全文获取类型
收费全文 | 7597篇 |
免费 | 340篇 |
国内免费 | 413篇 |
专业分类
化学 | 3130篇 |
晶体学 | 50篇 |
力学 | 198篇 |
综合类 | 12篇 |
数学 | 438篇 |
物理学 | 4522篇 |
出版年
2023年 | 48篇 |
2022年 | 73篇 |
2021年 | 98篇 |
2020年 | 151篇 |
2019年 | 135篇 |
2018年 | 165篇 |
2017年 | 136篇 |
2016年 | 255篇 |
2015年 | 223篇 |
2014年 | 282篇 |
2013年 | 375篇 |
2012年 | 797篇 |
2011年 | 813篇 |
2010年 | 590篇 |
2009年 | 662篇 |
2008年 | 510篇 |
2007年 | 565篇 |
2006年 | 367篇 |
2005年 | 264篇 |
2004年 | 256篇 |
2003年 | 202篇 |
2002年 | 217篇 |
2001年 | 145篇 |
2000年 | 152篇 |
1999年 | 132篇 |
1998年 | 142篇 |
1997年 | 60篇 |
1996年 | 59篇 |
1995年 | 47篇 |
1994年 | 35篇 |
1993年 | 35篇 |
1992年 | 32篇 |
1991年 | 29篇 |
1990年 | 41篇 |
1989年 | 25篇 |
1988年 | 26篇 |
1987年 | 12篇 |
1986年 | 21篇 |
1985年 | 26篇 |
1984年 | 15篇 |
1982年 | 17篇 |
1981年 | 18篇 |
1980年 | 12篇 |
1979年 | 16篇 |
1978年 | 14篇 |
1977年 | 6篇 |
1976年 | 10篇 |
1975年 | 6篇 |
1974年 | 10篇 |
1973年 | 8篇 |
排序方式: 共有8350条查询结果,搜索用时 15 毫秒
1.
Knowledge of the vibrational properties of nanoparticles is of fundamental interest since it is a signature of their morphology, and it can be utilized to characterize their physical properties. In addition, the vibration characteristics of the nanoparticles coupled with surrounding media and subjected to magnetic field are of recent interest. This paper develops an analytical approach to study the radial breathing-mode frequency of elastically confined spherical nanoparticles subjected to magnetic field. Based on Maxwell's equations, the nonlocal differential equation of radial motion is derived in terms of radial displacement and Lorentz's force. Bessel functions are used to obtain a frequency equation. The model is justified by a good agreement between the results given by the present model and available experimental and atomic simulation data. Furthermore, the model is used to elucidate the effect of nanoparticle size, the magnetic field and the stiffness of the elastic medium on the radial breathing-mode frequencies of several nanoparticles. Our results reveal that the effects of the magnetic field and the elastic medium are significant for nanoparticle with small size. 相似文献
2.
3.
In circuit-switched networks call streams are characterized by their mean and peakedness (two-moment method). The GI/M/C/0 system is used to model a single link, where the GI-stream is determined by fitting moments appropriately. For the moments of the overflow traffic of a GI/M/C/0 system there are efficient numerical algorithms available. However, for the moments of the freed carried traffic, defined as the moments of a virtual link of infinite capacity to which the process of calls accepted by the link (carried arrival process) is virtually directed and where the virtual calls get fresh exponential i.i.d. holding times, only complex numerical algorithms are available. This is the reason why the concept of the freed carried traffic is not used. The main result of this paper is a numerically stable and efficient algorithm for computing the moments of freed carried traffic, in particular an explicit formula for its peakedness. This result offers a unified handling of both overflow and carried traffics in networks. Furthermore, some refined characteristics for the overflow and freed carried streams are derived. 相似文献
4.
5.
6.
A method using third order moments for estimating the regression coefficients as well as the latent state scores of the reduced-rank regression model when the latent variable(s) are non-normally distributed is presented in this paper. It is shown that the factor analysis type indeterminacy of the regression coefficient matrices is eliminated. A real life example of the proposed method is presented. Differences of this solution with the reduced-rank regression eigen solution are discussed. 相似文献
7.
H.L. Xu A. Persson S. Svanberg 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):233-236
New radiative lifetime measurements based on time-resolved laser-induced fluorescence techniques are reported for 18 even-parity
levels belonging to the 4f5d26p and 4f
25d
2 configurations of Ce I and 6 even-parity levels belonging to the 5d26s, 4f5d6p, and 4f6s6p configurations of Ce II. Free neutral and singly ionized cerium atoms were produced by laser ablation. The Ce I and Ce II
levels range in energy from 26 545 to 29 102 cm-1, and 42 573 to 48 152 cm-1, respectively.
Received 25 September 2002 Published online 4 March 2003 相似文献
8.
通过系统研究A~190区超形变核中转动带的转动惯量、角动量顺排、旋称分裂随转动频率的变化规律, 结合我们用处理对力的粒子数守恒方法的计算结果, 对A~190区所有转动带的组态结构给出了一个整体的描述. 绝大多数超形变带都建立在强耦合轨道上, 例如中子[512]5/2, [624]9/2. 少数超形变带则建立在高j闯入轨道上, 即中子[761]3/2, [752]5/2. 根据我们提出的组态结构所进行的理论计算结果表明, A~190区所有转动带的一般行为、反常变化和带交叉都得到了满意的解释. 相似文献
9.
《Journal of Physics and Chemistry of Solids》2004,65(4):799-803
The application of theoretical methods based on density functional theory using generalized-gradient approximation functionals provides reasonable estimates of the exchange coupling constants for polynuclear transition metal complexes. Calculations for the complete, non-modeled Fe19 complex have been performed and a comparison with the experimental magnetic susceptibility values using Monte Carlo simulations is presented. 相似文献
10.
Hidetaka Tobita 《Journal of Polymer Science.Polymer Physics》2004,42(14):2801-2812
The matrix formula developed in the context of heterochain theory, M?w = M?wp + WF ( I ? M )?1 S , was applied to describe the molecular weight development during free‐radical multicomponent polymerization. All of the required probabilistic parameters are expressed in terms of the kinetic‐rate constants and the various concentrations associated with them. In free‐radical polymerization, the number of heterochain types, N, needs to be extrapolated to infinity, and such extrapolation is conducted with only three different N values. This matrix formula can be used as a benchmark test if other approximate approaches can give reasonable estimates of the weight‐average molecular weights. The moment equations with the average pseudo‐kinetic‐rate constants for branching and crosslinking reactions may provide poor estimates when the copolymer composition drift during polymerization is very significant. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2801–2812, 2004 相似文献