全文获取类型
收费全文 | 9292篇 |
免费 | 1048篇 |
国内免费 | 644篇 |
专业分类
化学 | 188篇 |
晶体学 | 40篇 |
力学 | 3981篇 |
综合类 | 114篇 |
数学 | 5009篇 |
物理学 | 1652篇 |
出版年
2024年 | 3篇 |
2023年 | 99篇 |
2022年 | 99篇 |
2021年 | 160篇 |
2020年 | 272篇 |
2019年 | 214篇 |
2018年 | 247篇 |
2017年 | 284篇 |
2016年 | 319篇 |
2015年 | 223篇 |
2014年 | 382篇 |
2013年 | 709篇 |
2012年 | 448篇 |
2011年 | 501篇 |
2010年 | 441篇 |
2009年 | 501篇 |
2008年 | 468篇 |
2007年 | 534篇 |
2006年 | 522篇 |
2005年 | 530篇 |
2004年 | 454篇 |
2003年 | 443篇 |
2002年 | 413篇 |
2001年 | 382篇 |
2000年 | 345篇 |
1999年 | 342篇 |
1998年 | 321篇 |
1997年 | 259篇 |
1996年 | 162篇 |
1995年 | 161篇 |
1994年 | 127篇 |
1993年 | 89篇 |
1992年 | 110篇 |
1991年 | 92篇 |
1990年 | 68篇 |
1989年 | 41篇 |
1988年 | 29篇 |
1987年 | 32篇 |
1986年 | 27篇 |
1985年 | 34篇 |
1984年 | 23篇 |
1983年 | 26篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1977年 | 4篇 |
1973年 | 2篇 |
1959年 | 2篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 262 毫秒
21.
Mingxin Wang 《Journal of Mathematical Analysis and Applications》2002,274(1):424-436
This paper deals with positive solutions of degenerate and quasilinear parabolic systems not in divergence form: ut=up(Δu+av), vt=vq(Δv+bu), with null Dirichlet boundary conditions and positive initial conditions, where p, q, a and b are all positive constants. The local existence and uniqueness of classical solution are proved. Moreover, it will be proved that all solutions exist globally if and only if ab?λ12, where λ1 is the first eigenvalue of −Δ in Ω with homogeneous Dirichlet boundary condition. 相似文献
22.
Substructuring preconditioners for saddle-point problems arising from Maxwell's equations in three dimensions 总被引:1,自引:0,他引:1
This paper is concerned with the saddle-point problems arising from edge element discretizations of Maxwell's equations in a general three dimensional nonconvex polyhedral domain. A new augmented technique is first introduced to transform the problems into equivalent augmented saddle-point systems so that they can be solved by some existing preconditioned iterative methods. Then some substructuring preconditioners are proposed, with very simple coarse solvers, for the augmented saddle-point systems. With the preconditioners, the condition numbers of the preconditioned systems are nearly optimal; namely, they grow only as the logarithm of the ratio between the subdomain diameter and the finite element mesh size.
23.
The finite-difference method is a numerical technique for obtaining approximate solutions to differential equations. The main
objective of the present study is to give a new aspect to the finite-difference method by using a variational derivative.
By applying this formulation, accurate values of the buckling loads of beams and frames with various end supports are obtained.
The performance of this formulation is verified by comparison with numerical examples in the literature
__________
Published in Prikladnaya Mekhanika, Vol. 41, No. 7, pp. 139–144, July 2005. 相似文献
24.
We consider the plane-strain buckling of a cylindrical shellof arbitrary thickness which is made of a Varga material andis subjected to an external hydrostatic pressure on its outersurface. The WKB method is used to solve the eigenvalue problemthat results from the linear bifurcation analysis. We show thatthe circular cross-section buckles into a non-circular shapeat a value of µ1 which depends on A1/A2 and a mode number,where A1 and A2 are the undeformed inner and outer radii, andµ1 is the ratio of the deformed inner radius to A1. Inthe large mode number limit, we find that the dependence ofµ1 on A1/A2 has a boundary layer structure: it is constantover almost the entire region of 0 < A1/A2 < 1 and decreasessharply from this constant value to unity as A1/A2 tends tounity. Our asymptotic results for A1 1 = O(1) and A1 1 = O(1/n) are shown to agree with the numerical resultsobtained by using the compound matrix method. 相似文献
25.
We treat here of the question of absorbing boundary conditionsfor nonlinear diffusion equations. We use the conditions designedfor the linear equation, we prove them to be well posed forthe nonlinear problem, and through numerical experiments thatthey are well suited for reactiondiffusion equations. 相似文献
26.
何先应 《南昌大学学报(理科版)》2004,28(4):338-340
设G是有限群。H是G的一个正规子群。P是|H|的一个素因子。P是H的一个Sylow p-子群。若下列条件之一满足。则H是p-幂零:1)P的极大子群都是G的CAP-子群且(|H|,P-1)=1;2)P的二次极大子群都是G的CAP-子群且(|H|,P^2-1)=1。特别地,若进一步假设G/H为P-幂零且(|G|,P-1)=1或(|G|,P^2-1)=1。则G自身亦为P-幂零。 相似文献
27.
Alessandro Conflitti 《Finite Fields and Their Applications》2003,9(4):423-431
We propose a probabilistic algorithm to reduce computing the greatest common divisor of m polynomials over a finite field (which requires computing m−1 pairwise greatest common divisors) to computing the greatest common divisor of two polynomials over the same field. 相似文献
28.
For an arbitrary bounded closed set E in the complex plane with complement Ω of finite connectivity, we study the degree of convergence of the lemniscates in Ω. 相似文献
29.
In the present paper we give necessary and sufficient conditions for the subgroup separability of the fundamental group of a finite graph of groups with finitely generated abelian vertex groups.
30.
A preconditioning approach based on the artificial compressibility formulation is extended to solve the governing equations for unsteady turbulent reactive flows with heat release, at low Mach numbers, on an unstructured hybrid grid context. Premixed reactants are considered and a flamelet approach for combustion modelling is adopted using a continuous quenched mean reaction rate. An overlapped cell‐vertex finite volume method is adopted as a discretisation scheme. Artificial dissipation terms for hybrid grids are explicitly added to ensure a stable, discretised set of equations. A second‐order, explicit, hybrid Runge–Kutta scheme is applied for the time marching in pseudo‐time. A time derivative of the dependent variable is added to recover the time accuracy of the preconditioned set of equations. This derivative is discretised by an implicit, second‐order scheme. The resulting scheme is applied to the calculation of an infinite planar (one‐dimensional) turbulent premixed flame propagating freely in reactants whose turbulence is supposed to be frozen, homogeneous and isotropic. The accuracy of the results obtained with the proposed method proves to be excellent when compared to the data available in the literature. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献