全文获取类型
收费全文 | 2197篇 |
免费 | 471篇 |
国内免费 | 116篇 |
专业分类
化学 | 425篇 |
晶体学 | 11篇 |
力学 | 155篇 |
综合类 | 39篇 |
数学 | 223篇 |
物理学 | 1931篇 |
出版年
2024年 | 6篇 |
2023年 | 22篇 |
2022年 | 47篇 |
2021年 | 61篇 |
2020年 | 66篇 |
2019年 | 38篇 |
2018年 | 39篇 |
2017年 | 74篇 |
2016年 | 106篇 |
2015年 | 54篇 |
2014年 | 124篇 |
2013年 | 165篇 |
2012年 | 146篇 |
2011年 | 154篇 |
2010年 | 124篇 |
2009年 | 150篇 |
2008年 | 151篇 |
2007年 | 166篇 |
2006年 | 145篇 |
2005年 | 125篇 |
2004年 | 120篇 |
2003年 | 96篇 |
2002年 | 83篇 |
2001年 | 75篇 |
2000年 | 63篇 |
1999年 | 49篇 |
1998年 | 59篇 |
1997年 | 38篇 |
1996年 | 43篇 |
1995年 | 25篇 |
1994年 | 38篇 |
1993年 | 25篇 |
1992年 | 14篇 |
1991年 | 15篇 |
1990年 | 13篇 |
1989年 | 13篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有2784条查询结果,搜索用时 15 毫秒
121.
In this paper, we develop an algorithmic method for the evaluation of the steady state probability vector of a special class of finite state Markov chains. For the class of Markov chains considered here, it is assumed that the matrix associated with the set of linear equations for the steady state probabilities possess a special structure, such that it can be rearranged and decomposed as a sum of two matrices, one lower triangular with nonzero diagonal elements, and the other an upper triangular matrix with only very few nonzero columns. Almost all Markov chain models of queueing systems with finite source and/or finite capacity and first-come-first-served or head of the line nonpreemptive priority service discipline belongs to this special class. 相似文献
122.
Mark T. DeMeuse 《Journal of Polymer Science.Polymer Physics》1994,32(10):1749-1757
Studies are presented of the dielectric properties of fully cured diethylene glycol bis (allyl carbonate) as a function of both frequency and temperature. It is shown that the characteristics of the fully cured system are dominated by a localized, secondary transition that is associated with motion of the carbonate unit. The glass transition is shown to contribute little to the dielectric properties within the temperature range 20–70°C. © 1994 John Wiley & Sons, Inc. 相似文献
123.
124.
125.
Yande Xu 《Optical Review》2004,11(5):303-307
This paper proposes a new measuring method called two-period interference fringe interferometry, for a step-profile altitude difference measurement. The principle of the method is different from that of the two-wavelength interferometry which is widely known. The two interference fringes with only slight difference between their spatial periods are obtained by turning a binary step-grating, and they produce a synthetic equivalent period much longer than either of the two periods alone. The interference fringes are produced by the ±1st-order beams diffracted from the grating. The intensity distribution of the interference pattern is independent of the wavelength of the laser-diode light source used. The measuring range of this method is much larger than that of the two-wavelength interferometery. Sinusoical phase modulating technique is easily applied to detect the phase distribution of the interference pattern by vibrating the grating sinusoidally. A plane reflector of 3mm thickness is measured to verify this novel method. 相似文献
126.
Taking into account the effects of quantum interference and interface scattering, combining the electron current with hole
current contribution to tunnel current, we study the coherent quantum transport in normal-metal/d-wave superconductor/ normal-metal (NM/d-wave SC/NM) double tunnel junctions by using extended Blonder-Tinkham-Klapwijk (BTK) approach. It is shown that all quasiparticle
transport coefficients and conductance spectrum exhibit oscillating behavior with the energy, in which periodic vanishing
of Andreev reflection (AR) above superconducting gap is found. In tunnel limit for the interface scattering strength taken
very large, there are a series of bound states of quasiparticles formed in SC. 相似文献
127.
Olivier Baconneau Alessandra Lunardi 《Transactions of the American Mathematical Society》2004,356(3):987-1005
We establish existence, uniqueness, and regularity results for solutions to a class of free boundary parabolic problems, including the free boundary heat equation which arises in the so-called ``focusing problem' in the mathematical theory of combustion. Such solutions are proved to be smooth with respect to time for positive , if the data are smooth.
128.
We solve a linear parabolic equation in d , d 1, with the third nonhomogeneous boundary condition using the finite element method for discretization in space, and the -method for discretization in time. The convergence of both, the semidiscrete approximations and the fully discretized ones, is analysed. The proofs are based on a generalization of the idea of the elliptic projection. The rate of convergence is derived also for variable time step-sizes. 相似文献
129.
讨论了低压微位移驱动电路及控制方法在光电轮廓仪上的运用。采用低压驱动电路驱动压电陶瓷相移器对参考光束进行相移,从而使仪器质量减轻、体积缩小、成本降低。在运用该电路时,为了解决压电陶瓷低电压区非线性误差大的问题,用PC计算机控制压电陶瓷上所加电压的电压值,由摄像头摄取图像并计算出干涉条纹的间隔,然后由PC计算机修改压电陶瓷上所加的电压值,直至干涉条纹相位差达到要求值。该方法的优点是:可消除压电陶瓷低压区的非线性误差,使得开环电路得到闭环的效果;可降低机械零部件的装配难度。 相似文献
130.
本文采用辛算法数值求解一维含时Gross-Pitaevskii(GP)方程.研究了存在陷俘势和撤掉陷俘势时两个凝聚体间的相互作用.发现当存在陷俘势时两个凝聚体间发生弹性碰撞;在零时刻撤掉陷俘势时两个凝聚体间发生干涉现象;当t=2时撤掉陷俘势两个凝聚体间发生了复杂现象. 相似文献