全文获取类型
收费全文 | 300篇 |
免费 | 39篇 |
专业分类
化学 | 4篇 |
晶体学 | 21篇 |
力学 | 1篇 |
数学 | 1篇 |
物理学 | 312篇 |
出版年
2015年 | 1篇 |
2014年 | 1篇 |
2013年 | 2篇 |
2011年 | 2篇 |
2010年 | 7篇 |
2009年 | 44篇 |
2008年 | 54篇 |
2007年 | 44篇 |
2006年 | 50篇 |
2005年 | 20篇 |
2004年 | 7篇 |
2003年 | 11篇 |
2002年 | 17篇 |
2001年 | 16篇 |
2000年 | 11篇 |
1999年 | 14篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 8篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1982年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有339条查询结果,搜索用时 15 毫秒
151.
The electronic band structures of GaAs1−xNx for x=0.009, 0.016, 0.031 and 0.062 are calculated ab initio using a supercell approach in connection with the full-potential linear muffin-tin orbital method. Corrections for the ‘LDA gap errors’ are made by adding external potentials which are adjusted to yield correct gaps in pure GaAs. Even small amounts of nitrogen modify significantly the conduction bands, which become strongly non-parabolic. The effective mass in the lowest conduction band thus exhibits strong k-vector dependence. Calculated variations of gaps and effective masses with x and externally applied pressure are presented and compared to a variety of experimental data. There are significant error bars on our results due to the use of the supercell approach. These are estimated by examining the effects of varying the geometrical arrangement of the N-atoms substituting As. However, the calculations show that the electron mass for x>0.009 is much larger than that of pure GaAs, and that it decreases with x. 相似文献
152.
We analyze vortex properties of the optical beams generated by a multi-level spiral phase plate (MLSPP) and find that this kind of beams consists of vortex components with topological charges of L − kM, where k is zero or any integer, M is the level number and L is the intrinsic topological charge of the MLSPP. We proved that the orbital angular momentum of the beams generated by a MLSPP reaches its maximum only if the phase steps (or the ratio of M to L) satisfies some special conditions. 相似文献
153.
Beam shaping and homogenization techniques are essential to optimize a large number of laser-material processing applications and laser-material interaction studies. In this paper, we present an innovative approach for modeling laser beam homogenization by means of the integration method. The numerical results are compared with experimental data, and the influence of the measurement technique is discussed. The enhancement of the homogenization capability using an asymmetric divider is also presented and discussed. 相似文献
154.
N. Ikeda F. Nakamura Y. Inotani K. Koga M. Koga S. Koto T. Sugimitsu H. Fujita S. Morinobu 《The European Physical Journal A - Hadrons and Nuclei》2000,9(2):213-220
The 16O(11B,12C)15N reaction at 41.25 MeV has been investigated using the kinematical coincidence method. Polarization tensors t20 and t40 of 12C[2+
1] for the quantization axis taken along the direction of propagation have been measured at center-of-mass angles (Θc.m.) between 48° and 62° by analyzing the energy spectrum of 12C[2+
1] modulated by the effect of γ-ray emission. The cross-sections of the transfer reactions leading to the 12C[g.s.]+15N[g.s.], 12C[2+
1]+15N[g.s.] and 12C[g.s.]+15N[3/2-
1] final states have also been measured in the range 48°≤Θc.m.≤ 120°. The polarization tensor terms of 12C[2+
1] largely deviating from zero have been observed, contrary to the prediction by the distorted-wave Born approximation (DWBA).
The one-step DWBA calculation also fails in describing the transfer reaction cross-sections. It is shown that the coupled
channel model calculation including excitations and reorientations in 11B and 12C satisfactorily reproduces both the tensor terms and the cross-sections of the transfer reactions. The multi-step processes
passing through the excited states of 11B are found to significantly contribute to the reaction.
Received: 3 July 2000 / Accepted: 15 September 2000 相似文献
155.
