首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   535篇
  免费   34篇
  国内免费   37篇
化学   4篇
力学   17篇
综合类   5篇
数学   454篇
物理学   126篇
  2023年   8篇
  2022年   8篇
  2021年   18篇
  2020年   24篇
  2019年   15篇
  2018年   15篇
  2017年   13篇
  2016年   14篇
  2015年   8篇
  2014年   35篇
  2013年   58篇
  2012年   18篇
  2011年   40篇
  2010年   14篇
  2009年   41篇
  2008年   42篇
  2007年   42篇
  2006年   19篇
  2005年   22篇
  2004年   15篇
  2003年   20篇
  2002年   21篇
  2001年   9篇
  2000年   7篇
  1999年   9篇
  1998年   17篇
  1997年   13篇
  1996年   14篇
  1995年   5篇
  1994年   6篇
  1993年   7篇
  1992年   2篇
  1988年   2篇
  1987年   1篇
  1985年   1篇
  1984年   1篇
  1978年   1篇
  1969年   1篇
排序方式: 共有606条查询结果,搜索用时 62 毫秒
501.
Boundary operators and boundary ground states in sine-Gordon model with a fixed boundary condition are studied using bosonization and q-deformed oscillators. We also study the boundary bound state for this case.  相似文献   
502.
罗婉华  刘忠永 《光子学报》1999,28(4):318-321
引入了一类新的积分变换,即对称变换。这类变换在空间域和空间频率域中实现的变换操作是相同的。换句话说,如果一个积分变换器对信号本身及其Fourier频谱作相同的变换操作,那么这种变换即为对称变换。给出了对称变换的成立条件,即当积分变换核是所谓的类自Fourier变换函数时,此变换即为对称变换。并提出了类自Fourier变换函数的一种构造方式。同时还指出,光学中的分数Fourier变换即是一种对称变换。  相似文献   
503.
In this paper, we propose an innovative chaotic system, combining fractional derivative and sine-hyperbolic nonlinearity with circuit execution. The study of this system is conducted via an analog circuit simulator, using two anti-parallel semiconductor diodes to provide hyperbolic sine nonlinearity, and to function as operational amplifiers. The multi-stability of the system is also enhanced with the help of multi-equilibrium points for distinct real orders of system. The system explores the generation of a four-wing attractor in different phases, both numerically and electronically. By changing the input parameters of the system, different graphs are generated for current flow in state, phase, and space, to confirm the precision of the fractional order derivatives. A reasonable simulation shows that the deliberate circuit provides effective chaos in terms of speed and accuracy, which is comensurate with the numerical simulation. This nonlinear chaotic behavior is utilized to encrypt sound (.wav), images (.jpg), and animated (.gif) data which are a major requirement for the security of communication systems. The proposed circuit performs chaos and cryptographic tasks with high-effective analog computation, and constitutes a novel approach to this area of research.  相似文献   
504.
一个新的混沌系统的动力学分析及混沌控制   总被引:6,自引:0,他引:6       下载免费PDF全文
蔡国梁  谭振梅  周维怀  涂文桃 《物理学报》2007,56(11):6230-6237
提出了一个新的混沌系统,研究了其基本动力学特性.设计了实现该系统的混沌电路,电路实验结果验证了系统的混沌行为.根据Lyapunov稳定性理论,采用自适应backstepping控制方法,把系统控制到一个有界点.数值仿真证明了该方法的有效性和可行性.  相似文献   
505.
在资产收益率及其波动率均满足随机跳跃且具有跳跃相关性的仿射扩散模型下,用广义双指数分布和伽玛分布分别刻画非对称性收益率及其波动率的跳跃波动变化,研究了具有几何平均特征的水平重置期权定价问题.通过Girsanov测度变换和多维Fourier逆变换方法,给出了此类重置期权定价的解析公式.最后,通过数值实例着重分析了联合跳跃...  相似文献   
506.
507.
A simple graph G is a 2-tree if G=K_3,or G has a vertex v of degree 2,whose neighbors are adjacent,and G-v is a 2-tree.Clearly,if G is a 2-tree on n vertices,then |E(G)|=2 n-3.A non-increasing sequence π=(d_1,...,d_n) of nonnegative integers is a graphic sequence if it is realizable by a simple graph G on n vertices.[Acta Math.Sin.Engl.Ser.,25,795-802(2009)] proved that if k≥2,n≥9/2 k~2+19/2 k and π=(d_1,...,d_n) is a graphic sequence with∑_(i=1)~n di(k-2)n,then π has a realization containing every 1-tree(the usual tree) on k vertices.Moreover,the lower bound(k-2)_n is the best possible.This is a variation of a conjecture due to Erdos and Sos.In this paper,we investigate an analogue problem for 2-trees and prove that if k≥3 is an integer with k≡i(mod 3),n≥ 20[k/3] ~2+31[k/3]+12 and π=(d_1,...,d_n) is a graphic sequence with ∑_(i=1)~n d_imax{k-1)(n-1), 2 [2 k/3] n-2 n-[2 k/3] ~2+[2 k/3]+1-(-1)~i}, then π has a realization containing every 2-tree on k vertices.Moreover,the lower bound max{(k-1)(n-1), 2[2 k/3]n-2 n-[2 k/3] ~2+[2 k/3]+1-(-1)~i}is the best possible.This result implies a conjecture due to [Discrete Math.Theor.Comput.Sci.,17(3),315-326(2016)].  相似文献   
508.
《Mathematische Nachrichten》2017,290(5-6):662-671
An irreducible algebraic variety X is rigid if it admits no nontrivial action of the additive group of the ground field. We prove that the automorphism group of a rigid affine variety contains a unique maximal torus . If the grading on the algebra of regular functions defined by the action of  is pointed, the group  is a finite extension of . As an application, we describe the automorphism group of a rigid trinomial affine hypersurface and find all isomorphisms between such hypersurfaces.  相似文献   
509.
《中国物理 B》2021,30(6):60509-060509
Complex chaotic sequences are widely employed in real world, so obtaining more complex sequences have received highly interest. For enhancing the complexity of chaotic sequences, a common approach is increasing the scroll-number of attractors. In this paper, a novel method to control system for generating multi-layer nested chaotic attractors is proposed.At first, a piecewise(PW) function, namely quadratic staircase function, is designed. Unlike pulse signals, each level-logic of this function is square constant, and it is easy to realize. Then, by introducing the PW functions to a modified Chua's system with cubic nonlinear terms, the system can generate multi-layer nested Chua's attractors. The dynamical properties of the system are numerically investigated. Finally, the hardware implementation of the chaotic system is used FPGA chip.Experimental results show that theoretical analysis and numerical simulation are right. This chaotic oscillator consuming low power and utilization less resources is suitable for real applications.  相似文献   
510.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号