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1.
A model dynamical system with a great many degrees of freedom is proposed for which the critical condition for the onset of collective oscillations, the evolution of a suitably defined order parameter, and its fluctuations around steady states can be studied analytically. This is a rotator model appropriate for a large population of limit cycle oscillators. It is assumed that the natural frequencies of the oscillators are distributed and that each oscillator interacts with all the others uniformly. An exact self-consistent equation for the stationary amplitude of the collective oscillation is derived and is extended to a dynamical form. This dynamical extension is carried out near the transition point where the characteristic time scales of the order parameter and of the individual oscillators become well separated from each other. The macroscopic evolution equation thus obtained generally involves a fluctuating term whose irregular temporal variation comes from a deterministic torus motion of a subpopulation. The analysis of this equation reveals order parameter behavior qualitatively different from that in thermodynamic phase transitions, especially in that the critical fluctuations in the present system are extremely small.Dedicated to Ilya Prigogine on the occasion of his 70th birthday.  相似文献
2.
液晶中一种稳定的相态:蓝相   总被引:2,自引:0,他引:2  
刘建军  沈曼  杨国琛 《物理》2003,32(5):327-331
文章描述了胆甾相液晶中蓝相的研究现况.蓝相(BP)是液晶中具有特殊性质的一个相态,它的序参量表现出三维空间周期性.蓝相是出现在一个狭小的温度间隔里(量级为0.1—1K)的稳定相态.文章对已观察到的BPⅠ,BPⅡ,BPⅢ(“雾”相)的性质做了简要的叙述.对研究液晶蓝相的主要理论——Ginzburg-Landau理论(唯象理论)作了介绍,并指出了蓝相研究的实际物理意义。  相似文献
3.
Quasiparticle (QP) planar tunneling spectroscopy is used to investigate the density of states (DoS) of YBa2Cu3O7 (YBCO). Temperature, crystallographic orientation, doping, damage and magnetic field dependencies confirm that the observed zero-bias conductance peak (ZBCP) is an Andreev bound state (ABS), an intrinsic property of a d-wave superconducting order parameter (OP) at an interface. In zero applied field, the splitting of the ZBCP below 8 K confirms a near-surface phase transition into a superconducting state with spontaneously broken time-reversal symmetry (BTRS). Tunneling into the ABS provides a phase-sensitive spectroscopy that can be used to measure a variety of DoS properties in an unconventional superconductor.  相似文献
4.
高Tc氧化物晶界结   总被引:1,自引:0,他引:1  
戴远东  马平  杨涛 《物理》2002,31(1):7-10
高温超导氧化物的晶界形成超导Josephson弱连接,人工制作的晶界(例如双晶衬底上外延生长高Tc超导薄膜形成的晶界)是弯曲的小折线,即晶界小面化了,超导序参数d波对称性和晶界小面化对晶界结的性质有重要影响,文章综述了近几年来国际上在有关方面的研究动态,。  相似文献
5.
研究了层状液晶的层状结构及有序性,用偏振光显微镜法确定了辛烷基苯酚聚氧乙烯醚(TritonX 100)与正癸醇体系25℃时层状液晶的区域,绘制了部分相图,并用核磁共振氢谱法(2H NMR)进一步验证;用自旋标记电子自旋共振法测定了层状液晶分子排列的有序参数,研究结果显示,不同组分TritonX 100 /n C10H21OH/H2O体系层状液晶的超精细偶合常数基本相同,表明层状液晶中的微极性是一致的.而有序参数随着TritonX 100含量的增加而增加,随着层状液晶中水含量的增加而减少;用小角度X射线衍射方法测定了层状液晶的层间距离,并计算了水分子在层状液晶中的渗透率,其渗透率约为50%.  相似文献
6.
Lyapunov function for the Kuramoto model of nonlinearly coupled oscillators   总被引:1,自引:0,他引:1  
A Lyapunov function for the phase-locked state of the Kuramoto model of non-linearly coupled oscillators is presented. It is also valid for finite-range interactions and allows the introduction of thermodynamic formalism such as ground states and universality classes. For the Kuramoto model, a minimum of the Lyapunov function corresponds to a ground state of a system with frustration: the interaction between the oscillators,XY spins, is ferromagnetic, whereas the random frequencies induce random fields which try to break the ferromagnetic order, i.e., global phase locking. The ensuing arguments imply asymptotic stability of the phase-locked state (up to degeneracy) and hold for any probability distribution of the frequencies. Special attention is given to discrete distribution functions. We argue that in this case a perfect locking on each of the sublattices which correspond to the frequencies results, but that a partial locking of some but not all sublattices is not to be expected. The order parameter of the phase-locked state is shown to have a strictly positive lower bound (r 1/2), so that a continuous transition to a nonlocked state with vanishing order parameter is to be excluded.  相似文献
7.
A velocity-adaptive Couzin model and its performance   总被引:1,自引:0,他引:1  
Typical collective behaviors in the Couzin model are exhibited by simulation, and some performances of the system such as convergence probability and relative size are analyzed. To provide an alternative to the constant-speed setting of the Couzin model, a velocity-adaptive strategy is presented. Simulation shows that in the new model both the convergence probability and the relative size are prominently enhanced.  相似文献
8.
The order parameter S of Fe–Pt nanoparticles is estimated from X-ray diffraction (XRD) patterns. The total intensity of a diffraction peak is obtained by Rietveld analysis as well as simply integrating the intensity. The Rietveld analysis is found to provide a plausible value of S even for a sample showing an XRD pattern with broad and overlapped peaks. Another order parameter Q, which is obtained from Mössbauer spectra, is introduced, and it is confirmed that Q is equivalent to the probability of Fe atoms being in the L10-type atomic arrangement. The coercivity of Fe–Pt nanoparticles is directly proportional to Q, while it vanishes at S=0.4, indicating that the magnetic property of Fe–Pt nanoparticles has a closer relationship to Q than S.  相似文献
9.
The temperature dependence of the spontaneous magnetization of epitaxial iron films with a thickness ranging from d=20 to 200 nm has been measured. The films are grown on GaAs (1 0 0) substrates which are covered by a 150 nm thick silver (1 0 0) buffer layer. For three-dimensional BCC iron it was observed already in 1929 that saturation of the spontaneous magnetization for T→0 is perfectly described by a T2 power law. On the other hand, for thin two-dimensional (2D) iron films a T3/2 law has been established in many recent experimental investigations. In our iron films grown on diamagnetic silver, this dimensionality change occurs at a thickness between d=100 and 200 nm. Comparison of the here-observed T3/2 coefficients with those on iron films grown on paramagnetic tungsten (1 1 0) shows that the 2D interactions are 20 times larger in the films on tungsten. Recent results on Fe films which are grown directly on GaAs (1 0 0) confirm that the substrate has a very strong effect on the coefficient of the T3/2 function, i.e. on the strength of the magnetic interactions in the films.  相似文献
10.
Some exact dynamic and static solutions of Landau–Lifshitz equations in antiferromagnets and ferromagnets found in this work. These solutions can be used for describing distribution of order parameter in small magnetic particles.  相似文献
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