全文获取类型
收费全文 | 23828篇 |
免费 | 4480篇 |
国内免费 | 3798篇 |
专业分类
化学 | 17141篇 |
晶体学 | 336篇 |
力学 | 1792篇 |
综合类 | 265篇 |
数学 | 2646篇 |
物理学 | 9926篇 |
出版年
2024年 | 39篇 |
2023年 | 453篇 |
2022年 | 713篇 |
2021年 | 745篇 |
2020年 | 965篇 |
2019年 | 865篇 |
2018年 | 794篇 |
2017年 | 714篇 |
2016年 | 1128篇 |
2015年 | 1141篇 |
2014年 | 1399篇 |
2013年 | 1747篇 |
2012年 | 2166篇 |
2011年 | 2259篇 |
2010年 | 1623篇 |
2009年 | 1504篇 |
2008年 | 1714篇 |
2007年 | 1515篇 |
2006年 | 1559篇 |
2005年 | 1307篇 |
2004年 | 1021篇 |
2003年 | 854篇 |
2002年 | 820篇 |
2001年 | 694篇 |
2000年 | 553篇 |
1999年 | 569篇 |
1998年 | 400篇 |
1997年 | 368篇 |
1996年 | 416篇 |
1995年 | 334篇 |
1994年 | 321篇 |
1993年 | 240篇 |
1992年 | 225篇 |
1991年 | 188篇 |
1990年 | 161篇 |
1989年 | 141篇 |
1988年 | 121篇 |
1987年 | 79篇 |
1986年 | 76篇 |
1985年 | 55篇 |
1984年 | 33篇 |
1983年 | 28篇 |
1982年 | 15篇 |
1981年 | 19篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1975年 | 1篇 |
1966年 | 1篇 |
1957年 | 7篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
A design of diode-pumped high-efficiency Nd:YVO4/LBO red laser is reported. Using critical phase-matching (CPM) LBO, 671 nm red laser was obtained from 1342 nm light by intracavity frequency doubling. With an incident pump laser of 800 mW, using type-I and type-II CPM LBO, 97 and 52 mWTEM00 mode red laser outputs were obtained, with optical-to-optical conversion efficiencies of up to 12.1% and 6.5%, respectively. 相似文献
32.
用能量法求多自由度振动系统的角频率 总被引:2,自引:1,他引:1
利用简谐振动能量方程,通过分析振幅矢量的关系,用能量法求多自由度振动系统的角频率或简正振动频率。 相似文献
33.
在北京同步辐射装置(BSRF)1W1B光束线和XAFS实验站上国内首次建立了硬X射线波段的磁圆二色实验(XMCD)方法. 以单晶金刚石作为相位延迟片, 在透射劳埃(Laue)模式下, 利用衍射双折射效应, 将入射的单色线偏振光转变为相应的左旋和右旋圆偏振光, 测量磁化样品对左旋和右旋圆偏振光吸收的差异, 获得了XMCD信号. 本实验使用透射方法测量了Pt-Fe合金Pt L2,3边的XMCD, 获得了XMCD信号. XMCD实验方法的建立, 为研究磁性材料尤其是磁性薄膜材料的电子结构和磁结构提供了实验基础. 相似文献
34.
35.
The results of laser induced deposition of copper on polyimide substrate from copper electrolyte solution are reported. Unlike most work reported in the literatures where CW Ar+ lasers were used, a second harmonic (532 nm wavelength) Q-switch Nd:YAG laser was used for our experiments. The deposition process was conducted by laser-catalyzing of the polyimide surface and subsequent photothermal-accelerated reduction of copper-complex ions in an alkaline reducing environment. The characteristics of the deposited copper line were investigated in terms of laser beam scanning speed, and the number of scans. The surface morphology and chemical composition of the deposited copper were analyzed using field emission scanning electron microscope (FESEM) and energy dispersive spectrometer (EDX). The optimum processing conditions have been identified. The copper deposit was found to adhere well to the substrate. 相似文献
36.
37.
Parallel to Cox's [JRSS B34 (1972) 187-230] proportional hazards model, generalized logistic models have been discussed by Anderson [Bull. Int. Statist. Inst. 48 (1979) 35-53] and others. The essential assumption is that the two densities ratio has a known parametric form. A nice property of this model is that it naturally relates to the logistic regression model for categorical data. In astronomic, demographic, epidemiological, and other studies the variable of interest is often truncated by an associated variable. This paper studies generalized logistic models for the two-sample truncated data problem, where the two lifetime densities ratio is assumed to have the form exp{α+φ(x;β)}. Here φ is a known function of x and β, and the baseline density is unspecified. We develop a semiparametric maximum likelihood method for the case where the two samples have a common truncation distribution. It is shown that inferences for β do not depend the nonparametric components. We also derive an iterative algorithm to maximize the semiparametric likelihood for the general case where different truncation distributions are allowed. We further discuss how to check goodness of fit of the generalized logistic model. The developed methods are illustrated and evaluated using both simulated and real data. 相似文献
38.
39.
40.
RUAN Manqi XU Gang & ZENG Jinyan Department of Physics Tsinghua University Beijing China Department of Physics Peking University Beijing China Correspondence should be addressed to Zeng Jinyan 《中国科学G辑(英文版)》2004,47(1):36-41
Foratwo-particle(spin1/2)systemthespinstateisdescribedusingavectorinafour-dimensionalHilbertspace.Inangularmomentumcouplingtheory[1],theangularmomentumuncouplingandcouplingrepresentationsareusuallyadopted.WhilethesimultaneouseigenstatesoftheCSCO(s1z,s2z),12,12,12and12,arechosenasthebasisofangularmomentumuncouplingscheme,thesimultaneouseigenstatesoftheCSCO(2,zSS),,SM(12=+Sss),arechosenasthebasisofangularmomentumcouplingscheme,1212100,2轾=-臌1212110,2轾=+臌121211,1,1.=-=Thefo… 相似文献