全文获取类型
收费全文 | 37493篇 |
免费 | 6552篇 |
国内免费 | 5237篇 |
专业分类
化学 | 27697篇 |
晶体学 | 412篇 |
力学 | 2051篇 |
综合类 | 393篇 |
数学 | 4851篇 |
物理学 | 13878篇 |
出版年
2024年 | 102篇 |
2023年 | 739篇 |
2022年 | 1048篇 |
2021年 | 1237篇 |
2020年 | 1571篇 |
2019年 | 1509篇 |
2018年 | 1311篇 |
2017年 | 1234篇 |
2016年 | 1917篇 |
2015年 | 1861篇 |
2014年 | 2093篇 |
2013年 | 2866篇 |
2012年 | 3330篇 |
2011年 | 3506篇 |
2010年 | 2452篇 |
2009年 | 2338篇 |
2008年 | 2566篇 |
2007年 | 2246篇 |
2006年 | 2100篇 |
2005年 | 1865篇 |
2004年 | 1512篇 |
2003年 | 1316篇 |
2002年 | 1400篇 |
2001年 | 1083篇 |
2000年 | 925篇 |
1999年 | 822篇 |
1998年 | 604篇 |
1997年 | 557篇 |
1996年 | 564篇 |
1995年 | 477篇 |
1994年 | 389篇 |
1993年 | 305篇 |
1992年 | 260篇 |
1991年 | 245篇 |
1990年 | 201篇 |
1989年 | 153篇 |
1988年 | 89篇 |
1987年 | 92篇 |
1986年 | 108篇 |
1985年 | 83篇 |
1984年 | 49篇 |
1983年 | 44篇 |
1982年 | 27篇 |
1981年 | 21篇 |
1980年 | 9篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1957年 | 10篇 |
1944年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
71.
Hongbo Zhang Rui Wang Kaixin Chen Han Yang Daming Zhang Maobin Yi Guoquan Wang Zhenchang Ma 《Optics & Laser Technology》2002,34(4):283-286
A new method, based on zero point of longitudinal electric field, was used to determine the spatial resolution of external electro-optic (EO) probing equipment. Considering the diffraction of Gauss beam, the result of external EO probing was simulated which was in accordance with the experiment. A spatial resolution <1 μm was demonstrated initially in our equipment using 650 nm laser diode as probe beam and semi-insulating GaP as probe tip. 相似文献
72.
We derive an explicit autocorrelation function (ACF) formula of state of polarization for a fiber transmission system with polarization mode dispersion (PMD) and polarization dependent loss (PDL), which is found to agree well with Monte Carlo simulation. Then we use the new ACF to investigate the combined effect of PMD and PDL on the polarization multiplexed scheme. We find the performance of the polarization multiplexed scheme can be deteriorated more severely than the case without PDL. 相似文献
73.
The crystal structure, magnetic and magnetotransport properties of the variation of B′-site transition metal in Sr2FeMO6 (M=Mo, W) with double perovskites structure have been investigated systematically. Measurements of magnetization vs. temperature at H=5 T show that Sr2FeMoO6 is a ferromagnet and Sr2FeWO6 is an antiferromagnet with TN∼35 K. Additionally, the large magnetoresistance ratio (MR) of ∼22% (H=3 T) at room temperature (RT) was observed in the Sr2FeWO6 compound. However, the Sr2FeMoO6 compound did not show any significant MR even at high fields and RT (MR∼1%; H=3 T and 300 K). The implications of these findings are supported by band structure calculations to explain the interaction between the 4d(Mo) and 5d(W) orbitals of transition metal ions and oxygen ions. 相似文献
74.
Kunyu Guo 《Journal of Functional Analysis》2004,213(2):380-411
This paper mainly concerns defect operators and defect functions of Hardy submodules, Bergman submodules over the unit ball, and Hardy submodules over the polydisk. The defect operator (function) carries key information about operator theory (function theory) and structure of analytic submodules. The problem when a submodule has finite defect is attacked for both Hardy submodules and Bergman submodules. Our interest will be in submodules generated by polynomials. The reason for choosing such submodules is to understand the interaction of operator theory, function theory and algebraic geometry. 相似文献
75.
By further generalizing the skew-symmetric triangular splitting iteration method studied by Krukier, Chikina and Belokon (Applied Numerical Mathematics, 41 (2002), pp. 89–105), in this paper, we present a new iteration scheme, called the modified skew-Hermitian triangular splitting iteration method, for solving the strongly non-Hermitian systems of linear equations with positive definite coefficient matrices. We discuss the convergence property and the optimal parameters of this new method in depth. Moreover, when it is applied to precondition the Krylov subspace methods like GMRES, the preconditioning property of the modified skew-Hermitian triangular splitting iteration is analyzed in detail. Numerical results show that, as both solver and preconditioner, the modified skew-Hermitian triangular splitting iteration method is very effective for solving large sparse positive definite systems of linear equations of strong skew-Hermitian parts. 相似文献
76.
77.
This paper is devoted to a detailed theoretical study of an ion pair SN2 reaction LiNCO+CH3F in the gas phase and in solution at the level of MP2(full)/6-31+G**//HF/6-31+G**. Two possible reaction mechanisms, inversion and retention, are discussed. There are eight possible reaction pathways. The inversion mechanism is more favorable no matter in the gas phase or in solution based on analyses of the transition structures. Methyl isocyanate should form preferentially in the gas phase and more stable methyl cyanate is the main product in solution. The retardation of the reaction in solvents was attributed to the difference in solvation in the separated reactants and in the transition state. 相似文献
78.
Song LI Guo Mao WANG Zhi Song LIU 《数学学报(英文版)》2005,21(6):1475-1486
The purpose of this paper is to investigate the mean size formula of wavelet packets in Lp for 0 〈 p ≤ ∞. We generalize a mean size formula of wavelet packets given in terms of the p-norm joint spectral radius and we also give some asymptotic formulas for the Lp-norm or quasi-norm on the subdivision trees. All results will be given in the general setting, 相似文献
79.
S. H. Park J. H. Chang M. Yang H. S. Ahn S. N. Yi K. Goto M. W. Cho T. Yao J. S. Song 《Current Applied Physics》2004,4(6):607-610
Photoluminescence (PL) linewidth broadening of CdxZn1 − xSe/ZnSe triple quantum wells, grown on GaAs substrates by molecular beam epitaxy (MBE), has been investigated. Various quantum well (QW) samples have been prepared with different QW thickness and composition (Cd-composition). Measured and calculated PL linewidth are compared. Both composition and thickness fluctuations are considered for the calculation with the parameters such as the volume of exciton, nominal thickness and composition of QWs. Surface roughness measured by atomic force microscopy (AFM) is used to estimate the interface roughness. Results show that when Cd-composition increases additional linewidth broadening due to Zn/Cd interdiffusion is enhanced. 相似文献
80.
乐毅 《宁波大学学报(理工版)》2004,17(4):437-440
从正交各向异性三维弹性动力学的控制方程出发,在求得四边简支矩形板自由振动频率和位移振型的基础上,构造了受迫振动的位移函数;利用自由振动位移振型的正交性,将控制方程的空间变量和时间变量分离,得到了广义质量、广义力和频率表示的关于时间的2阶常微分方程,从而得到了正交各向异性弹性矩形板在受迫振动下的位移场和应力场.给出了本文方法与薄板理论的算例. 相似文献