全文获取类型
收费全文 | 2697篇 |
免费 | 55篇 |
国内免费 | 8篇 |
专业分类
化学 | 1666篇 |
晶体学 | 20篇 |
力学 | 107篇 |
数学 | 495篇 |
物理学 | 472篇 |
出版年
2022年 | 27篇 |
2021年 | 50篇 |
2020年 | 48篇 |
2019年 | 29篇 |
2018年 | 31篇 |
2017年 | 24篇 |
2016年 | 75篇 |
2015年 | 43篇 |
2014年 | 53篇 |
2013年 | 136篇 |
2012年 | 134篇 |
2011年 | 151篇 |
2010年 | 92篇 |
2009年 | 87篇 |
2008年 | 150篇 |
2007年 | 150篇 |
2006年 | 138篇 |
2005年 | 130篇 |
2004年 | 106篇 |
2003年 | 101篇 |
2002年 | 82篇 |
2001年 | 43篇 |
2000年 | 33篇 |
1999年 | 33篇 |
1998年 | 28篇 |
1997年 | 37篇 |
1996年 | 57篇 |
1995年 | 30篇 |
1994年 | 39篇 |
1993年 | 32篇 |
1992年 | 35篇 |
1991年 | 29篇 |
1990年 | 22篇 |
1989年 | 30篇 |
1988年 | 20篇 |
1987年 | 23篇 |
1986年 | 23篇 |
1985年 | 24篇 |
1984年 | 25篇 |
1983年 | 26篇 |
1982年 | 29篇 |
1981年 | 16篇 |
1980年 | 24篇 |
1979年 | 19篇 |
1978年 | 16篇 |
1977年 | 17篇 |
1976年 | 13篇 |
1975年 | 13篇 |
1973年 | 15篇 |
1971年 | 10篇 |
排序方式: 共有2760条查询结果,搜索用时 15 毫秒
1.
2.
It is long known that the Fokker-Planck equation with prescribed constant coefficients of diffusion and linear friction describes
the ensemble average of the stochastic evolutions in velocity space of a Brownian test particle immersed in a heat bath of
fixed temperature. Apparently, it is not so well known that the same partial differential equation, but now with constant
coefficients which are functionals of the solution itself rather than being prescribed, describes the kinetic evolution (in
the N→∞ limit) of an
isolated
N-particle system with certain stochastic interactions. Here we discuss in detail this recently discovered interpretation.
An erratum to this article can be found at 相似文献
3.
Guido Wauters Jacques Dewaele Carlo Vandecasteele Richard Dams 《Mikrochimica acta》1989,98(4-6):157-162
Proton activation analysis was used for the determination of cadmium and lead in three sediment reference materials. The method is based on the111,112Cd(p, xn)111 In and the206,207,208Pb(p, xn)206Bi reactions.111In and206Bi were chemically separated by anion exchange. The results obtained were taken into account for the certification of the materials and are in the excellent agreement with the certified values. 相似文献
4.
5.
R. Pizzoferrato L. Lagonigro T. Ziller A. Di Carlo R. Paolesse F. Mandoj A. Ricci C. Lo Sterzo 《Chemical physics》2004,300(1-3):217-225
We study the infrared emission at 1.54 μm of an organolanthanide complex, Er(III)-tetraphenylporphyrin [Er(TPP)acac], both as a result of direct optical excitation and via energy transfer from host π-conjugate polymers of type poly(arylene–ethynylene) [PAE]. In the first case, the emission of the neat complex is characterized in inert transparent materials and a value of the quantum yield at 1.54 μm φIR=4×10−4 is measured. Then, fluorescence resonance transfer is investigated in blends of Er(TPP)acac with PAEs by monitoring the quenching of the polymer fluorescence along with the enhancement of both the visible emission of the ligand and the near-infrared band of Er3+. These different procedures allow a detailed analysis of the transfer efficiency within a specific implementation of the Förster model for polymeric donors. The experimental values of the critical radius R0, ranging from 1.3 to 2.5 nm for the different blends, are in good agreement with theory for a wide interval of the physical and spectroscopic parameters. This suggests that other mechanisms for excitation transfer do not play a significant role in these materials. 相似文献
6.
7.
Toluene adsorption reactions on the (1 1 0) surface of VSbO4 have been analyzed following the changes in the electronic structure of the hydrocarbon molecule and metal cation sites of the oxide using the Just Another Extended Hückel Molecular Orbital Program (JAEHMOP) code. The bonding character of these interactions has also been studied in the same theoretical framework. The calculations indicate that the exothermic hydrocarbon parallel interaction on Sb-V sites results in the weakening of one of the C-H bonds of the methyl fragment. This leads to a H-abstraction that involves the participation of a Sb-cation. Both methyl and phenyl fragments decrease their electronic population and so does the V-cation site. Most of these electrons are transferred to other V atoms in the bulk solid. As a result the LUMO of the toluene-oxide system fully populates. The analysis reveals that methyl-Sb bonding interactions mainly involve C2px and H1s orbitals with Sb5s orbital, while non-bonding phenyl-V interactions involve C2px orbitals with V3dx2−y2 orbital. This last interaction facilitates the desorption of the benzyl species after H-abstraction. 相似文献
8.
Peptidic aminopeptidase inhibitors, bestatin, phebestin and probestin have been prepared by stereo- and regiocontrolled reactions from a common α,β-epoxy ester precursor. 相似文献
9.
10.