全文获取类型
收费全文 | 13699篇 |
免费 | 2437篇 |
国内免费 | 1356篇 |
专业分类
化学 | 8592篇 |
晶体学 | 73篇 |
力学 | 2024篇 |
综合类 | 164篇 |
数学 | 1457篇 |
物理学 | 5182篇 |
出版年
2024年 | 15篇 |
2023年 | 123篇 |
2022年 | 244篇 |
2021年 | 357篇 |
2020年 | 451篇 |
2019年 | 460篇 |
2018年 | 486篇 |
2017年 | 478篇 |
2016年 | 575篇 |
2015年 | 630篇 |
2014年 | 876篇 |
2013年 | 1165篇 |
2012年 | 954篇 |
2011年 | 1015篇 |
2010年 | 819篇 |
2009年 | 958篇 |
2008年 | 939篇 |
2007年 | 831篇 |
2006年 | 850篇 |
2005年 | 710篇 |
2004年 | 690篇 |
2003年 | 612篇 |
2002年 | 452篇 |
2001年 | 379篇 |
2000年 | 331篇 |
1999年 | 298篇 |
1998年 | 254篇 |
1997年 | 234篇 |
1996年 | 188篇 |
1995年 | 205篇 |
1994年 | 149篇 |
1993年 | 124篇 |
1992年 | 101篇 |
1991年 | 61篇 |
1990年 | 85篇 |
1989年 | 66篇 |
1988年 | 41篇 |
1987年 | 53篇 |
1986年 | 39篇 |
1985年 | 26篇 |
1984年 | 32篇 |
1983年 | 12篇 |
1982年 | 21篇 |
1981年 | 24篇 |
1980年 | 9篇 |
1979年 | 20篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1971年 | 5篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The influence of the parameter of amplitude-phase coupling for nonlinear amplification on the phase-frequency characteristics of an injection laser in the regime of pumping current modulation has been investigated theoretically. The parameter is defined as the coefficient of proportionality between changes in the real and imaginary parts of the refractive index during variation of the density of photons in the cavity. The substantial dependence of the coefficient of phase modulation on the parameter of the amplitude-phase coupling for nonlinear amplification at small modulation frequencies is shown. A technique to determine the indicated parameter based on the frequency dependence of the ratio between the coefficients of phase and amplitude modulation is suggested. 相似文献
72.
加速牛顿迭代收敛的新方法 总被引:2,自引:0,他引:2
提出了加速牛顿迭代收敛的新思想,构造出一类加权牛顿迭代格式,通过选取最优加权因子,使得该格式具有高阶收敛性和较小的渐近误差常数。 相似文献
73.
74.
Joji Ohshita Ryosuke Taketsugu Yuki Nakahara Atsutaka Kunai 《Journal of organometallic chemistry》2004,689(20):3258-3264
Selective dehydrogenative coupling of di- and trihydrosilanes with alcohols catalyzed by PdCl2 or NiCl2 afforded alkoxyhydro- and dialkoxyhydrosilanes in good yield. Further treatment of the resulting alkoxyhydrosilanes with carbon tetrachloride or allyl bromide in the presence of the same catalyst led to the formation of alkoxychloro- and alkoxybromosilanes, respectively. Similar reactions of dialkoxyhydrosilanes with carbon tetrachloride afforded dialkoxychlorosilanes in good yield, although contamination of small amounts of trialkoxysilanes and alkoxydichlorosilanes was detected in the products. Selective substitution of the alkoxyhalosilanes with nucleophiles is also reported. 相似文献
75.
The paper addresses the problem of a semi-infinite plane crack along the interface between two isotropic half-spaces. Two methods of solution have been considered in the past: Lazarus and Leblond [1998a. Three-dimensional crack-face weight functions for the semi-infinite interface crack-I: variation of the stress intensity factors due to some small perturbation of the crack front. J. Mech. Phys. Solids 46, 489-511, 1998b. Three-dimensional crack-face weight functions for the semi-infinite interface crack-II: integrodifferential equations on the weight functions and resolution J. Mech. Phys. Solids 46, 513-536] applied the “special” method by Bueckner [1987. Weight functions and fundamental fields for the penny-shaped and the half-plane crack in three space. Int. J. Solids Struct. 23, 57-93] and found the expression of the variation of the stress intensity factors for a wavy crack without solving the complete elasticity problem; their solution is expressed in terms of the physical variables, and it involves five constants whose analytical representation was unknown; on the other hand, the “general” solution to the problem has been recently addressed by Bercial-Velez et al. [2005. High-order asymptotics and perturbation problems for 3D interfacial cracks. J. Mech. Phys. Solids 53, 1128-1162], using a Wiener-Hopf analysis and singular asymptotics near the crack front.The main goal of the present paper is to complete the solution to the problem by providing the connection between the two methods. This is done by constructing an integral representation for Lazarus-Leblond's weight functions and by deriving the closed form representations of Lazarus-Leblond's constants. 相似文献
76.
77.
Vattoly J. MajoJaya Prabhakaran J.John MannJ.S. Dileep Kumar 《Tetrahedron letters》2003,44(47):8535-8537
A novel and convergent palladium catalyzed synthesis of 2-arylbenzothiazoles has been investigated. The key step in the synthesis is a Suzuki biaryl coupling of 2-bromobenzothiazole with aryl boronic acids to provide a variety of 2-arylbenzothiazole derivatives in good yield. The synthetic utility of this methodology is demonstrated by the synthesis of 2-(4-aminophenyl)-6-methoxybenzothiazole, a PET probe precursor for the in vivo imaging of Alzheimer's disease. 相似文献
78.
魏立平 《数学的实践与认识》2004,34(4):1-4
综合运用国内外多种测量量表对大学生的心理素质进行诊断与测试 ,并应用多元统计分析方法对其心理素质结构主因素进行定量分析 ,在此基础上建立了心理素质诊断模型 ,并运用该模型对实际问题进行了分析 . 相似文献
79.
80.
Auguet C. Martorell F. Moll F. Torra V: 《Journal of Thermal Analysis and Calorimetry》2002,70(1):277-290
The miniaturized calorimetric devices furnish a reduced working flat surface and permits measurements with extremely low-mass
quantities. The experimental sensitivity shows relevant position dependence with x-y surface coordinates and with z-distance. The device identification is realized via a 2-D model based in Fourier general equation.
Using the Marquardt method the experimental flat surface device can be identified and the fitted parameters used to simulate
the behavior of the experimental system. From the model, the effects of several dissipation configurations can be evaluated.
Also, via the RC-analogy, a way to 3-D experimental devices is roughly described.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献