全文获取类型
收费全文 | 9022篇 |
免费 | 3113篇 |
国内免费 | 2039篇 |
专业分类
化学 | 1651篇 |
晶体学 | 135篇 |
力学 | 1109篇 |
综合类 | 442篇 |
数学 | 3069篇 |
物理学 | 7768篇 |
出版年
2024年 | 66篇 |
2023年 | 216篇 |
2022年 | 240篇 |
2021年 | 309篇 |
2020年 | 210篇 |
2019年 | 254篇 |
2018年 | 192篇 |
2017年 | 311篇 |
2016年 | 292篇 |
2015年 | 341篇 |
2014年 | 702篇 |
2013年 | 495篇 |
2012年 | 546篇 |
2011年 | 658篇 |
2010年 | 655篇 |
2009年 | 672篇 |
2008年 | 804篇 |
2007年 | 588篇 |
2006年 | 622篇 |
2005年 | 652篇 |
2004年 | 680篇 |
2003年 | 615篇 |
2002年 | 531篇 |
2001年 | 447篇 |
2000年 | 376篇 |
1999年 | 347篇 |
1998年 | 285篇 |
1997年 | 298篇 |
1996年 | 282篇 |
1995年 | 256篇 |
1994年 | 236篇 |
1993年 | 173篇 |
1992年 | 186篇 |
1991年 | 172篇 |
1990年 | 140篇 |
1989年 | 160篇 |
1988年 | 52篇 |
1987年 | 48篇 |
1986年 | 17篇 |
1985年 | 15篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 11篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 765 毫秒
31.
定义了一类相空间中的准几率分布函数系,这个准几率分布函数系直接建立在具有更加广泛意义的量子相空间Schr?dinger方程解的基础之上,其中定义α=αp-i?q和α=(1-α)q+i?p.发现了两个有趣的关系.(1)建立的量子相空间Schr?dinger方程的解实际上是对函数φ(λ)exp[i(1-α)qp]做窗口Fourier变换.(2)这个窗口函数g(λ)起着选择窗口形式的作用,而且不同的窗口对应着不同的分布函数.当g(λ)是一个代表Gauss窗的Gauss函数的时候,准几率分布函数就是一个类似于Husimi的分布函数fHLα(q,p);当g(λ)是一个表示椭圆的复函数时,准几率分布函数就是一个椭圆分布函数fEα(q,p);再在g(λ)为复函数的基础上附加α=0,就可得到标准序分布函数fS(q,p)、反标准序分布函数fAS(q,p)和Wigner分布函数fW(q,p),此时g(λ)表示高度为1/12π?而长度为λ的矩形窗.
关键词:
窗口Fourier变换
相空间
Wigner分布函数 相似文献
32.
33.
34.
35.
Quantum Inequality for Negative Energy Density States of Massive Dirac Field in Four-Dimensional Spacetime 下载免费PDF全文
Negative energy density and the quantum inequality are examined for the Dirac field. A proof is given of the quantum inequality for negative energy densities in the massive Dirac field produced by the superposition of two single particle electron states. 相似文献
36.
A sample of 1233 events is used to study the general characteristics of {}^{16}O-Em interactions at 4.5 A GeV/c. Multiplicity and angular distributions of slow particles and correlations among them are discussed. The present data are compared with the corresponding results from the interactions of other projectiles at the same energy and also the same projectile at different energies. The results indicate that black particle production is independent of the energy and mass of the projectile, but for grey particles it is dependent on the mass of projectile. 相似文献
37.
The Langevin equation is used to simulate the fission process of ^112Sn ^112Sn and ^116Sn ^116Sn. The mass distribution of the fission fragments are given by assuming the process of symmetric fission or asymmetric fission with the Gaussian probability sampling. The isoscaling behaviour has been observed from the analysis of fission fragments of both the reactions, and the isoscaling parameter α seems to be sensitive to the width of fission probability and the beam energy. 相似文献
38.
Singlet-Triplet Transition in Quantum Dots Confined by Triangular and Bowl-Like Potentials: the Effect of Electric Fields 下载免费PDF全文
We theoretically investigate the energy spectra of two-electron two-dimensional (2e 2D) quantum dots (QDs) confined by triangular potentials and bowl-like potentials in a magnetic field by exact diagonalization in the framework of effective mass theory. An in-plane electric field is found to contribute to the singlet-triplet transition of the ground state of the 2e 2D QDs confined by triangular or bowl-like potentials in a perpendicular magnetic field. The stronger the in-plane electric field, the smaller the magnetic field for the total spin of the ground states in the dot systems to change from S = 0 to S = 1. However, the influence of an in-plane electric field on the singlettriplet transition of the ground state of two electrons in a triangular QD modulated by a perpendicular magnetic field is quite small because the triangular potential just deviates from the harmonic potential well slightly. We find that the strength of the perpendicular magnetic field needed for the spin singlet-triplet transition of the ground state of the QD confined by a bowl-like potential is reduced drastically by applying an in-plane electric field. 相似文献
39.
We present a possible explanation to the tiny positive cosmological constant under the frame of AdS5 spacetime embedded by a dS4 brahe. We calculate the dark energy density by summing the zero point energy of massive scalar fields in AdS5 spacetime. Under the assumption that the radius of AdS5 spacetime is of the same magnitude as the radius of observable universe, the dark energy density in dS4 brahe is obtained, which is smaller than the observational value. The reasons are also discussed. 相似文献
40.
WUHao ZHANGBixing WANGChenghao 《声学学报:英文版》2005,24(1):21-32
The multi-path effect of the acoustical wave in a solid plate is studied. The multireflection and wave conversion of the cylindrical compressional and shear waves, which are excited by an infinite strip on a free surface of the solid plate, are analyzed thoroughly by the far-field approximation method. The concise analytical representations of the cylindrical waves are obtained. The time reversal processing is then applied to the propagation of the cylindrical waves and analyzed theoretically and experimentally. It is shown that the waves coming from different array elements and different paths all arrive at the original place after the time reversal operation. It indicates that the time reversal can compensate automatically the wave aberration caused by the multi-path effect. The self-adaptive focusing of the time reversal field is also analyzed quantificationally by the focusing gain and the ratio of the principal to the second lobe. The effects of the focus position and the aperture of the transducer array on the focused field are also investigated. It shows that theoretical and experimental results are consistent to each other very well. 相似文献