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   5933篇
  免费   743篇
  国内免费   318篇
化学   206篇
晶体学   6篇
力学   771篇
综合类   154篇
数学   4650篇
物理学   1207篇
  2025年   9篇
  2024年   74篇
  2023年   78篇
  2022年   80篇
  2021年   91篇
  2020年   150篇
  2019年   143篇
  2018年   173篇
  2017年   192篇
  2016年   219篇
  2015年   134篇
  2014年   228篇
  2013年   426篇
  2012年   414篇
  2011年   309篇
  2010年   283篇
  2009年   324篇
  2008年   373篇
  2007年   348篇
  2006年   350篇
  2005年   317篇
  2004年   283篇
  2003年   234篇
  2002年   245篇
  2001年   179篇
  2000年   204篇
  1999年   153篇
  1998年   128篇
  1997年   132篇
  1996年   97篇
  1995年   109篇
  1994年   69篇
  1993年   72篇
  1992年   58篇
  1991年   37篇
  1990年   48篇
  1989年   27篇
  1988年   20篇
  1987年   19篇
  1986年   21篇
  1985年   16篇
  1984年   18篇
  1983年   9篇
  1982年   18篇
  1980年   10篇
  1979年   9篇
  1978年   13篇
  1977年   13篇
  1974年   7篇
  1973年   7篇
排序方式: 共有6994条查询结果,搜索用时 15 毫秒
21.
For conformal mixing repellers such as Julia sets and nonlinear one-dimensional Cantor sets, we connect the pressure of a smooth transformation on the repeller with its generalized dimensions, entropies, and Liapunov exponents computed with respect to a set of equilibrium Gibbs measures. This allows us to compute the pressure by means of simple numerical algorithms. Our results are then extended to axiom-A attractors and to a nonhyperbolic invariant set of the line. In this last case, we show that a first-order phase transition appears in the pressure.  相似文献   
22.
In flat spacetime, the fourth space coordinate in special relativity (SR) is equivalent to the coordinate time tE. We will show, however, that this definition of physical time is not unique. Another natural choice of coordinate time, tA, with absolute synchronization is allowed. Spacetime would exhibit dual properties, namely relativistic and absolute. In an arbitrary inertial frame, the relationship of the above two kinds of coordinate time corresponds to a resynchronization, and the Lorentz transformations can be written in an alternative form, which is called the generalized Galilean transformation (GGT). Although the absolute property is still hidden in nearly all types of experiments, the advantages of the above approach are as follows: (1) It will give us a deeper understanding of SR, including the basis of length contraction, time dilation and the interaction between moving objects and the physical vacuum. (2) It will provide a wider research domain than SR; for example, superluminal motion is predicted and has obtained growing experimental support.  相似文献   
23.
An improved generalized admittance (GAM) matrix technique is presented in this paper. Matrix transformation eliminates the singularity factor of GAM, denominator (1+Γ), because of new presentations of GAM. The relationship equations between II-port current and I-port incidence wave is computed by mode matching method. The generalized scattering matrix (GSM) of waveguide structure and its discontinuity problems is obtained with relationship equations and reflection coefficients. The GSM’s of millimeter-wave multistepped bend and T-junction in rectangular waveguide are computed by the improved GAM technique. The results comparisons between the proposed method and commercial software HFSS10.0 show the validity of the proposed method, which improves the validity of the GAM technique and reduces mathematical efforts. It is general, very efficient and can be used to solve other complicated and multiport network problems.  相似文献   
24.
Utilizing the Wronskian technique, a combined Wronskian condition is established for a (3+1)-dimensional generalized KP equation. The generating functions for matrix entries satisfy a linear system of new partial differential equations. Moreover, as applications, examples of Wronskian determinant solutions, including N-soliton solutions, periodic solutions and rational solutions, are computed.  相似文献   
25.
A minimal system-plus-reservoir model yielding a nonergodic Langevin equation is proposed, which originates from the cubic-spectral density of environmental oscillators and momentum-dependent coupling. This model allows ballistic diffusion and classical localization simultaneously, in which the fluctuation-dissipation relation is still satisfied but the Khinchin theorem is broken. The asymptotical equilibrium for a nonergodic system requires the initial thermal equilibrium, however, when the system starts from nonthermal conditions, it does not approach the equilibration even though a nonlinear potential is used to bound the particle, this can be confirmed by the zerotb law of thermodynamics. In the dynamics of Brownian localization, due to the memory damping function inducing a constant term, our results show that the stationary distribution of the system depends on its initial preparation of coordinate rather than momentum. The coupled oscillator chain with a fixed end boundary acts as a heat bath, which has long been used in studies of collinear atom/solid-surface scattering and lattice vibration, we investigate this problem from the viewpoint of nonergodicity.  相似文献   
26.
Wavefields endowed with the coherence-induced property of optical twist have recently attracted a good deal of theoretical and experimental attention. We present the generalized radiometric theory of fields generated by twisted Gaussian Schell-model sources. The effects introduced by the novel, rotationally symmetric, twist phenomenon in the radiant intensity, generalized radiance, radiant emittance (irradiance), and the radiation efficiency are assessed. The radiance becomes directionally skewed as a result of the twist, whereas the radiant intensity remains axially symmetric. The twist reduces the radiation efficiency and broadens the radiation distribution, in agreement with the notion that the twist decreases the effective coherence. Several special cases, such as quasihomogeneous sources, are analyzed in detail. The radiometric results, which are physically consistent with the superposition models of twisted sources, are demonstrated by illustrative examples.  相似文献   
27.
In this paper, by introducing some appropriate transformation and with the help of symbolic computation, we study exact travelling wave solutions for the high-order modified Boussinesq equation, a single nonlinear reaction-diffusion equation and a generalized nonlinear Schrödinger equation with nonlinear terms of any order by use of the extended-tanh method. Thus, some new exact travelling-wave solutions, which contain kink-shaped solitons, bell-shaped solitons, periodic solutions, combined formal solitons, rational solutions and singular solitons for these equations, are obtained.  相似文献   
28.
Dense coding using superpositions of Bell-states is proposed. The generalized Grover's algorithm is used to prepare the initial entangled states, and the reverse process of the quantum algorithm is used to determine the entangled state in the decoding measurement. Compared with the previous schemes, the superpositions of two Bell-states are exploited. Our scheme is demonstrated using a nuclear magnetic resonance (NMR) quantum computer. The corresponding manipulations are obtained. Experimental results show a good agreement between theory and experiment. We also generalize the scheme to transmit eight messages by introducing an additional two-state system.  相似文献   
29.
The generalized Kullback-Leibler divergence (K-Ld) in Tsallis statistics [constrained by the additive duality of generalized statistics (dual generalized K-Ld)] is here reconciled with the theory of Bregman divergences for expectations defined by normal averages, within a measure-theoretic framework. Specifically, it is demonstrated that the dual generalized K-Ld is a scaled Bregman divergence. The Pythagorean theorem is derived from the minimum discrimination information principle using the dual generalized K-Ld as the measure of uncertainty, with constraints defined by normal averages. The minimization of the dual generalized K-Ld, with normal averages constraints, is shown to exhibit distinctly unique features.  相似文献   
30.
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