全文获取类型
收费全文 | 8686篇 |
免费 | 340篇 |
国内免费 | 363篇 |
专业分类
化学 | 593篇 |
晶体学 | 41篇 |
力学 | 881篇 |
综合类 | 24篇 |
数学 | 5647篇 |
物理学 | 2203篇 |
出版年
2024年 | 7篇 |
2023年 | 81篇 |
2022年 | 76篇 |
2021年 | 104篇 |
2020年 | 139篇 |
2019年 | 144篇 |
2018年 | 148篇 |
2017年 | 177篇 |
2016年 | 182篇 |
2015年 | 197篇 |
2014年 | 433篇 |
2013年 | 645篇 |
2012年 | 420篇 |
2011年 | 576篇 |
2010年 | 483篇 |
2009年 | 569篇 |
2008年 | 605篇 |
2007年 | 623篇 |
2006年 | 425篇 |
2005年 | 307篇 |
2004年 | 313篇 |
2003年 | 276篇 |
2002年 | 232篇 |
2001年 | 211篇 |
2000年 | 218篇 |
1999年 | 216篇 |
1998年 | 183篇 |
1997年 | 175篇 |
1996年 | 154篇 |
1995年 | 157篇 |
1994年 | 117篇 |
1993年 | 90篇 |
1992年 | 77篇 |
1991年 | 47篇 |
1990年 | 60篇 |
1989年 | 39篇 |
1988年 | 36篇 |
1987年 | 32篇 |
1986年 | 54篇 |
1985年 | 48篇 |
1984年 | 40篇 |
1983年 | 29篇 |
1982年 | 39篇 |
1981年 | 30篇 |
1980年 | 46篇 |
1979年 | 44篇 |
1978年 | 34篇 |
1977年 | 25篇 |
1976年 | 13篇 |
1974年 | 7篇 |
排序方式: 共有9389条查询结果,搜索用时 31 毫秒
61.
Lubomír Kubáček 《Mathematica Slovaca》2007,57(6):571-588
The multivariate model, where not only parameters of the mean value of the observation matrix, but also some other parameters
occur in constraints, is considered in the paper. Some basic inference is presented under the condition that the covariance
matrix is either unknown, or partially unknown, or known.
Supported by the grant of the Council of Czech Republic MSM 6 198 959 214. 相似文献
62.
This paper discusses a class of second-order derivative nonlinear Schrödinger equations which are used to describe the upper-hybrid oscillation propagation. By establishing a variational problem, applying the potential well argument and the concavity method, we prove that there exists a sharp condition for global existence and blow-up of the solutions to the nonlinear Schrödinger equation. In addition, we also answer the question: how small are the initial data, the global solutions exist? 相似文献
63.
A. Aghajani 《Journal of Mathematical Analysis and Applications》2007,326(2):1076-1089
We consider the nonlinear Euler differential equation t2x″+g(x)=0. Here g(x) satisfies xg(x)>0 for x≠0, but is not assumed to be sublinear or superlinear. We present implicit necessary and sufficient condition for all nontrivial solutions of this system to be oscillatory or nonoscillatory. Also we prove that solutions of this system are all oscillatory or all nonoscillatory and cannot be both. We derive explicit conditions and improve the results presented in the previous literature. We extend our results to the extended equation t2x″+a(t)g(x)=0. 相似文献
64.
65.
This study provides a stability theory for the nonlinear least-squares formulation of estimating the diffusion coefficient in a two-point boundary-value problem from an error-corrupted observation of the state variable. It is based on analysing the projection of the observation on the nonconvex attainable set.This research was started while G. Chavent visited the Technical University of Graz. Support through the Steiermaerkische Landesregierung is gratefully acknowledged. 相似文献
66.
A. Gerasimov 《Journal of statistical physics》1993,70(3-4):939-948
The analysis is carried out of the response of the center of gravity (dipole moment) of the distribution of noninteracting thermalized nonlinear oscillators to a sinusoidal driving force. Heat bath coupling is modeled by damping and noise. The driving is weak, but the frequency is resonant, so that there is a nonlinear resonance in the phase space. The response has a linear part that can be obtained from the perturbation analysis and a small nonlinear correction that is specific for the resonant structure. 相似文献
67.
OSCILLATION OF A FORCED SECOND ORDER NONLINEAR EQUATION ¥KONGQINGKAI;ZHANGBINGGENAbstract:Thispapergivesseveralcriteriaontheo... 相似文献
68.
We consider a spatially distributed hybrid system consisting of a convection/reaction system in which the reaction switches discontinuously in time between modes, independently at each spatial point on reaching “switching thresholds”. The model involves a novel formulation for evolution of the free boundary between the modal regions. 相似文献
69.
This paper presents two differential systems, involving first and second order derivatives of problem functions, respectively, for solving equality-constrained optimization problems. Local minimizers to the optimization problems are proved to be asymptotically stable equilibrium points of the two differential systems. First, the Euler discrete schemes with constant stepsizes for the two differential systems are presented and their convergence theorems are demonstrated. Second, we construct algorithms in which directions are computed by these two systems and the stepsizes are generated by Armijo line search to solve the original equality-constrained optimization problem. The constructed algorithms and the Runge–Kutta method are employed to solve the Euler discrete schemes and the differential equation systems, respectively. We prove that the discrete scheme based on the differential equation system with the second order information has the locally quadratic convergence rate under the local Lipschitz condition. The numerical results given here show that Runge–Kutta method has better stability and higher precision and the numerical method based on the differential equation system with the second information is faster than the other one. 相似文献
70.
In this paper we prove the existence of a solution of a coupled system involving a two phase incompressible flow in the ground and the mechanical deformation of the porous medium where the porosity is a function of the global pressure. The model is strongly coupled and involves a nonlinear degenerate parabolic equation. In order to show the existence of a weak solution, we consider a sequence of related uniformly parabolic problems and apply the Schauder fixed point theorem to show that they possess a classical solution. We then prove the relative compactness of sequences of solutions by means of the Fréchet-Kolmogorov theorem; this yields the convergence of a subsequence to a weak solution of the parabolic system. 相似文献