全文获取类型
收费全文 | 664219篇 |
免费 | 5661篇 |
国内免费 | 1674篇 |
专业分类
化学 | 344338篇 |
晶体学 | 10052篇 |
力学 | 31748篇 |
综合类 | 26篇 |
数学 | 83191篇 |
物理学 | 202199篇 |
出版年
2021年 | 5852篇 |
2020年 | 6485篇 |
2019年 | 7306篇 |
2018年 | 9550篇 |
2017年 | 9746篇 |
2016年 | 13633篇 |
2015年 | 7593篇 |
2014年 | 12651篇 |
2013年 | 29759篇 |
2012年 | 22563篇 |
2011年 | 26961篇 |
2010年 | 20003篇 |
2009年 | 19872篇 |
2008年 | 25246篇 |
2007年 | 24977篇 |
2006年 | 22873篇 |
2005年 | 20524篇 |
2004年 | 18976篇 |
2003年 | 17213篇 |
2002年 | 16946篇 |
2001年 | 18598篇 |
2000年 | 14388篇 |
1999年 | 11134篇 |
1998年 | 9446篇 |
1997年 | 9300篇 |
1996年 | 8711篇 |
1995年 | 7967篇 |
1994年 | 7876篇 |
1993年 | 7509篇 |
1992年 | 8409篇 |
1991年 | 8734篇 |
1990年 | 8437篇 |
1989年 | 8342篇 |
1988年 | 8210篇 |
1987年 | 8057篇 |
1986年 | 7688篇 |
1985年 | 9800篇 |
1984年 | 10137篇 |
1983年 | 8367篇 |
1982年 | 8709篇 |
1981年 | 8298篇 |
1980年 | 7840篇 |
1979年 | 8566篇 |
1978年 | 8817篇 |
1977年 | 8784篇 |
1976年 | 8591篇 |
1975年 | 8144篇 |
1974年 | 7955篇 |
1973年 | 8117篇 |
1972年 | 5849篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Aldo A. Martínez-Merino 《Annals of Physics》2006,321(2):318-330
A proposal for the Hamilton-Jacobi theory in the context of the covariant formulation of Hamiltonian systems is done. The current approach consists in applying Dirac’s method to the corresponding action which implies the inclusion of second-class constraints in the formalism which are handled using the procedure of Rothe and Scholtz recently reported. The current method is applied to the non-relativistic two-dimensional isotropic harmonic oscillator employing the various symplectic structures for this dynamical system recently reported. 相似文献
992.
Laser Doppler vibrometer (LVD) has been the most favorite instrument for precision dynamics measurement due to its non-contact, high accuracy and high resolution. However, LDV can only give the dynamic data of a particular location on the entire feature. In order to get the whole field data, a laser beam-scanning mechanism has to be implemented. Currently, motor-driven scanning mirror is used to move the measurement probe from one point to another. The mechanical vibrations of the scanning mirror will reduce the measurement accuracy. This paper introduces a novel scanning LDV optical system embodied in an acousto-optic deflector scanning mechanism. It can improve the measurement accuracy since there is no mechanical motion involved. One main advantage of this system is that it generates a laser scanning beam in parallel that is different from the beam scanning in the conventional scanning laser Doppler vibrometer (SLDV). The new system has a board scanning range. The measurement target size ranges from few tens of millimeters down to 10 μm. We have demonstrated the capability of the novel system on scanning measurements of features as big as ultra-precision cutting tool to features as tiny as AFM cantilever. We believe that the novel SLDV will find profound potential applications in the precision engineering field. 相似文献
993.
994.
995.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 6, pp. 965–969, June, 1991. 相似文献
996.
997.
The paper presents an analytical study of blood flow through a stenosed artery using a suitable mathematical model. The artery is modelled as an anisotropic viscoelastic cylindrical tube containing a non-Newtonian viscous incompressible fluid representing blood. The blood flow is assumed to be characterized by the Herschel–Bulkley model. The effect of the surrounding connective tissues on the motion of the arterial wall has been incorporated. Initially, the relevant solutions of the boundary value problem are obtained in the Laplace transform space, through the use of a suitable finite difference technique. Laplace inversion is carried out by employing suitable numerical techniques. Finally, the variations of the vascular wall displacements, the velocity distribution of the blood flow, the flux, the resistance to flow and the wall shear stress in the stenotic region are quantified through numerical computations and presented graphically. 相似文献
999.
A. A. Loginov O. A. Morozov E. A. Soldatov V. P. Fidelman 《Radiophysics and Quantum Electronics》2006,49(8):633-639
In this work, we propose a method for nonlinear digital filtering of phase-shift keyed signals with different carrier frequencies
on the basis of separating the phase discontinuities of the input signals. The method allows one to avoid compensation for
unknown frequency shift in the problems of determining the time delay of signals in the case of multichannel propagation.
The efficiency of the proposed method is shown for the signals which are short informative packages with the phase-shift keying
against the noise background in the presence of the Doppler effect.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 8, pp. 704–711, August 2006. 相似文献
1000.
A. R. Meenakshi 《Journal of Applied Mathematics and Computing》2006,22(3):277-287
In this paper, necessary and sufficient conditions are given for a product of Toeplitz fuzzy matrices to be Toeplitz. As an application, a criterion for normality of Toeplitz fuzzy matrices is derived and conditions are deduced for symmetric idempotency of Toeplitz fuzzy matrices. We discuss similar results for Hankel fuzzy matrices. Keywords: Fuzzy matrix, Toeplitz and Hankel matrices. 相似文献