全文获取类型
收费全文 | 371097篇 |
免费 | 3771篇 |
国内免费 | 1441篇 |
专业分类
化学 | 192891篇 |
晶体学 | 5982篇 |
力学 | 17281篇 |
综合类 | 8篇 |
数学 | 41576篇 |
物理学 | 118571篇 |
出版年
2020年 | 2747篇 |
2019年 | 2984篇 |
2018年 | 3679篇 |
2017年 | 3621篇 |
2016年 | 5873篇 |
2015年 | 3980篇 |
2014年 | 6036篇 |
2013年 | 16410篇 |
2012年 | 12643篇 |
2011年 | 15857篇 |
2010年 | 10667篇 |
2009年 | 10745篇 |
2008年 | 14572篇 |
2007年 | 14513篇 |
2006年 | 13889篇 |
2005年 | 12659篇 |
2004年 | 11628篇 |
2003年 | 10127篇 |
2002年 | 10040篇 |
2001年 | 11659篇 |
2000年 | 8909篇 |
1999年 | 6931篇 |
1998年 | 5626篇 |
1997年 | 5553篇 |
1996年 | 5342篇 |
1995年 | 4863篇 |
1994年 | 4683篇 |
1993年 | 4678篇 |
1992年 | 5020篇 |
1991年 | 5145篇 |
1990年 | 4680篇 |
1989年 | 4647篇 |
1988年 | 4686篇 |
1987年 | 4517篇 |
1986年 | 4280篇 |
1985年 | 6017篇 |
1984年 | 6162篇 |
1983年 | 5017篇 |
1982年 | 5357篇 |
1981年 | 5161篇 |
1980年 | 5001篇 |
1979年 | 5105篇 |
1978年 | 5215篇 |
1977年 | 5135篇 |
1976年 | 5199篇 |
1975年 | 4873篇 |
1974年 | 4840篇 |
1973年 | 4951篇 |
1972年 | 3282篇 |
1971年 | 2566篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
TOPOLOGY DESIGN OF STRUCTURES SUBJECTED TO PERIODIC LOADING 总被引:5,自引:0,他引:5
C.S. JOG 《Journal of sound and vibration》2002,253(3):687-709
Although a lot of attention in the topology optimization literature has focused on the optimization of eigenfrequencies in free vibration problems, relatively little work has been done on the optimization of structures subjected to periodic loading. In this paper, we propose two measures, one global and the other local, for the minimization of vibrations of structures subjected to periodic loading. The global measure which we term as the “dynamic compliance” reduces the vibrations in an overall sense, and thus has important implications from the viewpoint of reducing the noise radiated from a structure, while the local measure reduces the vibrations at a user-defined point. Both measures bring about a reduction in the vibration level by moving the natural frequencies which contribute most significantly to the measures, away from the driving frequencies, although, as expected, in different ways. Quite surprisingly, the structure of the dynamic compliance optimization problem turns out to be very similar to the structure of the static compliance optimization problem. The availability of analytical sensitivities results in an efficient algorithm for both measures. We show the effectiveness of the measures by presenting some numerical examples. 相似文献
72.
73.
I. J. Lozada J. C. Osorio D. V. Griffiths M. Cerrolaza 《Numerical Methods for Partial Differential Equations》2006,22(2):296-316
The semi‐analytical integration of an 8‐node plane strain finite element stiffness matrix is presented in this work. The element is assumed to be super‐parametric, having straight sides. Before carrying out the integration, the integral expressions are classified into several groups, thus avoiding duplication of calculations. Symbolic manipulation and integration is used to obtain the basic formulae to evaluate the stiffness matrix. Then, the resulting expressions are postprocessed, optimized, and simplified in order to reduce the computation time. Maple symbolic‐manipulation software was used to generate the closed expressions and to develop the corresponding Fortran code. Comparisons between semi‐analytical integration and numerical integration were made. It was demonstrated that semi‐analytical integration required less CPU time than conventional numerical integration (using Gaussian‐Legendre quadrature) to obtain the stiffness matrix. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2006 相似文献
74.
C Falugi A Diaspro C Angelini M L Pedrotti M Raimondo M Robello 《Micron (Oxford, England : 1993)》2002,33(3):233-239
Confocal laser scanning microscopy (CLSM) was used to examine molecules related to the cholinergic neurotransmission system and detected at all the larval stages of Paracentrotus lividus, by histochemical and immunohistochemical methods. CLSM, providing spatial resolution of the cells located both at the larval surface and at depth, allows a complete mapping in a three-dimensional volumetric frame. At early larval stages acetylcholinesterase- as well as choline acetyltransferase-like molecules were found mainly in the gut wall cells, and along the ciliary bands of the arms, together with muscarinic acetylcholine receptors. At perimetamorphic stages, cholinergic molecules were present in the ciliate strands along the arms, in the larval body and in the rudiment. At metamorphosis, positivity to cholinergic molecules translocated to the juvenile, where a high frequency of mAChR- and ChAT-like positive cells was found. 相似文献
75.
Nonlinear Theory of Spectra of Thermally Stimulated Currents in Complex Crystals with Hydrogen Bonds
Tonkonogov M. P. Ismailov Zh. T. Timokhin V. M. Fazylov K. K. Kalitka V. A. Baimukhanov Z. K. 《Russian Physics Journal》2002,45(10):1008-1018
The nonlinear theory of thermally stimulated depolarization currents is developed. The theory explains the processes of hetero- and homocharge relaxation in complex crystals with hydrogen bonds and allows the relaxation oscillator parameters to be calculated using the quadratic approximation for the external electric field. 相似文献
76.
O. Kortner M.P. Locher V.E. Markushin P. Weber O. Wigger 《The European Physical Journal C - Particles and Fields》2002,25(3):353-360
We study correlations in the exclusive reaction at rest with complete reconstruction of the kinematics for each event. The inclusive distribution is fairly flat at small
invariant mass of the pion pair while a small enhancement in the double differential distribution is observed for small invariant
masses of both pion pairs. Dynamical models with resonances in the final state are shown to be consistent with the data while
the stochastic HBT mechanism is not supported by the present findings.
Received: 26 February 2002 / Revised version: 22 July 2002 / Published online: 30 August 2002 相似文献
77.
Z. V. Golubenko A. S. Kamzin L. P. Ol’khovik M. M. Khvorov Z. I. Sizova V. P. Shabatin 《Physics of the Solid State》2002,44(9):1698-1702
Magnetization and remagnetization processes in a close-packed nanodispersed barium hexaferrite powder sample in the magnetically stable state were analyzed. Reversibility effects were discussed in terms of interparticle interaction. Judging from the magnetization curve and the parameters characterizing remagnetization irreversibility, the sample under study is a model system of small Stoner-Wohlfarth particles. 相似文献
78.
79.
80.
We discuss a mass change that has its origin in the action of forces on an object. This phenomenon, well-known in the context of quantum field theory (mass renormalization), can be discussed systematically in both classical and quantum mechanics in a framework given by Stückelberg. We employ this framework to resolve an interesting conflict of opinions between Schopenhauer and Hegel in the mid-19th century. We show that Hegel, Kant, and Schopenhauer demonstrated remarkable prescience in their views as seen from a modern perspective. 相似文献