全文获取类型
收费全文 | 15772篇 |
免费 | 1444篇 |
国内免费 | 1576篇 |
专业分类
化学 | 3775篇 |
晶体学 | 229篇 |
力学 | 1976篇 |
综合类 | 280篇 |
数学 | 9897篇 |
物理学 | 2635篇 |
出版年
2024年 | 35篇 |
2023年 | 160篇 |
2022年 | 192篇 |
2021年 | 279篇 |
2020年 | 392篇 |
2019年 | 362篇 |
2018年 | 340篇 |
2017年 | 416篇 |
2016年 | 464篇 |
2015年 | 339篇 |
2014年 | 646篇 |
2013年 | 1090篇 |
2012年 | 806篇 |
2011年 | 920篇 |
2010年 | 907篇 |
2009年 | 960篇 |
2008年 | 1073篇 |
2007年 | 1126篇 |
2006年 | 943篇 |
2005年 | 873篇 |
2004年 | 789篇 |
2003年 | 829篇 |
2002年 | 694篇 |
2001年 | 552篇 |
2000年 | 509篇 |
1999年 | 484篇 |
1998年 | 404篇 |
1997年 | 349篇 |
1996年 | 291篇 |
1995年 | 254篇 |
1994年 | 209篇 |
1993年 | 145篇 |
1992年 | 138篇 |
1991年 | 112篇 |
1990年 | 97篇 |
1989年 | 74篇 |
1988年 | 68篇 |
1987年 | 54篇 |
1986年 | 59篇 |
1985年 | 61篇 |
1984年 | 53篇 |
1983年 | 25篇 |
1982年 | 56篇 |
1981年 | 43篇 |
1980年 | 29篇 |
1979年 | 26篇 |
1978年 | 16篇 |
1977年 | 9篇 |
1976年 | 12篇 |
1972年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Geertsma’s analytical method is often used to compute strain and stress changes around a compacting geological reservoir. The present work extends Geertsma’s solution by adding a rigid layer beneath the compacting reservoir. Analytical formulae are presented for all the components of displacement of a point in the subsurface. Our derivation includes the correction of an error found in the paper written by Sharma in 1956. 相似文献
992.
J.H. Carneiro de Araujo P.D. Gomes 《Journal of Computational and Applied Mathematics》2010,234(8):2562-3631
A three-field finite element scheme designed for solving systems of partial differential equations governing time-dependent viscoelastic flows is studied. Once a classical backward Euler time discretization is performed, the resulting three-field system of equations allows for a stable approximation of velocity, pressure and extra stress tensor, by means of continuous piecewise linear finite elements, in both two- and three- dimensional space. This is proved to hold for the linearized form of the system. An advantage of the new formulation is the fact that it provides an algorithm for the explicit iterative resolution of system nonlinearities. Convergence in an appropriate sense applying to these three flow fields is demonstrated. 相似文献
993.
Shengqiang Tang Xiaoliang Huang Wentao Huang 《Applied mathematics and computation》2010,216(10):2881-2890
By using the bifurcation theory of dynamical systems to the generalized Kadomtsov-Petviashvili-Benjamin-Bona-Mahony equation, the existence of solitary wave solutions, compactons solution, non-smooth periodic cusp wave solutions and uncountably infinite many smooth periodic wave solutions is obtained. Under different parametric conditions, various sufficient conditions to guarantee the existence of the above solutions are given. Some exact explicit parametric representations of the above waves are determined. 相似文献
994.
Stability and bifurcation analysis of a delayed predator-prey model of prey dispersal in two-patch environments 总被引:1,自引:0,他引:1
In this paper, a class of delayed predator-prey model of prey dispersal in two-patch environments is considered. By analyzing the associated characteristic transcendental equation, its linear stability is investigated and Hopf bifurcation is demonstrated. Some explicit formulae determining the stability and the direction of the Hopf bifurcation periodic solutions bifurcating from Hopf bifurcations are obtained by using the normal form theory and center manifold theory. Some numerical simulation for justifying the theoretical analysis are also provided. Finally, biological explanations and main conclusions are given. 相似文献
995.
