全文获取类型
收费全文 | 2634篇 |
免费 | 398篇 |
国内免费 | 157篇 |
专业分类
化学 | 324篇 |
晶体学 | 6篇 |
力学 | 238篇 |
综合类 | 39篇 |
数学 | 1282篇 |
物理学 | 1300篇 |
出版年
2023年 | 19篇 |
2022年 | 40篇 |
2021年 | 56篇 |
2020年 | 62篇 |
2019年 | 56篇 |
2018年 | 74篇 |
2017年 | 69篇 |
2016年 | 71篇 |
2015年 | 66篇 |
2014年 | 122篇 |
2013年 | 218篇 |
2012年 | 147篇 |
2011年 | 150篇 |
2010年 | 132篇 |
2009年 | 175篇 |
2008年 | 188篇 |
2007年 | 165篇 |
2006年 | 152篇 |
2005年 | 138篇 |
2004年 | 104篇 |
2003年 | 107篇 |
2002年 | 113篇 |
2001年 | 80篇 |
2000年 | 89篇 |
1999年 | 80篇 |
1998年 | 50篇 |
1997年 | 63篇 |
1996年 | 48篇 |
1995年 | 35篇 |
1994年 | 28篇 |
1993年 | 32篇 |
1992年 | 34篇 |
1991年 | 33篇 |
1990年 | 36篇 |
1989年 | 21篇 |
1988年 | 22篇 |
1987年 | 30篇 |
1986年 | 13篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1973年 | 2篇 |
1971年 | 3篇 |
排序方式: 共有3189条查询结果,搜索用时 15 毫秒
991.
Alessandro Michelangeli Alessandro Olgiati 《Journal of Nonlinear Mathematical Physics》2017,24(3):426-464
We derive the equations for the non-linear effective dynamics of a so called pseudo-spinor Bose-Einstein condensate, which emerges from the linear many-body Schrödinger equation at the leading order in the number of particles. The considered system is a three-dimensional diluted gas of identical bosons with spin, possibly confined in space, and coupled with an external time-dependent magnetic field; particles also interact among themselves through a short-scale repulsive interaction. The limit of infinitely many particles is monitored in the physically relevant Gross-Pitaevskii scaling. In our main theorem, if at time zero the system is in a phase of complete condensation (at the level of the reduced one-body marginal) and with energy per particle fixed by the Gross-Pitaevskii functional, then such conditions persist also at later times, with the one-body orbital of the condensate evolving according to a system of non-linear cubic Schrödinger equations coupled among themselves through linear (Rabi) terms. The proof relies on an adaptation to the spinor setting of Pickl’s projection counting method developed for the scalar case. Quantitative rates of convergence are available, but not made explicit because evidently non-optimal. In order to substantiate the formalism and the assumptions made in the main theorem, in an introductory section we review the mathematical formalisation of modern typical experiments with pseudo-spinor condensates. 相似文献
992.
Efficient pulse sequences for measuring 1H–1H coupling constants (JHH) in strongly coupled spin systems, named selective J‐resolved‐HMQC‐1 and ‐2, have been developed. In the strongly coupled spin systems such as ‐CH2‐CHA(OH)‐CHB(OH)‐CH2‐, measurements of 3JHAHB are generally difficult owing to the complicated splitting caused by the adjacent CH2 protons. For easier and accurate measurements of 3JHAHB in such a spin system, a selective excitation pulse is incorporated into the J‐resolved HMQC pulse sequence. In the proposed methods, only two strongly coupled protons, HA and HB which are excited by a selective pulse, are observed as J‐resolved HMQC signals. The cross peaks of HA and HB appear as doublets owing to 3JHAHB along the F1 dimension in the selective J‐resolved HMQC‐1 and ‐2 experiments. The efficiency of the proposed pulse sequences has been demonstrated in application to the stereochemical studies of the complicated natural product, monazomycin. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
993.
We study once‐reinforced random walk on . For this model, we derive limit results on all moments of its range using Tauberian theory. 相似文献
994.
用热线风速仪采集了圆喷嘴空气射流的速度时间序列,并采用一种基于最大Lyapunov指数不变性的混沌时间序列分析方法,计算了出口雷诺数在939≤Re≤3758范围内的速度信号的最大Lyapunov指数以及湍流的非拟序脉动.结果表明,最大Lyapunov指数随着雷诺数的增加而增大,随着离开喷嘴出口距离的增加而减小,而且最大Lyapunov指数的倒数与关联时间是正相关的.湍流的非拟序脉动随着雷诺数的增加以及随着离开喷嘴出口距离的增加均是逐渐增大的,而且湍流的非拟序脉动与Kolmogorov尺度是负相关的. 相似文献
995.
