全文获取类型
收费全文 | 177246篇 |
免费 | 598篇 |
国内免费 | 137篇 |
专业分类
化学 | 74031篇 |
晶体学 | 2660篇 |
力学 | 10441篇 |
综合类 | 1篇 |
数学 | 32594篇 |
物理学 | 58254篇 |
出版年
2021年 | 878篇 |
2020年 | 977篇 |
2019年 | 1117篇 |
2018年 | 10338篇 |
2017年 | 11207篇 |
2016年 | 6203篇 |
2015年 | 1873篇 |
2014年 | 1867篇 |
2013年 | 3438篇 |
2012年 | 7302篇 |
2011年 | 15974篇 |
2010年 | 9789篇 |
2009年 | 9915篇 |
2008年 | 13790篇 |
2007年 | 17344篇 |
2006年 | 3010篇 |
2005年 | 9237篇 |
2004年 | 5733篇 |
2003年 | 5650篇 |
2002年 | 3636篇 |
2001年 | 2418篇 |
2000年 | 1979篇 |
1999年 | 1303篇 |
1998年 | 1183篇 |
1997年 | 1064篇 |
1996年 | 1098篇 |
1995年 | 950篇 |
1994年 | 910篇 |
1993年 | 901篇 |
1992年 | 941篇 |
1991年 | 1019篇 |
1990年 | 958篇 |
1989年 | 993篇 |
1988年 | 914篇 |
1987年 | 861篇 |
1986年 | 823篇 |
1985年 | 963篇 |
1984年 | 1078篇 |
1983年 | 925篇 |
1982年 | 930篇 |
1981年 | 844篇 |
1980年 | 799篇 |
1979年 | 885篇 |
1978年 | 1012篇 |
1977年 | 949篇 |
1976年 | 880篇 |
1975年 | 829篇 |
1974年 | 842篇 |
1973年 | 858篇 |
1972年 | 602篇 |
排序方式: 共有10000条查询结果,搜索用时 422 毫秒
71.
Planar laser-induced fluorescence visualisation is used to investigate nonuniformities in the flow of a hypersonic conical nozzle. Possible causes for the nonuniformity are outlined and investigated, and the problem is shown to be due to a small step at the nozzle throat. Entrainment of cold boundary layer gas is postulated as the cause of the signal nonuniformity.
PACS 47.80.Jk, 47.40.Ki, 47.60.+i 相似文献
72.
A. Foussats C. Repetto O. P. Zandron O. S. Zandron 《International Journal of Theoretical Physics》2002,41(6):1053-1082
In order to describe the dynamics of the t–J model, two different families of first-order Lagrangians in terms of the generators of the Hubbard algebra are found. Such families correspond to different dynamical second-class constrained systems. The quantization is carried out by using the path-integral formalism. In this context the introduction of proper ghost fields is needed to render the model renormalizable. In each case the standard Feynman diagrammatics is obtained and the renormalized physical quantities are computed and analyzed. In the first case a nonperturbative large-N expansion is considered with the purpose of studying the generalized Hubbard model describing N-fold-degenerate correlated bands. In this case the 1/N correction to the renormalized boson propagator is computed. In the second case the perturbative Lagrangian formalism is developed and it is shown how propagators and vertices can be renormalized to each order. In particular, the renormalized ferromagnetic magnon propagator coming from our formalism is studied in details. As an example the thermal softening of the magnon frequency is computed. The antiferromagnetic case is also analyzed, and the results are confronted with previous one obtained by means of the spin-polaron theories. 相似文献
73.
Stephen C. Littlechild 《The Journal of the Operational Research Society》1996,47(5):601-611
In this Blackett Lecture, Professor Littlechild, Director General of Electricity Supply in the UK's Office of Electricity Regulation, renews acquaintance with some models he has developed over the years, introduces some models he has recently met, and discusses models that it would seem to be worthwhile developing. He concludes that for all concerned in the electricity industry, success depends on ever improving decision-making, in which OR has a vital role. 相似文献
74.
V. I. Verkhoturov O. S. Grafodatskii V. I. Simanchuk A. V. Kargapol'tsev 《Russian Physics Journal》1993,36(9):865-869
Experimental results are presented on acoustic probing of electric fields in solid insulators. An experimental apparatus and methods are described for acoustic measurements of the bulk space charge density and electric field strength in solid insulators. The sensitivity and spatial resolution of the acoustic probe technique are determined.Institute of Introscopy Research, Polytechnical University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 62–67, September, 1993. 相似文献
75.
We study spectral properties of discrete Schrödinger operators with potentials obtained via dimerization of a class of aperiodic sequences. It is shown that both the nature of the autocorrelation measure of a regular sequence and the presence of generic (full probability) singular continuous spectrum in the hull of primitive and palindromic (four block substitution) potentials are robust under dimerization. Generic results also hold for circle potentials. We illustrate these results with numerical studies of the quantum mean square displacement as a function of time. The numerical techniques provide a very fast algorithm for the time evolution of wave packets. 相似文献
76.
The changes in the magnetization of yttrium iron garnet (YIG) when irradiated by a pulsed neodymium laser beam with wavelength
λ=1.06 μm are investigated. Measurements are performed in the temperature range from 100 K to 600 K in various external magnetic
fields. YIG single crystals grown along the crystallographic (100), (110), and (111) directions are chosen so that the external
anisotropy of the indicated processes can be determined. Characteristic temperature intervals dominated by different mechanisms
of variation of the magnetization under the influence of a laser pulse are discussed.
Fiz. Tverd. Tela (St. Petersburg) 39, 1263–1266 (July 1997) 相似文献
77.
78.
I. V. Ukrainets S. G. Taran O. V. Gorokhova P. A. Bezuglyi A. V. Turov 《Chemistry of Heterocyclic Compounds》1994,30(2):204-207
In a solution of DMF, 2-carbethoxymethyl-4H-3,1-benzoxazin-4-one reacts with primarily aromatic amines basically with the formation of the corresponding 2-carbethoxymetlzyl-3-arylquinazolin-4(3H)-ones. Possible mechanisms of these chemical transformations are reported and discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 225–228, February, 1994. Original article submitted June 28, 1993. 相似文献
79.
80.
The electron-impact mass spectra of a number of phenylpropanoids and iridoid glycosides containing a phenylethanoid fragment in their structure have been studied. This has revealed features of the formation of fragments of 4-hydroxyphenylethyl and 3,4-dihydroxyphenylethyl alcohols and also of fragments of phenylethylamine and indolylethylamine derivatives present in the structures of the compounds investigated. 相似文献