全文获取类型
收费全文 | 4243篇 |
免费 | 316篇 |
国内免费 | 304篇 |
专业分类
化学 | 272篇 |
晶体学 | 3篇 |
力学 | 313篇 |
综合类 | 20篇 |
数学 | 3089篇 |
物理学 | 1166篇 |
出版年
2024年 | 9篇 |
2023年 | 89篇 |
2022年 | 50篇 |
2021年 | 54篇 |
2020年 | 94篇 |
2019年 | 101篇 |
2018年 | 96篇 |
2017年 | 85篇 |
2016年 | 89篇 |
2015年 | 92篇 |
2014年 | 195篇 |
2013年 | 361篇 |
2012年 | 193篇 |
2011年 | 258篇 |
2010年 | 225篇 |
2009年 | 305篇 |
2008年 | 349篇 |
2007年 | 315篇 |
2006年 | 235篇 |
2005年 | 199篇 |
2004年 | 211篇 |
2003年 | 178篇 |
2002年 | 163篇 |
2001年 | 117篇 |
2000年 | 107篇 |
1999年 | 111篇 |
1998年 | 87篇 |
1997年 | 96篇 |
1996年 | 67篇 |
1995年 | 47篇 |
1994年 | 53篇 |
1993年 | 36篇 |
1992年 | 38篇 |
1991年 | 14篇 |
1990年 | 10篇 |
1989年 | 17篇 |
1988年 | 9篇 |
1987年 | 14篇 |
1986年 | 10篇 |
1985年 | 22篇 |
1984年 | 14篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1974年 | 3篇 |
1973年 | 1篇 |
排序方式: 共有4863条查询结果,搜索用时 15 毫秒
21.
In this paper, we discuss the viscosity solutions of the weakly coupled systems of fully nonlinear second-order degenerate parabolic equations and their Cauchy-Dirichlet problem. We prove the existence, uniqueness and continuity of viscosity solution by combining Perron's method with the technique of coupled solutions. The results here generalize those in Proc. London Math. Soc. 63 (1991) 212-240 and Comm. Partial Differential Equations 16 (1991) 1095-1128. 相似文献
22.
This paper investigates the existence of positive solutions of a singular boundary value problem with negative exponent similar
to standard Emden-Fowler equation. A necessary and sufficient condition for the existence of C[0, 1] positive solutions as
well as C1[0, 1] positive solutions is given by means of the method of lower and upper solutions with the Schauder fixed point theorem. 相似文献
23.
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
24.
Xian Xu 《Journal of Mathematical Analysis and Applications》2004,291(2):673-689
In this paper, some multiplicity results for positive solutions of some singular semi-positone three-point boundary value problem be obtained by using the fixed point index method. 相似文献
25.
Qinghai Wang 《Czechoslovak Journal of Physics》2004,54(1):143-146
This paper investigates finite-dimensional PT-symmetric Hamiltonians. It is shown here that there are two ways to extend real symmetric Hamiltonians into the complex domain: (i) The usual approach is to generalize such Hamiltonians to include complex Hermitian Hamiltonians. (ii) Alternatively, one can generalize real symmetric Hamiltonians to include complex PT-symmetric Hamiltonians. In the first approach the spectrum remains real, while in the second approach the spectrum remains real if the PT symmetry is not broken. Both generalizations give a consistent theory of quantum mechanics, but if D>2, a D-dimensional Hermitian matrix Hamiltonian has more arbitrary parameters than a D-dimensional PT-symmetric matrix Hamiltonian. 相似文献
26.
Carl M. Bender 《Czechoslovak Journal of Physics》2004,54(1):13-28
The Hamiltonian H specifies the energy levels and the time evolution of a quantum theory. It is an axiom of quantum mechanics that H be Hermitian. The Hermiticity of H guarantees that the energy spectrum is real and that the time evolution is unitary (probability preserving). In this talk we investigate an alternative formulation of quantum mechanics in which the mathematical requirement of Hermiticity is replaced by the more physically transparent condition of space-time reflection (PT) symmetry. We show that if the PT symmetry of a Hamiltonian H is not broken, then the spectrum of H is real. Examples of PT-symmetric non-Hermitian Hamiltonians are H=p
2+ix
3 and H=p
2-x
4. The crucial question is whether PT-symmetric Hamiltonians specify physically acceptable quantum theories in which the norms of states are positive and the time evolution is unitary. The answer is that a Hamiltonian that has an unbroken PT symmetry also possesses a physical symmetry that we call C. Using C, we show how to construct an inner product whose associated norm is positive definite. The result is a new class of fully consistent complex quantum theories. Observables exhibit CPT symmetry, probabilities are positive, and the dynamics is governed by unitary time evolution. 相似文献
27.
28.
In this paper, by using elementary analysis, we establish some new Lyapunov-type inequalities for nonlinear systems of differential equations, special cases of which contain the well-known equations such as Emden-Fowler-type and half-linear equations. The inequalities obtained here can be used as handy tools in the study of qualitative behaviour of solutions of the associated equations. 相似文献
29.
关于《一类奇异边值问题的正解》的注记 总被引:3,自引:0,他引:3
文[4]通过构造反例断言文[1]中定理的必要性证明有误,本文首先指出文[4] 的这个断言不正确,然后对文[4]中定理2.1作了本质性的改进. 相似文献
30.
An exponentially fitted special second-order finite difference method is presented for solving singularly perturbed two-point boundary value problems with the boundary layer at one end (left or right) point. A fitting factor is introduced in a tri-diagonal finite difference scheme and is obtained from the theory of singular perturbations. Thomas Algorithm is used to solve the system and its stability is investigated. To demonstrate the applicability of the method, we have solved several linear and non-linear problems. From the results, it is observed that the present method approximates the exact solution very well. 相似文献