全文获取类型
收费全文 | 16236篇 |
免费 | 2765篇 |
国内免费 | 2248篇 |
专业分类
化学 | 14816篇 |
晶体学 | 187篇 |
力学 | 374篇 |
综合类 | 135篇 |
数学 | 1291篇 |
物理学 | 4446篇 |
出版年
2024年 | 48篇 |
2023年 | 199篇 |
2022年 | 356篇 |
2021年 | 812篇 |
2020年 | 865篇 |
2019年 | 665篇 |
2018年 | 545篇 |
2017年 | 598篇 |
2016年 | 845篇 |
2015年 | 732篇 |
2014年 | 887篇 |
2013年 | 1503篇 |
2012年 | 1019篇 |
2011年 | 895篇 |
2010年 | 813篇 |
2009年 | 918篇 |
2008年 | 979篇 |
2007年 | 1022篇 |
2006年 | 932篇 |
2005年 | 849篇 |
2004年 | 819篇 |
2003年 | 762篇 |
2002年 | 552篇 |
2001年 | 484篇 |
2000年 | 497篇 |
1999年 | 454篇 |
1998年 | 409篇 |
1997年 | 296篇 |
1996年 | 245篇 |
1995年 | 236篇 |
1994年 | 207篇 |
1993年 | 133篇 |
1992年 | 129篇 |
1991年 | 80篇 |
1990年 | 58篇 |
1989年 | 64篇 |
1988年 | 51篇 |
1987年 | 35篇 |
1986年 | 39篇 |
1985年 | 49篇 |
1984年 | 27篇 |
1983年 | 10篇 |
1982年 | 20篇 |
1981年 | 25篇 |
1980年 | 24篇 |
1979年 | 13篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Kamil Walczak 《Central European Journal of Physics》2006,4(1):8-19
The rate-equation approach is used to describe sequential tunneling through a molecular junction in the Coulomb blockade regime.
Such device is composed of molecular quantum dot (with discrete energy levels) coupled with two metallic electrodes via potential
barriers. Based on this model, we calculate nonlinear transport characteristics (conductance-voltage and current-voltage dependences)
and compare them with the results obtained within a self-consistent field approach. It is shown that the shape of transport
characteristics is determined by the combined effect of the electronic structure of molecular quantum dots and by the Coulomb
blockade. In particular, the following phenomena are discussed in detail: the suppression of the current at higher voltages,
the charging-induced rectification effect, the charging-generated changes of conductance gap and the temperature-induced as
well as broadening-generated smoothing of current steps. 相似文献
92.
Dielectric relaxation study of the binary mixtures of poly(vinyl pyrrolidone) (PVP) (Mw=24000, 40000 and 360000 g mol−1) with ethyl alcohol (EA) and poly(ethylene glycol)s (PEGs) (Mw=200 and 400 g mol−1) in dilute solutions of dioxane were carried out at 10.1 GHz and 35°C. The relaxation time of PVP-EA mixtures was interpreted
by the consideration of a wait-and-switch model in the local structure of self-associated ethyl alcohol molecules and also
the PVP chain length as a geometric constraint for the reorientational motion of ethyl alcohol molecules. The formation of
complexes and effect of PVP chain length on the molecular dynamics, chain flexibility and stretching of PEG molecules in PVP-PEG
mixtures were explored from the comparative values of dielectric relaxation time. Further, relaxation time values in dioxane
and benzene solvent confirm the viscosity independent molecular dynamics in PVP-EA mixtures but the values vary significantly
with the non-polar solvent environment. 相似文献
93.
Recently, we have developed a new tight-binding quantum chemical molecular dynamics program “Colors” for combinatorial computational chemistry approach. This methodology is based on our original tight-binding approximation and realized over 5000 times acceleration compared to the conventional first-principles molecular dynamics method. In the present study, we applied our new program to the simulations on various realistic large-scale models of the automotive three-way catalysts, ultrafine Pt particle/CeO2(111) support. Significant electron transfer from the Pt particle to the CeO2(111) surface was observed and it was found to strongly depend on the size of the Pt particle. Furthermore, our simulation results suggest that the reduction of the Ce atom due to the electron transfer from the Pt particle to the CeO2 surface is a main reason for the strong interaction of the Pt particle and CeO2(111) support. 相似文献
94.
Jean-Marie Lehn 《Journal of Chemical Sciences》1994,106(5):915-922
The article discusses molecular recognition and overviews the key concepts -storage and retrieval of chemical information
by molecular structures, supramolecular reagents and catalysts, molecular transport, semiochemistry and self assembly. The
prospects of controlling supramolecular architecture through engineered molecular recognition and design of ‘programmed systems’
controlled by molecular information are also discussed. 相似文献
95.
96.
F.F. Karpeshin J. da Providência C. Providência J. da Providência Jr 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(3):319-326
Two types of extreme collective motion, large-amplitude many-phonon vibration of the ionic core and rotation of the cluster
with high angular momenta, are considered. The interplay between vibration and collective motion towards fission is discussed.
A new mechanism of formation and rupture of the neck is proposed which is based on the Franck-Condon principle, and accounts
for the interplay between vibration and fission. Under rotation, the change of the shape of the cluster and a phase transition
from axially symmetric to triaxial ellipsoid are predicted. For studying the effects, vibrational motion can be induced by
laser radiation. Rotational motion may arise in collisions of clusters.
Received 26 April 2001 and Received in final form 15 October 2001 相似文献
97.
98.
Thermotropic copolyester fibers of oxynaphthoate and oxybenzoate have been subjected to conditions that promote solid-state polymerization as well as annealing. The annealing process causes the crystals to perfect with a simultaneous increase in heat of fusion and melting temperature. Solid-state polymerization, a reaction rate-controlled process, causes the polymer viscosity average molecular weight to increase by chain extension from about 14,000 g/mole to more than 87,000 g/mole with a simultaneous impressive increase in tenacity from about 10 g/d (1.2 GPa) to almost 30 g/d (3.7 GPa). To understand the changes in mechanical properties, we have modeled the fiber structure as short rod-like molecules poorly bonded to a continuous matrix of parallel molecules. Lengthening of the reinforcing molecules facilitates better transfer of load from matrix to molecules, resulting in higher tenacity fibers. © 1994 John Wiley & Sons, Inc. 相似文献
99.
We study the behavior of dynamic programming methods for the tree edit distance problem, such as [P. Klein, Computing the edit-distance between unrooted ordered trees, in: Proceedings of 6th European Symposium on Algorithms, 1998, p. 91–102; K. Zhang, D. Shasha, SIAM J. Comput. 18 (6) (1989) 1245–1262]. We show that those two algorithms may be described as decomposition strategies. We introduce the general framework of cover strategies, and we provide an exact characterization of the complexity of cover strategies. This analysis allows us to define a new tree edit distance algorithm, that is optimal for cover strategies. 相似文献
100.