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   536402篇
  免费   59891篇
  国内免费   347篇
  596640篇
  2018年   5311篇
  2017年   5159篇
  2016年   7074篇
  2015年   8903篇
  2014年   10671篇
  2013年   15496篇
  2012年   17218篇
  2011年   17591篇
  2010年   11843篇
  2009年   10876篇
  2008年   15303篇
  2007年   15881篇
  2006年   14807篇
  2005年   14210篇
  2004年   14047篇
  2003年   13373篇
  2002年   12906篇
  2001年   28427篇
  2000年   28275篇
  1999年   22024篇
  1998年   6761篇
  1997年   7326篇
  1996年   6754篇
  1995年   6245篇
  1994年   6008篇
  1993年   5979篇
  1992年   17093篇
  1991年   16331篇
  1990年   15748篇
  1989年   15248篇
  1988年   13962篇
  1987年   12964篇
  1986年   12076篇
  1985年   11844篇
  1984年   9688篇
  1983年   8105篇
  1982年   6008篇
  1981年   5391篇
  1980年   5112篇
  1979年   8969篇
  1978年   6830篇
  1977年   6289篇
  1976年   5668篇
  1975年   6253篇
  1974年   6776篇
  1973年   6562篇
  1972年   6002篇
  1971年   5441篇
  1970年   4694篇
  1969年   4415篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
In order to assess the requirement for the Arg-Gly-Asp-Ser (RGDS) consensus adhesion sequence in von Willebrand factor (vWF) for vWF binding to platelets and endothelial cells, point mutations were introduced into this sequence by site-directed mutagenesis. A glycine to alanine substitution yielded RADS-vWF, while an aspartate to glutamate substitution resulted in RGES-vWF. Recombinant RADS-vWF and RGES-vWF, purified from transformed Chinese hamster ovary cells, were compared with recombinant wild type vWF (WT-vWF) in functional assays with platelets and human umbilical vein endothelial cells (HU-VECs). High molecular weight RADS-vWF and RGES-vWF multimers inhibited binding of 125I-vWF to a mixture of insolubilized native type I and III collagen and competed effectively with 125I-vWF for binding to formalin-fixed platelets in the presence of ristocetin, indicating functional collagen and platelet glycoprotein Ib binding. However, RADS-vWF and RGES-vWF were unable to displace the binding of 125I-vWF to thrombin or ADP-activated platelets. The attachment of HUVECs to either RADS-vWF or RGES-vWF coated surfaces was reduced and spreading was almost completely inhibited, compared with WT-vWF. We conclude that point mutations of the RGDS sequence in vWF selectively impair binding to platelet glycoprotein IIb/IIIa and the HUVEC vitronectin receptor.  相似文献   
962.
963.
Ovariectomized Syrian hamsters treated by female sex steroids during a 1-month period show gallbladder surface epithelial changes in the fundic area consistent with apical bulging and decapitations of the epithelial cells. These events were detected in the infundibulum and the fundic or body regions of estrogen- and estrogen+progesterone-treated hamsters. In control hamsters, these events were restricted to the region in the vicinity of the bile duct. Following steroid treatment, intraluminal deposits detected resembled Ca-bilirubinate deposits described in previous studies while decapitations are similar to endometrial epithelium changes associated with hormonal physiological changes or treatments. Moreover some small electron-dense deposits are comparable to those found in human cholesterol gallstones. This report indicates that, besides an alteration in bile composition, cell fragments originating from the surface epithelium of the bile duct and/or of the gallbladder mucosal epithelium could participate in gallstone nucleation.  相似文献   
964.
A fluorescent probe was used to study hydrocortisone (10 microM) action on mitogen-stimulated free cytoplasmic calcium level in lymphocytes of patients with bronchial asthma. The patients were divided into two groups according to their sensitivity to glucocorticoid therapy. Hydrocortisone-specific calcium-blocking effect was absent in hormone-resistant patients. Lymphocytes of hormone-sensitive patients responded to hydrocortisone administration by a decline of mitogen-induced calcium level.  相似文献   
965.
A transcribed gene in an intron of the human factor VIII gene   总被引:18,自引:0,他引:18  
  相似文献   
966.
The oriental persimmon (Diospyros kaki Lf) is believed to have originated in China with subsequent introduction into Japan and Korea in ancient times. The species was then brought to Europe, Brazil and the USA from Japan in the 19th century. Recent studies highlighted the poor state of identification of cultivars in these countries due to incorrect labelling and presence of synonyms among local varieties. Thus, molecular marker characterization of germplasm resources is of great value for genetic resource preservation and plant breeding of persimmon. Therefore, to identify accessions for further plant breeding and germplasm management, 37 microsatellite loci were developed from a CT/AG‐enriched persimmon genomic library.  相似文献   
967.
968.
969.
970.
The Proceedings of the ECSA 21 symposium on Marine and Estuarine Gradients are reviewed. It is emphasised that this is probably the first time that a full set of papers on the tidal freshwater sections of estuaries has appeared. There is however some ambiguity in the terminology applied to such waters, and a more consistent terminology is proposed. In particular the estuary is defined as reaching upstream as far as the tidal limit, irrespective of salinity. A wide variety of gradients within estuaries and coastal waters are considered, but it is apparent that the crucial spatial gradients are based on salinity, oxygen and turbidity, and that many other gradients are co-variables with these parameters. Temperature is also important for temporal gradients.  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