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   5440篇
  免费   148篇
  国内免费   18篇
化学   3993篇
晶体学   18篇
力学   63篇
数学   968篇
物理学   564篇
  2020年   49篇
  2019年   53篇
  2016年   92篇
  2015年   91篇
  2014年   100篇
  2013年   163篇
  2012年   159篇
  2011年   224篇
  2010年   113篇
  2009年   104篇
  2008年   213篇
  2007年   207篇
  2006年   211篇
  2005年   241篇
  2004年   184篇
  2003年   163篇
  2002年   162篇
  2001年   76篇
  2000年   73篇
  1999年   67篇
  1998年   51篇
  1997年   72篇
  1996年   69篇
  1995年   73篇
  1994年   52篇
  1993年   53篇
  1992年   67篇
  1991年   47篇
  1990年   68篇
  1989年   41篇
  1988年   64篇
  1987年   66篇
  1986年   41篇
  1985年   96篇
  1984年   56篇
  1983年   60篇
  1982年   68篇
  1981年   62篇
  1980年   48篇
  1979年   64篇
  1978年   68篇
  1977年   51篇
  1976年   73篇
  1975年   72篇
  1974年   52篇
  1973年   46篇
  1972年   39篇
  1970年   45篇
  1967年   36篇
  1966年   41篇
排序方式: 共有5606条查询结果,搜索用时 437 毫秒
111.
112.
113.
Choquet expected utility which uses capacities (i.e. nonadditive probability measures) in place of-additive probability measures has been introduced to decision making under uncertainty to cope with observed effects of ambiguity aversion like the Ellsberg paradox. In this paper we present necessary and sufficient conditions for stochastic dominance between capacities (i.e. the expected utility with respect to one capacity exceeds that with respect to the other one for a given class of utility functions). One wide class of conditions refers to probability inequalities on certain families of sets. To yield another general class of conditions we present sufficient conditions for the existence of a probability measureP with f dC= f dP for all increasing functionsf whenC is a given capacity. Examples includen-th degree stochastic dominance on the reals and many cases of so-called set dominance. Finally, applications to decision making are given including anticipated utility with unknown distortion function.  相似文献   
114.
A method is presented that can be used (a) to determine the several lowest eigenvalues and eigenvectors of large symmetric matrices, (b) to solve the generalized eigenvalue problem associated with energy-dependent operators, that arises in computations involving energy-dependent many-body Green's functions and in the evaluation of the true parameters of the effective valence shell hamiltonian, and (c) to directly evaluate the matrices associated with resolvent operators. The applicability to large configuration mixing calculations arises when the N-electron basis functions can be easily broken down to a few dominant configurations (the primary block) and their complement. Using the partitioning technique, the effective hamiltonian within the primary block is directly evaluated. The method is extended to evaluation of the dynamical polarizability tensor, which effectively contains the contributions from all of the eigenstates of a hamiltonian matrix, without the necessity of explicitly calculating its eigenvalues and eigenvectors.  相似文献   
115.
The highly explosive molecules As(N(3))(3) and Sb(N(3))(3) were obtained in pure form by the reactions of the corresponding fluorides with (CH(3))(3)SiN(3) in SO(2) and purification by sublimation. The crystal structures and (14)N NMR, infrared, and Raman spectra were determined, and the results compared to ab initio second-order perturbation theory calculations. Whereas Sb(N(3))(3) possesses a propeller-shaped, pyramidal structure with perfect C(3) symmetry, the As(N(3))(3) molecule is significantly distorted from C(3) symmetry due to crystal packing effects.  相似文献   
116.
p-Carborane has been vinylated on the 2-B-atom in high yields using the Heck reaction. Thus, the reaction between 2-iodo-p-carborane and various styrenes [4-H-, 4-C(6)H(4)-, 4-Cl-, 4-Br-, 4-NO(2)-, 4-CH(3)O-, and 4-CH(3)-] resulted in the production of the corresponding trans-beta-(2-B-p-carboranyl)styrene in DMF solution when reacted in the presence of silver phosphate and the palladacycle Herrmann's catalyst.  相似文献   
117.
Abstract The excitation of the eosin-human serum albumin complex has been investigated with spectral and photochemical techniques. Measurements of the changes in absorption and fluorescence spectra induced by complexing have shown that the first eosin molecule is held more strongly than the next few and that multiple binding leads to an enhanced fluorescence self-quenching. Flash photolytic measurements indicate that dye-dye quenching interactions enhance triplet eosin formation, and that oxygen quenching of the triplet is suppressed when the dye is singly bound. The quantum yield for aerobic photobleaching of the complex has been measured and is interpreted in terms of these findings.  相似文献   
118.
Seven copper(II)-complexes 1-7 with the ligand 2,2'-selenobis(4,6-di-tert-butylphenol) providing [O,Se,O]-donor atoms have been isolated and characterized. Three of them 1, 2 and 3 are mononuclear, two 4 and 7 dinuclear and 5, 6 are trinuclear. The crystal structures of the complexes were determined by X-ray diffraction and the electronic structures were established by various physical methods including EPR and variable temperature (2-290 K) susceptibility measurements. The magnetic behaviour of the compounds 4-6 exhibits antiferromagnetic exchange coupling resulting in well-isolated S(t)= 1/2 ground state for 5 and 6 and a diamagnetic spin state for 4. Complexes 5 and 6 belong to the class of asymmetric trinuclear copper(II) complexes modelling the trinuclear copper site in multicopper oxidases. Complex 1 is a catalyst in the presence of a strong base for the aerial oxidation of primary alcohols to the corresponding aldehydes. A dinuclear complex, seemed to be 4, prepared in situ has been found to be a catalyst for the aerial oxidation of primary amines containing alpha-C-H atoms. Primary kinetic isotope effects show that H-abstraction from the alpha-carbon atom of a coordinated substrate (alcoholato or amine) is the rate-determining step in both cases. Two functional models for the metalloenzymes galactose oxidase and amine oxidases are thus described.  相似文献   
119.
The preparation and properties of smooth and stable films of cyclodextrin polymers are described. The commercially available water soluble prepolymers of-, -, and-cyclodextrin of low molecular masses were crosslinked with glutaric dialdehyde. Side-chain unreacted aldehyde groups were reduced with sodium borohydride. For the-cyclodextrin polymer, optimum film performance was found for a 1:10 mass ratio of glutaric dialdehyde to prepolymer, which corresponds to a molar ratio of glutaric dialdehyde to cyclodextrin units of about 1.75: 1. Such films, of thickness 2.4 µm, were prepared on metallic or glassy-carbon substrates for characterization by scanning-electron microscopy, and for studies with the electrochemical quartz-crystal microbalance.  相似文献   
120.
Tentative Synthesis of ‘Bis(triasterane)’ and Synthesis of the Heterocyclic (Tricyclo[4.4.1.01,6]undeca-3,8-diene-11,11-dimethyl)sulfite The synthesis of the bis(triasterane) ( 1 ) has been tried; the reaction of ‘isotetraline’ (1,4,5,8-Tetrahydronaphthalene; 2 ) with diazomalonate yielded the tricyclic systems 5 and 6 , and not 4 . Hydrolysis of 5 gave the monocarboxylic acid 7 , and not the dicarboxylic acid 9 . The latter could be obtained from the dibromoderivative 8 , but 9 couldn't be converted to the acyl chloride 10 . The reduction of 9 with LiAlH4 yielded the crystalline diol 11 , which was cyclized with SOCl2 to the heterocycle 12 . The spectral data of the new compounds 5, 6, 7, 11 and 12 are reported and discussed.  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