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   532536篇
  免费   59642篇
  国内免费   345篇
  592523篇
  2018年   5218篇
  2017年   5085篇
  2016年   6942篇
  2015年   8760篇
  2014年   10473篇
  2013年   15240篇
  2012年   16945篇
  2011年   17324篇
  2010年   11687篇
  2009年   10727篇
  2008年   15135篇
  2007年   15689篇
  2006年   14657篇
  2005年   14048篇
  2004年   13912篇
  2003年   13267篇
  2002年   12799篇
  2001年   28353篇
  2000年   28213篇
  1999年   21976篇
  1998年   6723篇
  1997年   7302篇
  1996年   6733篇
  1995年   6208篇
  1994年   5981篇
  1993年   5956篇
  1992年   17041篇
  1991年   16289篇
  1990年   15697篇
  1989年   15207篇
  1988年   13920篇
  1987年   12938篇
  1986年   12043篇
  1985年   11814篇
  1984年   9660篇
  1983年   8083篇
  1982年   5992篇
  1981年   5376篇
  1980年   5096篇
  1979年   8942篇
  1978年   6814篇
  1977年   6273篇
  1976年   5647篇
  1975年   6236篇
  1974年   6762篇
  1973年   6543篇
  1972年   5979篇
  1971年   5428篇
  1970年   4679篇
  1969年   4399篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
961.
962.
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   
963.
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   
964.
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   
965.
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   
966.
967.
968.
969.
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   
970.
Cadmium (200 ppm) applied through the rooting medium to 30-day-old wheat plants decreased chlorophyll content, net CO2 exchanges and PSII activity by 34, 54 and 43% respectively. Thylakoid total lipids, total glycolipids, total phospholipids and total neutral lipids decreased by 22, 23, 12 and 25%, respectively, under cadmium treatment. Thylakoid membrane glycolipids had three major constituents, viz. monogalactosyl diacylglycerol, digalactosyl diacylglycerol and sulphoquinovosyl diacylglycerol. Monogalactosyl diacylglycerol and digalactosyl diacylglycerol contents decreased by 32 and 27%, respectively, under cadmium. Cadmium application also decreased the concentration of phosphatidyl glycerol and phosphatidyl choline to the extent of about 57 and 31%, respectively. On the other hand, phosphatidic acid and free fatty acids content showed an increase. These compositional changes in thylakoid membranes might be responsible for reduced PSII activity and rate of photosynthesis as observed under cadmium treatment.  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