全文获取类型
收费全文 | 391040篇 |
免费 | 1975篇 |
国内免费 | 554篇 |
专业分类
化学 | 182461篇 |
晶体学 | 5843篇 |
力学 | 22387篇 |
综合类 | 9篇 |
数学 | 56065篇 |
物理学 | 126804篇 |
出版年
2020年 | 4162篇 |
2019年 | 5055篇 |
2018年 | 7448篇 |
2017年 | 7610篇 |
2016年 | 9529篇 |
2015年 | 4427篇 |
2014年 | 8436篇 |
2013年 | 15849篇 |
2012年 | 12898篇 |
2011年 | 15125篇 |
2010年 | 12612篇 |
2009年 | 12806篇 |
2008年 | 14587篇 |
2007年 | 14379篇 |
2006年 | 12883篇 |
2005年 | 11205篇 |
2004年 | 10841篇 |
2003年 | 10027篇 |
2002年 | 10335篇 |
2001年 | 10476篇 |
2000年 | 8117篇 |
1999年 | 6190篇 |
1998年 | 5689篇 |
1997年 | 5480篇 |
1996年 | 5010篇 |
1995年 | 4464篇 |
1994年 | 4505篇 |
1993年 | 4507篇 |
1992年 | 4586篇 |
1991年 | 5074篇 |
1990年 | 4999篇 |
1989年 | 5048篇 |
1988年 | 4695篇 |
1987年 | 4773篇 |
1986年 | 4461篇 |
1985年 | 5353篇 |
1984年 | 5548篇 |
1983年 | 4724篇 |
1982年 | 4972篇 |
1981年 | 4633篇 |
1980年 | 4286篇 |
1979年 | 4924篇 |
1978年 | 5103篇 |
1977年 | 5296篇 |
1976年 | 5450篇 |
1975年 | 5057篇 |
1974年 | 4887篇 |
1973年 | 5132篇 |
1972年 | 4303篇 |
1971年 | 3944篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Fundamental processes in long air gap discharges 总被引:2,自引:0,他引:2
I. Gallimberti G. Bacchiega Anne Bondiou-Clergerie Philippe Lalande 《Comptes Rendus Physique》2002,3(10):854
The development of atmospheric lightning is initiated and sustained by the formation in virgin air of ‘streamer corona’ and ‘leader’ discharges, very similar to those observed in laboratory long sparks. Therefore, the experimental and theoretical investigations of these laboratory discharges have become of large interest to improve the physical knowledge of the lightning process and to develop self-consistent models that could be applied to new protection concepts.In the present paper the fundamental processes of the subsequent phases of long air gap discharges are analyzed, from the first corona inception and development to the leader channel formation and propagation. For all these processes simulations models are discussed that have been essentially derived and simplified by the authors, in order to develop sequential time-dependent simulation of the laboratory breakdown, with both positive and negative voltages. The possibility of extending these models to the case of natural lightning is discussed in the companion paper, presented in this same volume. To cite this article: I. Gallimberti et al., C. R. Physique 3 (2002) 1335–1359. 相似文献
122.
I. A. Bol'shakov 《Journal of Mathematical Sciences》1991,56(1):2263-2279
Systems for automatic detection and correction of spelling errors in natural language texts are considered. The development of such systems for both English and Russian (and for inflected languages in general, including all Slavic languages) is discussed. An approach associated with morphological analysis of the wordforms in the given text is described. The topics considered in the paper include the main methods of automatic spelling correction, levels of automation of the spelling error correction process, the effect of the type of computer used, the use of spelling error correctors in a stand-alone mode and in combination with word-processing software, and the maintenance of auxiliary dictionaries.Translated from Itogi Nauki i Tekhniki, Seriya Teoriya Veroyatnostei, Matematicheskaya Statistika, Teoreticheskaya Kibernetika, Vol. 28, pp. 111–139, 1988. 相似文献
123.
