全文获取类型
收费全文 | 131742篇 |
免费 | 22068篇 |
国内免费 | 16155篇 |
专业分类
化学 | 92587篇 |
晶体学 | 1666篇 |
力学 | 7848篇 |
综合类 | 1007篇 |
数学 | 16062篇 |
物理学 | 50795篇 |
出版年
2024年 | 424篇 |
2023年 | 2484篇 |
2022年 | 4473篇 |
2021年 | 4697篇 |
2020年 | 5072篇 |
2019年 | 4985篇 |
2018年 | 4596篇 |
2017年 | 4219篇 |
2016年 | 6281篇 |
2015年 | 6241篇 |
2014年 | 7597篇 |
2013年 | 9861篇 |
2012年 | 11871篇 |
2011年 | 12079篇 |
2010年 | 8591篇 |
2009年 | 8261篇 |
2008年 | 8839篇 |
2007年 | 7839篇 |
2006年 | 7414篇 |
2005年 | 6307篇 |
2004年 | 4909篇 |
2003年 | 3958篇 |
2002年 | 3744篇 |
2001年 | 3098篇 |
2000年 | 2687篇 |
1999年 | 2661篇 |
1998年 | 2206篇 |
1997年 | 1922篇 |
1996年 | 1938篇 |
1995年 | 1737篇 |
1994年 | 1528篇 |
1993年 | 1241篇 |
1992年 | 1109篇 |
1991年 | 980篇 |
1990年 | 806篇 |
1989年 | 640篇 |
1988年 | 495篇 |
1987年 | 417篇 |
1986年 | 400篇 |
1985年 | 328篇 |
1984年 | 226篇 |
1983年 | 192篇 |
1982年 | 149篇 |
1981年 | 108篇 |
1980年 | 76篇 |
1979年 | 38篇 |
1978年 | 30篇 |
1976年 | 24篇 |
1975年 | 25篇 |
1957年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Summary The electronic absorption and e.s.r. spectra of a crystal of the title compound [Cu(H2O)2 (C4H5O5)2] were recorded and experimental results are discussed quantitatively, using ligand field theory and the radial wave function of bound CuII. The electronic structure of the compound is consistent with its crystal structure. 相似文献
92.
Song LI Guo Mao WANG Zhi Song LIU 《数学学报(英文版)》2005,21(6):1475-1486
The purpose of this paper is to investigate the mean size formula of wavelet packets in Lp for 0 〈 p ≤ ∞. We generalize a mean size formula of wavelet packets given in terms of the p-norm joint spectral radius and we also give some asymptotic formulas for the Lp-norm or quasi-norm on the subdivision trees. All results will be given in the general setting, 相似文献
93.
本文讨论了每个元都有幂等元作为右单位元的左消半群与幂单半群N的Schuzenberger积M◇N的ρ类,证明了这种半群M与N的Schuzenberger积M◇N的ρ类是右E一半适合半群和弱E-headged半群. 相似文献
94.
95.
使用Monte Carlo模拟的方法得出了随机粗糙表面,在Kirchhoff近似的基础上,利用数值分析的方法分析了一维随机粗糙表面的散射特征,得出了一维随机粗糙表面散射分布曲线,我们还考虑了遮蔽效应的影响,并且讨论了Kirchhoff近似的有效性。 相似文献
96.
Jihua Zhang Xi WangWeidong Yu Tao FengFumin Zhang Zhihong ZhengQiong Li Xianghuai Liu 《Solid State Communications》2003,127(4):289-293
Effects of ion impinging on the microstructure and field electron emission properties of screen-printed carbon nanotube films were investigated. We observed that the plasma treatment modified the microstructure of CNTs along with the remarkable increase of emission site density. With the prolongation of ion impinging time, the emission current falls down first, and then rises up to higher than that of the untreated films. It is proposed that the change of emission characteristics is due to the different emission mechanisms. After the treatment, electrons are emitted predominantly from the nano-nodes on the tube wall instead from the nanotube tips. 相似文献
97.
A new family of photonucleases, naphthalimide-thiazoles was synthesized and evaluated. These compounds intercalated into DNA efficiently and damaged DNA photochemically at concentrations as low as 5 μM. Mechanistic experiment suggests that a novel naphthalimide-thiazole radical produced via an excited triple state might be involved in the DNA photodamage. Different activity may arise from the impact of substituents at 2-phenyl ring of thiazole on the electron population of excited triple state according to AM1 semi-empirical calculation. 相似文献
98.
99.
A new stochastic method of reconstructing porous media 总被引:1,自引:0,他引:1
We present a new stochastic method of reconstructing porous medium from limited morphological information obtained from two-dimensional
micro- images of real porous medium. The method is similar to simulated annealing method in the capability of reconstructing
both isotropic and anisotropic structures of multi-phase but differs from the latter in that voxels for exchange are not selected
completely randomly as their neighborhood will also be checked and this new method is much simpler to implement and program.
We applied it to reconstruct real sandstone utilizing morphological information contained in porosity, two-point probability
function and linear-path function. Good agreement of those references verifies our developed method’s powerful capability.
The existing isolated regions of both pore phase and matrix phase do quite minor harm to their good connectivity. The lattice
Boltzmann method (LBM) is used to compute the permeability of the reconstructed system and the results show its good isotropy
and conductivity. However, due to the disadvantage of this method that the connectivity of the reconstructed system’s pore
space will decrease when porosity becomes small, we suggest the porosity of the system to be reconstructed be no less than
0.2 to ensure its connectivity and conductivity. 相似文献
100.