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   623710篇
  免费   63197篇
  国内免费   777篇
  2018年   6711篇
  2017年   6361篇
  2016年   8630篇
  2015年   10896篇
  2014年   13186篇
  2013年   18151篇
  2012年   21431篇
  2011年   22275篇
  2010年   15029篇
  2009年   13515篇
  2008年   19598篇
  2007年   20270篇
  2006年   19161篇
  2005年   18107篇
  2004年   18278篇
  2003年   17230篇
  2002年   16853篇
  2001年   25861篇
  2000年   25605篇
  1999年   20241篇
  1998年   7322篇
  1997年   7182篇
  1996年   6817篇
  1995年   6440篇
  1994年   6164篇
  1993年   6109篇
  1992年   16599篇
  1991年   16727篇
  1990年   16441篇
  1989年   15957篇
  1988年   14808篇
  1987年   13989篇
  1986年   13215篇
  1985年   13157篇
  1984年   10787篇
  1983年   9230篇
  1982年   6788篇
  1981年   6017篇
  1980年   5728篇
  1979年   10056篇
  1978年   8050篇
  1977年   7228篇
  1976年   6842篇
  1975年   8021篇
  1974年   8785篇
  1973年   8570篇
  1972年   7685篇
  1971年   7162篇
  1970年   6076篇
  1969年   5990篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
The paper presents data on a change in lysozyme content in tissues of spleen, liver and heart in fry of the Lena River sturgeon exposed to the presence of sublethal concentrations of Hg2+, Cd2+, and Cu2+ under conditions of chronic experiment. It has been shown that the lysozyme content in fish tissues varies and has a phasic character. The amplitude of fluctuations of this parameter depends on the moment of sampling, nature of the toxicant, and structural-functional organization of the studied organs.  相似文献   
43.
The goal of this study was to develop a new implantable transducer for measuring anterior cruciate ligament (ACL) graft tension postoperatively in patients who have undergone ACL reconstructive surgery. A unique approach was taken of integrating the transducer into a femoral fixation device. To devise a practical in vivo calibration protocol for the fixation device transducer (FDT), several hypotheses were investigated: (1) The use of a cable versus the actual graft as the means for applying load to the FDT during calibration has no significant effect on the accuracy of the FDT tension measurements; (2) the number of flexion angles at which the device is calibrated has no significant effect on the accuracy of the FDT measurements; (3) the friction between the graft and femoral tunnel has no significant effect on measurement accuracy. To provide data for testing these hypotheses, the FDT was first calibrated with both a cable and a graft over the full range of flexion. Then graft tension was measured simultaneously with both the FDT on the femoral side and load cells, which were connected to the graft on the tibial side, as five cadaver knees were loaded externally. Measurements were made with both standard and overdrilled tunnels. The error in the FDT tension measurements was the difference between the graft tension measured by the FDT and the load cells. Results of the statistical analyses showed that neither the means of applying the calibration load, the number of flexion angles used for calibration, nor the tunnel size had a significant effect on the accuracy of the FDT. Thus a cable may be used instead of the graft to transmit loads to the FDT during calibration, thus simplifying the procedure. Accurate calibration requires data from just three flexion angles of 0, 45, and 90 deg and a curve fit to obtain a calibration curve over a continuous range of flexion within the limits of this angle group. Since friction did not adversely affect the measurement accuracy of the FDT, the femoral tunnel can be drilled to match the diameter of the graft and does not need to be overdrilled. Following these procedures, the error in measuring graft tension with the FDT averages less than 10 percent relative to a full-scale load of 257 N.  相似文献   
44.
45.
46.
47.
48.
49.
50.
Besides vobtusine and vobtusine-lactone, deoxyvobtusine was isolated from the leaves of Voacanga grandifolia (Miq. Rolfe. Spectral and chemical evi  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