全文获取类型
收费全文 | 3663篇 |
免费 | 597篇 |
国内免费 | 348篇 |
专业分类
化学 | 379篇 |
晶体学 | 19篇 |
力学 | 483篇 |
综合类 | 91篇 |
数学 | 2441篇 |
物理学 | 1195篇 |
出版年
2024年 | 6篇 |
2023年 | 55篇 |
2022年 | 50篇 |
2021年 | 77篇 |
2020年 | 118篇 |
2019年 | 86篇 |
2018年 | 132篇 |
2017年 | 133篇 |
2016年 | 162篇 |
2015年 | 118篇 |
2014年 | 185篇 |
2013年 | 272篇 |
2012年 | 198篇 |
2011年 | 210篇 |
2010年 | 172篇 |
2009年 | 191篇 |
2008年 | 220篇 |
2007年 | 212篇 |
2006年 | 206篇 |
2005年 | 208篇 |
2004年 | 174篇 |
2003年 | 181篇 |
2002年 | 176篇 |
2001年 | 179篇 |
2000年 | 139篇 |
1999年 | 119篇 |
1998年 | 93篇 |
1997年 | 68篇 |
1996年 | 93篇 |
1995年 | 52篇 |
1994年 | 35篇 |
1993年 | 32篇 |
1992年 | 29篇 |
1991年 | 34篇 |
1990年 | 21篇 |
1989年 | 9篇 |
1988年 | 19篇 |
1987年 | 17篇 |
1986年 | 13篇 |
1985年 | 16篇 |
1984年 | 10篇 |
1983年 | 13篇 |
1982年 | 10篇 |
1981年 | 5篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 11篇 |
1977年 | 6篇 |
1976年 | 10篇 |
1974年 | 4篇 |
排序方式: 共有4608条查询结果,搜索用时 546 毫秒
1.
We report optical and nonlinear optical properties of CuS quantum dots and nanoparticles prepared through a nontoxic, green, one-pot synthesis method. The presence of surface states and defects in the quantum dots are evident from the luminescent behavior and enhanced nonlinear optical properties measured using the open aperture Z-scan, employing 5 ns laser pulses at 532 nm. The quantum dots exhibit large effective third order nonlinear optical coefficients with a relatively lower optical limiting threshold of 2.3 J cm−2, and the optical nonlinearity arises largely from absorption saturation and excited state absorption. Results suggest that these materials are potential candidates for designing efficient optical limiters with applications in laser safety devices. 相似文献
2.
Mourad Kainane Mezadek Mohamed Kainane Mezadek Michael Reissig 《Mathematical Methods in the Applied Sciences》2020,43(6):3117-3147
In this paper, we study the global (in time) existence of small data solutions to the Cauchy problem for the semilinear wave equation with friction, viscoelastic damping, and a power nonlinearity. We are interested in the connection between regularity assumptions for the data and the admissible range of exponents p in the power nonlinearity. 相似文献
3.
Ieva
Dauickait Amos S. Lawless Jennifer A. Scott Peter Jan van Leeuwen 《Numerical Linear Algebra with Applications》2020,27(5)
We consider the large sparse symmetric linear systems of equations that arise in the solution of weak constraint four‐dimensional variational data assimilation, a method of high interest for numerical weather prediction. These systems can be written as saddle point systems with a 3 × 3 block structure but block eliminations can be performed to reduce them to saddle point systems with a 2 × 2 block structure, or further to symmetric positive definite systems. In this article, we analyse how sensitive the spectra of these matrices are to the number of observations of the underlying dynamical system. We also obtain bounds on the eigenvalues of the matrices. Numerical experiments are used to confirm the theoretical analysis and bounds. 相似文献
4.
本文定义了二阶微分方程的弱 Carathéodory解 ,在不涉及紧型条件的情形下 ,直接用迭代法证明了 Banach空间二阶非线性常微分方程两点边值问题存在唯一解 ,并给出逼近解迭代序列的误差估计 ,对周期边值问题得到类似的结果 相似文献
5.
6.
Agnieszka Kaamajska 《Mathematical Methods in the Applied Sciences》2006,29(11):1307-1325
The weak limits of sequences {f(uν)}ν∈? where uν's are vector‐valued µ‐measurable functions defined on a compact set Ω and f is (possibly) discontinuous are investigated. As shown by the author (J. Conv. Anal. (to appear)), they are described in terms of integral formulae involving parametrized measures independent of f, similarly as in the classical theorem by Young and its generalization due to DiPerna and Majda. In the present paper we describe the supports of the involved parametrized measures. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
7.
8.
9.
Within the framework of a piecewise homogeneous body model, with the use of three-dimensional geometrically nonlinear exact equations of elasticity theory, a method for determining the stress—strain state in unidirectional fibrous composites with locally curved fibers is developed for the case where the interaction between the fibers is neglected. All the investigations are carried out for an infinite elastic body containing a single locally curved fiber. Numerical results illustrating the effect of geometrical nonlinearity on the distribution of the self-balanced normal and shear stresses acting on the interface and arising as a result of local curving of the fiber are presented.__________Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 41, No. 4, pp. 433–448, July–August, 2005. 相似文献
10.
We study nonlinear dynamics of optical pulse propagation in the spectral region inside the polariton gap. It is shown that the Kerr nonlinearity can lead to formation of solitary waves in this region of frequencies. 相似文献