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   467779篇
  免费   51475篇
  国内免费   168篇
  2018年   4772篇
  2017年   4566篇
  2016年   6259篇
  2015年   7802篇
  2014年   9197篇
  2013年   13101篇
  2012年   15712篇
  2011年   16427篇
  2010年   10758篇
  2009年   9560篇
  2008年   14776篇
  2007年   15309篇
  2006年   14343篇
  2005年   13594篇
  2004年   13547篇
  2003年   12687篇
  2002年   12524篇
  2001年   18694篇
  2000年   18873篇
  1999年   14745篇
  1998年   5440篇
  1997年   5622篇
  1996年   5328篇
  1995年   4988篇
  1994年   4866篇
  1993年   4881篇
  1992年   12052篇
  1991年   11925篇
  1990年   11667篇
  1989年   11250篇
  1988年   10802篇
  1987年   10393篇
  1986年   9650篇
  1985年   9574篇
  1984年   8135篇
  1983年   7057篇
  1982年   5481篇
  1981年   4913篇
  1980年   4727篇
  1979年   7699篇
  1978年   6140篇
  1977年   5650篇
  1976年   5447篇
  1975年   5888篇
  1974年   6533篇
  1973年   6390篇
  1972年   5913篇
  1971年   5394篇
  1970年   4766篇
  1969年   4700篇
排序方式: 共有10000条查询结果,搜索用时 406 毫秒
991.
The case of a 53 years old woman was described in whom a congenital factor XIII deficiency was suspected because of deforming scars and hemorrhagic diathesis. A thromboelastographic declination of elasticity as well as decreased factor XIII level up to 5% of normal range were only found in all hemostatic examinations. In 2 children factor XIII decreased to half of its normal level, whereas in the youngest daughter that level was 25%. Sporadically the girl had mild diathesis. No changes in thromboelastograms were observed in members of the patient's family. The platelet function was unchanged in all examined cases.  相似文献   
992.
The isoelectric point of the camel and the human β-endorphin, of the α-endorphin and the enkephalins were determined by analytical isoelectric focusing on 1 mm thin polyacrylamide gel slab. The difficulty of staining peptides as short as β-endorphin or smaller was overcomed using a modification of Bibring and Baxandall's or Faupel and Von Arx's staining method. The camel β-endorphin gives two bands having isoelectric point of 10.3 and 10.4, the human β-endorphin focus at pH 9.9, while α-endorphin, leu and met-enkephalin at pH 5.9, 5.5 and 5.45 respectively. The staining method described coupled with the isoelectric focusing seems to be fit for discriminating β-endorphin in a crude rat pituitary extract.  相似文献   
993.
The influence of surfactant depletion on clearance from the lungs of inhaled technetium-99m-labeled diethylenetriamine pentaacetate (99mTc-DTPA) was studied in rabbits. Surfactant was removed by repeated lung lavage with isotone saline. To minimize structural damage to the lungs, pressure generated insufflation with short expiration was utilized. Aerosolized 99mTc-DTPA was administered via a bag-in-bottle system. Radioactivity was measured with a gamma camera and time-activity curves were obtained over the base of the right lung. Six nonlavaged rabbits served as controls. In six lavaged rabbits clearance of 99mTc-DTPA was significantly faster than in controls. In three rabbits given natural surfactant into the trachea after lung lavage, 99mTc-DTPA was eliminated faster than in controls but slower than in surfactant-depleted animals. The results indicate a role of surfactant on clearance rate of 99mTc-DTPA from rabbit lungs. Measurements of 99mTc-DTPA clearance may be useful in studying the function of the surfactant system in different lung disorders.  相似文献   
994.
995.
996.
997.
False Images     
  相似文献   
998.
Monocytes/macrophages play a critical role in the initiation and progression of a variety of glomerulonephritides. We sought to define the interactions between physiologically activated human monocytes and glomerular mesangial cells (MC) by employing a cell culture system that permits the accurate assessment of the contribution of soluble factors and cell-to-cell contact. Human peripheral blood monocytes, primed with IFN-gamma and GM-CSF, were activated with CD40 ligand (CD40L) or TNF-alpha and cocultured with MC. CD40L-activated monocytes induced higher levels of IL-6, monocyte chemoattractant protein-1 (MCP-1) and ICAM-1 synthesis by MC. Separation of CD40L-activated monocytes from MC by a porous membrane decreased the mesangial synthesis of IL-6 by 80% and ICAM-1 by 45%, but had no effect on MCP-1. Neutralizing Abs against the beta 2 integrins, LFA-1 and Mac-1, decreased IL-6 production by 40 and 50%, respectively. Ligation of mesangial surface ICAM-1 directly enhanced IL-6, but not MCP-1, production. Simultaneous neutralization of soluble TNF-alpha and IL-1 beta decreased MCP-1 production by 55% in membrane-separated cocultures of MC/CD40L-activated monocytes. Paraformaldehyde-fixed CD40L-activated monocytes (to preserve membrane integrity but prevent secretory activity), cocultured with MC at various ratios, induced IL-6, MCP-1, and ICAM-1 synthesis by MC. Plasma membrane preparations from activated monocytes also induced mesangial IL-6 and MCP-1 synthesis. The addition of plasma membrane enhanced TNF-alpha-induced mesangial IL-6 production by approximately 4-fold. Together, these data suggest that the CD40/CD40L is essential for optimal effector function of monocytes, that CD40L-activated monocytes stimulate MC through both soluble factors and cell-to-cell contact mediated pathways, and that both pathways are essential for maximum stimulation of MC.  相似文献   
999.
1000.
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