全文获取类型
收费全文 | 17372篇 |
免费 | 2618篇 |
国内免费 | 1044篇 |
专业分类
化学 | 7507篇 |
晶体学 | 69篇 |
力学 | 898篇 |
综合类 | 77篇 |
数学 | 6652篇 |
物理学 | 5831篇 |
出版年
2024年 | 34篇 |
2023年 | 225篇 |
2022年 | 393篇 |
2021年 | 571篇 |
2020年 | 735篇 |
2019年 | 700篇 |
2018年 | 555篇 |
2017年 | 685篇 |
2016年 | 971篇 |
2015年 | 804篇 |
2014年 | 1100篇 |
2013年 | 1591篇 |
2012年 | 933篇 |
2011年 | 891篇 |
2010年 | 723篇 |
2009年 | 913篇 |
2008年 | 1056篇 |
2007年 | 1041篇 |
2006年 | 860篇 |
2005年 | 632篇 |
2004年 | 545篇 |
2003年 | 594篇 |
2002年 | 587篇 |
2001年 | 452篇 |
2000年 | 473篇 |
1999年 | 397篇 |
1998年 | 374篇 |
1997年 | 268篇 |
1996年 | 218篇 |
1995年 | 177篇 |
1994年 | 180篇 |
1993年 | 156篇 |
1992年 | 148篇 |
1991年 | 96篇 |
1990年 | 91篇 |
1989年 | 91篇 |
1988年 | 105篇 |
1987年 | 73篇 |
1986年 | 69篇 |
1985年 | 106篇 |
1984年 | 80篇 |
1983年 | 25篇 |
1982年 | 50篇 |
1981年 | 47篇 |
1980年 | 48篇 |
1979年 | 38篇 |
1978年 | 33篇 |
1977年 | 34篇 |
1976年 | 30篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 527 毫秒
91.
The objective of this paper is to analyze under what well-known operations the class of quasipolyhedral convex functions,
which can be regarded as an extension of that of polyhedral convex functions, is closed. The operations that will be considered
are those that preserve polyhedral convexity, such that the image and the inverse image under linear transformations, right
scalar multiplication (including the case where λ=0+) and pointwise addition.
相似文献
92.
A direct central collision of two identical bodies of revolution is studied. A nonstationary mixed boundary-value problem with an unknown moving boundary is formulated. Its solution is represented by a series in term of Bessel functions. An infinite system of Volterra equations of the second kind for the unknown expansion coefficients is derived by satisfying the boundary conditions. The basic characteristics of the collision process are determined depending on the curvature of the frontal surface of the bodies 相似文献
93.
The motion of a particle in the field of an electromagnetic monopole (in the Coulomb–Dirac field) perturbed by an axially symmetric potential after quantum averaging is described by an integrable system. Its Hamiltonian can be written in terms of the generators of an algebra with quadratic commutation relations. We construct the irreducible representations of this algebra in terms of second-order differential operators; we also construct its hypergeometric coherent states. We use these states in the first-order approximation with respect to the perturbing field to obtain the integral representation of the eigenfunctions of the original problem in terms of solutions of the model Heun-type second-order ordinary differential equation and present the asymptotic approximation of the corresponding eigenvalues. 相似文献
94.
Jiang Wei 《Journal of Mathematical Analysis and Applications》2004,297(1):305-316
The eigenvalue and the stability of singular differential systems with delay are considered. Firstly we investigate some properties of the eigenvalue, then give the exact exponential estimation for the fundamental solution, and finally discuss the necessary and sufficient condition of uniform asymptotic stability. 相似文献
95.
陈守信 《数学物理学报(A辑)》2003,23(4):419-430
对一阶拟线性双曲方程组一类广义Riemann问题,该文在一定条件下证明了,包含一个接触间断和一个中心波以及包含一个接触间断和一个激波的间断解的整体存在性和唯一性. 相似文献
96.
We use the Jacobi method to construct various integrable systems, such as the Stäckel systems and Toda chains, related to various root systems. We find canonical transformations that relate integrals of motion for the generalized open Toda chains of types B
n, C
n, and D
n. 相似文献
97.
Nail H Ibragimov Gazanfer Ünal 《Journal of Mathematical Analysis and Applications》2004,297(1):152-168
A new definition for the approximate symmetries of Itô dynamical system is given. Determining systems of approximate symmetries for Itô and Stratonovich dynamical systems have been obtained. It has been shown that approximate conservation laws can be found from the approximate symmetries of stochastic dynamical systems which do not arise from a Hamiltonian. The results have been applied to an example. 相似文献
98.
This paper develops a theory for the global solution of nonconvex optimization problems with parameter-embedded linear dynamic systems. A quite general problem formulation is introduced and a solution is shown to exists. A convexity theory for integrals is then developed to construct convex relaxations for utilization in a branch-and-bound framework to calculate a global minimum. Interval analysis is employed to generate bounds on the state variables implied by the bounds on the embedded parameters. These bounds, along with basic integration theory, are used to prove convergence of the branch-and-bound algorithm to the global minimum of the optimization problem. The implementation of the algorithm is then considered and several numerical case studies are examined thoroughly 相似文献
99.
It is suggested that the question of existence of a jamming phase transition in a broad class of single-lane cellular-automaton traffic models may be studied using a correspondence to the asymmetric chipping model. In models where such correspondence is applicable, jamming phase transition does not take place. Rather, the system exhibits a smooth crossover between free-flow and jammed states, as the car density is increased. 相似文献
100.
Based on the generalized Huygens–Fresnel diffraction integral and the expansion of the hard aperture function into a finite sum of complex Gaussian functions, the approximate analytical expression of elegant Laguerre–Gaussian beams passing through a paraxial ABCD optical system with an annular aperture is derived. Meanwhile, the corresponding closed-forms for the unapertured, circular apertured or circular black screen cases are also given. The obtained results provide more convenience for studying their propagation and transformation than the usual way by using diffraction integral formula directly. Some numerical examples are given to illustrate the propagation properties of elegant Laguerre–Gaussian beams. 相似文献