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   299397篇
  免费   35133篇
  国内免费   220篇
  2018年   2582篇
  2017年   2433篇
  2016年   3305篇
  2015年   4420篇
  2014年   5289篇
  2013年   7216篇
  2012年   8258篇
  2011年   8431篇
  2010年   5572篇
  2009年   5363篇
  2008年   7534篇
  2007年   7654篇
  2006年   7504篇
  2005年   7181篇
  2004年   7057篇
  2003年   6824篇
  2002年   6681篇
  2001年   17319篇
  2000年   17479篇
  1999年   13347篇
  1998年   3902篇
  1997年   4170篇
  1996年   3885篇
  1995年   3522篇
  1994年   3497篇
  1993年   3581篇
  1992年   10414篇
  1991年   10346篇
  1990年   9836篇
  1989年   9669篇
  1988年   9006篇
  1987年   8374篇
  1986年   7574篇
  1985年   7430篇
  1984年   5851篇
  1983年   5092篇
  1982年   3635篇
  1981年   3194篇
  1980年   3046篇
  1979年   5365篇
  1978年   4126篇
  1977年   3760篇
  1976年   3306篇
  1975年   3785篇
  1974年   3953篇
  1973年   3896篇
  1972年   3425篇
  1971年   3190篇
  1970年   2825篇
  1969年   2743篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Cells from cranial and spinal arachnoid membranes of humans were grown in culture. Their growth characteristics, morphology and details of their cytoskeletal composition are described. Arachnoid membranes, obtained at autopsy, were finely minced and incubated in tissue culture medium. Monolayers of cells of homogeneous morphology grew from these tissue fragments. The cells were flat and polygonal. They divided slowly to form non-overlapping monolayers of low cell density. Electron microscopic examination of cultured arachnoid cells revealed numerous desmosome-like tight junctions and abundant intermediate filaments (tonofilaments). Both morphological features are characteristic of arachnoid cells in situ, but not of cells in the fibroblast-rich dura mater. Immunofluorescence microscopy with monoclonal antibodies demonstrated cytokeratin in the cytoplasm of primary cultures of arachnoid cells. Thus we demonstrated that these cultured cells retained certain of the specific differentiated properties of arachnoid cells in situ and that they are not fibroblasts (which lack tight junctions and cytokeratins). To our knowledge, there have been no previous reports of in vitro growth of arachnoid cells. This in vitro model should be useful in studying the response of arachnoid cells to a variety of substances thought to be involved in the chronic inflammatory condition of the meninges known as arachnoiditis.  相似文献   
972.
973.
974.
975.
976.
977.
A study was made of the effect of T-activin on the biosynthesis of immune gamma-interferon. It was shown that in 27% of patients with chronic nonspecific pulmonary diseases, production of gamma-interferon by lymphocytes was substantially reduced during exacerbation of inflammatory process in the lungs. It was discovered that T-activin was not an interferon inductor but enhanced its synthesis in patients with a low capacity of producing immune interferon even at small doses of interferon inductor. The preparation does not produce any effect on this process in normal subjects and in patients showing the normal level of gamma-interferon. Thus T-activin can be used for stimulation of interferonogenesis.  相似文献   
978.
Sorption of aromatic compounds from aqueous solutions by cryotextures and suspensions of native cornstarches was studied by capillary gas chromatography. Acetophenone and benzyl alcohol were not sorbed by cryotropic-cornstarch gel and native-cornstarch suspension. A linear concentration dependence was found for aldehydes. Phenylethyl alcohol was characterized by a nonlinear concentration dependence. The presence of a benzene ring contributed to decreased binding (relative to the level characteristic of aliphatic compounds). The degree of binding depended considerably on the type of functional group in the aromatic compounds. Cryotextures were more potent than granules of native cornstarch in binding aromatic compounds.  相似文献   
979.
22 livers with multiple metastases from different primaries were injected with acrylate resin and examined stereoscopically. All metastases had developed an individual pattern of vascularization. The metastases of 8 out of 12 livers injected via the portal vein showed a distinct blood supply by the portal vessels. In all 16 livers with arterial hypervascularized metastases the development of pathological tumor vessels could be demonstrated. All metastases of the same liver showed an identical pattern of vascularization. Larger branches of the hepatic vein always were displaced by the growing tumor. It was impossible however to infer from the vascularization pattern of the metastases to the primaries. The clinical relevance of these anatomical findings will be discussed.  相似文献   
980.
E T Salih  A G Pillay 《Acta anatomica》1985,122(4):212-215
Aminoglutethimide, a corticosteroid inhibitor, administered at a daily dose of 150 mg per kg body weight, showed a dramatic interference with ovarian histology in the rat. The drug caused thinning of the germinal epithelium and disruption of the layers of the follicular cells. It also resulted in the appearance of cytoplasmic vacuoles and distortion of follicle cell nuclei. In the corpus luteum, it caused shrinkage of the lutein cells, resulting in large spaces between the cords of cells. It also arrested immature follicles at various stages of their development. Our results indicate that aminoglutethimide, by modifying ovarian structure in the rat, interferes with the ovulation process.  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