全文获取类型
收费全文 | 10701篇 |
免费 | 1622篇 |
国内免费 | 1791篇 |
专业分类
化学 | 8669篇 |
晶体学 | 189篇 |
力学 | 581篇 |
综合类 | 149篇 |
数学 | 1256篇 |
物理学 | 3270篇 |
出版年
2024年 | 31篇 |
2023年 | 164篇 |
2022年 | 332篇 |
2021年 | 319篇 |
2020年 | 434篇 |
2019年 | 408篇 |
2018年 | 341篇 |
2017年 | 299篇 |
2016年 | 518篇 |
2015年 | 512篇 |
2014年 | 584篇 |
2013年 | 788篇 |
2012年 | 860篇 |
2011年 | 927篇 |
2010年 | 797篇 |
2009年 | 744篇 |
2008年 | 817篇 |
2007年 | 812篇 |
2006年 | 706篇 |
2005年 | 565篇 |
2004年 | 514篇 |
2003年 | 407篇 |
2002年 | 453篇 |
2001年 | 367篇 |
2000年 | 229篇 |
1999年 | 207篇 |
1998年 | 150篇 |
1997年 | 108篇 |
1996年 | 111篇 |
1995年 | 86篇 |
1994年 | 71篇 |
1993年 | 73篇 |
1992年 | 64篇 |
1991年 | 57篇 |
1990年 | 58篇 |
1989年 | 30篇 |
1988年 | 18篇 |
1987年 | 23篇 |
1986年 | 18篇 |
1985年 | 21篇 |
1984年 | 7篇 |
1983年 | 14篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1974年 | 4篇 |
1928年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
A simple and accurate algorithm (phase scanning method) is proposed for 3D surface contouring and dynamic response determination of a vibrating object. A sinusoidal fringe pattern is projected onto a low-frequency vibrating object by a programmable liquid crystal display projector. The fringe patterns are captured by a high-speed CCD camera with a telecentric gauging lens. Phase values are evaluated point by point using phase scanning method. From the phase values of each point on the object, the contour of the specimen at different instants of vibration can be retrieved. In this paper, a small vibrating coin is used to demonstrate the validity of the method and the experimental results are compared with test results on a stationary coin using four-step phase shifting and fast Fourier transform methods. The technique is especially useful in applications where the vibrating object has a complicated shape. 相似文献
42.
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
43.
44.
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
45.
§ 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
46.
47.
48.
Cun Feng Fan David A. Waldman Shaw Ling Hsu 《Journal of Polymer Science.Polymer Physics》1991,29(2):235-246
Raman mechanical spectroscopy was used to examine interfacial effects on the stress distribution in model polydiacetylene fiber/epoxy composites. Epoxy release agents were coated on fiber surfaces to modify the interfacial adhesion properties. The modified fiber surfaces were then characterized by scanning electron microscopy and x-ray photoelectron spectroscopy as well as optical microscopy. No difference in the maximum stress value or stress distribution was observed for the two types of fibers, coated or uncoated, used in composites. This suggests that adhesion properties at the composite interface do not affect tensile stress transfer efficiency nor, therefore, the composite tensile modulus along the fiber axis direction in uniaxial composites. Experimental data were also compared with theoretical calculations assuming perfect bonding between fiber and matrix, and idealized frictional force transfer mechanism at the fiber–matrix interface. 相似文献
49.
50.