全文获取类型
收费全文 | 254059篇 |
免费 | 3857篇 |
国内免费 | 1567篇 |
专业分类
化学 | 138265篇 |
晶体学 | 3799篇 |
力学 | 10365篇 |
综合类 | 53篇 |
数学 | 28502篇 |
物理学 | 78499篇 |
出版年
2021年 | 1833篇 |
2020年 | 2065篇 |
2019年 | 2360篇 |
2018年 | 2718篇 |
2017年 | 2660篇 |
2016年 | 4214篇 |
2015年 | 2995篇 |
2014年 | 4359篇 |
2013年 | 11844篇 |
2012年 | 8922篇 |
2011年 | 10969篇 |
2010年 | 7195篇 |
2009年 | 7113篇 |
2008年 | 9702篇 |
2007年 | 9802篇 |
2006年 | 8962篇 |
2005年 | 8336篇 |
2004年 | 7472篇 |
2003年 | 6615篇 |
2002年 | 6500篇 |
2001年 | 7502篇 |
2000年 | 5609篇 |
1999年 | 4406篇 |
1998年 | 3700篇 |
1997年 | 3701篇 |
1996年 | 3449篇 |
1995年 | 3252篇 |
1994年 | 3093篇 |
1993年 | 3114篇 |
1992年 | 3400篇 |
1991年 | 3419篇 |
1990年 | 3240篇 |
1989年 | 3175篇 |
1988年 | 3244篇 |
1987年 | 3084篇 |
1986年 | 2990篇 |
1985年 | 4070篇 |
1984年 | 4201篇 |
1983年 | 3461篇 |
1982年 | 3791篇 |
1981年 | 3680篇 |
1980年 | 3556篇 |
1979年 | 3578篇 |
1978年 | 3807篇 |
1977年 | 3639篇 |
1976年 | 3842篇 |
1975年 | 3416篇 |
1974年 | 3555篇 |
1973年 | 3852篇 |
1972年 | 2340篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
A flow visualization of the two-dimensional rigid fling-clap motions of the flat-plate wing is performed to get the knowledge
of fling-clapping mechanism that might be employed by insects during flight. In this numerical visualization, the time-dependent
Navier-Stokes equations are solved for two types of wing motion; ‘fling followed by clap and pause motion’ and ‘cyclic fling-clapping
motion’. The result is observed regarding the main flow features such as the sequential development of the two families of
separation vortex pairs and their movement. For the ‘fling followed by clap and pause motion’, a strong separation vortex
pair of counterrotation develops in the opening between the wings in the fling phase and they then move out from the opening
in the following clap phase. For ‘the cyclic fling-clapping motion’, the separation vortex pair developed in the outside space
in the clap phase move into the opening in the following fling phase. The separation vortex pair in the opening developed
in the fling phase of the cyclic motion is observed to be stronger than those of the ‘fling followed by clap and pause motion’.
Regarding the strong fling separation vortex and the weak clap separation vortex above it in the opening, the flow pattern
of the fling phase of the cyclic fling and clap motion is different to that of the fling phase of the first cycle. The flow
pattern of the third cycle of the cyclic fling-clapping motion is observed to be almost same as that of the second cycle.
Therefore, a periodicity of the flow pattern is established after the second cycle. 相似文献
962.
We study theoretically a nonlinear response of the planar metal/dielectric nanostructures constituted from periodical array
of ultra thin silver layers and the layers of Kerr-like nonlinear dielectric. We predict hysteresis-type dependences of the
components of the tensor of effective dielectric permittivity on the field intensity allowing the change in material transmission
properties from transparent to opaque and back at extremely low intensities of the light. It makes possible to control the
light by light in all-optical nanoscale devices and circuits. 相似文献
963.
V. M. Nagirnyi R. D. Apostolova E. M. Shembel’ 《Russian Journal of Applied Chemistry》2006,79(9):1443-1446
The surface morphology of V2O5, Co2O3, and MnO2 electroplated under different electrolysis conditions was studied. The nature of the electrocrystallization of these materials was suggested on the basis of the analysis results. 相似文献
964.
The FRS-ESR facility at GSI provides one of the most efficient methods for direct mass measurements. In the present experiment,
exotic nuclei were produced via fragmentation of 152Sm projectiles in a thick beryllium target at 500-600 MeV/u, separated in-flight with the fragment separator FRS, and injected
into the storage-cooler ring ESR. Time-resolved Schottky Mass Spectrometry was applied for mass measurements of stored and
electron-cooled bare and few-electron ions. 373 different nuclides were identified by means of the spectra of their revolution
frequencies. Masses for 18 nuclides (84Zr, 92Ru, 94Rh, 107,108,110Sb, 111,112,114I, 118Ba, 122,123La, 124Ce, 127Pr, 129Nd, 132Pm, 134Sm, 137Eu) have been determined for the first time. Masses for 111,112I and 113Xe have been obtained via known α-decay energies. The experiment and first results will be presented. 相似文献
965.
966.
Sufficient conditions are presented for the stabilizability and global controllability of certain natural Lagrangian systems with a non-negative potential energy when there are ideal unilateral constraints. In the general case, the number of controls is less than the number of degrees of freedom and the controls are bounded by preassigned quantities. Examples of globally controlled systems with two degrees of freedom are considered in which the action of the unilateral constraints is modelled within the framework of classical collision theory. 相似文献
967.
S. H. Faller R. W. Holloway S. C. Lee 《Journal of Radioanalytical and Nuclear Chemistry》1989,137(1):9-16
An investigation of cold fusion of deuterium was performed by electrolyzing heavy water in a cell containing a palladium cathode while monitoring levels of tritium and neutron-capture gamma rays. No activity was detected that would indicate a sustained fusion reaction had taken place. Activities that were observed can be attributed to electrolytic enrichment and a normal cosmic-ray induced background. 相似文献
968.
The solid solubility in the systems Y2O2S---La2O2S, Y2O2S---Gd2O2S, and Gd2O2S---La2O2S has been investigated. Solid solutions of all compounds, throughout the whole composition range, were readily obtained, using coprecipitated oxalates and a polysulfide flux. 相似文献
969.
970.
We give a new independent self-dual 3-basis for the trivial variety with two binary operations.
Received October 24, 2006; accepted in final form January 25, 2007. 相似文献