全文获取类型
收费全文 | 4575篇 |
免费 | 464篇 |
国内免费 | 221篇 |
专业分类
化学 | 3118篇 |
晶体学 | 23篇 |
力学 | 211篇 |
综合类 | 6篇 |
数学 | 748篇 |
物理学 | 1154篇 |
出版年
2023年 | 65篇 |
2022年 | 72篇 |
2021年 | 95篇 |
2020年 | 110篇 |
2019年 | 102篇 |
2018年 | 128篇 |
2017年 | 117篇 |
2016年 | 151篇 |
2015年 | 153篇 |
2014年 | 187篇 |
2013年 | 295篇 |
2012年 | 330篇 |
2011年 | 351篇 |
2010年 | 204篇 |
2009年 | 197篇 |
2008年 | 285篇 |
2007年 | 261篇 |
2006年 | 239篇 |
2005年 | 285篇 |
2004年 | 230篇 |
2003年 | 174篇 |
2002年 | 142篇 |
2001年 | 98篇 |
2000年 | 81篇 |
1999年 | 85篇 |
1998年 | 53篇 |
1997年 | 54篇 |
1996年 | 64篇 |
1995年 | 55篇 |
1994年 | 36篇 |
1993年 | 45篇 |
1992年 | 52篇 |
1991年 | 37篇 |
1990年 | 30篇 |
1989年 | 18篇 |
1988年 | 13篇 |
1987年 | 21篇 |
1986年 | 21篇 |
1985年 | 26篇 |
1984年 | 21篇 |
1983年 | 17篇 |
1982年 | 19篇 |
1981年 | 22篇 |
1980年 | 14篇 |
1979年 | 16篇 |
1978年 | 16篇 |
1976年 | 18篇 |
1974年 | 14篇 |
1973年 | 13篇 |
1948年 | 14篇 |
排序方式: 共有5260条查询结果,搜索用时 15 毫秒
21.
THE ASYMPTOTIC SOLUTION FOR A CLASS OF SINGULARLY PERTURBED PROBLEM FOR SEMILINEAR SINGULAR EQUATION
The singularly perturbed boundary value problem for a class of semilinearsingular equation is considered. Using a simple and special method the asym-ptotic behavior of solution is studied. 相似文献
22.
E. Possenriede P. Jacobs H. Kröse O. F. Schirmer 《Applied Physics A: Materials Science & Processing》1992,55(1):73-81
On the basis of a previous identification of paramagnetic defects in nominally undoped as grown BaTiO3 single crystals, we have investigated the changes of the concentrations of these centers and their optical absorptions under illumination with light of varying wavelengths. The most pronounced charge transfers occur by hole ionization of Fe4+ and — to a lesser extent — of Cr5+ and Cr4+. At low temperatures the created holes are trapped in the form of O–-ions next to Al3+ or unknown acceptor defects. Corresponding Fe4+ and O– absorptions have been identified. 相似文献
23.
24.
We establish new estimates for the Laplacian, the div–curl system, and more general Hodge systems in arbitrary dimension, with an application to minimizers of the Ginzburg–Landau energy. To cite this article: J. Bourgain, H. Brezis, C. R. Acad. Sci. Paris, Ser. I 338 (2004). 相似文献
25.
The kinetics and the equilibrium constant of the chlorine transfer reaction between monochloramine NH2Cl and the amines: C2H5NH2, (CH3)2CHNH2, (CH3)2NH, and (C2H5)2NH are investigated by spectrophotometry in aqueous medium at 25°C, in the pH range from 8 to 13 and for an ionic strength equal to 1.03 ± 0.05M. For a concentration of total ammonia equal to 1M, the observed rate constant is pH independent below 8 and above 12.8 and reaches a maximum located between the pKas of NH4+ and RR'NH2+. From these results and those obtained earlier for NH2Cl and CH3NH2, the reaction is shown to involve an interaction between neutral molecules NH2Cl and RR'NH, subject to general acid catalysis. The ability of an interaction corresponding to a specific catalysis and involving NH3Cl+ and RR'NH rather than NH2Cl and RR'NH2+ is also discussed. The activation parameters are given for each reaction. 相似文献
26.
在局部区域上的奇摄动反应扩散方程初始边值问题 总被引:2,自引:2,他引:0
本文是讨论一类在局部区域上的奇摄动反应扩散初始边值问题.利用算子理论和 不动点原理,得到了相应问题解的存在性和唯一性. 相似文献
27.
非线性时滞反应扩散方程组的奇摄动 总被引:1,自引:1,他引:0
本文研究了一类奇摄动非线性时滞反应扩散方程组,利用微分不等式方法,得到了解的一致有效的渐近展开式. 相似文献
28.
Herve Loïc 《Integral Equations and Operator Theory》1998,32(2):199-215
LetX be a locally compact space, andT, a quasi-compact positive operator onC
0(X), with positive spectral radius,r. Then the peripheral spectrum ofT is a finite set of poles containingr, and the residue of the resolvent ofT at each peripheral pole is of finite rank. Using the concept of closed absorbing set, we develop an iterative process that gives the order,p, ofr, some special bases of the algebraic eigenspaces ker(T-r)
p
and ker(T
*-r)
p
, and finally the dimension of the algebraic eigenspace associated to each peripheral pole. 相似文献
29.
A striking size dependence of the mean-square displacement of diffusing particles in the two-dimensional lattice gas of hard squares has been observed by Monte Carlo simulation. It is shown that the size effect is due to the formation of a stable cage structure in small lattices when the particle concentration is high. The formation of cages is governed by a new type of percolation problem related to bootstrap percolation. 相似文献
30.
Zhishen Mo Lixiao Wang Hongfang Zhang Ping Han Baotong Huang 《Journal of Polymer Science.Polymer Physics》1987,25(9):1829-1837
Wide-angle X-ray scattering from presumed block copolymers of polypropylene (PP) and ethylene-propylene copolymer (EPR), i.e., PP-EPR and PP-EPR-PP, synthesized by sequential polymerization with δ-TiCl3? Et2AlCl, was examined and compared with WAXS of mechanical blends and chain-transfer mixtures of PP and EPR with comparable compositions. The peak at 2θ = 20° for both the copolymers and the mixtures was attributed to the γ modification of PP in EPR. A strong variation in the ratio of diffraction intensities I040/I110 of PP in block copolymers and mixtures was explained in terms of crystallite growth in different directions. Analysis of the patterns and calculation of crystallinity, crystallite size, and lattice parameters led to the conclusion that block structure existed in the prepared copolymers. 相似文献