1988年   14668篇
  1987年   13572篇
  1986年   12630篇
  1985年   12484篇
  1984年   10235篇
  1983年   8584篇
  1982年   6380篇
  1981年   5754篇
  1980年   5420篇
  1979年   9443篇
  1978年   7206篇
  1977年   6625篇
  1976年   5986篇
  1975年   6613篇
  1974年   7152篇
  1973年   6945篇
  1972年   6268篇
  1971年   5736篇
  1970年   4962篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
131.
132.
133.
134.
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   
135.
136.
137.
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   
138.
139.
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   
140.
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   
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