全文获取类型
收费全文 | 1923篇 |
免费 | 186篇 |
国内免费 | 103篇 |
专业分类
化学 | 165篇 |
晶体学 | 2篇 |
力学 | 636篇 |
综合类 | 34篇 |
数学 | 567篇 |
物理学 | 808篇 |
出版年
2024年 | 3篇 |
2023年 | 14篇 |
2022年 | 40篇 |
2021年 | 34篇 |
2020年 | 43篇 |
2019年 | 44篇 |
2018年 | 37篇 |
2017年 | 33篇 |
2016年 | 43篇 |
2015年 | 38篇 |
2014年 | 84篇 |
2013年 | 125篇 |
2012年 | 91篇 |
2011年 | 117篇 |
2010年 | 93篇 |
2009年 | 93篇 |
2008年 | 108篇 |
2007年 | 112篇 |
2006年 | 100篇 |
2005年 | 115篇 |
2004年 | 126篇 |
2003年 | 84篇 |
2002年 | 105篇 |
2001年 | 72篇 |
2000年 | 44篇 |
1999年 | 51篇 |
1998年 | 58篇 |
1997年 | 55篇 |
1996年 | 34篇 |
1995年 | 24篇 |
1994年 | 32篇 |
1993年 | 29篇 |
1992年 | 34篇 |
1991年 | 11篇 |
1990年 | 15篇 |
1989年 | 11篇 |
1988年 | 5篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 4篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有2212条查询结果,搜索用时 15 毫秒
31.
To date, there are very few studies on the transition beyond second Hopf bifurcation in a lid-driven square cavity, due to the difficulties in theoretical analysis and numerical simulations. In this paper, we study the characteristics of the third Hopf bifurcation in a driven square cavity by applying a consistent fourth-order compact finite difference scheme rectently developed by us. We numerically identify the critical Reynolds number of the third Hopf bifurcation located in the interval of (13944.7021,13946.5333) by the method of bisection. Through Fourier analysis, it is discovered that the flow becomes chaotic with a characteristic of period-doubling bifurcation when the Reynolds number is beyond the third bifurcation critical interval. Nonlinear time series analysis further ascertains the flow chaotic behaviors via the phase diagram, Kolmogorov entropy and maximal Lyapunov exponent. The phase diagram changes interestingly from a closed curve with self-intersection to an unclosed curve and the attractor eventually becomes strange when the flow becomes chaotic. 相似文献
32.
Régis Brugiere et Pierre Lucasson 《辐射效应与固体损伤》2013,168(1):55-57
The nature of the electron bombarded aluminium electrical recovery process has been studied by combining quenches with irradiations. Measured Frenkel pair formation rates per incident electrons as well as annealing kinetics emphasize the role of impurity interstitial trapping. 相似文献
33.
Crack propagation on the basal planes in zinc was examined by means of in situ fracture testing of pre-cracked single crystals, with specific attention paid to the fracture mechanism. During quasistatic loading, crack propagation occurred in short bursts of dynamic crack extension followed by periods of arrests, the latter accompanied by plastic deformation and blunting of the crack-tip. In situ observations confirmed nucleation and propagation of microcracks on parallel basal planes and plastic deformation and failure of the linking ligaments. Pre-existing twins in the crack path serve as potent crack arrestors. The crystallographic orientation of the crack growth direction on the basal plane was found to influence both the fracture load as well as the deformation at the crack-tip, producing fracture surfaces of noticeably different appearances. Finite element analysis incorporating crystal plasticity was used to identify dominant slip systems and the stress distribution around the crack-tip in plane stress and plane strain. The computational results are helpful in rationalizing the experimental observations including the mechanism of crack propagation, the orientation dependence of crack-tip plasticity and the fracture surface morphology. 相似文献
34.
In this paper, based on the implicit Runge-Kutta(IRK) methods, we derive a class of parallel scheme that can be implemented on the parallel computers with Ns(N is a positive even number) processors efficiently, and discuss the iteratively B-convergence of the Newton iterative process for solving the algebraic equations of the scheme, secondly we present a strategy providing initial values parallelly for the iterative process. Finally, some numerical results show that our parallel scheme is higher efficient as N is not so large. 相似文献
35.
36.
37.
余桑 《应用数学和力学(英文版)》1987,8(12):1115-1131
Despite its beauty and grandeur the theory of GR still appears to be incomplete in thefollowing ways:(1)It cannot accommodate the asymmetric total energy momentum tensor whoseasymmetry has been shown to exist in the presence of electromagnetism.(2)The law of angular momentum balance as an exact equation is not an automaticconsequence of the field equations as is the case with the law of linear momentum balance.(3)The four degrees of arbitrariness left by the contracted second Bianchi identitymakes a unique solution of the field equations unattainable without extra (unphysical)postulates.To answer the challenge posed by the above assertions we propose in this paper tocomplete Einstein’s theory by postulating the principle fibre bundle P[M,SU(2)]for theunderlying geometry of the 4-dimensional spacetime,where the structre group SU (2) isthe real representation of the special complex unitary group of dimension 2. SU (2) leavesconcurrently invariant the metric form dS~2=g_(αβ)dx~αdx~β and the fundamenta 相似文献
38.
We experimentally show that computing with attractors leads to fast adaptive behavior in which dynamical associations can be made between different inputs which initially produce sharply distinct outputs. We do so by first defining a set of simple local procedures which allow a computing array to change its state in time so as to produce classical Pavlovian conditioning. We then examine the dynamics of coalescence and dissociation of attractors with a number of quantitative experiments. We also show how such arrays exhibit generalization and differentiation of inputs in their behavior. 相似文献
39.
40.
封闭圆内开缝圆自然对流换热的振荡特性 总被引:1,自引:0,他引:1
本文通过数值计算探讨了封闭圆内开缝圆自然对流换热的振荡特性。数值计算以整个圆为计算区域,采用了非稳态的数学模型和具有QUICK差分格式的SIMPLE算法。在相同条件下计算结果和实验结果符合很好。数值结果显示, 当几何结构一定时,Rayleigh数Ra小于某个临界值时,流动和换热处于稳态,并且关于垂直中心线对称;Ra大于这个临界值时,流动和换热是振荡的,非对称的。数值实验还表明,流动和换热出现振荡时的临界Rayleigh数Rac与开缝圆的开缝度有关,且流动和换热的振荡会出现对称振荡和非对称振荡两种情形。 相似文献