全文获取类型
收费全文 | 15437篇 |
免费 | 2953篇 |
国内免费 | 2704篇 |
专业分类
化学 | 12040篇 |
晶体学 | 90篇 |
力学 | 1307篇 |
综合类 | 128篇 |
数学 | 2852篇 |
物理学 | 4677篇 |
出版年
2024年 | 49篇 |
2023年 | 235篇 |
2022年 | 391篇 |
2021年 | 605篇 |
2020年 | 756篇 |
2019年 | 702篇 |
2018年 | 562篇 |
2017年 | 633篇 |
2016年 | 1017篇 |
2015年 | 939篇 |
2014年 | 1098篇 |
2013年 | 1536篇 |
2012年 | 1171篇 |
2011年 | 1244篇 |
2010年 | 1029篇 |
2009年 | 1182篇 |
2008年 | 1105篇 |
2007年 | 1146篇 |
2006年 | 1029篇 |
2005年 | 821篇 |
2004年 | 654篇 |
2003年 | 630篇 |
2002年 | 382篇 |
2001年 | 320篇 |
2000年 | 319篇 |
1999年 | 239篇 |
1998年 | 207篇 |
1997年 | 214篇 |
1996年 | 114篇 |
1995年 | 121篇 |
1994年 | 106篇 |
1993年 | 86篇 |
1992年 | 72篇 |
1991年 | 48篇 |
1990年 | 50篇 |
1989年 | 41篇 |
1988年 | 33篇 |
1987年 | 28篇 |
1986年 | 18篇 |
1985年 | 27篇 |
1984年 | 16篇 |
1983年 | 12篇 |
1982年 | 20篇 |
1981年 | 12篇 |
1980年 | 13篇 |
1979年 | 11篇 |
1978年 | 15篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 781 毫秒
111.
Stochastic mechanism of relaxation, in which a dipole waits until a favourable condition for reorientation exists, is discussed. Assuming that an imposed direction of a dipole moment may be changed when a migrating defect reaches the dipole, we present a mathematically rigorous scheme relating the local random characteristics of a macroscopic system to its effective relaxation behaviour. We derive a relaxation function (the Burr survival probability) that is characterized by the stretched exponential or the power-law behaviour. 相似文献
112.
研究了条件泛函及其导数的非参数估计,对随机与固定设计的条件泛函,分别利用核估计和非参数加权估计,在核函数及权函数满足一定条件下,证明了估计一致强收敛于待估函数的速度可达到最优。从而进一步推广和发展了Hrdle,etal.(1988)、Severini,etal.(1992)的许多结果。 相似文献
113.
114.
动态模糊随机信息处理的数学方法 总被引:1,自引:1,他引:0
本文系统地概述了我们近年来提出的动态模糊随机信息处理的数学方法,内容包括模糊随机变量、模糊随机过程和模糊随机微分方程的基本解法等方面的基本概念、基本定义和某些重要的定理,以及动态系统的模糊随机响应与可靠性分析的方法等。这些方法是为我们研究工程实际问题的需要逐步发展起来的,对于处理某些类型的问题简便实用。 相似文献
115.
Stephan H. Irsen Peter Kroll Richard Dronskowski Thomas E. Weirich Matthias Epple 《无机化学与普通化学杂志》2003,629(10):1751-1759
Tetrasulfur tetranitride, S4N4, reacts with elemental Cu within inert solvents to a black‐blue material of approximate composition Cu7S4N4 which is totally amorphous to X‐rays and which cannot be made crystalline by either thermal treatment or electron radiation. Cu7S4N4 explodes if heated above 234 °C or when subjected to mechanical shock to eventually yield copper(I) sulfide; this together with the characteristic infrared spectrum of Cu7S4N4 indicates the presence of molecular S4N4 units inside the amorphous phase. The metastable nature of Cu7S4N4 is also mirrored by electron microscopy which furthermore allows the structural characterization of its degradation products. Based on experimental EXAFS data offering characteristic Cu—N and Cu—S distances, a theoretical crystalline approximant of Cu7S4N4 was suggested and structurally optimized by density‐functional total‐energy calculations including periodic boundary conditions. This model incorporates a central S4N4 unit bonded to three shells of Cu atoms of different functionalities; in addition, a partial rupture of the S4N4 unit is likely to allow for a lowering of the total energy of the metastable phase. The latter observation supports the impossibility to make Cu7S4N4 crystallize using 4N4 crystallize using whatever kind of measures. 相似文献
116.
117.
蔡建平 《Annals of Differential Equations》2004,20(1):14-20
This paper investigates the periodic boundary value problems for a class of second order functional differential equations. The monotone iterative technique and the maximum principle are applied to obtain the existence of maximal and minimal solutions. 相似文献
118.
OSCILLATION FOR SOLUTIONS OF SYSTEMS OF N-TH ORDER PARTIAL FUNCTIONAL DIFFERENTIAL EQUATIONS 总被引:5,自引:0,他引:5
林文贤 《Annals of Differential Equations》2004,20(3):266-272
In this paper, some sufficient conditions for the oscillation for solutions to systems of n-th order partial functional differential equations are obtained. 相似文献
119.
Michelle J. S. Spencer Andrew Hung Ian K. Snook Irene Yarovsky 《Surface science》2003,540(2-3):420-430
The adsorption of atomic S on the Fe(1 1 0) surface is examined using density functional theory (DFT). Three different adsorption sites are considered, including the atop, hollow and bridge sites and the S is adsorbed at a quarter monolayer coverage in a p(2 × 2) arrangement. The hollow site is found to be the most stable, followed by the bridge and atop sites. At all three sites, S adsorption results in relatively minor surface reconstruction, with the most significant being that for the hollow site, with lateral displacements of 0.09 Å. Comparisons between S-adsorbed and pure Fe surfaces revealed reductions in the magnetic moments of surface-layer Fe atoms in the vicinity of the S. At the hollow site, the presence of S causes an increase in the surface Fe d-orbital density of states between 4 and 5 eV. However, S adsorption has no significant effect on the structure and magnetic properties of the lower substrate layers. 相似文献
120.
Wolfgang W. Schoeller 《无机化学与普通化学杂志》2003,629(5):816-827
The particular role of the phosphaneiminato ligand as a donor is investigated for a) nitrenes (phosphinidenes) and carbenes and b) cubane formation with transition metals. Accordingly, and as shown for the case a) the ligand is a stronger π‐donor than an amino group and can be considered as a special case of imine‐type substituents. The latter are very effective in π‐donation. In the case b), i.e. the cubane formation with transition metals, one has to consider transition metals with a partially or completely filled d‐shell (with electrons). Hence depending on the transition metal, cubanes are build with weak ferromagnetic coupled or closed shell systems. For the cubanes with closed shell character the matter of insertion of halide anions is discussed. In the last chapter of the review the bond stretching in the dithionitrosyl complexes with rhenium is characterized. 相似文献