全文获取类型
收费全文 | 179篇 |
免费 | 16篇 |
国内免费 | 37篇 |
专业分类
化学 | 22篇 |
晶体学 | 1篇 |
力学 | 5篇 |
数学 | 14篇 |
物理学 | 190篇 |
出版年
2021年 | 1篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 3篇 |
2015年 | 4篇 |
2014年 | 5篇 |
2013年 | 7篇 |
2012年 | 5篇 |
2011年 | 15篇 |
2010年 | 5篇 |
2009年 | 14篇 |
2008年 | 17篇 |
2007年 | 18篇 |
2006年 | 17篇 |
2005年 | 17篇 |
2004年 | 6篇 |
2003年 | 20篇 |
2002年 | 3篇 |
2001年 | 11篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 9篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 7篇 |
1994年 | 1篇 |
1993年 | 4篇 |
1992年 | 1篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有232条查询结果,搜索用时 15 毫秒
1.
2.
The first part of this paper gives a theoretical study of the mechanics of contact of an AFM tip on viscous materials. Analytical expressions are derived showing the non-linear behaviors specifically related to the use of dynamic operation modes of AFM on viscous materials. A detailed analysis of the dissipated energy as a function of the tip indentation is presented. The second part is dedicated to a theoretical analysis investigating the domain of stability of the oscillator and the influence of the machine. The theoretical approach includes the electronic feedback loop used with the frequency modulation mode. Because the interaction between the tip and the sample produces a dynamical non-linear behavior, an unstable branch occurs that can change the stability of the oscillator. In particular, a sudden jump of the oscillating tip can be produced. In spite of the complexity of the problem, the analytical approach ends with two simple equations. The two equations provide an unambiguous way of discriminating between the contributions from the machine and the tip sample interaction. 相似文献
3.
D.J. Wagg 《International Journal of Non》2005,40(8):1076-1087
Periodic sticking motions can occur in vibro-impact systems for certain parameter ranges. When the coefficient of restitution is low (or zero), the range of periodic sticking motions can become large. In this work the dynamics of periodic sticking orbits with both zero and non-zero coefficient of restitution are considered. The dynamics of the periodic orbit is simulated as the forcing frequency of the system is varied. In particular, the loci of Poincaré fixed points in the sticking plane are computed as the forcing frequency of the system is varied. For zero coefficient of restitution, the size of the sticking region for a particular choice of parameters appears to be maximized. We consider this idea by computing the sticking region for zero and non-zero coefficient of restitution values. It has been shown that periodic sticking orbits can bifurcate via the rising/multi-sliding bifurcation. In the final part of this paper, we describe three types of post-bifurcation behavior which occur for the zero coefficient of restitution case. This includes two types of rising bifurcation and a border orbit crossing event. 相似文献
4.
The effect of magnetic field on electron energy spectrum, wave functions and probabilities of intraband quantum transitions in multilayered spherical quantum-dot-quantum-well (QDQW) CdSe/ZnS/CdSe/ZnS is studied. Computations are performed in the framework of the effective mass approximation and rectangular potential barriers model. The wave functions are expanded over the complete basis of functions obtained as exact solutions of the Schrodinger equation for the electron in QDQW without the magnetic field.It is shown that magnetic field takes off the spectrum degeneration with respect to the magnetic quantum number and changes the localization of electron in the nanostructure. The field stronger effects on the spherically-symmetric states, especially in the case of electron location in the outer potential well. The magnetic field changes more the radial distribution of probability of electron location in QDQW than the angular one. The oscillator strengths of intraband quantum transitions are calculated as functions of the magnetic field induction and their selection rules are established. 相似文献
5.
