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   144226篇
  免费   4908篇
  国内免费   2726篇
化学   82674篇
晶体学   2267篇
力学   6156篇
综合类   191篇
数学   14142篇
物理学   46430篇
  2021年   1161篇
  2020年   1437篇
  2019年   1376篇
  2018年   1246篇
  2017年   1157篇
  2016年   2186篇
  2015年   1883篇
  2014年   2369篇
  2013年   6125篇
  2012年   5145篇
  2011年   6212篇
  2010年   3939篇
  2009年   3588篇
  2008年   5172篇
  2007年   5222篇
  2006年   5124篇
  2005年   4932篇
  2004年   4155篇
  2003年   3755篇
  2002年   3603篇
  2001年   3976篇
  2000年   3054篇
  1999年   2655篇
  1998年   2228篇
  1997年   2232篇
  1996年   2107篇
  1995年   2064篇
  1994年   1843篇
  1993年   1777篇
  1992年   1947篇
  1991年   1936篇
  1990年   1850篇
  1989年   1792篇
  1988年   1770篇
  1987年   1761篇
  1986年   1647篇
  1985年   2179篇
  1984年   2304篇
  1983年   1911篇
  1982年   2236篇
  1981年   2043篇
  1980年   2086篇
  1979年   2058篇
  1978年   2186篇
  1977年   2090篇
  1976年   2115篇
  1975年   2054篇
  1974年   1895篇
  1973年   2102篇
  1972年   1282篇
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
231.
The Hawking effect of a nonuniformly rectilinearly accelerating Kinnersley black hole is studied. Its horizons are rotationally symmetric. Its Hawking temperature depends not only on the time, but also on the polar angle. When a Kinnersley black hole touches its Rindler horizon, the Hawking temperature at the contact point is reduced to zero. But at the opposite pole of the black hole, the Hawking temperature increases rapidly. A jet appears as a tail of the accelerating black hole.  相似文献   
232.
The aim of this paper is to extend our knowledge about the gas-dynamic processes in arcs during immobility time. For this purpose, the conservation equations in a magnetohydrodynamic approximation were coupled with the thermochemical and Maxwell equations. Special features arc the introduction of dissociation and ionization of nitrogen and oxygen, and the simultaneous calculation of the distributions of current density and magnetic induction in the arc. Numerical calculations were performed with a reduced two-dimensional (2-D) time-dependent model. Results of the calculations were compared with measurements. The development in time of the measured and calculated are voltage and arc chamber pressure show very good agreement. The pumping effect of the double vortex in the arc region was confirmed by optical measurements. It is concluded that the three-layer model is a good representation for the main physical features during the immobility time, and that the presence of highly conducting gas in the downstream region of the arc is essential for its downstream movement  相似文献   
233.
阎江  谢绳武 《光学学报》1998,18(10):295-1299
报道了KDP晶体中的三倍频产生的实验研究,计算了比较了直接三倍频过程和级联过程对KDP晶体三阶有效非线性系数的贡献,并探讨了KDP作为非线性晶体材料三阶非线性系数测量基准的可行性。  相似文献   
234.
The origin of the widely observed enhancement of rates for electron-ion recombination at very low energies is still unknown. We investigated the recombination of Au25+ with free electrons in a merged-beams experiment at the UNILAC accelerator of the GSI in Darmstadt. At E rel= 0 eV we found an enormous enhancement factor of 365 compared to the theory of radiative recombination. An increase of the electron density by a factor of 10 had not much influence on the measured rate coefficient. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
235.
We consider initial boundary value problems for the equations of the one-dimensional motion of a viscous, heat-conducting gas with density-dependent viscosity that decreases (to zero) with decreasing density. We prove that if the viscosity does not decrease to zero too rapidly, then smooth solutions exist globally in time.  相似文献   
236.
Book reviews     
Adlard  E. R.  Davies  I. W.  Shelton  C. G. 《Chromatographia》1995,41(9-10):612-615
  相似文献   
237.
238.
Studies that focus on the decision making process can be classified in (at least) two ways: by psychological content and by contextual content. The first describes the degree to which the analysis focuses on the mental processes associated with decision making and the second deals with the degree to which the analysis is dependent upon the study's context. Several studies are examined in terms of where they fall in this two-dimensional taxonomy. Two analyses of maritime command and control conducted by the authors are examined more fully within this taxonomy. Both are context full, but are at opposite ends of the psychological content spectrum. These categorizations are useful in focusing future research aimed at developing models of decision making.  相似文献   
239.
240.
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