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   450577篇
  免费   55825篇
  国内免费   283篇
  506685篇
  2018年   3841篇
  2017年   3517篇
  2016年   5491篇
  2015年   8213篇
  2014年   9212篇
  2013年   12931篇
  2012年   14926篇
  2011年   15036篇
  2010年   9919篇
  2009年   9191篇
  2008年   13113篇
  2007年   13595篇
  2006年   12282篇
  2005年   12110篇
  2004年   11865篇
  2003年   11320篇
  2002年   10826篇
  2001年   21678篇
  2000年   21804篇
  1999年   17420篇
  1998年   6244篇
  1997年   6485篇
  1996年   6309篇
  1995年   5708篇
  1994年   5759篇
  1993年   5581篇
  1992年   13670篇
  1991年   12981篇
  1990年   12667篇
  1989年   12526篇
  1988年   11186篇
  1987年   10804篇
  1986年   9890篇
  1985年   9683篇
  1984年   8214篇
  1983年   7082篇
  1982年   5537篇
  1981年   5015篇
  1980年   4660篇
  1979年   7709篇
  1978年   5935篇
  1977年   5438篇
  1976年   5078篇
  1975年   5384篇
  1974年   5825篇
  1973年   5672篇
  1972年   5108篇
  1971年   4733篇
  1970年   3924篇
  1969年   3857篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
991.
992.
C D Fitch 《Life sciences》1977,20(7):1281-1284
Studies of infective potency were done to determine why chloroquine-resistant P.berghei is an obligate parasite of immature erythrocytes. Infective potency was estimated from the length of time required for mice to develop parasitemia of 2% (delay in parasitemia). The delay in parasitemia was an inverse linear function of the logarithm of the number of parasites inoculated. A single regression line fitted the data both for susceptible and for resistant parasites, indicating identical infective potencies which, in turn, indicates that chloroquine-resistant P.berghei selects and preferentially infects immature erythrocytes whereas it rejects mature erythrocytes.  相似文献   
993.
994.
995.
996.
997.
998.
A multi-sample slippage test based on ordered observations has been given. The test statistic is based on the sum of ranks of the sample. The probability distribution of the test statistic has been worked out for small sample and it turns out to be chi-square distribution for large sample. The analytical procedure has been explained by a numerical example.  相似文献   
999.
We describe the use of a suprahyoid flap for reconstruction in the lower anterior neck. It has been most useful for immediately closing pharyngostomes and for resurfacing defects from the excision of squamous cell carcinoma of the larynx or other neoplasms involving the skin. This flap provides a good deal of viable tissue, it can easily be rotated without a delay procedure, and the donor area is closed by direct suture. We present our experience with 22 cases.  相似文献   
1000.
The cat hindlimb contains several long, biarticular strap muscles composed of parallel muscle fascicles that attach to short tendons. Three of these muscles--sartorius, tenuissimus, and semitendinosus--were studied by dissecting individual gold-stained fibers and determining the surface distribution of acetylcholinesterase-stained end-plate zones. In each muscle, fascicles were composed of muscle fibers that ran only part of the fascicle length and tapered to end as fine strands that interdigitated with other tapering fibers within the muscle mass. Most muscle fibers measured 2-3 cm in length. Fascicles of muscle fibers were crossed by short transverse bands of endplates (1 mm wide by 1-5 mm long) that were spaced at fairly regular intervals from the origin to the insertion of the muscle. The endplate pattern suggested that the fiber fascicles were organized into multiple longitudinal strips. In the sartorius, the temporospatial distribution of electromyographic (EMG) activity evoked by stimulating fine, longitudinal branches of the parent nerve confirmed that each strip was selectively innervated by a small subset of the motor axons. These axons appeared to distribute their endings throughout the entire length of the fascicles, providing for synchronous activation of their in-series fibers.  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