全文获取类型
收费全文 | 3378篇 |
免费 | 548篇 |
国内免费 | 318篇 |
专业分类
化学 | 233篇 |
晶体学 | 13篇 |
力学 | 484篇 |
综合类 | 63篇 |
数学 | 2694篇 |
物理学 | 757篇 |
出版年
2024年 | 8篇 |
2023年 | 18篇 |
2022年 | 32篇 |
2021年 | 50篇 |
2020年 | 85篇 |
2019年 | 88篇 |
2018年 | 89篇 |
2017年 | 118篇 |
2016年 | 120篇 |
2015年 | 81篇 |
2014年 | 125篇 |
2013年 | 308篇 |
2012年 | 149篇 |
2011年 | 166篇 |
2010年 | 188篇 |
2009年 | 213篇 |
2008年 | 262篇 |
2007年 | 246篇 |
2006年 | 222篇 |
2005年 | 226篇 |
2004年 | 168篇 |
2003年 | 209篇 |
2002年 | 153篇 |
2001年 | 144篇 |
2000年 | 119篇 |
1999年 | 114篇 |
1998年 | 99篇 |
1997年 | 79篇 |
1996年 | 62篇 |
1995年 | 41篇 |
1994年 | 49篇 |
1993年 | 31篇 |
1992年 | 19篇 |
1991年 | 13篇 |
1990年 | 12篇 |
1989年 | 7篇 |
1988年 | 15篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 18篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1936年 | 1篇 |
排序方式: 共有4244条查询结果,搜索用时 15 毫秒
31.
32.
A. Y. M. Chin 《Acta Mathematica Hungarica》2004,102(4):337-342
Let R be an associative ring with unit and let N(R) denote the set of nilpotent elements of R. R is said to be stronglyπ-regular if for each x∈R, there exist a positive integer n and an element y∈R such that x
n=x
n
+1
y and xy=yx. R is said to be periodic if for each x∈R there are integers m,n≥ 1 such that m≠n and x
m=x
n. Assume that the idempotents in R are central. It is shown in this paper that R is a strongly π-regular ring if and only if N(R) coincides with the Jacobson radical of R and R/N(R) is regular. Some similar conditions for periodic rings are also obtained.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
33.
g1.IntroductionWeconsiderthefollowingfirstorderquasilinearhyperbolicequationswithinternaIdissipa-tlveterm:U, A(U)U. F(U)=o(1.1)whereUeR2isunknownvectorfunction,A(U)is2X2knownsmoothmatrix,F(U)is2X2knownsmoothvectorfunction.Itiswell-knownthatCauchyproblemoftheequations(l.1)hasbeenwidelystudied(Ll-6J),however,theequations(l.1)withperiedicinitialdatahasbeenhardlystudiedandonesfindthatitiscomplicatedforproblemwithperiodicinitialdata.Becausetheperiodicdis-turbanceLlirectlyinfluencesthebounde… 相似文献
34.
35.
Ottokar Leminger 《Optical and Quantum Electronics》2002,34(5-6):435-443
Photonic crystals exhibit band gaps, meaning that electromagnetic fields cannot propagate in them for specific ranges of wavelengths
and directions. The calculation of band structure diagrams has been intensively studied and is now well understood. In contrast
to that, so-called wave-vector diagrams (i.e. dispersion surfaces, depicting the loci of all relevant wave vectors at a fixed
wavelength) are less known and used. In principle, they show how the effective index of the structure depends on the direction
of propagation. A method to calculate explicitly wave-vector diagrams for two-dimensional photonic crystals is derived which
leads finally to quadratic eigenvalue problems. Results for square and triangular lattices are presented and some applications
are discussed. 相似文献
36.
Bernard Bialecki 《Numerical Algorithms》1994,8(2):167-184
Cyclic reduction and Fourier analysis-cyclic reduction (FACR) methods are presented for the solution of the linear systems which arise when orthogonal spline collocation with piecewise Hermite bicubics is applied to boundary value problems for certain separable partial differential equations on a rectangle. On anN×N uniform partition, the cyclic reduction and Fourier analysis-cyclic reduction methods requireO(N
2log2
N) andO(N
2log2log2
N) arithmetic operations, respectively. 相似文献
37.
De Ming ZHU Ying SUN 《数学学报(英文版)》2007,23(8):1495-1504
In this paper, we study the dynamical behavior for a 4-dimensional reversible system near its heteroclinic loop connecting a saddle-focus and a saddle. The existence of infinitely many reversible 1-homoclinic orbits to the saddle and 2-homoclinic orbits to the saddle-focus is shown. And it is also proved that, corresponding to each 1-homoclinic (resp. 2-homoclinic) orbit F, there is a spiral segment such that the associated orbits starting from the segment are all reversible 1-periodic (resp. 2-periodic) and accumulate onto F. Moreover, each 2-homoclinic orbit may be also accumulated by a sequence of reversible 4-homoclinic orbits. 相似文献
38.
By utilizing a fixed point theorem on cone,some new results on the existence of positive periodic solutions for nonautonomous differential equations with delay are derived. 相似文献
39.
40.
对于具有周期单元的分层介质材料高反射区的波长范围,提供一种简明的估计分析方法.基于Floquet定理,分析了有限周期单元分层介质的光子带隙特性,给出分层介质的高反射区波长范围.讨论了分层介质高反射区和周期单元禁带之间的关系.计算表明,高反射区和周期单元禁带的中心波长彼此一致.并且,随着分层介质周期单元数的增多,高反射区的深度和带宽就越接近于周期单元禁带的深度和宽度.最后,讨论周期分层介质的光子带隙特性与入射角及其与极化的变化关系.
关键词:
分层介质
带隙特性
周期单元
高反射区 相似文献