全文获取类型
收费全文 | 28585篇 |
免费 | 4089篇 |
国内免费 | 2295篇 |
专业分类
化学 | 4227篇 |
晶体学 | 276篇 |
力学 | 5774篇 |
综合类 | 324篇 |
数学 | 10465篇 |
物理学 | 13903篇 |
出版年
2024年 | 36篇 |
2023年 | 291篇 |
2022年 | 514篇 |
2021年 | 576篇 |
2020年 | 758篇 |
2019年 | 639篇 |
2018年 | 657篇 |
2017年 | 816篇 |
2016年 | 917篇 |
2015年 | 797篇 |
2014年 | 1257篇 |
2013年 | 2047篇 |
2012年 | 1447篇 |
2011年 | 1674篇 |
2010年 | 1557篇 |
2009年 | 2089篇 |
2008年 | 2050篇 |
2007年 | 1939篇 |
2006年 | 1889篇 |
2005年 | 1572篇 |
2004年 | 1427篇 |
2003年 | 1323篇 |
2002年 | 1231篇 |
2001年 | 1039篇 |
2000年 | 954篇 |
1999年 | 891篇 |
1998年 | 826篇 |
1997年 | 640篇 |
1996年 | 527篇 |
1995年 | 379篇 |
1994年 | 348篇 |
1993年 | 242篇 |
1992年 | 246篇 |
1991年 | 214篇 |
1990年 | 170篇 |
1989年 | 150篇 |
1988年 | 116篇 |
1987年 | 100篇 |
1986年 | 102篇 |
1985年 | 93篇 |
1984年 | 79篇 |
1983年 | 54篇 |
1982年 | 63篇 |
1981年 | 47篇 |
1980年 | 33篇 |
1979年 | 31篇 |
1978年 | 30篇 |
1977年 | 23篇 |
1976年 | 20篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
The paper's focus is the calculation of unsteady incompressible 2D flows past airfoils. In the framework of the primitive variable Navier–Stokes equations, the initial and boundary conditions must be assigned so as to be compatible, to assure the correct prediction of the flow evolution. This requirement, typical of all incompressible flows, viscous or inviscid, is often violated when modelling the flow past immersed bodies impulsively started from rest. Its fulfillment can however be restored by means of a procedure enforcing compatibility, consisting in a pre‐processing of the initial velocity field, here described in detail. Numerical solutions for an impulsively started multiple airfoil have been obtained using a finite element incremental projection method. The spatial discretization chosen for the velocity and pressure are of different order to satisfy the inf–sup condition and obtain a smooth pressure field. Results are provided to illustrate the effect of employing or not the compatibility procedure, and are found in good agreement with those obtained with a non‐primitive variable solver. In addition, we introduce a post‐processing procedure to evaluate an alternative pressure field which is found to be more accurate than the one resulting from the projection method. This is achieved by considering an appropriate ‘unsplit’ version of the momentum equation, where the velocity solution of the projection method is substituted. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
42.
This paper presents the applications of digital image correlation technique to the mesoscopic damage and fracture study of
some granular based composite materials including steelfiber reinforced concrete, sandstone and crystal-polymer composite.
The deformation fields of the composite materials resulted from stress localization were obtained by the correlation computation
of the surface images with loading steps and thus the related damage prediction and fracture parameters were evaluated. The
correlation searching could be performed either directly based on the gray levels of the digital images or from the wavelet
transform (WT) coefficients of the transform spectrum. The latter was developed by the authors and showed higher resolution
and sensitivity to the singularity detection. Because the displacement components came from the rough surfaces of the composite
materials without any coats of gratings or fringes of optical interferometry, both surface profiles and the deformation fields
of the composites were visualized which was helpful to compare each other to analyze the damage of those heterogeneous materials.
The project supported by the National Natural Science Foundation of China (10125211 and 10072002), the Scientific Committee
of Yunnan Province for the Program of Steel Fiber Reinforced Concrete, and the Institute of Chemical Materials, CAEP at Mianyang 相似文献
43.
