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   1785篇
  免费   71篇
  国内免费   21篇
化学   1197篇
晶体学   38篇
力学   24篇
数学   356篇
物理学   262篇
  2023年   12篇
  2022年   24篇
  2021年   38篇
  2020年   23篇
  2019年   25篇
  2018年   39篇
  2017年   29篇
  2016年   53篇
  2015年   59篇
  2014年   82篇
  2013年   139篇
  2012年   102篇
  2011年   124篇
  2010年   77篇
  2009年   69篇
  2008年   95篇
  2007年   78篇
  2006年   69篇
  2005年   85篇
  2004年   56篇
  2003年   57篇
  2002年   60篇
  2001年   28篇
  2000年   23篇
  1999年   21篇
  1998年   17篇
  1997年   20篇
  1996年   19篇
  1995年   24篇
  1994年   19篇
  1993年   14篇
  1992年   16篇
  1991年   15篇
  1990年   20篇
  1989年   17篇
  1988年   13篇
  1987年   14篇
  1986年   14篇
  1985年   14篇
  1984年   18篇
  1983年   10篇
  1982年   15篇
  1981年   18篇
  1980年   9篇
  1979年   9篇
  1978年   9篇
  1977年   9篇
  1975年   10篇
  1968年   7篇
  1962年   8篇
排序方式: 共有1877条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
The present paper is a continuation of comprehensive study regarding to synthesis and properties of pyrazoles and their derivatives. In its framework an experimental and theoretical studies of thermal decomposition of the 3,3-diphenyl-4-(trichloromethyl)-5-nitropyrazoline were performed. It was found, that the decompositions of the mentioned pyrazoline system in the solution and at the melted state proceed via completely different molecular mechanisms. These mechanisms have been explained in the framework of the Molecular Electron Density Theory (MEDT) with the computational level of B3LYP/6-31G(d). A Bonding Evolution Theory (BET) examination of dehydrochlorination of the 3,3-diphenyl-4-(trichloromethyl)-5-nitropyrazoline permits elucidation of the molecular mechanism. It was found, that on the contrary for most known HCl extrusion processes in solution, this reaction is realised via single-step mechanism.  相似文献   
5.
崔凯  杨国伟 《中国物理快报》2005,22(11):2738-2741
Based on the homotopy mapping, a globally convergent method of parameter inversion for non-equilibrium convection-dispersion equations (CDEs) is developed. Moreover, in order to further improve the computational efficiency of the algorithm, a properly smooth function, which is derived from the sigmoid function, is employed to update the homotopy parameter during iteration. Numerical results show the feature of global convergence and high performance of this method. In addition, even the measurement quantities are heavily contaminated by noises, and a good solution can be found.  相似文献   
6.
7.
8.
Following the general scheme of the convariant path integral quantization of gauge systems, two alternative formulations of the first quantized closed bosonic string in a position representation are presented. In both approaches the covariant path integral representations of the propagator and of the higher order off-shell amplitudes are constructed. For a wide class of gauges the explicit formulae for off-shell amplitudes are obtained. This paper is the continuation of our previous work where the corresponding problems in the open string case were considered [20].  相似文献   
9.
Summary At first, a necessary and sufficient condition for a K?hler-Norden manifold to be holomorphic Einstein is found. Next, it is shown that the so-called (real) generalized Einstein conditions for K?hler-Norden manifolds are not essential since the scalarcurvature of such manifolds is constant. In this context, we study generalized holomorphic Einstein conditions. Using the one-to-one correspondence between K?hler-Norden structures and holomorphic Riemannian metrics, we establish necessary and sufficient conditions for K?hler-Norden manifolds to satisfy the generalized holomorphic Einstein conditions. And a class of new examples of such manifolds is presented. Finally, in virtue of the obtained results, we mention that Theorems 1 and 2 of H. Kim and J. Kim [10] are not true in general.  相似文献   
10.
Zbigniew Lonc 《Order》1994,11(2):149-158
We show that in an ordered setP of width 3 there always exists a fibre (i.e., a subset intersecting each maximal nontrivial antichain) of size at most 11/18|P|. This improves previously known results.Research supported by Polish KBN Grant 2 2037 92 03.  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