In this work, a new way of achieving the recovery from the EL2 metastable state is reported and analyzed theoretically. Despite being an old problem, no definitive picture of the EL2 center has been established to date. For this reason, long past the days of effervescent research on the EL2, new models and investigations keep appearing in the literature as, for example, the recently proposed autocatalytic model to describe the inter-defect correlation during the thermal recovery process [A. Fukuyama, T. Ikari, Y. Akashi, M. Suemitsu, Phys. Rev. B 67 (2003) 113202]. In the course of a re-evaluation of the EL2 for nanosecond volume holographic storage, we found that a strong laser pulse is capable of destroying the metastable state and decided to investigate further this effect. The experiment reported here consists of monitoring the transmission of a λ = 1.05 μm continuous-wave (CW) laser, used to populate the metastable state, while subjecting the sample to the incidence of a strong λ = 1.06 μm laser pulse. A full simulation of the problem has been carried out and the results could be fit very well by assuming a recovery induced by electron-hole recombination and a nonlinear free-carrier production mechanism. It is perhaps worth noting that such a fast recovery induced by the nanosecond laser may prove to be an interesting tool to initiate a recovery process (even at low temperature) in a controlled way to check the predictions of the recently proposed autocatalytic recovery process. 相似文献
156.
Yunbo Li 《Optics Communications》2006,266(2):686-690
We numerically analyze the effects of radius and phase shift of phase objects on the diffraction image of the 4f coherent imaging system, a system used for measuring the third-order nonlinear refractive index. The selection of the aperture radius is discussed. We prove that when the phase object radius is 0.1 time of the aperture radius and the phase change of the phase object is 0.57π, one can get the highest sensitivity for nonlinear refraction measurement. 相似文献
157.
Arūnas Jagminas Marija Kurtinaitien? Gintaras Valin?ius 《Applied Surface Science》2006,252(6):2360-2367
A new simple method for modification of the porous alumina barrier-layer is described and characterized by the voltammetric, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical impedance spectroscopy (EIS) techniques. The method is based on re-anodization of porous alumina under galvanostatic conditions in the anodizing bath that, in addition to conventional anodization solution components, contains fluoride salts: (NH4)2SiF6 or NH4F. During first few minutes of alumina re-anodization, the sharp drop of anodizing voltage was observed, which is indicative of chemical/electrochemical transformations of the alumina barrier-layer. As a result, the scalloped structure of the barrier-layer changes drastically, becoming smooth and finely grained. Upon re-anodization, a significant loss of insulating ability of the barrier-layer and considerable increase in its capacitance were observed, while the variation of the constant phase element was found to be consistent with the oxide film morphology transformations observed by microscopy techniques. All these changes intensify with fluoride concentration increase. Curiously, (NH4)2SiF6 exhibited about three-fold stronger effect on the barrier-layer properties than NH4F, thus allowing us to hypothesize about possible chemical break up of SiF62− anion and the formation of the AlF3 phase inside the alumina pores. 相似文献
159.
The main conditions and parameters for obtaining surface relief total internal reflection diffraction gratings in conical mounting are presented. Calculated and experimental investigations reveal that there are ranges of grating periods, incidence angles, diffraction angles and gratings depths for which such gratings could be obtained, both for TE and TM polarizations. With optimized grating parameters the diffraction efficiency of the total internal reflection diffraction gratings can be greater than 90%. 相似文献
160.
The effect of electron-beam irradiation on the magnetic properties of (Ga1−xMnx)As thin films grown on GaAs (100) substrates by using molecular beam epitaxy was investigated. The ferromagnetic transition temperature (Tc) of the annealed (Ga0.933Mn0.067)As thin films was 160 K. The Tc value for the as-grown (Ga0.933Mn0.067)As thin films drastically decreased with increasing electron-beam current. This significant decrease in the Tc value due to electron-beam irradiation originated from the transformation of Mn substituted atoms, which contributed to the ferromagnetism, into Mn interstitials or Mn-related clusters. These results indicate that the magnetic properties of (Ga1−xMnx)As thin films grown on GaAs (100) substrates are significantly affected by electron-beam irradiation. 相似文献