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   1541505篇
  免费   26225篇
  国内免费   8070篇
化学   794259篇
晶体学   21423篇
力学   79297篇
综合类   127篇
数学   259161篇
物理学   421533篇
  2021年   13815篇
  2020年   16204篇
  2019年   16342篇
  2018年   18694篇
  2017年   17558篇
  2016年   31057篇
  2015年   21714篇
  2014年   31008篇
  2013年   75352篇
  2012年   48958篇
  2011年   54524篇
  2010年   44217篇
  2009年   44868篇
  2008年   50736篇
  2007年   48914篇
  2006年   47487篇
  2005年   43743篇
  2004年   41376篇
  2003年   37003篇
  2002年   36295篇
  2001年   37139篇
  2000年   30218篇
  1999年   25123篇
  1998年   22099篇
  1997年   21882篇
  1996年   21752篇
  1995年   19632篇
  1994年   19188篇
  1993年   18748篇
  1992年   19817篇
  1991年   19874篇
  1990年   19071篇
  1989年   18996篇
  1988年   18734篇
  1987年   18527篇
  1986年   17501篇
  1985年   23849篇
  1984年   24727篇
  1983年   20675篇
  1982年   22123篇
  1981年   21283篇
  1980年   20654篇
  1979年   21331篇
  1978年   22287篇
  1977年   22073篇
  1976年   21840篇
  1975年   20623篇
  1974年   20288篇
  1973年   20672篇
  1972年   15121篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
The synthesis of benzazepine analogues of the opium alkaloid noscapine ( 1 ) is described. The benzazepines 2 and 3 were prepared starting from nornarceine ethyl ester ( 4 ; readily available from 1 ) in several steps. X-Ray analysis of compound 2 revealed that it is not a diastereosisomer mixture but a racemate of the threo-form and thus has the same configuration as 1 .  相似文献   
132.
Publication list     
The helium atom in its ground state, subject to strong magnetic fields, is treated using a variational method. Trial functions consisting of Gaussians with nonlinear parameters variationally optimized are used. The form of these functions is a generalized s-symmetry-state properly modified to admit spatial deformation along the direction on which the magnetic field is applied. © 1994 John Wiley & Sons, Inc.  相似文献   
133.
The evaluation of second derivatives of the electronic energy for nonvariational wave functions using an energy functional is discussed. It is shown that, in certain cases, the formation of the first-order relaxed density matrix leads to an efficient algorithm for the calculation of second-order response properties. Detailed formulas are given for second-order Møller–Plesset perturbation theory. © 1994 John Wiley & Sons, Inc.  相似文献   
134.
A set of exact conditions is compiled for the purpose of developing and testing approximations for the exchange-correlation energy as a functional of the electron density. Special emphasis is placed upon recently developed density-scaling relationships. Commonly used generalized gradient approximations are compared against several of these conditions. A direct tabular comparison of these functionals (not of calculated properties) with one another is also made. © 1994 John Wiley & Sons, Inc.  相似文献   
135.
136.
137.
The applicability of differential electrolytic potentiometry as a detection system in flow injection analysis is investigated. A computer-controlled injector which delivers precise volumes of sample solutions in a reproducible manner was developed. Conditions such as current density employed, the concentrations of the solutions used and the flow rate were optimized. Chloride in water was determined by means of this system. The relation between chloride concentration and the measured signal was found to be Nernstian for solutions of concentrations above 6 μg ml−1 chloride. For solutions below this concentration, the relation is linear.  相似文献   
138.
An estimate of the factors which influence the rate of growth of filamentary silicon crystals in a standard chloride system using a quartz reactor with hot walls is given. It is shown that a diffusion form of crystallization is observed under the conditions investigated.Voronezh State Technical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 22–26, October, 1995.  相似文献   
139.
On the basis of the method of successive approximations in formal series we construct systems of particular solutions of the equations of planar and flexural harmonic vibrations of thin rectilinear anisotropic plates with a plane of symmetry of elastic properties parallel to the faces. The solutions constructed are classified as special sk-functions of generalized complex variables. Translated fromTeoreticheskaya i Prikladnaya Mekhanika No. 24, 1993, pp. 54–61.  相似文献   
140.
We present the results of an experimental investigation of a RF splitting of57Fe hyperfine lines in the regime of NMR and Mössbauer double resonance. The experiments have been performed as a function of RF field intensity and static magnetic field magnitude. The intensity of the RF components and the separation between them are extremely sensitive to the frequency and amplitude of the RF magnetic field. The RF splitting of hyperfine lines is inversely proportional to the strength of the static magnetic field.  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