全文获取类型
收费全文 | 10616篇 |
免费 | 1718篇 |
国内免费 | 3493篇 |
专业分类
化学 | 6327篇 |
晶体学 | 399篇 |
力学 | 902篇 |
综合类 | 163篇 |
数学 | 5038篇 |
物理学 | 2998篇 |
出版年
2024年 | 24篇 |
2023年 | 91篇 |
2022年 | 213篇 |
2021年 | 280篇 |
2020年 | 353篇 |
2019年 | 341篇 |
2018年 | 339篇 |
2017年 | 518篇 |
2016年 | 649篇 |
2015年 | 429篇 |
2014年 | 632篇 |
2013年 | 1201篇 |
2012年 | 950篇 |
2011年 | 922篇 |
2010年 | 822篇 |
2009年 | 839篇 |
2008年 | 882篇 |
2007年 | 847篇 |
2006年 | 718篇 |
2005年 | 663篇 |
2004年 | 530篇 |
2003年 | 512篇 |
2002年 | 453篇 |
2001年 | 407篇 |
2000年 | 331篇 |
1999年 | 317篇 |
1998年 | 268篇 |
1997年 | 219篇 |
1996年 | 184篇 |
1995年 | 162篇 |
1994年 | 156篇 |
1993年 | 105篇 |
1992年 | 79篇 |
1991年 | 52篇 |
1990年 | 56篇 |
1989年 | 31篇 |
1988年 | 41篇 |
1987年 | 26篇 |
1986年 | 15篇 |
1985年 | 27篇 |
1984年 | 19篇 |
1983年 | 20篇 |
1982年 | 24篇 |
1981年 | 18篇 |
1980年 | 17篇 |
1979年 | 12篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 9篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
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
72.
A. BOURHIM 《数学年刊B辑(英文版)》2004,25(3):369-382
In this note, the local spectral properties of unilateral operator weighted shifts arestudied. 相似文献
73.
The specific heat and related thermophysical properties of liquid Fe77.5Cu13Mo9.5 monotectic alloy were investigated by an electromagnetic levitation drop calorimeter over a wide temperature range from 1482 to 1818 K. A maximum undercooling of 221 K (0.13 Tm) was achieved and the specific heat was determined as 44.71 J·mol-1·K-1. The excess specific heat, enthalpy change, entropy change and Gibbs free energy difference of this alloy were calculated on the basis of experimental results. It was found that the calculated results by traditional estimating methods can only describe the solidification process under low undercooling conditions. Only the experimental results can reflect the reality under high undercooling conditions. Meanwhile, the thermal diffusivity, thermal conductivity, and sound speed were derived from the present experimental results. Furthermore, the solidified microstructural morphology was examined, which consists of (Fe) and (Cu) phases. The calculated interface energy was applied to exploring the correlation between competitive nucleation and solidification microstructure within monotectic alloy. 相似文献
74.
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
75.
76.
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
77.
关于非齐次m阶马氏信源的渐近均分割性 总被引:4,自引:0,他引:4
本文研究非齐次m阶马氏信源的渐近均分割性,首先我们得到关于此种信源m 1元函数的一类强极限定理,作为推论,得到关于任意非齐次m阶马氏信源状态和熵密度的几个极限定理,最后得到一类非齐次m阶马氏信源的渐近均分割性。 相似文献
78.
四溴双酚A锑铝双金属化合物的合成及其阻燃性能 总被引:1,自引:0,他引:1
以四溴双酚A(TBA)合成了在水和空气中稳定的四溴双酚A合锑铝双金属化合物(TBASA).通过IR、1HNMR和元素分析予以表征,并研究了其对聚乙烯(PE)和聚环氧乙烷(PEO)的阻燃性能.结果表明,这种分子中含有溴、锑和铝的化合物,对聚乙烯和聚环氧乙烷等高聚物材料有高的阻燃性能与消烟效果. 相似文献
79.
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
80.
S.V. Astashkin F.A. Sukochev 《Journal of Mathematical Analysis and Applications》2007,336(2):1231-1258
We catalogue all Marcinkiewicz function and sequence spaces with the Banach-Saks property and present necessary and sufficient conditions for a wide subclass of spaces to possess the p-Banach-Saks property, 1<p<∞. We apply our results to several open problems. 相似文献