全文获取类型
收费全文 | 3081篇 |
免费 | 630篇 |
国内免费 | 1265篇 |
专业分类
化学 | 2331篇 |
晶体学 | 154篇 |
力学 | 249篇 |
综合类 | 79篇 |
数学 | 471篇 |
物理学 | 1692篇 |
出版年
2024年 | 8篇 |
2023年 | 50篇 |
2022年 | 146篇 |
2021年 | 130篇 |
2020年 | 113篇 |
2019年 | 120篇 |
2018年 | 122篇 |
2017年 | 172篇 |
2016年 | 138篇 |
2015年 | 165篇 |
2014年 | 206篇 |
2013年 | 324篇 |
2012年 | 270篇 |
2011年 | 278篇 |
2010年 | 278篇 |
2009年 | 297篇 |
2008年 | 327篇 |
2007年 | 250篇 |
2006年 | 280篇 |
2005年 | 237篇 |
2004年 | 174篇 |
2003年 | 118篇 |
2002年 | 116篇 |
2001年 | 135篇 |
2000年 | 142篇 |
1999年 | 87篇 |
1998年 | 49篇 |
1997年 | 29篇 |
1996年 | 27篇 |
1995年 | 22篇 |
1994年 | 26篇 |
1993年 | 20篇 |
1992年 | 19篇 |
1991年 | 12篇 |
1990年 | 19篇 |
1989年 | 9篇 |
1988年 | 13篇 |
1987年 | 8篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 11篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 2篇 |
排序方式: 共有4976条查询结果,搜索用时 15 毫秒
1.
The stable phase equilibria of quaternary systems LiBr-NaBr-MgBr2-H2O and LiBr-KBr-MgBr2-H2O at 298.15 K were studied by both experimental measurement(isothermal solution saturation method) and theoretical prediction(Pitzer model). The solubilities of the saturated solution have been determined experimentally and two stable phase diagrams and relevant water diagrams of the two quaternary systems were obtained. Results show that quaternary system LiBr-NaBr-MgBr2-H2O is hydrate II type as NaBr and NaBr·2H2O coexistence. Its phase diagram consists of only one invariant point, four univariant curves, and five crystallization fields. The quaternary system LiBr-KBr-MgBr2-H2O is a complex type as the double salt KBr·MgBr2·6H2O formed. In addition to this double salt, the three single salts LiBr·2H2O, KBr and MgBr2·6H2O also crystallize. In this paper, the solubilities of phase equilibria in above quaternary systems were also calculated by the Pitzer's electrolyte solution model. All the needed parameters can be obtained from the literature or be fitted by experimental data. On the Basis of the experimental and calculated results, the phase diagram of the quaternary system was plotted for comparison. It shows that the calculation results are consistent with the experimental ones. 相似文献
2.
3.
4.
5.
6.
Two-dimensional 4,4-bipyridyllead halides, PbI2 (4,4'-bpy) (1) and PbBr2 (4,4'-bpy) (2), were synthesized. The structures were determined by means of X-ray single crystal diffraction.The structure shows a distorted octahedral configuration with six-coordinated central lead atoms. In crystals 1 and 2, the molecules are packed in a two-dimensional network structure through bridging halide atoms and 4,4'-bipyridine ligands between the adjacent lead atoms. 相似文献
7.
A Continuation Method of Parameter Inversion for Non-Equilibrium Convection-Dispersion Equation 总被引:1,自引:0,他引:1 下载免费PDF全文
Based on the homotopy mapping, a globally convergent method of parameter inversion for non-equilibrium convection-dispersion equations (CDEs) is developed. Moreover, in order to further improve the computational efficiency of the algorithm, a properly smooth function, which is derived from the sigmoid function, is employed to update the homotopy parameter during iteration. Numerical results show the feature of global convergence and high performance of this method. In addition, even the measurement quantities are heavily contaminated by noises, and a good solution can be found. 相似文献
8.
三种群食物链交错扩散模型的整体 总被引:1,自引:0,他引:1
本文应用能量估计方法和Gagliardo-Nirenberg型不等式证明了一类强耦合反应扩散系统整体解的存在性和一致有界性,该系统是带自扩散和交错扩散项的三种群Lotka-Volterra食物链模型.通过构造Lyapunov函数给出了该模型正平衡点全局渐近稳定的充分条件. 相似文献
9.
10.
We study the decoherence process of an exact solvable model that consists of a central spin-1/2 coupling to the surrounding anisotropy spin-1/2 chain in transverse fields. The Loschrnidt echo is calculated to study the character of decoherence with different degree of anisotropy. Our results show that the degree of anisotropy γ greatly affects the decoherence process of the central spin-system when the spin chain is in weak transverse fields, but it gives weak effect in the strong transverse field. The decoherence process of the central system changed dramatically along the line of the critical points, and this may be explained as the reflection of quantum phase transitions. 相似文献