全文获取类型
收费全文 | 19121篇 |
免费 | 2699篇 |
国内免费 | 2523篇 |
专业分类
化学 | 13868篇 |
晶体学 | 275篇 |
力学 | 1217篇 |
综合类 | 230篇 |
数学 | 2269篇 |
物理学 | 6484篇 |
出版年
2024年 | 28篇 |
2023年 | 270篇 |
2022年 | 428篇 |
2021年 | 480篇 |
2020年 | 653篇 |
2019年 | 602篇 |
2018年 | 511篇 |
2017年 | 488篇 |
2016年 | 794篇 |
2015年 | 758篇 |
2014年 | 976篇 |
2013年 | 1330篇 |
2012年 | 1472篇 |
2011年 | 1620篇 |
2010年 | 1193篇 |
2009年 | 1184篇 |
2008年 | 1290篇 |
2007年 | 1258篇 |
2006年 | 1190篇 |
2005年 | 986篇 |
2004年 | 853篇 |
2003年 | 659篇 |
2002年 | 639篇 |
2001年 | 547篇 |
2000年 | 443篇 |
1999年 | 450篇 |
1998年 | 428篇 |
1997年 | 352篇 |
1996年 | 345篇 |
1995年 | 275篇 |
1994年 | 289篇 |
1993年 | 211篇 |
1992年 | 191篇 |
1991年 | 163篇 |
1990年 | 173篇 |
1989年 | 104篇 |
1988年 | 95篇 |
1987年 | 102篇 |
1986年 | 96篇 |
1985年 | 85篇 |
1984年 | 55篇 |
1983年 | 46篇 |
1982年 | 42篇 |
1981年 | 32篇 |
1980年 | 28篇 |
1979年 | 16篇 |
1978年 | 20篇 |
1977年 | 9篇 |
1976年 | 11篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The sound field both in the loudspeaker box and in the room is calculated by an analytical solution of three-dimensional wave equation. It is shown in theory that the amplitude response in small rooms is affected by the following positions: driver position on the front panel of the box, box position in the room, absorption material position in the box and absorption material position on the interior walls of the room. Both our computer prediction and experiments prove that the optimum positions are beneficial to the amplitude response. 相似文献
82.
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
83.
84.
Yingyu Hu Guoqiao Lai Yongjia Shen Yongfang Li 《Monatshefte für Chemie / Chemical Monthly》2004,33(2):1167-1172
Zinc(II) and magnesium(II) phthalocyanines bearing four substituted propylenedithiotetrathiafulvalene (PDT-TTF) units were synthesized and characterized by NMR, MS, EA, and UV/VIS spectra. The absorption peaks of two target molecules were hypsochromically shifted compared with the phthalocyanine parent compound. Studies using cyclic voltammetry indicated that introduction of Zn and Mg as central metals enhanced the electronwithdrawing between the phthalocyanine core and the PDT-TTF unit, thus losing one electron to form (PDT-TTF)+ becomes more difficult. 相似文献
85.
Hong-wei Zhang Shao-ying Zhang Bao-gen Shen Helmut Kronmüller 《Journal of magnetism and magnetic materials》2003,260(3):352-360
The magnetization behavior in nanocrystalline permanent magnets has been investigated using mean field Stoner–Wohlfarth model. The model is comparatively simple but allows the numerical treatment of extended nanostructures. The predominant intergrain exchange coupling is expressed by a mean field constant Nm in spite of no explicit relationship between Nm and the microstructure. By this model, the experimental phenomena, such as the remanence enhancement, the shape of demagnetization curve, the irreversible magnetization, the exchange bias field and their respective temperature dependence, can be well explained. The Nm dependence of magnetic properties has been extensively discussed in the present paper. 相似文献
86.
ChunXiaLI YingXiaLI LingBoYU HuaZHANG SiftDongCHU HuaShiGUAN 《中国化学快报》2003,14(8):776-778
A convenient synthetic route was developed for the synthesis of the novel glycolipids: 1,2-di-O-acyl-3-O-(2‘-acylamide-2‘-denxy-ct-D-glucopyranosyl)-sn-glycerols. 10 new compounds of glycolipids with different acyl groups were obtained. 相似文献
87.
5‐Methylene‐2‐oxazolidinone (1) and 5‐methylene‐1,3‐thiazolidine‐2‐thione (4) react with various isocyanates to give the corresponding urethanes 3 and 5 in high yields in the presence of palladium(0) or palladium(II) catalyst under mild reaction conditions. A mechanism is proposed. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
88.
§ 1. Introduction Anecessaryandsufficientconditionandasufficientconditiontoensurethataset valuedmappingandasingle valuedmappinginacompletemetricspaceandacompleteconvexmetricspacehavingacommonfixedpointarerespectivelygivenin [1 ] .Meanwhilethemainresultsin[2 ]— [5]areimprovedandextendedin [1 ] .Inthispaper ,theexistenceatcommonfixedpointsoftwoset valuedmappingandasing valuedmappingwerestudied ,andthecorrespond ingresultsin [1 ]— [5]wereextendedandimproved .Let(X ,d)beanon emptymetricspa… 相似文献
89.
Spectral and Pseudospectral Approximations Using Hermite Functions: Application to the Dirac Equation 总被引:1,自引:0,他引:1
We consider in this paper spectral and pseudospectral approximations using Hermite functions for PDEs on the whole line. We first develop some basic approximation results associated with the projections and interpolations in the spaces spanned by Hermite functions. These results play important roles in the analysis of the related spectral and pseudospectral methods. We then consider, as an example of applications, spectral and pseudospectral approximations of the Dirac equation using Hermite functions. In particular, these schemes preserve the essential conservation property of the Dirac equation. We also present some numerical results which illustrate the effectiveness of these methods. 相似文献
90.