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   413837篇
  免费   44451篇
  国内免费   241篇
  458529篇
  2021年   3624篇
  2018年   4302篇
  2017年   3868篇
  2016年   5863篇
  2015年   8610篇
  2014年   9985篇
  2013年   13248篇
  2012年   15822篇
  2011年   16017篇
  2010年   10482篇
  2009年   9764篇
  2008年   14044篇
  2007年   14065篇
  2006年   13542篇
  2005年   12943篇
  2004年   12905篇
  2003年   12093篇
  2002年   11645篇
  2001年   19312篇
  2000年   19162篇
  1999年   15092篇
  1998年   5432篇
  1997年   5316篇
  1996年   4924篇
  1995年   4528篇
  1994年   4412篇
  1993年   4422篇
  1992年   11461篇
  1991年   11281篇
  1990年   10714篇
  1989年   10575篇
  1988年   9783篇
  1987年   9138篇
  1986年   8225篇
  1985年   8197篇
  1984年   6733篇
  1983年   5848篇
  1982年   4453篇
  1981年   4056篇
  1980年   3828篇
  1979年   5985篇
  1978年   4804篇
  1977年   4392篇
  1976年   3942篇
  1975年   4276篇
  1974年   4587篇
  1973年   4436篇
  1972年   3815篇
  1971年   3539篇
  1970年   3184篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
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   
994.
995.
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   
996.
997.
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   
998.
999.
T. C. Lacalli 《Protoplasma》1973,78(4):433-442
Summary The ultrastructure of cytokinesis inM. rotata is described with particular attention to the early stages. At prophase a girdle of primary wall material is deposited at the cell isthmus. The girdle thickens medially, a septum is established and grows inward to separate the daughter semicells by telophase. It is argued that the wall microtubules present at the isthmus are not responsible for delimiting the area over which the girdle is initially deposited, but may participate in girdle deposition and thickening. An important role is ascribed to the secondary wall which, at the isthmus, is devoid of pore bodies and slime. The inner wall surface could, at the isthmus, provide the substratum required for unitial girdle deposition. Though microtubules may be associated with septum initiation, they appear to play no part in subsequent septum growth.  相似文献   
1000.
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