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   1749篇
  免费   246篇
  国内免费   57篇
化学   111篇
晶体学   1篇
力学   344篇
综合类   37篇
数学   774篇
物理学   785篇
  2025年   11篇
  2024年   33篇
  2023年   30篇
  2022年   39篇
  2021年   51篇
  2020年   60篇
  2019年   61篇
  2018年   40篇
  2017年   60篇
  2016年   55篇
  2015年   40篇
  2014年   67篇
  2013年   123篇
  2012年   68篇
  2011年   111篇
  2010年   98篇
  2009年   98篇
  2008年   117篇
  2007年   91篇
  2006年   108篇
  2005年   84篇
  2004年   78篇
  2003年   80篇
  2002年   61篇
  2001年   54篇
  2000年   60篇
  1999年   45篇
  1998年   41篇
  1997年   34篇
  1996年   19篇
  1995年   12篇
  1994年   20篇
  1993年   9篇
  1992年   5篇
  1991年   11篇
  1990年   7篇
  1989年   13篇
  1988年   9篇
  1987年   11篇
  1986年   4篇
  1985年   3篇
  1984年   2篇
  1983年   2篇
  1982年   8篇
  1981年   4篇
  1979年   2篇
  1978年   2篇
  1977年   4篇
  1959年   1篇
  1957年   1篇
排序方式: 共有2052条查询结果,搜索用时 15 毫秒
1.
A cylindrical waveguide gyro-peniotron amplifier is analysed theoretically in this paper. By a ballistic method and directly using the energy conservation in the beam-wave system, a set of interaction equations for the cylindrical waveguide gyro-peniotron amplifier is derived. Computer simulation shows that under defined conditions an interaction efficiency of 47%, an output power of 240kW at a gain of 22. 5 dB and a 3 dB-instantaneous bandwidth of 1. 9% for a central frequency of 35GHz, TE03 mode gyro-peniotron amplifier could be achieved. The influence of the operation parameters on the amplifier performance is also presented.  相似文献   
2.
C. S. Unnikrishnan 《Pramana》2005,65(3):359-379
I discuss in detail the result that the Bell’s inequalities derived in the context of local hidden variable theories for discrete quantized observables can be satisfied only if a fundamental conservation law is violated on the average. This result shows that such theories are physically nonviable, and makes the demarcating criteria of the Bell’s inequalities redundant. I show that a unique correlation function can be derived from the validity of the conservation law alone and this coincides with the quantum mechanical correlation function. Thus, any theory with a different correlation function, like any local hidden variable theory, is incompatible with the fundamental conservation laws and space-time symmetries. The results are discussed in the context of two-particle singlet and triplet states, GHZ states, and two-particle double slit interferometry. Some observations on quantum entropy, entanglement, and nonlocality are also discussed.  相似文献   
3.
We study weno(2r − 1) reconstruction [D.S. Balsara, C.W. Shu, Monotonicity prserving weno schemes with increasingly high-order of accuracy, J. Comput. Phys. 160 (2000) 405–452], with the mapping (wenom) procedure of the nonlinear weights [A.K. Henrick, T.D. Aslam, J.M. Powers, Mapped weighted-essentially-non-oscillatory schemes: achieving optimal order near critical points, J. Comput. Phys. 207 (2005) 542–567], which we extend up to weno17 (r=9)(r=9). We find by numerical experiment that these procedures are essentially nonoscillatory without any stringent cfl limitation (cfl∈[0.8,1])(cfl[0.8,1]), for scalar hyperbolic problems (both linear and scalar conservation laws), provided that the exponent pβpβ in the definition of the Jiang–Shu [G.S. Jiang, C.W. Shu, Efficient implementation of weighted eno schemes, J. Comput. Phys. 126 (1996) 202–228] nonlinear weights be taken as pβ=rpβ=r, as originally proposed by Liu et al. [X.D. Liu, S. Osher, T. Chan, Weighted essentially nonoscillatory schemes, J. Comput. Phys. 115 (1994) 200–212], instead of pβ=2pβ=2 (this is valid both for weno and wenom reconstructions), although the optimal value of the exponent is probably pβ(r)∈[2,r]pβ(r)[2,r]. Then, we apply the family of very-high-order wenompβ=rwenompβ=r reconstructions to the Euler equations of gasdynamics, by combining local characteristic decomposition [A. Harten, B. Engquist, S. Osher, S.R. Chakravarthy, Uniformly high-order accurate essentially nonoscillatory schemes iii, J. Comput. Phys. 71 (1987) 231–303], with recursive-order-reduction (ror) aiming at aleviating the problems induced by the nonlinear interactions of characteristic fields within the stencil. The proposed ror algorithm, which generalizes the algorithm of Titarev and Toro [V.A. Titarev, E.F. Toro, Finite-volume weno schemes for 3-D conservation laws, J. Comput. Phys. 201 (2004) 238–260], is free of adjustable parameters, and the corresponding rorwenompβ=rrorwenompβ=r schemes are essentially nonoscillatory, as Δx→0Δx0, up to r=9r=9, for all of the test-cases studied. Finally, the unsplit linewise 2-D extension of the schemes is evaluated for several test-cases.  相似文献   
4.
