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   11812篇
  免费   893篇
  国内免费   982篇
化学   985篇
晶体学   20篇
力学   857篇
综合类   115篇
数学   9779篇
物理学   1931篇
  2024年   20篇
  2023年   106篇
  2022年   123篇
  2021年   140篇
  2020年   242篇
  2019年   265篇
  2018年   286篇
  2017年   323篇
  2016年   351篇
  2015年   237篇
  2014年   458篇
  2013年   949篇
  2012年   475篇
  2011年   529篇
  2010年   522篇
  2009年   747篇
  2008年   873篇
  2007年   795篇
  2006年   709篇
  2005年   652篇
  2004年   484篇
  2003年   582篇
  2002年   489篇
  2001年   393篇
  2000年   383篇
  1999年   378篇
  1998年   315篇
  1997年   313篇
  1996年   187篇
  1995年   161篇
  1994年   151篇
  1993年   98篇
  1992年   77篇
  1991年   73篇
  1990年   76篇
  1989年   57篇
  1988年   68篇
  1987年   51篇
  1986年   45篇
  1985年   68篇
  1984年   65篇
  1983年   27篇
  1982年   51篇
  1981年   42篇
  1980年   43篇
  1979年   34篇
  1978年   33篇
  1977年   43篇
  1976年   30篇
  1974年   17篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Developed and reported are compact yet efficient correlating basis sets for the 57La and 89Ac atoms, missing in the literature. Good performance of these correlating sets is exemplified in molecular applications to diatomic oxides and fluorides. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010  相似文献   
952.
The thermal reactions of cationic 3d transition‐metal hydrides MH+ (M=Sc–Zn, except V and Cu) with ammonia have been studied by gas‐phase experiments and computational methods. There are three primary reaction channels: 1) H2 elimination by N? H bond activation, 2) ligand exchange under the formation of M(NH3)+, and 3) proton transfer to yield NH4+. Computational studies of these three reaction channels have been performed for the couples MH+/NH3 (M=Sc–Zn) to elucidate mechanistic aspects and characteristic reaction patterns of the first row. For N? H activation, σ‐bond metathesis was found to be operative.  相似文献   
953.
新型有序结构分子聚集体的构筑   总被引:4,自引:0,他引:4       下载免费PDF全文
本文概述了近年来我们在新型有序结构分子聚集体构筑方面取得的一些主要成绩,并展望了今后进一步的研究和发展方向。  相似文献   
954.
Properties of target species can be estimated by various means including interpolations in periodic charts. Interpolation is equivalent to numerical solution of the Laplace equation. A test of this equivalence, within some confidence level, for any N-atomic molecule surrounded by 4N nearest neighbors: the sum of the second differences of the data in all directions must be zero. Since very few molecules have 4N neighbors with known data, the test becomes: the sum of the averages of the second differences must be zero. The validity of these tests is explored. For radii of main-group atoms, and for internuclear separations of their diatomic combinations, the averages are different from zero and the sums of the averages are zero to within one if second-nearest neighbors are used. Dissociation potentials pass the tests but with larger scatter. Predictions for dissociation potentials, using iterative interpolation within boundaries on which there are known data, are reviewed.  相似文献   
955.
 Computational schemes are presented with which to evaluate the electrostatic Coulomb energy in relativistic molecular electronic structure calculations using a basis of four-component Dirac spinor amplitudes. We demonstrate that algorithms may be constructed and implemented which differ only in minor details from those in common use in nonrelativistic quantum chemistry, and that the four-component formalism is neither as complicated nor as expensive as has been suggested recently in the literature. Spherically symmetrical atomic basis sets are presented which indicate that accurate representations of the Coulomb energy may be obtained using modest expansions of the electronic density in a scalar auxiliary basis set of spherical harmonic Gaussian-type functions. Received: 15 April 2002 / Accepted: 15 May 2002 / Published online: 29 July 2002  相似文献   
956.
Summary An optimization procedure for the separation of flavonoids from St John's Wort by reversed-phase high-performance liquid chromatography on monolithic stationary phase is described. Three-component mobile phase systems are studied using experimental design methodology. The starting experimental domain is a triangle, each vertex of which is a pure component. From preliminary isocratic experiments, truncations in the domain are performed leading to a quadrilateral shape working domain with no symmetry. To cope with both separation and analysis time, desirability functions are used. Optimal conditions are finally given by binary systems and the four flavonoids are separated in less than seven minutes.  相似文献   
957.
By high-precision dynamic calorimetry the temperature dependences of heat capacity of dimethylene urethane (DMU) between 320 and 370 K and partially crystalline poly(dimethylene urethane) (PDMU) in the range 326-490 K at standard pressure have been determined within ±1.5%. The thermodynamic characteristics of fusion of the substances, namely the temperature interval of melting, temperature, enthalpy and entropy of fusion, as well as the characteristics of devitrification and glassy state for poly(dimethylene urethane) have been estimated. The first and the second cryoscopic constants have been calculated for dimethylene urethane. The experimental data obtained in the present work and literature findings on the heat capacity of the substances were used to calculate their thermodynamic functions: the heat capacity C°p (T), enthalpy H°(T)−H°(0), entropy S°(T) and Gibbs function G°(T)−H°(0) over the range from T→0 to (370-480) K. Based on the data, the thermodynamic characteristics of polymerization process with five-membered ring opening ΔpolH°, ΔpolS° and ΔpolG° of dimethylene urethane with the formation of linear partially crystalline poly(dimethylene urethane) have been evaluated.  相似文献   
958.
A closed‐form expression has been derived to obtain the N‐dimensional rectangular atomic wave functions. The wave functions can be obtained straightforwardly with the knowledge of the angular momentum quantum numbers and the dimension and there is no need to employ recursive methods as in previous works. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 88: 263–274, 2002  相似文献   
959.
旅澳学者裘凌沧教授积几十年微量元素科学研究成果,突破传统学科概念的束缚,以东方哲学为核心,运用近代系统工程学方法,分析了生命元素周期变化节律平衡与健康的关系,包括:内、外环境生命元素的特性,系统节律平衡是生命健康的基础和系统节律平衡调控的途径。本文分期刊出。  相似文献   
960.
The generator coordinate method was implemented in the unrestricted Hartree‐Fock formalism. Weight functions were built from Gaussian generator functions for 1s, 2s, and 2p orbitals of carbon and oxygen atoms. These weight functions show a similar behavior to those found in the generator coordinate restricted Hartree‐Fock method, i.e., they are smooth, continuous, and tend to zero in the limits of integration. Moreover, the weight functions obtained are different for spin‐up and spin‐down electrons what is a result from spin polarization. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012  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