为了分析高功率准分子激光主振荡功率放大(MOPA)系统中各光学元件稳定性对靶面光斑定位精度的影响,建立了分析模型,利用分析结果指导高稳定性镜架设计以满足系统实验需求。根据高功率准分子激光MOPA系统特点,有效地简化了系统光路,建立了系统光路模型;按照系统打靶精度要求,利用三维坐标变换和光线追迹法,计算得到了系统单个光学元件稳定性对靶面光斑定位精度的影响规律;最后,对自行设计的镜架进行了稳定性测量。计算结果表明,反射镜的旋转变化和透镜垂直光轴的平移变化是影响靶面光斑定位精度的主要因素,且主放大光路中反射镜在X方向和Y方向上最大的变化范围分别不能超过0.8和1.6μrad。实际测量结果表明,设计的镜架在X方向和Y方向最大的变化范围分别为0.6和0.81μrad,满足系统实验要求。 相似文献
6.
Using molecular dynamics simulations, we investigate the oscillatory behaviors of carbon nanotube oscillators containing sp3-hybridized defects formed by hydrogen chemisorption. It is found that the presence of these defects significantly affects the kinetic and potential energies of the nanotube systems, which in turn affects their oscillation periods and frequencies. We have also studied the oscillatory characteristics of the oscillators containing sp3-hybridized Stone-Wales defects. Our results show that it is possible to control the motion of the inner nanotube by introducing sp3-hybridized defects on the outer nanotube, which provides a potential way to tune the oscillatory behavior of nanotube oscillators. 相似文献
7.
In this paper, we consider a neural network model consisting of two coupled oscillators with delayed feedback and excitatory-to-excitatory connection. We study how the strength of the connections between the oscillators affects the dynamics of the neural network. We give a full classification of all equilibria in the parameter space and obtain its linear stability by analyzing the characteristic equation of the linearized system. We also investigate the spatio-temporal patterns of bifurcated periodic oscillations by using the symmetric bifurcation theory of delay differential equations combined with representation theory of Lie groups. Moreover, the stability and bifurcation direction of the bifurcated periodic solutions are obtained by employing center manifold reduction and normal form theory. Some numerical simulations are provided to illustrate the theoretical results. 相似文献
8.
H. O. Di Rocco 《Il Nuovo Cimento D》1990,12(11):1485-1490
Summary The shifts and widths of prominent XeII transitions are calculated in the semi-empirical approach; a very good agreement with
experimental values is obtained. The oscillator strengths were calculated using complete intermediate coefficients after energy
matrix diagonalization.
The author of this paper has agreed to not receive the proofs for correction. 相似文献
9.
Peter Spietz Uldis Gross Edgars Smalins Johannes Orphal John P. Burrows 《Spectrochimica Acta Part B: Atomic Spectroscopy》2001,56(12):2465-2478
The 183.038 nm resonance absorption transition of I(2P3/2) has been studied using a flash photolysis set-up for gas-phase chemistry and a radio frequency powered electrodeless discharge lamp filled with iodine. The dependence of self-absorption and self-reversal on iodine partial pressure in the discharge volume was measured. The optimum iodine partial pressure, with self-absorption minimized and acceptable intensity, is determined to be approximately 2.5×10−3 mbar. A method is described to estimate the temperature of the emitting atoms using direct measurements of relative absorption at different absorber concentrations. This yields an emission temperature of 923±50 K. Using this temperature, the oscillator strength for the I(2P3/2) transition at 183.038 nm is determined to be f=(3.87±0.57)×10−3, corresponding to an absorption cross-section at the center of the line of σ=(5.42±0.8)×10−14 cm2 atom−1. This shows a difference from one of two earlier measurements, but is close to the other. The remaining difference from the latter measurement is probably due to tendencies of opposite biases inherent to the experiments. 相似文献
10.
Z.G. Zhang Z.S. Li S. Svanberg P. Palmeri P. Quinet E. Biémont 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(3):301-305
Lifetimes of three levels belonging to the configuration 4f
135d with J = 1 in Yb III have been measured for the first time using the time-resolved laser-induced fluorescence method. Experimental
transition probabilities have been deduced for the transitions between the levels studied and the ground state. The comparison
of the experimental lifetimes with theoretical data, deduced within the relativistic Hartree-Fock (HFR) approach, underlines
the dramatic importance of an adequate consideration of core-polarization effects in the theoretical model and the sensitivity
of one of the lifetime values to small correlation effects.
Received 2 April 2001 相似文献