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   2023340篇
  免费   202025篇
  国内免费   1773篇
  2227138篇
  2018年   20971篇
  2017年   19825篇
  2016年   30575篇
  2015年   44257篇
  2014年   52541篇
  2013年   78843篇
  2012年   60646篇
  2011年   55001篇
  2010年   52275篇
  2009年   51062篇
  2008年   50149篇
  2007年   50413篇
  2006年   50566篇
  2005年   51450篇
  2004年   50214篇
  2003年   47348篇
  2002年   45044篇
  2001年   67794篇
  2000年   65985篇
  1999年   57040篇
  1998年   30020篇
  1997年   29837篇
  1996年   28693篇
  1995年   26807篇
  1994年   26357篇
  1993年   26027篇
  1992年   48747篇
  1991年   47391篇
  1990年   45995篇
  1989年   45997篇
  1988年   42461篇
  1987年   41148篇
  1986年   38357篇
  1985年   39776篇
  1984年   35541篇
  1983年   31268篇
  1982年   27370篇
  1981年   25652篇
  1980年   24193篇
  1979年   32904篇
  1978年   27987篇
  1977年   25867篇
  1976年   24851篇
  1975年   26048篇
  1974年   27895篇
  1973年   27826篇
  1972年   24623篇
  1971年   22670篇
  1970年   19750篇
  1969年   19475篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The Oral History and Literature of the Wolof People of Waalo, Northern Senegal. Samba Diop. Lewiston, Canada; Edwin Mellen Press, 1995. 389 pp.  相似文献   
992.
Individual-site isotherms add experimental data which may allow for a more detailed definition of the parameters in a system with interacting binding sites. Individual-site isotherms accomplish the following: (A) In general, they define little more than the total or combined isotherm except to reveal the existence of different sites. (B) Under the limiting conditions of symmetrical interactions in two site systems they define: (1) the ratio of the unperturbed or intrinsic binding constants rather than their actual values, (2) the unperturbed shape of the total isotherm, that is, the shape of the total isotherm if there were no ligand dependent interactions between the sites, and (3) the perturbation of the shape of the total isotherm derived from interactions between the sites. (C) They do not define the nature of the interactions; that is, they do not resolve the free energies of the interactions between the sites. (D) When some assumptions about the nature of the interactions are made they may aid in defining some free energies of interaction between the sites.  相似文献   
993.
994.
995.
996.
997.
998.
The muscle phase of Trichinella spiralis and of Trichinella sp. isolated in the Arctic was compared in experimental and wild animals. Reproductive capacity indices (RCI) of the Trichinella sp. isolate were significantly lower in laboratory rodents but were similar to T. spiralis in wild rodents. Sprague-Dawley rats were the most refractory to the Trichinella sp. isolate of all laboratory rodents. Outbred strains of mice were more susceptible to both T. spiralis and the Trichinella sp. isolate than inbred strains of mice. T. spiralis muscle larvae survived longer in mice and the survival of both T. spiralis and the Trichinella sp. isolate larvae was higher in female mice. While single pair interbreeding experiments showed reproductive isolation between T. spiralis and the Trichinella sp. isolate, multiple pair and transplant breeding experiments showed reproductive compatibility. Male and female infective larvae of T. spiralis and the Trichinella sp. isolate differed morphometrically, but a convergence in size of worms was observed after prolonged passages of the parasites in mice. Passaging history of the isolate and host species was found to have a significant effect on Trichinella morphology. It is proposed that the Trichinella sp. isolate is a physiological variant of T. spiralis and not a distinct species.  相似文献   
999.
Elevated serum gamma-glutamyl transferase (GGT) levels were found in 29% of 155 chronic alcoholics undergoing detoxification treatment. Alkaline phosphatase (AP) was increased in 16%, alanine aminotransferase--SGPT (ALT) in 12% of the patients, while 23% had elevations of either AP or ALT or both. Of the foregoing parameters, GGT was the best single indicator of liver involvement. In course of the follow-ups GGT/ALT correlation improved, but GGT/AP correlation deteriorated. In 9 patients, abstinence during follow-up was associated with progressive decrease in previously elevated serum GGT. Because of its unique sensitivity, GGT may be useful as a screening and/or monitoring aid in alcoholism.  相似文献   
1000.
We have used a quantitative titration assay for mixed lymphocyte interactions to determine the additivity of responses of rat lymphocyte populations to simultaneous stimulation with major histocompatibility complex alloantigens from pairs of apparently unrelated rat strains. Our inability to detect strict additive stimulation led us to investigate inclusion among allo-reactive lymphocyte populations. After specific depletion of reactivity to PVG by negative selection through an AO × PVG F1 hybrid rat, AO thoracic duct lymphocytes showed an asymmetrical loss of reactivity to the unrelated strains DA and F344. We suggest that this differential loss of reactivity probably reflects alloantigen sharing among rat strains which had been previously undetected using other less sensitive techniques for the quantitation of lymphocyte reactivity after specific depletion of allo-reactive cells.  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