全文获取类型
收费全文 | 494037篇 |
免费 | 6445篇 |
国内免费 | 1856篇 |
专业分类
化学 | 268241篇 |
晶体学 | 7242篇 |
力学 | 20623篇 |
综合类 | 9篇 |
数学 | 59694篇 |
物理学 | 146529篇 |
出版年
2020年 | 3476篇 |
2019年 | 3680篇 |
2018年 | 4137篇 |
2017年 | 3977篇 |
2016年 | 7119篇 |
2015年 | 5345篇 |
2014年 | 7627篇 |
2013年 | 22754篇 |
2012年 | 16795篇 |
2011年 | 20937篇 |
2010年 | 13292篇 |
2009年 | 13245篇 |
2008年 | 18957篇 |
2007年 | 19246篇 |
2006年 | 18265篇 |
2005年 | 16817篇 |
2004年 | 15055篇 |
2003年 | 13388篇 |
2002年 | 13081篇 |
2001年 | 14674篇 |
2000年 | 11309篇 |
1999年 | 9015篇 |
1998年 | 7395篇 |
1997年 | 7235篇 |
1996年 | 7117篇 |
1995年 | 6547篇 |
1994年 | 6224篇 |
1993年 | 6115篇 |
1992年 | 6752篇 |
1991年 | 6685篇 |
1990年 | 6269篇 |
1989年 | 6102篇 |
1988年 | 6330篇 |
1987年 | 5999篇 |
1986年 | 5785篇 |
1985年 | 8200篇 |
1984年 | 8394篇 |
1983年 | 6869篇 |
1982年 | 7498篇 |
1981年 | 7390篇 |
1980年 | 7135篇 |
1979年 | 7232篇 |
1978年 | 7468篇 |
1977年 | 7314篇 |
1976年 | 7383篇 |
1975年 | 6967篇 |
1974年 | 6933篇 |
1973年 | 7273篇 |
1972年 | 4391篇 |
1971年 | 3309篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
Models, describing relativistic particles, where Lagrangian densities depend linearly on both the curvature and the torsion of the trajectories, are revisited in D=3 space forms. The moduli spaces of trajectories are completely and explicitly determined using the Lancret program. The moduli subspaces of closed solitons in the three sphere are also determined. 相似文献
942.
This work deals with the problem of noise generated by water supply systems in homes. Measurements were made in situ to determine normal conditions of installations and noise levels generated in different rooms in the home. In order to determine the sources of noise and the best construction methods to minimise noise generation, a laboratory was also built to reproduce the conditions of this type of installation in homes. Tests were carried out in this laboratory on different configurations of type of tap, installation material, walling and fastening of the installation, to allow quantitative determination of the differences in noise generation between the various configurations used in households. 相似文献
943.
The construction of non-Abelian affine Toda models is discussed in terms of its underlying Lie algebraic structure. It is shown that a subclass of such non-conformal two-dimensional integrable models naturally leads to the construction of a pair of actions, which share the same spectra and are related by canonical transformations. 相似文献
944.
F. R. Ling B. Wang T. Geng S. Q. Fang W. Yuan D. D. Teng C. X. Guan 《Optics & Laser Technology》2004,36(7):541-544
In this paper experimental studies of nonvolatile photorefractive holographic recording in Ce:Cu:LiNbO3 crystals doped with Sc(0,1,2,3 mol%) were carried out. The Sc:Ce:Cu:LiNbO3 crystals were grown by the Czochralski method and oxidized in Nb2O5 powders. The nonvolatile holographic recording in Sc:Ce:Cu:LiNbO3 crystals was realized by the two-photon fixed method. We found that the recording time of Sc:Ce:Cu:LiNbO3 crystal became shorter with the increase of Sc doping concentration, especially doping with Sc(3 mol%), which exceeds the so-called threshold, and there was little loss of nonvolatile diffraction efficiencies between Sc(3 mol%):Ce:Cu:LiNbO3 and Ce:Cu:LiNbO3 crystals. 相似文献
945.
J. Mlynár J. Ongena The EFDA JET Contributions I. Duran M. Hron R. Pánek V. Petržílka F. Žáček 《Czechoslovak Journal of Physics》2004,54(3):C28
JET (Joint European Torus) is the largest tokamak in the world and the only fusion facility able to operate with Tritium, the fusion fuel, and Beryllium, the ITER first wall material. JET also features the most complete remote handling equipment for invessel maintenance. As a multinational research center, JET provides logistic experience in preparing for operation of the global facility, tokamak ITER.Experiments on JET are focused on ITER-relevant studies, in particular on detailing the operational scenarios (EL My H-modes and advanced regimes), on enhancing the heating systems, on developing diagnostics for burning plasmas etc. Pioneering real-time control techniques have been implemented that maximize performance and minimize internal disturbances of JET plasmas. In helium plasmas, ion cyclotron heating (ICRH) created fast α-particles, mimicking their populations in future burning plasmas. The recent successful Trace Tritium campaign provided important new data on fuel transport. Current enhancements on JET include a new ITER-like ELM-resilient high power ICRH antenna (7 MW) and over twenty new diagnostics that will further extend the JET scientific capabilities and push the facility even closer to the ITER parameters.A special mention is given to the involvement of the fusion experts from Association EURATOM-IPP.CR, who have been actively participating in the collective use of JET facility for more than three years. 相似文献
946.
The paper concerns several diagnostic techniques, which have been used in pulsed-power plasma experiments, i.e. Plasma-Focus and Z-Pinch devices, and which can be adapted to studies of Magnetic Confinement Fusion (MCF) facilities, e.g. Stellarators and Tokamaks. The application of Nuclear Track Detectors (NTDs) for time-integrated ion measurements in MCF experiments is described and the use of such detectors for time-resolved ion measurements is discussed. The application of special ?erenkov-type detectors for time resolved measurements of fast runaway electrons is considered. Also discussed is the use of selected nuclear reactions for measurements of fusion products, e.g. fast neutrons. 相似文献
947.
Abnormalities in the cochlear function usually cause broadening of the auditory filters which reduces the speech intelligibility. An attempt to apply a spectral enhancement algorithm has been undertaken to improve the identification of Polish vowels by subjects with cochlear-based hearing-impairment. The identification scores of natural (unprocessed) vowels and spectrally enhanced (processed) vowels has been measured for hearing-impaired subjects. It has been found that spectral enhancement improves vowel scores by about 10% for those subjects, however, a wide variation in individual performance among subjects has been observed. The overall vowels identification scores obtained were 85% for natural vowels and 96% for spectrally enhanced vowels. 相似文献
948.
We prove that every noetherian affine PI Hopf algebra has finite injective dimension, which answers a question of Brown (1998).
949.
1D-nanostructural zinc oxide (ZnO) with different shapes have been synthesized on p-type Si(1 0 0) and glass substrates via vapor phase growth by heating pure zinc powder at temperatures between 480 and 570 °C. The different ZnO nanostructures depend on the substrates and the growth temperatures. Scanning electron microscopy and X-ray diffraction revealed that a well-aligned nanowires array, which are vertical to the substrate of Si(1 0 0) with 18 sides on their heads, but six sides on their stems, has been formed at 480 °C. Raman study on the ZnO nanostructures shows that the coupling strength between electron and phonon determined by the ratio of the second- to the first-order Raman scattering cross-sections declines with decreasing diameter of the nanowires. However, a little changes of the coupling strength in terms of the width of the nanobelts have been observed. 相似文献
950.
We suggest a new, more global, approach to the study of geodesically equivalent metrics which is based on application of the theory of integrable geodesic flows. Bibliography: 17 titles. 相似文献