全文获取类型
收费全文 | 13370篇 |
免费 | 2097篇 |
国内免费 | 1959篇 |
专业分类
化学 | 10556篇 |
晶体学 | 229篇 |
力学 | 687篇 |
综合类 | 169篇 |
数学 | 1548篇 |
物理学 | 4237篇 |
出版年
2024年 | 41篇 |
2023年 | 223篇 |
2022年 | 441篇 |
2021年 | 431篇 |
2020年 | 553篇 |
2019年 | 552篇 |
2018年 | 451篇 |
2017年 | 408篇 |
2016年 | 693篇 |
2015年 | 686篇 |
2014年 | 798篇 |
2013年 | 1032篇 |
2012年 | 1136篇 |
2011年 | 1222篇 |
2010年 | 946篇 |
2009年 | 827篇 |
2008年 | 909篇 |
2007年 | 853篇 |
2006年 | 828篇 |
2005年 | 606篇 |
2004年 | 601篇 |
2003年 | 449篇 |
2002年 | 520篇 |
2001年 | 386篇 |
2000年 | 270篇 |
1999年 | 241篇 |
1998年 | 171篇 |
1997年 | 156篇 |
1996年 | 128篇 |
1995年 | 87篇 |
1994年 | 97篇 |
1993年 | 81篇 |
1992年 | 67篇 |
1991年 | 68篇 |
1990年 | 67篇 |
1989年 | 46篇 |
1988年 | 47篇 |
1987年 | 29篇 |
1986年 | 29篇 |
1985年 | 34篇 |
1984年 | 17篇 |
1983年 | 25篇 |
1982年 | 17篇 |
1981年 | 11篇 |
1980年 | 13篇 |
1978年 | 14篇 |
1976年 | 10篇 |
1975年 | 9篇 |
1974年 | 9篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
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
52.
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
53.
§ 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
54.
55.
用传统的预测效度估计法估计高考预测效度,其估计值往往偏低。为此,本文应用回归分析中混合估计理论提出了高考预测效度的混合估计。这种估计是预测效度的无偏估计,并解决了预测效度估计值偏低的问题。 相似文献
56.
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
57.
CLIFFORDMARTINGALESΦ-EQUIVALENCEBETWEENS(f)ANDf¥LONGRULIN;QIANTAO(InstituteofMathematics,AcademiaSinica,Beijing100080,China.)... 相似文献
58.
59.
利用集合在某点的相依切锥、法向锥和可行方向锥等研究向量优化问题的有效点、 弱有效点和真有效点的特征,对局部有效点、局部弱有效点和局部真有效点与集合的各 锥之间的关系作了刻画. 相似文献
60.
Z.J. Liu H.H. Long W.C. Ye X.X. Zou Z.L. Qin E.P. Li J.S. Chen 《Journal of magnetism and magnetic materials》2006
In this paper, specific issues related to high-density perpendicular magnetic recording processes, such as transition noise properties and cross-track correlation lengths, were investigated with the help of micromagnetic analysis. The effects of media parameters were taken into consideration, including intergranular exchange coupling, and exchange distribution, irregular grain shapes, magnetization saturation distribution, and anisotropy distribution. The micromagnetic simulation results showed that the effect of anisotropy distribution on transition noise is more significant than magnetization saturation distribution, and it is crucial to reduce this effect to achieve a high signal-to-noise ratio. Additionally, a new method to further estimate the partial erasure threshold was proposed to approximate the partial erasure effects, and the relation between the microtrack jitter and total track jitter was investigated. 相似文献