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   293648篇
  免费   34647篇
  国内免费   152篇
  328447篇
  2018年   2407篇
  2016年   3093篇
  2015年   4051篇
  2014年   4935篇
  2013年   6773篇
  2012年   7725篇
  2011年   7937篇
  2010年   5213篇
  2009年   5048篇
  2008年   7172篇
  2007年   7345篇
  2006年   7226篇
  2005年   6938篇
  2004年   6818篇
  2003年   6647篇
  2002年   6493篇
  2001年   17274篇
  2000年   17461篇
  1999年   13318篇
  1998年   3866篇
  1997年   4132篇
  1996年   3856篇
  1995年   3494篇
  1994年   3470篇
  1993年   3544篇
  1992年   10413篇
  1991年   10332篇
  1990年   9827篇
  1989年   9659篇
  1988年   9006篇
  1987年   8379篇
  1986年   7580篇
  1985年   7424篇
  1984年   5845篇
  1983年   5088篇
  1982年   3617篇
  1981年   3188篇
  1980年   3037篇
  1979年   5352篇
  1978年   4116篇
  1977年   3753篇
  1976年   3313篇
  1975年   3780篇
  1974年   3948篇
  1973年   3891篇
  1972年   3422篇
  1971年   3184篇
  1970年   2823篇
  1969年   2744篇
  1968年   2412篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
A patient who developed Hodgkin''s disease four years after infectious mononucleosis had elevated serum antibody titres to Epstein-Barr virus and delayed hypersensitivity reactions to membrane antigens prepared from fresh autologous spleen, from spleen cells of another Hodgkin''s patient, and from cell lines known to carry the Epstein-Barr virus genome. Additional studies in more lymphoma patients will be needed to determine the significance of the reactivity against tumour and virus-associated antigens which has been documented in this patient.  相似文献   
932.
933.
934.
The effect of inert helium and argon gases on the tissue respiration has been studied on lymphocyte suspensions of white rats. It is shown that normoxic helium-oxygen mixture induces almost a two-fold increase of the O2 uptake by lymphocytes as compared with the control (air). No deviations in the value of the studied parameter are revealed in case of replacement of nitrogen from air by argon. Significance of the membrane structure in realization of effects of inert gases is under discussion.  相似文献   
935.
936.
Experimental measurements of the radial restricted linear energy transfer (LETr) for alpha beams of 18.3 MeV/n in tissue-equivalent gas were presented. The radial dose distribution for the alpha beam was deduced from the restricted LET measurements. A differential W value for the alpha particle in the tissue-equivalent gas was also deduced. The result for the differential W value was 29.0 +/- 0.9 eV/ion pair. The radial dose varied according to an inverse-square function with distance from the track center for radii larger than 0.026 micron. The maximum extension of the track, the penumbra radius, as 2.73 +/- 1.67 microns, which was less than predicted by calculations (7-9 microns).  相似文献   
937.
938.
A morphometric study of kainic acid- (KA) induced lesions was designed for the study of the interaction of the diamines U-5449A and U-50488H with excitatory amino acids, and the dose-response relationship thereof. IC50S determined for binding at the kappa receptor and other opioid receptors demonstrated the lack of kappa activity of U-54494A, a structurally related analog of U-50488H. Both opiate kappa receptor related anticonvulsant diamines were tested for their ability to protect the mouse hippocampus from the cytopathological changes induced by KA in neurons and glia. The damage observed with i.c.v. KA in mouse was restricted to neurons of the CA3 pyramidal region and glia of the hippocampus. It involved massive cell loss and shrunken neurons with dark cytoplasm and nuclei. Groups treated with combinations of KA and U-54494A or U-50488H showed scarce damage, but patches of necrotic changes were still observed. Control animals treated with saline (i.c.v.) and U-54494A (s.c.) or U-50488H (s.c.) did not suffer any noticeable alterations of the polymorphic layers of the hippocampal formation. Image analysis of the CA3 area of the hippocampus was used to quantitate the vacuolization induced by KA lesions in the control and treated groups. By this method, both U-54494A and U-50488H were shown to protect this area in a dose-related fashion as evidenced by reduced vacuolization. The anticonvulsant properties of these compounds may result in the antagonism of the excitotoxic lesions. More specifically, the ability of these diamines to block depolarization-induced influxes of Ca++ may protect the CA3 cells from the cytotoxic effects of persistent depolarization.  相似文献   
939.
Natural heparin complexes proved to activate the anticoagulation system. The obtained experimental data convincingly confirm that glutamic acid alone, and particularly in a complex with heparin, has a considerable preventive potential and efficiently protects experimental animals with induced diabetes mellitus.  相似文献   
940.
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