全文获取类型
收费全文 | 7344篇 |
免费 | 1350篇 |
国内免费 | 695篇 |
专业分类
化学 | 5096篇 |
晶体学 | 43篇 |
力学 | 438篇 |
综合类 | 44篇 |
数学 | 930篇 |
物理学 | 2838篇 |
出版年
2024年 | 22篇 |
2023年 | 145篇 |
2022年 | 251篇 |
2021年 | 280篇 |
2020年 | 349篇 |
2019年 | 264篇 |
2018年 | 247篇 |
2017年 | 238篇 |
2016年 | 353篇 |
2015年 | 386篇 |
2014年 | 419篇 |
2013年 | 523篇 |
2012年 | 672篇 |
2011年 | 716篇 |
2010年 | 455篇 |
2009年 | 412篇 |
2008年 | 457篇 |
2007年 | 427篇 |
2006年 | 408篇 |
2005年 | 290篇 |
2004年 | 257篇 |
2003年 | 166篇 |
2002年 | 192篇 |
2001年 | 121篇 |
2000年 | 134篇 |
1999年 | 147篇 |
1998年 | 128篇 |
1997年 | 144篇 |
1996年 | 126篇 |
1995年 | 116篇 |
1994年 | 100篇 |
1993年 | 99篇 |
1992年 | 68篇 |
1991年 | 59篇 |
1990年 | 58篇 |
1989年 | 33篇 |
1988年 | 32篇 |
1987年 | 31篇 |
1986年 | 11篇 |
1985年 | 24篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1916年 | 1篇 |
排序方式: 共有9389条查询结果,搜索用时 0 毫秒
1.
2.
We investigate terahertz radiation(T-rays) from a pentacene organic diode at room temperature. The quantum chemistry calculation for frequency-related Huang–Rhys factor of pentacene is also carried out. The results demonstrate that the T-rays can come from a bending vibration of pentacene skeleton after the energy of pentacene exciton transferring to the vibrational excited state via electron–phonon coupling. Frequency and natural bond orbital analytics of pentacene and its derivatives are performed in order to explain the result and develop new materials to get higher emission. This work provides a new way to produce T-rays with a simple device at room temperature. 相似文献
3.
4.
Understanding and control of the surface properties such as molecular orientations are of great importance in numerous applications of ionic liquids. However, there remain discrepancies among the previous experimental and theoretical studies on the surface orientation and structures of room temperature ionic liquids(RTIL) systems. In this article, the orientation of 1-butyl-3-methylimidazolium([bmin]) cation at the air/liquid interface of a characteristic RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate([bmim][PF6]), was investigated by the sum frequency generation vibrational spectroscopy(SFG-VS). Detailed polarization and experimental configuration analyses of the SFG-VS spectra showed the possibility of a small spectral splitting in the CH3 symmetric stretching region, which can be further attributed to the probable existence of multiple orientations for the interfacial [bmim] cations. In addition, the(N)–CH3 vibrations were absent, ruling out the prediction by several recent molecular dynamics simulations which state that portions of the [bmim] cations orient with a standing-up(N)–CH3 group at the ionic liquid surface. Hence, new realistic theoretical models have to be developed to reflect the complex nature of the ionic liquid surface. 相似文献
5.
6.
We have obtained expressions of the accelerating effect in Kerr-Newman Kasuya field. These expressionsinclude four parameters: mass m, angular momentum a, electric charge q, and magnetic charge φ. Furthermore we studyits special case (vi = 0). We get the following conclusion. In the gravitation field of souse mass with electric charge qand magnetic charge b, the acceleration of test particle has not only radial component but also transverse component.When θ = 0, the acceleration is minimum, and when θ = π/2, the acceleration is maximum. Furthermore, we discussthe effects of electric charge q and magnetic charge φ respectively. 相似文献
7.
A Modified Quasi-Newton Method for Structured Optimization with Partial Information on the Hessian 总被引:2,自引:0,他引:2
This paper develops a modified quasi-Newton method for structured unconstrained optimization with partial information on the
Hessian, based on a better approximation to the Hessian in current search direction. The new approximation is decided by both
function values and gradients at the last two iterations unlike the original one which only uses the gradients at the last
two iterations. The modified method owns local and superlinear convergence. Numerical experiments show that the proposed method
is encouraging comparing with the methods proposed in [4] for structured unconstrained optimization
Presented at the 6th International Conference on Optimization: Techniques and Applications, Ballarat, Australia, December
9–11, 2004 相似文献
8.
该文讨论一类带有奇异系数的双重调和方程{△^2u-μu/|x|^s=f(x,u),x∈Ω,u=δu/δv=0,x∈δΩ,这里Ω包含R^N是包含0的有界光滑区域,u∈H0^2(Ω),μ∈R是参数,0≤s≤2,△^2=△△表示双重拉普拉斯算子,当f(x,u)=u^p,p=2N/N-4时,上述问题就是一个临界双重调和问题,该文运用Sobolev-Hardy不等式和变分方法,得到它的解的存在性的一些结果。 相似文献
9.
Nickel complexes 1–4 ligated with 2,9-disubstituted-1,10-phenanthroline were synthesized and characterized by FT-IR spectra and elemental analysis.
The molecular structure of complex 2 was confirmed by X-ray crystal diffraction analysis. Activated with methylaluminoxane (MAO), those complexes showed moderate
activities for ethylene oligomerization.
Published in Kinetika i Kataliz, 2007, Vol. 48, No. 5, pp. 710–714.
This article was submitted by the authors in English. 相似文献
10.