全文获取类型
收费全文 | 18036篇 |
免费 | 1841篇 |
国内免费 | 858篇 |
专业分类
化学 | 607篇 |
晶体学 | 18篇 |
力学 | 2334篇 |
综合类 | 123篇 |
数学 | 12794篇 |
物理学 | 4859篇 |
出版年
2024年 | 37篇 |
2023年 | 194篇 |
2022年 | 177篇 |
2021年 | 294篇 |
2020年 | 517篇 |
2019年 | 484篇 |
2018年 | 493篇 |
2017年 | 506篇 |
2016年 | 497篇 |
2015年 | 450篇 |
2014年 | 826篇 |
2013年 | 1908篇 |
2012年 | 757篇 |
2011年 | 1076篇 |
2010年 | 864篇 |
2009年 | 1175篇 |
2008年 | 1166篇 |
2007年 | 1092篇 |
2006年 | 1009篇 |
2005年 | 766篇 |
2004年 | 714篇 |
2003年 | 673篇 |
2002年 | 664篇 |
2001年 | 552篇 |
2000年 | 557篇 |
1999年 | 489篇 |
1998年 | 422篇 |
1997年 | 388篇 |
1996年 | 293篇 |
1995年 | 205篇 |
1994年 | 182篇 |
1993年 | 152篇 |
1992年 | 124篇 |
1991年 | 101篇 |
1990年 | 92篇 |
1989年 | 66篇 |
1988年 | 57篇 |
1987年 | 55篇 |
1986年 | 39篇 |
1985年 | 64篇 |
1984年 | 101篇 |
1983年 | 51篇 |
1982年 | 66篇 |
1981年 | 66篇 |
1980年 | 58篇 |
1979年 | 57篇 |
1978年 | 54篇 |
1977年 | 34篇 |
1976年 | 27篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
The unique global existence of a solution to nonstationary Navier–Stokes system with prescribed nonzero flux F(t) in an infinite three‐dimensional pipe is proved. The obtained solution remains close to the corresponding nonstationary Poiseuille flow. Moreover, it converges to the Poiseuille flow as |x3|→∞. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
952.
A simple procedure is proposed for the assessment of reinforced rectangular concrete columns under combined biaxial bending
and axial loads and for the design of a correct amount of FRP-strengthening for underdesigned concrete sections. Approximate
closed-form equations are developed based on the load contour method originally proposed by Bresler for reinforced concrete
sections. The 3D failure surface is approximated along its contours, at a constant axial load, by means of equations given
as the sum of the acting/resisting moment ratio in the directions of principal axes of the sections, raised to a power depending
on the axial load, the steel reinforcement ratio, and the section shape. The method is extended to FRP-strengthened sections.
Moreover, to make it possible to apply the load contour method in a more practical way, simple closed-form equations are developed
for rectangular reinforced concrete sections with a two-way steel reinforcement and FRP strengthenings on each side. A comparison
between the approach proposed and the fiber method (which is considered exact) shows that the simplified equations correctly
represent the section interaction diagram.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 44, No. 3, pp. 443–462, May–June, 2008. 相似文献
953.
考虑下列二阶脉冲微分系统解的振动性{(r(t))(x′(t)σ)′ a(t)(x([t]))δ e(t)sgn x(t)=0,t≠n,t≥0,n∈Z ,x(n)=gn(x(n-)),x′(n)=hn(x′(n-)),t=n,n=1,2,…,其中s,d是任意给定的正奇数的商.借助脉冲微分不等式得到了保证上述系统所有有界解振动的若干充分条件,并给出例子说明定理的应用. 相似文献
954.
高正晖 《数学的实践与认识》2008,38(11):178-183
研究了一类含连续分布滞量和阻尼项的非线性双曲型偏微分方程组运用黎卡提变换获得了该方程组在两类边值条件下解振动的充分条件. 相似文献
955.
V. A. Dougalis F. Sturm G. E. Zouraris 《Mathematical Methods in the Applied Sciences》2009,32(12):1519-1540
We consider the third‐order Claerbout‐type wide‐angle parabolic equation (PE) of underwater acoustics in a cylindrically symmetric medium consisting of water over a soft bottom B of range‐dependent topography. There is strong indication that the initial‐boundary value problem for this equation with just a homogeneous Dirichlet boundary condition posed on B may not be well‐posed, for example when B is downsloping. We impose, in addition to the above, another homogeneous, second‐order boundary condition, derived by assuming that the standard (narrow‐angle) PE holds on B, and establish a priori H2 estimates for the solution of the resulting initial‐boundary value problem for any bottom topography. After a change of the depth variable that makes B horizontal, we discretize the transformed problem by a second‐order accurate finite difference scheme and show, in the case of upsloping and downsloping wedge‐type domains, that the new model gives stable and accurate results. We also present an alternative set of boundary conditions that make the problem exactly energy conserving; one of these conditions may be viewed as a generalization of the Abrahamsson–Kreiss boundary condition in the wide‐angle case. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
956.
957.
R. Filliger M.-O. Hongler L. Streit 《Journal of Optimization Theory and Applications》2008,137(3):497-505
We present an exactly soluble optimal stochastic control problem involving a diffusive two-states random evolution process and connect it to a nonlinear reaction-diffusion type of equation by using the technique of logarithmic transformations. The work generalizes the recently established connection between the non-linear Boltzmann-like equations introduced by Ruijgrok and Wu and the optimal control of a two-states random evolution process. In the sense of this generalization, the nonlinear reaction-diffusion equation is identified as the natural diffusive generalization of the Ruijgrok–Wu and Boltzmann model. 相似文献
958.
Houde Han Ming Yan 《计算数学(英文版)》2008,(6):816-824
In this paper, we introduce a mixed finite element method on a staggered mesh for the numerical solution of the steady state Navier-Stokes equations in which the two components of the velocity and the pressure are defined on three different meshes. This method is a conforming quadrilateral Q1 × Q1 - P0 element approximation for the Navier-Stokes equations. First-order error estimates are obtained for both the velocity and the pressure. Numerical examples are presented to illustrate the effectiveness of the proposed method. 相似文献
959.
Several choices of scaling are investigated for a coupled system of parabolic partial differential equations in a two‐phase medium at the microscopic scale. This system may be regarded as modelling a reaction–diffusion problem, the Stokes problem of single‐phase flow of a slightly compressible fluid or as a heat conduction problem (with or without interfacial resistance), for example. It is shown that, starting with the same problem on the microscopic scale, different choices of scaling of the diffusion coefficients (resp. permeability or conductivity) and the interfacial‐exchange coefficient lead to different types of macroscopic systems of equations. The characterization of the limit problems in terms of the scaling parameters constitutes a modelling tool because it allows to determine the right type of limit problem. New macroscopic models, not previously dealt with, arise and, for some scalings, classical macroscopic models are recovered. Using the method of two‐scale convergence, a unified approach yielding rigorous proofs is given covering a very broad class of different scalings. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
960.
A. A. Abramov V. I. Ul’yanova L. F. Yukhno 《Computational Mathematics and Mathematical Physics》2009,49(3):474-481
The index of the homogeneous self-adjoint boundary value problem for the Hamiltonian systems of ordinary differential equations is introduced. It is assumed that the system has a nontrivial solution. The relationship between the index of an eigenvalue of the nonlinear eigenvalue problem and the index of the corresponding homogeneous problem is established. Properties of the index of the problem and those of the eigenvalue are examined. 相似文献