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   276108篇
  免费   2395篇
  国内免费   923篇
化学   145886篇
晶体学   3955篇
力学   10469篇
综合类   2篇
数学   31418篇
物理学   87696篇
  2020年   2393篇
  2019年   2676篇
  2018年   2704篇
  2017年   2596篇
  2016年   4384篇
  2015年   3088篇
  2014年   4440篇
  2013年   12429篇
  2012年   9210篇
  2011年   11409篇
  2010年   7339篇
  2009年   7220篇
  2008年   10246篇
  2007年   10429篇
  2006年   9672篇
  2005年   9055篇
  2004年   8113篇
  2003年   7235篇
  2002年   7097篇
  2001年   7792篇
  2000年   5865篇
  1999年   4690篇
  1998年   3957篇
  1997年   4025篇
  1996年   3759篇
  1995年   3514篇
  1994年   3376篇
  1993年   3416篇
  1992年   3692篇
  1991年   3737篇
  1990年   3532篇
  1989年   3547篇
  1988年   3590篇
  1987年   3394篇
  1986年   3305篇
  1985年   4481篇
  1984年   4669篇
  1983年   3797篇
  1982年   4314篇
  1981年   4170篇
  1980年   4032篇
  1979年   4070篇
  1978年   4318篇
  1977年   4090篇
  1976年   4303篇
  1975年   3838篇
  1974年   3972篇
  1973年   4242篇
  1972年   2656篇
  1971年   2044篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
Semi-empirical model potential calculations have been performed for bound and continuum properties of Li? and Na?. The calculated electron affinities of the 2s21S state of Li? and the 3s21S and 3p23Pe states of Na? are in agreement with the calculations of Norcross and with experimental data. Positions of possible autoionizing states are calculated using projection and root stabilization methods. The Stieltjes imaging method of Langhoff is employed to compute the photodetachment cross sections of Li? and Na? and the results are in excellent agreement with the close-coupling calculations of Moores and Norcross. A comparison of variational and numerical results for the coupled time-dependent Hartree-Fock photoionization of helium shows that good Stieltjes imaging results can be obtained with a very small basis set for the variational calculation. The continuous photoemission profile for the 3p23Pe state of Na? is also obtained.  相似文献   
992.
The reaction of cycloheptane, cyclooctane, and cyclododecane with carbon monoxide under pressure in the presence of anhydrous aluminium chloride has been investigated. Cycloheptane leads to acetylcyclohexane and trans-2-methyl-cyclohexane carboxylic acid as main products. Cyclooctane yields 3- and trans-4-acetyl-methylcyclohexane and various dimethylcyclohexane carboxylic acids. From cyclododecane a mixture of numerous ketones has been obtained besides a mixture of acids.  相似文献   
993.
Zusammenfassung Es seiG eine endliche Untergruppe der orthogonalen Gruppe (det=±1) des k mitk=2 oder 3 undN eine endliche Menge von Punkten des k , welche unterG invariant ist. Dies gibt Anlass zu einer Permutationsdarstellung vonG im Vektorraum der komplexen Funktionen aufN.In Abschn. 3 wird für eine symmetriegerechte Basis angegeben. Dabei sind die Funktionswerte jeweils exakt tabelliert.
Let G be a finite subgroup of the orthogonal group (det=±1) of k wherek=2 or 3 and letN be a finite set of points of k , which is invariant underG. In this way one gets a permutation representation ofG in the vector space of the complex functions onN.In Section 3, a symmetry adapted basis is given for , where the function values are tabulated exactly.


Im Buch [1] wurden lediglich die Diedergruppen behandelt (in Abschn. 3.1).  相似文献   
994.
Summary Uniform consistency and weak convergence is proved of estimators of the transition probabilities of an arbitrary finite state space Markov renewal process, based on n independent and identically distributed right censored realizations of the process. The approach uses the theory of stochastic integrals and counting processes. It is shown how the results may be extended to the non-identically distributed case and to general censorship under suitable conditions.  相似文献   
995.
The reflectivity and transmitivity of a spatially dispersive crystal for S-polarized incident light are calculated for a microscopical model in which the interaction among the crystal planes is assumed to fall exponentially with distance. The angle of incidence is arbitrary and the deduced formulae are valid from X-ray to the visible light region. The generalization to the more complicated models is briefly discussed. For solving the problem an algebraic formulation of the Ewald dynamical theory of diffraction is used.  相似文献   
996.
In the actinides bothi 13/2 protons andj 15/2 neutrons are close to the Fermi surface. At rapid rotation these high-j particles will unpair and align their orbital angular momentum along the axis of rotation giving rise tos-bands that cross the ground-state band. Coulomb excitation of the odd nuclei 237 93 Np (established up to the 45/2+ state) and 235 92 U (established up to the 51/2? state) provides specific information about these band crossings: From the saturating alignment of the odd high-j particle in both nuclei at intermediate rotational frequencies we find the aligned angular momentum of thei 13/2 protons-band to be 6.6? while the corresponding value for thej 15/2 neutrons-band is 5.5?. At more rapid rotation above ?ω=0.18 MeV we observe additional alignment in235U. This is ascribed to the interaction of the protons-band. From the gradual onset of the additional alignment we deduce that forZ=92 the protons-band interacts strongly with the ground-state band and from a comparison of the actual amount of alignment with the full value of 6.6? we estimate the crossing to occur around ?gw c p =0.25 MeV.  相似文献   
997.
First experiments with the arrangement described in part I of this paper resulted in three spurious effects: shifting of characteristic values due to ageing effects, dissymmetric behaviour of wall charges and currents with respect to the voltage pulse sign, and backfiring. The comparison between the direct and the indirect methods demonstrated the sensitivity of the indirect ones to uncertainties and variations in effective cell capacities. The wall charge density distributions are axially symmetric and can be described in the electrode range by ? (x) = ae.  相似文献   
998.
Assume that in one unit of time a node is stored in the stack or is removed from the top of the stack during postorder-traversing of a binary tree. If all binary trees are equally likely the average stack size aftert units of time and the variance is computed as a function of the proportion=t/n.Part of this paper was presented at the 6th Colloquium on Automata, Languages and Programming, ICALP' 79, July 1979.  相似文献   
999.
We calculate the observable critical temperature dependence of the transport coefficients entering the hydrodynamic form of the dynamic structure factor of4He belowT . Application of our recently introduced nonlinear renormalization-group analysis yields quantitative agreement with previous light scattering experiments in the hydrodynamic region. This resolves a long-standing problem in the critical dynamics below the superfluid transition of4He.Supported in part by the Fonds zur Förderung der wissenschaftlichen Forschung  相似文献   
1000.
In a Minkowski plane with parallelisms + and one postulates triple transitivity of + -preserving bijections of points onto points such that circles map on circles. This postulate corresponds almost exactly to Axiom G of [2]. A coordinatization may then be accomplished by introduction of a quaternary operation, after a coordinate frame consisting of three distinct concircular points has been fixed. All circles except those in one derived affine plane are points (x,y) with y=[x,a,b,c]. This derived plane then turns out to be a nearfield-plane. The quaternary operation satisfies [x,a,b,c]=[x–a,0,0,1]c+b. In a symmetric Minkowski plane, which, in view of [1], is coordinatized by a commutative field, y=[x,a,b,c] becomes (x–a)(y–b)=c, yielding the well known hyperbola model.Dedicated to Werner Burau on his 70th birthdayPresented to the Conference on Geometry, University of Haifa, March 10, 1975.  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