全文获取类型
收费全文 | 15704篇 |
免费 | 2609篇 |
国内免费 | 2171篇 |
专业分类
化学 | 15287篇 |
晶体学 | 182篇 |
力学 | 636篇 |
综合类 | 77篇 |
数学 | 160篇 |
物理学 | 4142篇 |
出版年
2024年 | 55篇 |
2023年 | 209篇 |
2022年 | 906篇 |
2021年 | 769篇 |
2020年 | 834篇 |
2019年 | 619篇 |
2018年 | 498篇 |
2017年 | 530篇 |
2016年 | 772篇 |
2015年 | 694篇 |
2014年 | 783篇 |
2013年 | 1419篇 |
2012年 | 946篇 |
2011年 | 822篇 |
2010年 | 736篇 |
2009年 | 815篇 |
2008年 | 917篇 |
2007年 | 970篇 |
2006年 | 878篇 |
2005年 | 811篇 |
2004年 | 791篇 |
2003年 | 748篇 |
2002年 | 514篇 |
2001年 | 457篇 |
2000年 | 458篇 |
1999年 | 414篇 |
1998年 | 382篇 |
1997年 | 291篇 |
1996年 | 238篇 |
1995年 | 233篇 |
1994年 | 196篇 |
1993年 | 121篇 |
1992年 | 136篇 |
1991年 | 70篇 |
1990年 | 59篇 |
1989年 | 67篇 |
1988年 | 46篇 |
1987年 | 36篇 |
1986年 | 36篇 |
1985年 | 44篇 |
1984年 | 27篇 |
1983年 | 10篇 |
1982年 | 14篇 |
1981年 | 23篇 |
1980年 | 23篇 |
1979年 | 13篇 |
1978年 | 10篇 |
1977年 | 12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.
S. F. Chekmarev R. Mitri V. Bonaci-Koutecký 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):45-48
The ab initio molecular
dynamics (AIMD) [1] is combined with the heuristic, successive
confinement method of surveying a potential energy surface (PES)
[2], thereby offering a framework for the simulation study of
kinetics and equilibrium properties of metallic clusters. This
approach is applied to the study of Au4,
a cluster possessing a simple but specific PES, which consists
of very shallow and deep basins and due to this presents a
challenge to the conventional AIMD methods. Among other things,
the probabilities of the transitions between isomers have been
found, and on this basis, both the time-dependent and
equilibrium populations of the isomers have been calculated for
the conditions typical of the NeNePo experiments [3] in the
femtosecond pump-probe spectroscopy. 相似文献
92.
Advanced analytical models have been developed at the ILK, which offer a possibility of calculating the vibro-acoustic and damping behavior of textile-reinforced composite shells and plates with account of shear effects. The simulation models elaborated have been verified on selected examples, and the analytical results were fully corroborated by accompanying numerical calculations for typical lay-ups.__________Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 41, No. 3, pp. 289–302, May–June, 2005. 相似文献
93.
HL-2A tokamak, the first tokamak with divertor in China, has been constructed and put into operation in 2002. The main parameters are R=1.65 m, a=0.4 m, BT=2.8 T, Ip = 0. 48 MA. The divertor of HL-2A is unique, because it is characterized with a large closed divertor chamber. The device has double divertor chamber, but now it is operating with lower single null configuration to study the physics of divertor for the next step design of a divertor. Supersonic molecular beam injection (SMBI) system with LN2 cooling trap was first installed and demonstrated on the HL-2A tokamak in 2004. The first results of SMBI into HL-2A plasma are to demonstrate the function of the HL-2A divertor and to observe the cold pulse propagation during multi-pulse SMBI on HL-2A Tokamak. 相似文献
94.
95.
Akira Shimazu Tukasa Miyazaki Shigeru Katayama Yasuo Ito 《Journal of Polymer Science.Polymer Physics》2003,41(3):308-318
The ortho‐positronium (o‐Ps) lifetime τ3 and its intensity I3 in various fluorinated polyimides were determined by the positron annihilation technique and were studied with the spin–lattice relaxation time T1 and the propylene permeability, solubility, diffusivity, and permselectivity for propylene/propane in them. τ3, I3, and the distribution of τ3 changed when the bulky moieties in the polyimides were changed. The polyimides, having both large τ3 and I3 values, exhibited a short T1 and a high permeability with a low permselectivity. The propylene permeability and diffusivity were exponentially correlated with the product of I3 and the average free‐volume hole size estimated from τ3. In highly plasticized states induced by the sorption of propylene, the permeability increased with the propylene pressure in excellent agreement with the change in the free‐volume hole properties probed by o‐Ps. The large and broad distribution of the free‐volume holes and increased local chain mobility for the 2,2‐bis(3,4‐decarboxyphenyl) hexafluoropropane dianhydride‐based polyimides are thought to be important physical properties for promoting penetrant‐induced plasticization. These results suggest that o‐Ps is a powerful probe of not only the free‐volume holes but also the corresponding permeation mechanism and penetrant‐induced plasticization phenomenon. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 308–318, 2003 相似文献
96.
An efficient time-domain algorithm for plane non-linear flexural vibrations of multi-layered composite beams, which are driven into the inelastic range by severe transverse loadings, is presented. The influence of an axial static preload is considered in the sense of the quasi-linear second-order theory of structures. The inelastic parts of strain are treated as additional sources of selfstress in the linear elastic background-structure, driving the elastic response into the inelastic one. The efficiency of this exact formulation lies in the fact that linear solution techniques can be used in their most powerful form: Rubin's useful formulation for the quasi-static second-order transfer-matrix of linear elastic structures is applied in combination with modal analysis. Having in mind multi-metal beams, the classical lamination theory is assumed to be valid. Beams with overhang composed of ideal elastic-plastic and viscoplastic layers are studied as example structures. The fictitious sources of selfstress are calculated from the different material laws of the layers in a numerical time-stepping procedure, where a generalized midpoint-rule in combination with Crisfield's secant-Newton procedure is used. 相似文献
97.
98.
99.
S.F. Lienin R. Brüschweiler R.R. Ernst 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,131(2):184-190
The viscosity-dependent retarding effect of a polymeric solvent on the rotation of small solute molecules is investigated by13C NMR relaxation measurements. It is found that the relaxation data of 1,3-dibromoadamantane in highly viscous polymeric chlorotrifluoroethene can be explained neither by isotropic nor by realistic anisotropic tumbling in a single environment. The experimental data are rationalized in terms of fast exchange between at least two environments with correlation times differing by up to two orders of magnitude. The study shows that a uniform retardation of molecular tumbling by a polymeric solvent, desirable for shifting the NMR observation window in studies of intramolecular mobility, is not always feasible. 相似文献
100.