全文获取类型
收费全文 | 258607篇 |
免费 | 4004篇 |
国内免费 | 654篇 |
专业分类
化学 | 145623篇 |
晶体学 | 3999篇 |
力学 | 8962篇 |
综合类 | 16篇 |
数学 | 29930篇 |
物理学 | 74735篇 |
出版年
2021年 | 2223篇 |
2020年 | 2564篇 |
2019年 | 2775篇 |
2018年 | 3316篇 |
2017年 | 3372篇 |
2016年 | 5461篇 |
2015年 | 3800篇 |
2014年 | 5184篇 |
2013年 | 12657篇 |
2012年 | 9951篇 |
2011年 | 11461篇 |
2010年 | 7997篇 |
2009年 | 7733篇 |
2008年 | 10199篇 |
2007年 | 9920篇 |
2006年 | 9256篇 |
2005年 | 8549篇 |
2004年 | 7615篇 |
2003年 | 6882篇 |
2002年 | 6410篇 |
2001年 | 7300篇 |
2000年 | 5748篇 |
1999年 | 4340篇 |
1998年 | 3400篇 |
1997年 | 3298篇 |
1996年 | 3345篇 |
1995年 | 2985篇 |
1994年 | 2946篇 |
1993年 | 2744篇 |
1992年 | 3391篇 |
1991年 | 3202篇 |
1990年 | 3180篇 |
1989年 | 3096篇 |
1988年 | 3114篇 |
1987年 | 3114篇 |
1986年 | 2959篇 |
1985年 | 3805篇 |
1984年 | 3780篇 |
1983年 | 2974篇 |
1982年 | 3071篇 |
1981年 | 3135篇 |
1980年 | 2871篇 |
1979年 | 3187篇 |
1978年 | 3135篇 |
1977年 | 3248篇 |
1976年 | 3103篇 |
1975年 | 2789篇 |
1974年 | 2763篇 |
1973年 | 2733篇 |
1968年 | 1863篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
991.
992.
We characterize the sequences of orthogonal polynomials on the unit circle whose derivatives are also orthogonal polynomials on the unit circle. Some relations for the sequences of derivatives of orthogonal polynomials are provided. Finally, we pose some problems about orthogonality-preserving maps and differential equations for orthogonal polynomials on the unit circle. 相似文献
993.
Exponential growth is estimated for integral operators with continuous periodic kernels of exponential type. The result is
applied to the boundary-value problem for a general hyperbolic differential equation having periodic coefficients with Goursat
boundary conditions. It is proved that the exponential characteristic for such a boundary-value problem has canonical form.
__________
Translated from Sovremennaya Matematika i Ee Prilozheniya (Contemporary Mathematics and Its Applications), Vol. 38, Suzdal
Conference-2004, Part 3, 2006. 相似文献
994.
We construct a three-parameter family of contact metric structures on the unit tangent sphere bundle T
1
M of a Riemannian manifold M and we study some of their special properties related to the Levi-Civita connection. More precisely, we give the necessary
and sufficient conditions for a constructed contact metric structure to be K-contact, Sasakian, to satisfy some variational conditions or to define a strongly pseudo-convex CR-structure. The obtained
results generalize classical theorems on the standard contact metric structure of T
1
M. 相似文献
995.
Anuradha Sharma Gurmeet K. Bakshi Madhu Raka 《Finite Fields and Their Applications》2007,13(4):1071-1085
Polyadic codes constitute a special class of cyclic codes and are generalizations of quadratic residue codes, duadic codes, triadic codes, m-adic residue codes and split group codes, which have good error-correcting properties. In this paper, we give necessary and sufficient conditions for the existence of polyadic codes of prime power length. Examples of some good codes arising from the family of polyadic codes of prime power length are also given. 相似文献
996.
997.
The classical Voigt functions occur frequently in a wide variety of problems in astrophysical spectroscopy, emission, absorption
and transfer of radiation in heated atmosphere, and plasma dispersion, and indeed also in the theory of neutron reactions.
Here, in the present paper, by applying several known upper bounds for the first-kind Bessel function J
ν
(x) given recently by (for example) Landau, Olenko and Krasikov, sharp bounding inequalities are obtained for the unified multivariable
Voigt function V
μ,ν
(x; y) in terms of the confluent Fox-Wright function 1ψ0 and its incomplete variant 1ψ0. Connections of the unified multivariable Voigt function V
μ,ν
(x; y) with other unifications and generalizations of the classical Voigt function are also briefly pointed out. 相似文献
998.
T. K. Melik-Barkhudarov 《Journal of Contemporary Physics (Armenian Academy of Sciences)》2007,42(5):173-177
An approach is discussed which allows one to describe within the framework of the single model the aggregative states of a system of atoms obeying the Fermi statistics. A phase diagram is obtained containing both the critical point where the distinctions between the liquid and vapor vanish and the triple point where the liquid, vapor, and crystal are in equilibrium. 相似文献
999.
D. Boilley A. Marchix B. Jurado K. -H. Schmidt 《The European Physical Journal A - Hadrons and Nuclei》2007,33(1):47-52
We propose a new formula for the saddle-to-scission time that is more general that the one based on Kramers' approach. Its
validity and applicability is then studied in detail. Such a formula is useful for the evaluation of the fission time of very
heavy nuclei. 相似文献
1000.
Choyal Y. Minami K. Granatstein V.L. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2004,32(6):2157-2168
The linear dispersion relation of a backward-wave oscillator (BWO), derived earlier by the authors, is modified to include effects of RF surface current at the beam-vacuum interface. This modified dispersion relation results in an unstable interaction between the slow cyclotron mode (SCM) and the structure mode in addition to the conventional Cherenkov instability caused by the slow space charge mode. Numerical analysis is then carried out using parameters of a BWO experiment at University of Maryland. Fine structure of the SCM instability is elucidated. The analysis indicates that BWO radiation would not be suppressed near cyclotron absorption in an infinitely long system. 相似文献