V. Čápek 《Czechoslovak Journal of Physics》1991,41(10):975-989
A review of ideas leading to full rejection of any finite or partially-infinite order kinetic equation linearized in external field is given on grounds of the time-convolution Generalized Master Equations (GME). By two examples (two-level and band conduction problem), it is shown how standard kinetic equations result from GME in the lowest order approximations which obscure, however, a direct correspondence with the Kubo linear response theory. Without approximations, on the other hand, the rigorous approach is shown to be fully equivalent with the Kubo results. It is argued and illustrated that usual technical simplicity and seeming physical lucidity of standard theories (connected with the presence of field-independent transfer or scattering rates in the fielddependent linearized theory) are just owing to structural features which are solely due to the lowest order approximations involved. These features (i.e. also the possibility of standard physical interpretation of kinetic phenomena) are proved to disappear completely as far as the theory goes properly to higher orders. 相似文献
124.
125.
V. A. Artamonov 《Journal of Mathematical Sciences》1991,57(2):2959-3009
A survey of the development of the theory of universal algebras in the years 1976–1988. Such basic directions of development of this theory as classes of universal algebras (varieties, quasivarieties, etc.), Mal'tsev conditions, congruences, sheaves, homomorphisms, subalgebras, products of algebras, clones of operations, completeness, systems of equations in algeberas, and connections with computer mathematics show up in it. Considerable attention is given to concrete classes of algebras (p-algebras, BCK-algebras, unary algebras, etc.).Translated from Itogi Nauki i Tekhniki, Seriya Algebra, Topologiya, Geometriya, Vol. 27, pp. 45–124, 1989. 相似文献
126.
127.
S. K. Godunov V. T. Zhukov O. B. Feodoritova 《Computational Mathematics and Mathematical Physics》2006,46(6):971-982
An algorithm is constructed for calculating invariant subspaces of symmetric hyperbolic systems arising in electromagnetic, acoustic, and elasticity problems. Discrete approximations are calculated for subspaces that correspond to minimal eigenvalues and smooth eigenfunctions. Difficulties related to the presence of an infinite-dimensional kernel in the differential operator are successfully handled. The efficiency of the algorithm is demonstrated using acoustics equations. 相似文献
128.
Multi-quantum well heterostructures (MQWHs) of the novel Ga(NAsP)/GaP material system have been grown, pseudomorphically strained to GaP-substrate. The crystalline perfection is verified by transmission electron microscopy (TEM). For As-concentrations in excess of about 70%, a direct band structure and adequate luminescence efficiency for laser device application is observed. Temperature-dependent photoluminescence (PL) investigations show the influence of carrier localisation and non-radiative recombination processes typical for dilute nitride materials. With rising N content in the active material, the emission wavelength shifts towards longer wavelength, leading to Ga(NAs)/GaP MQW structures with photon energies below the indirect band gap of silicon (Si). At the same time the luminescence intensity drops due to an increase in non-radiative carrier traps and/or structural degradation. 相似文献
129.
K. E. Mochalov O. A. Ustinova S. A. Strel’tsov S. L. Grokhovskii A. L. Zhuze I. R. Nabiev A. V. Sukhanova V. A. Oleinikov 《Optics and Spectroscopy》2002,93(4):493-500
Topotecan (TPT), a water-soluble derivative of camptothecin (inhibitor of human DNA topoiomerase I), has found wide application in cancer chemotherapy. The central problem in using topotecan is the presence of lactone rings in its molecules, which undergo hydrolysis at a physiological pH yielding an inactive and even toxic form of the drug. The analysis of Raman spectra of TPT in H2O and D2O solutions made it possible to assign the spectral bands to the vibrations of particular molecular groups. Spectral features indicative of the opening of the lactone rings of the TPT molecules, deprotonation of the hydroxyl groups in their quinoline fragments, and of possible participation of the hydroxyl and carbonyl groups in H bonding are found. The data obtained are necessary to study the molecular mechanisms of TPT-DNA interaction and the formation of ternary complexes between TPT, DNA, and DNA topoisomerase I. 相似文献
130.