本文运用信息保存法对低速二维的流动现象进行模拟,考察了低速条件下的有限平板绕流以及微槽道气体流动问题。研究表明:在对低速流动的模拟过程中,运用IP法在能够获得较好的结果的同时,具有比DSMC方法更高的计算效率。 相似文献
44.
An alternative discretization of pressure‐correction equations within pressure‐correction schemes for the solution of the incompressible Navier–Stokes equations is introduced, which improves the convergence and robustness properties of such schemes for non‐orthogonal grids. As against standard approaches, where the non‐orthogonal terms usually are just neglected, the approach allows for a simplification of the pressure‐correction equation to correspond to 5‐point or 7‐point computational molecules in two or three dimensions, respectively, but still incorporates the effects of non‐orthogonality. As a result a wide range (including rather high values) of underrelaxation factors can be used, resulting in an increased overall performance of the underlying pressure‐correction schemes. Within this context, a second issue of the paper is the investigation of the accuracy to which the pressure‐correction equation should be solved in each pressure‐correction iteration. The scheme is investigated for standard test cases and, in order to show its applicability to practical flow problems, for a more complex configuration of a micro heat exchanger. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
45.
D. Wuensch 《Annalen der Physik》2003,12(9):519-542
Theodor Kaluza (1885–1954) attracted the attention of the physical community since 1921 with his unified field theory of gravitation and electromagnetism in five dimensions. Despite Einstein's great interest in Kaluza's theory, 50 years elapsed before it contributed toward a paradigm shift in modern theoretical physics. The biography of this still unknown scientist is briefly presented along with an outline of his work in physics. A short history of the theories of unification and the dimensionality of space‐time is followed by a discussion of the significance of Kaluza's five‐dimensional unified theory in modern physics from the point of view of superstring and M‐theory. 相似文献
46.
V. A. Demin 《Fluid Dynamics》2008,43(4):524-532
The free oscillations of a capillary bridge whose equilibrium shape is determined by the surface tension forces and the static gravity field are investigated. The values of 25 “lower” levels of the spectrum of natural oscillations of the capillary bridge are found for various control parameters in accordance with the experimental conditions. 相似文献
47.
48.
Yirang Yuan 《Numerical Methods for Partial Differential Equations》2003,19(5):665-681
For the coupled system of multilayer fluid dynamics in porous media, the modified characteristic finite difference fractional steps method applicable to parallel arithmetic is put forward and two‐dimensional and three‐dimensional schemes are used to form a complete set. Some techniques, such as calculus of variations, energy method, piecewise biquadratic interpolation, multiplicative commutation rule of difference operators, decomposition of high order difference operators and prior estimates are adopted. Optimal order estimates in L2 norm are derived to determine the error in the approximate solution. This method has already been applied to the numerical simulation of multilayer fluid dynamics in porous media. © 2003 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 19: 665–681, 2003. 相似文献
49.
Ioan Tomescu 《Journal of Graph Theory》2003,43(3):210-222
In the set of graphs of order n and chromatic number k the following partial order relation is defined. One says that a graph G is less than a graph H if ci(G) ≤ ci(H) holds for every i, k ≤ i ≤ n and at least one inequality is strict, where ci(G) denotes the number of i‐color partitions of G. In this paper the first ? n/2 ? levels of the diagram of the partially ordered set of connected 3‐chromatic graphs of order n are described. © 2003 Wiley Periodicals, Inc. J Graph Theory 43: 210–222, 2003 相似文献
50.
The frequency or dispersion relation for the least‐squares mixed formulation of the shallow‐water equations is analysed. We consider the use of different approximation spaces corresponding to co‐located and staggered meshes, respectively. The study includes the effect of Coriolis, and the dispersion properties are compared analytically and graphically with those of the mixed Galerkin formulation. Numerical solutions of a test problem to simulate slow Rossby modes illustrate the theoretical results. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献