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   222992篇
  免费   2548篇
  国内免费   1355篇
化学   123726篇
晶体学   3348篇
力学   8951篇
综合类   64篇
数学   24556篇
物理学   66250篇
  2020年   1975篇
  2019年   2137篇
  2018年   2520篇
  2017年   2552篇
  2016年   3758篇
  2015年   2444篇
  2014年   3573篇
  2013年   8925篇
  2012年   7732篇
  2011年   9440篇
  2010年   6681篇
  2009年   6490篇
  2008年   8850篇
  2007年   8944篇
  2006年   8424篇
  2005年   7739篇
  2004年   6904篇
  2003年   6075篇
  2002年   6018篇
  2001年   6720篇
  2000年   5091篇
  1999年   3686篇
  1998年   3052篇
  1997年   3010篇
  1996年   3029篇
  1995年   2632篇
  1994年   2736篇
  1993年   2599篇
  1992年   2842篇
  1991年   2913篇
  1990年   2721篇
  1989年   2626篇
  1988年   2563篇
  1987年   2506篇
  1986年   2525篇
  1985年   3306篇
  1984年   3364篇
  1983年   2807篇
  1982年   3053篇
  1981年   2814篇
  1980年   2608篇
  1979年   2791篇
  1978年   2996篇
  1977年   3032篇
  1976年   3059篇
  1975年   2794篇
  1974年   2906篇
  1973年   2956篇
  1972年   2318篇
  1971年   1845篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
The gauge compensation fields induced by the differential operators of the Stueckelberg-Schrödinger equation are discussed, as well as the relation between these fields and the standard Maxwell fields; An action is constructed and the second quantization of the fields carried out using a constraint procedure. The properties of the second quantized matter fields are discussed.  相似文献   
32.
The micro element content of food is an important quality index due to the action of these elements on human health. In this article, we discuss how to ensure the reliability of analytical data on micro elements in order to truly represent the condition of food. Sampling, treatment of the analytical sample, selection of the analytical method, standard solution, and certified reference material, blank test, calibration of the instrument and equipment, application of the quality control chart, assessment of the final analytical result, and quality assurance system are briefly described. Received: 5 July 2001 Accepted: 19 November 2001  相似文献   
33.
34.
Although the most important use of nuclear magnetic resonance imaging (MRI) continues to be for diagnostic medicine, recognition is being gained for many nonmedical applications. Examples include the following areas: petrogeology, food, agriculture, polymers and polymer-composites, and pharmaceuticals. These areas all involve studies of species that have short spin-spin relaxation times, and consequently need far fast gradient switching. These technical details are discussed and typical applications given.  相似文献   
35.
In this paper we construct a primitive, non-symmetric 3-class association scheme with parameters v = 36, v1 = 7, p111 = 0 and p211 = 4 and show that such a scheme is determined by its parameters.  相似文献   
36.
TheSU(2) rotation matricesD (j), specified in terms of axis and angle of rotation, are expressed as linear combination of normalized irreducible tensorial matricces (NITM) of rankl = 0 to 2j rotated to the polar angles of the axis. The rotated NITM are constructed from spherical harmonics of the same rank. Since this formulation requires no matrix products, it may be computationally more efficient than Euler angle formulas, particularly for largej. Rotated NITM and formulas for theD (j) withj = 1/2 andj = 1 are written out explicitly. A formula for the structure constants of the products of conformable NITM is also given in terms of 3-j and 6-j symbols.  相似文献   
37.
Silver nitrate-acetonitrile and π iodine-benzene complexes in thermotropic liquid crystals have been studied by 1H, 2H, and 13C NMR spectroscopy and by optical microscopy. Evidence for at least two silver complexes in each liquid crystal is presented.  相似文献   
38.
We study a generalization of the notion of the chromatic number of a graph in which the colors assigned to adjacent vertices are required to be, in a certain sense, far apart. © 1993 John Wiley & Sons, Inc.  相似文献   
39.
40.
Experimental data demonstrate that a study of accelerated aging can enable prognostication of the working capacity and storage life of polymeric formulations used in aircraft components on the basis of changes in thermogravimetric constants of these polymeric formulations.  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