《Physics and Chemistry of Liquids》2012,50(3):247-255
Abstract The solubility of indole n-octane, n-decane and n-dodecane has been measured at several temperatures. The three systems exhibit limited solubilities with upper critical solution temperatures. The critical exponents of the three systems, evaluated from the experimental data, are found to be the same within the limits of experimental error: β = 0.50 ± 0.4. 相似文献
996.
C. M. McKenna 《辐射效应与固体损伤》2013,168(1-4):93-110
A review of techniques for electrical measurement of high current ion beams is presented. A computer analysis of the secondary-particle current-collection schemes is made for dosimetry-cup configurations commonly used on ion implanters with electrostatic scanning. The design of a dosimetry cup for a high current implanter with mechanical scanning is discussed. Also beam monitoring techniques for uniformity measurements are reviewed. 相似文献
997.
In this paper we investigate the stability of linear singular systems of difference equations with variable coefficients by the projector-based approach. We study the preservation of uniform/exponential stability when the system coefficients are subject to allowable perturbations. A Bohl–Perron type theorem is obtained which provides a necessary and sufficient condition for the boundedness of solutions of nonhomogenous systems. The notion of Bohl exponent is introduced and we characterize the relation between the exponential stability and the Bohl exponent. Finally, robustness of the Bohl exponent with respect to allowable perturbations is investigated. 相似文献
998.
Li Wang 《Journal of Mathematical Analysis and Applications》2011,383(2):541-552
In this paper, a singular elliptic system involving multiple critical exponents and the Caffarelli-Kohn-Nirenberg inequality is investigated. By using the extremals of the best Hardy-Sobolev constants, the existence and multiplicity of positive solutions to the system are established. 相似文献
999.
《Molecular physics》2012,110(19-20):2343-2348
It is known that the Λ-tensor (an array of Lagrange multipliers), necessary for evaluating analytic energy gradients in the coupled-cluster theory, is diagrammatically disconnected in general. This means that the number of non-negligible elements in the Λ-tensor grows faster than linearly with the number of calculated particles. At a formal level, when evaluating the gradients of the coupled-cluster energy, this could prevent obtaining a linear scaling of the operational cost with respect to the number of correlated particles. It is shown that in ground/excited-state coupled-cluster calculations, based on localized orbitals, the disconnected part of the Λ-tensor, as well as the disconnected part of the left-hand excited-state eigenvector, can be ignored, thus justifying the use of standard screening techniques employed in linear-scaling schemes. 相似文献
1000.
Principal parametric resonances of a slender cantilever beam subject to axial narrow-band random excitation of its base 总被引:1,自引:0,他引:1
The non-linear integro-differential equations of motion for a slender cantilever beam subject to axial narrow-band random excitation are investigated. The method of multiple scales is used to determine a uniform first-order expansion of the solution of equations. According to solvability conditions, the non-linear modulation equations for the principal parametric resonance are obtained. Firstly, The largest Lyapunov exponent which determines the almost sure stability of the trivial solution is quantificationally resolved, in which, the modified Bessel function of the first kind is introduced. Results show that the increase of the bandwidth facilitates the almost sure stability of the trivial response and stabilizes the system for a lower acceleration oscillating amplitude but intensifies the instability of the trivial response for a higher one. Secondly, the first and second order non-trivial steady state response of the system is obtained by perturbation method and the corresponding amplitude–frequency curves are calculated when the bandwidth is very small. Results show that the effective non-linearity of whether the amplitude expectation of the first order steady state response or the amplitude expectation of the second order steady state response is of the hardening type for the first mode, whereas for the second mode the effective non-linearity of whether the amplitude expectation of the first order steady state response or the amplitude expectation of the second order steady state response is of the softening type. Finally, the stochastic jump and bifurcation is investigated for the first and second modal parametric principal resonance. The basic jump phenomena indicate that, under the conditions of system parameters with a smaller bandwidth, the most probable motion is around the non-trivial branch of the amplitude response curve, whereas with a higher bandwidth, the most probable motion is around the trivial one of the amplitude response curve. However, the stochastic jump is sometimes more sensitive to the change of the bandwidth, in other words, a small change of bandwidth may induce a series of stochastic jump and bifurcation. 相似文献