通过求解2+1维de-Sitter时空中零测地线方程得到光线的轨迹方程,对轨迹方程进行分析发现其不存在封闭的轨迹解.  相似文献   
5.
From a consideration of extended hadron structure in the microlocal anisotropic space-time, the mesonic and baryonic states with their internal quantum numbers such as strangeness, hypercharge, baryon number are constructed. The SU 3 baryonic multiplets of baryons with spin (j + ) are generated from the SU 3 mesonic multiplets of mesons with spin j. The meson–baryon mass differences are also derived here. The composite particle field of hadrons for the macroscopic space-time are obtained. In particular, the meson field and one particle meson state are considered here. These one particle hadron states of the macroscopic space-time also possess the quantum numbers (strangeness, hypercharge, etc.) which are regarded as the manifestations of the anisotropic nature of the microlocal space-time. The composite fields constructed here are usable in the reduction formulae of the S-matrix approach for strong interaction.  相似文献   
6.
We use the hydrodynamic formulation of Scale Relativity Theory to analyze the TDGL equation. As a result, London equations come naturally from the system, when equating to zero the real velocity, the imaginary one turns real, the superconducting fluid act as a subquantum medium energy accumulator, the vector potential, the real and the imaginary velocity are all written in terms of the elliptic function. When solving the resulted system by means of WKBJ method, we get tunneling and quantization. In other words, scale transformation laws produce, on the motion equation of particles governed by the TDGL equation, under some peculiar assumptions, effects which are analogous to those of a “macroscopic quantum mechanics”.  相似文献   
7.
Hydrodynamic properties for a class of nondiffusive particle systems are investigated. The method allows one to study local equilibria for a class of asymmetric zero-range processes, and applies as well to other models, such as asymmetric simple exclusion and misanthropes. Attractiveness is an essential ingredient. The hydrodynamic equations present shock wave phenomena. Preservation of local equilibrium is proven to hold away from the shocks. The problem of breakdown of local ergodicity at the shocks, which was investigated by D. Wick in a particular model, remains open in this more general setup.  相似文献   
8.
In shock wave theory there are two considerations in selecting the physically relevant shock waves.There is the admissibility criterion for the well-posedness of hyperbolic conservation laws.Another consideraztion concerns the entropy production across the shochs.The latter is natural from the physical point of view,but is not sufficient in its straightforward formulation,if the system is not genuinely nonlinear.In this paper we propose the principles of increasing entropy production and that of the superposition of shocks.These principles arc shown to be equivalent to the admissibility criterion.  相似文献   
9.
新模式热电联产系统:联产供热的一个发展   总被引:4,自引:0,他引:4  
1前言经济的迅猛发展,能源与水源的供需矛盾的突出,环保形势的严峻要求用能的“文明化”。文明用能应是跨世纪和新世纪用能战略的基本原则。文明用能的一个极重要方面就是对热能的文明利用问。热电联产是热能文明利用不可替代的途径。本文提出一种热电联产的新模式,旨在通过这种模式把联产供热规模化,大幅度地节约能源和水资源,减轻电能与热能的生产对环境的不利影响。最近中央提出的可持续发展战略,应成为我们今后技术研究的一个指导性方针。节约能源、水源和保护环境是这一战略的重要组成部分。在世界范围内,对节约资源保护环境问…  相似文献   
10.
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