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   205747篇
  免费   2473篇
  国内免费   516篇
化学   113401篇
晶体学   3662篇
力学   8071篇
综合类   11篇
数学   19722篇
物理学   63869篇
  2020年   1854篇
  2019年   2024篇
  2018年   2296篇
  2017年   2430篇
  2016年   3679篇
  2015年   2329篇
  2014年   3716篇
  2013年   9269篇
  2012年   6786篇
  2011年   8252篇
  2010年   5832篇
  2009年   5790篇
  2008年   7370篇
  2007年   7273篇
  2006年   6865篇
  2005年   6242篇
  2004年   5695篇
  2003年   5214篇
  2002年   5018篇
  2001年   6206篇
  2000年   4682篇
  1999年   3567篇
  1998年   2803篇
  1997年   2752篇
  1996年   2645篇
  1995年   2478篇
  1994年   2361篇
  1993年   2196篇
  1992年   2865篇
  1991年   2751篇
  1990年   2699篇
  1989年   2723篇
  1988年   2746篇
  1987年   2751篇
  1986年   2614篇
  1985年   3330篇
  1984年   3344篇
  1983年   2623篇
  1982年   2730篇
  1981年   2800篇
  1980年   2556篇
  1979年   2894篇
  1978年   2876篇
  1977年   3007篇
  1976年   2826篇
  1975年   2565篇
  1974年   2517篇
  1973年   2474篇
  1972年   1706篇
  1968年   1707篇
排序方式: 共有10000条查询结果,搜索用时 515 毫秒
991.
992.
993.
The physical mixtures of hydroxocarbonates of Cu and Ni with aluminium were activated using a laboratory planetary mill. The chemical reactions and alloy formations as the effects of grinding were followed by the phase analysis of solid products based on the thermogravimetry and X-ray diffractometry. Experimental evidence indicates that the nature of reactions and products of mechanical activation was dependent on the amount of aluminium and time of grinding. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
994.
Muon spin relaxation (μSR) and nuclear magnetic resonance (NMR) are powerful probes of magnetism, which have been extensively applied to studies of spin gap systems. Comparison of results obtained with the two techniques gives complementary results, as each is sensitive to different aspects of spin gap magnetism. We discuss recent μSR measurements of the spin ladder compounds Sr n?1Cu n+1O2n , pure and doped Haldane materials (Y2?x Ca x )Ba(Ni1?y Mg y )O5, and doped spin Peierls compounds (Cu1?x Zn x )(Ge1?y Si y )O3.  相似文献   
995.
996.
In Venkaiah [1] an algorithm for solving linear optimization problems based on the idea of the projective algorithm of Karmarkar, is proposed. The essential simplification in the new algorithm is the use of a fixed projection operator. In this way the algorithm requires onlyO(n 2 ) operations to obtain a sufficient exact solution. In this note it is shown that in some special cases the algorithm of Venkaiah yields a feasible solution that is far from the optimal one.  相似文献   
997.
998.
The processing of oil sands materials and upgrading of bitumens present a variety of problems for conventional technologies. This article describes a preliminary study of the concept of using microwave induced catalytic techniques to decompose the complex and viscous hydrocarbon compounds contained in these materials to allow efficient extraction of volatile and economically useful organic products such as C2 and C3 hydrocarbons. Addition of water to the tar sand material prior to reaction facilitated separation from the sand component as well as promoting the formation of economically very useful, liquid, oxygenated hydrocarbon products.  相似文献   
999.
1000.
Many materials exhibit various magnetic phenomena as a function of magnetic field, temperature and/or pressure. Usually, bulk magnetic measurements provide first information on the magnetic state of the material by measuring their response on the applied magnetic field. However, it is necessary to investigate materials also on a microscopic scale. This is often done by means of neutron scattering. In this contribution we discuss basic ideas of this method and we report on few experimental results obtained with a split-pair coil 14.5 T superconducting magnet which can be combined with dilution stick offering temperatures as low as 30 mK and/or with a small clamped-type pressure cell which offers pressure up to 1.0 GPa.  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