Yong-Qi Wu 《Applied mathematics and computation》2010,216(11):3154-3161
In this paper, the one- and two-periodic wave solutions for the (3+1)-dimensional Kadomtsev-Petviashvili equation are presented by means of the Hirota’s bilinear method and the Riemann theta function. The rigorous proofs on asymptotic behaviors of these two solutions are given that soliton solution can be obtained from the periodic wave solution in an appropriate limiting procedure. 相似文献
996.
Let R ∈ Cn×n be a nontrivial involution, i.e., R2 = I and R ≠ ±I. A matrix A ∈ Cn×n is called R-skew symmetric if RAR = −A. The least-squares solutions of the matrix inverse problem for R-skew symmetric matrices with R∗ = R are firstly derived, then the solvability conditions and the solutions of the matrix inverse problem for R-skew symmetric matrices with R∗ = R are given. The solutions of the corresponding optimal approximation problem with R∗ = R for R-skew symmetric matrices are also derived. At last an algorithm for the optimal approximation problem is given. It can be seen that we extend our previous results [G.X. Huang, F. Yin, Matrix inverse problem and its optimal approximation problem for R-symmetric matrices, Appl. Math. Comput. 189 (2007) 482-489] and the results proposed by Zhou et al. [F.Z. Zhou, L. Zhang, X.Y. Hu, Least-square solutions for inverse problem of centrosymmetric matrices, Comput. Math. Appl. 45 (2003) 1581-1589]. 相似文献
997.
The variable-coefficient Kadomtsev-Petviashvili (KP) equation is hereby under investigation. Painlevé analysis is given out, and an auto-Bäcklund transformation is presented via the truncated Painlevé expansion. Based on the auto-Bäcklund transformation, new analytic solutions are given, including the soliton-like and periodic solutions. It is also reduced to a (1+1)-dimensional partial differential equation via classical Lie group method and the Painlevé I equation by CK direct method. 相似文献
998.
The two dimensional diffusion equation of the form is considered in this paper. We try a bi-cubic spline function of the form as its solution. The initial coefficients Ci,j(0) are computed simply by applying a collocation method; Ci,j = f(xi, yj) where f(x, y) = u(x, y, 0) is the given initial condition. Then the coefficients Ci,j(t) are computed by X(t) = etQX(0) where X(t) = (C0,1, C0,1, C0,2, … , C0,N, C1,0, … , CN,N) is a one dimensional array and the square matrix Q is derived from applying the Galerkin’s method to the diffusion equation. Note that this expression provides a solution that is not necessarily separable in space coordinates x, y. The results of sample calculations for a few example problems along with the calculation results of approximation errors for a problem with known analytical solution are included. 相似文献
999.
Similarity solutions for flow and heat transfer over a permeable surface with convective boundary condition 总被引:1,自引:0,他引:1
Anuar Ishak 《Applied mathematics and computation》2010,217(2):837-1362
The steady laminar boundary layer flow over a permeable flat plate in a uniform free stream, with the bottom surface of the plate is heated by convection from a hot fluid is considered. Similarity solutions for the flow and thermal fields are possible if the mass transpiration rate at the surface and the convective heat transfer from the hot fluid on the lower surface of the plate vary like x−1/2, where x is the distance from the leading edge of the solid surface. The governing partial differential equations are first transformed into ordinary differential equations, before being solved numerically. The effects of the governing parameters on the flow and thermal fields are thoroughly examined and discussed. 相似文献
1000.
In this paper, the modified Fornberg-Whitham equation is studied by using the bifurcation theory and the method of phase portraits analysis. In some parametric conditions, some peakons and solitary waves are found and their exact parametric representations in explicit form are obtained. 相似文献