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   12923篇
  免费   1762篇
  国内免费   976篇
化学   7035篇
晶体学   48篇
力学   488篇
综合类   243篇
数学   2552篇
物理学   5295篇
  2024年   35篇
  2023年   171篇
  2022年   473篇
  2021年   487篇
  2020年   453篇
  2019年   383篇
  2018年   354篇
  2017年   555篇
  2016年   607篇
  2015年   610篇
  2014年   829篇
  2013年   867篇
  2012年   865篇
  2011年   769篇
  2010年   661篇
  2009年   779篇
  2008年   770篇
  2007年   741篇
  2006年   668篇
  2005年   691篇
  2004年   592篇
  2003年   454篇
  2002年   366篇
  2001年   318篇
  2000年   278篇
  1999年   245篇
  1998年   206篇
  1997年   179篇
  1996年   187篇
  1995年   149篇
  1994年   96篇
  1993年   93篇
  1992年   89篇
  1991年   65篇
  1990年   77篇
  1989年   60篇
  1988年   75篇
  1987年   62篇
  1986年   42篇
  1985年   48篇
  1984年   35篇
  1983年   30篇
  1982年   44篇
  1981年   19篇
  1980年   15篇
  1979年   19篇
  1978年   14篇
  1977年   7篇
  1976年   9篇
  1973年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
This paper describes the performance and simulation of a compact integrated optical processor for the real-time reconstruction of two-dimensional images in airborne stripmap synthetic aperture radar applications. The functional behavior of the processor is explained in some detail. The design criteria are briefly given. The simulation step allowed the main processor characteristics and properties to be identified. A number of comparisons were obtained in airborne SAR mission scenarios between the predictions of the optical device and those achieved by the modern electronic digital approach, based on the wavefront reconstruction method by matched filtering.  相似文献   
42.
成玉娟  惠华等 《光子学报》2002,31(6):743-747
在分析红外图象和视图象差异的基础上,研究了一种适用于可视图像序列的运动小目标检测算法。受目标影响的象素点具有较弱的时间相关性,即相对普通象素点有较大的时间方差,根据此特征,用管道更新的方法产生新方差图象序列,再用管道更新的方法累积,增加信噪比,然后用基于统计均值的自适应门限方法分割出目标,最后将原图象的梯度倒数作为象素点强度的加权,有效地抑制灰度突变边界的传感器噪音,保存目标点。  相似文献   
43.
关于PFI-代数与剩余格   总被引:10,自引:0,他引:10  
朱怡权  曹喜望 《数学进展》2006,35(2):223-231
本文提出了一种强FI代数-PFI代数,并且深入研究了它的性质,借此进一步揭示了FI-代数和剩余格之间更加密切的联系,进而以FI-代数为基本框架建立了R0-代数、正则剩余格等逻辑系统的结构特征(包括对隅结构)及其相互关系.这种以FI-代数为基础来统一处理剩余格和R0-代数的方法,同样适合于格蕴涵代数和MV代数等代数结构,而且从中更能清楚地看出它们之间的密切联系,也将有助于对相应形式逻辑系统与模糊推理的研究.  相似文献   
44.
We show, via a straightforward calculation, that it is feasible to detect nuclear spin echoes in a ferromagnetic thin film by electrical means. The detection scheme is based on the deflection of the electronic magnetization when the nuclear magnetization reforms during an echo. This deflection is observed as a time-dependent magnetoresistive signal.  相似文献   
45.
The mass spectrum ofcb meson is investigated with an effective quark-antiquark potential of the form -αc/r +Ar νwith ν varying from 0.5 to 2.0. TheS andP-wave masses, pseudoscalar decay constant, weak decay partial widths in spectator model and the lifetime ofB cmeson are computed. The properties calculated here are found to be in good agreement with other theoretical and experimental values at potential index,ν = 1  相似文献   
46.
We report on the status of the LPCTrap experiment, devoted to measure the β–ν angular correlation in the pure Gamow–Teller decay of 6He. This measurement is motivated by the search for the presence of tensor type contributions to the weak interaction. The 6He ions are confined in a novel transparent Paul trap. The β particles and the recoil ions are detected in coincidence to deduce the angular correlation parameter. The commissioning run performed in 2005 has given the proof of principle of this experiment. Up to 105 coincidences were recorded during a second run in 2006.  相似文献   
47.
We prove equivalence of the definitions by the author and by Korevaar and Schoen of the Sobolev classes of mappings of a domain of an arithmetic n-dimensional space to a metric space.  相似文献   
48.
49.
A class of Cauchy problems for interesting complicated periodic pseudodifferential equations is considered. By the Galerkin-wavelet method and with weak solutions one can find sufficient conditions to establish convergence estimates of weak Galerkin-wavelet solutions to a Cauchy problem for this class of equations.

  相似文献   

50.
The signals of a single-pulse echo (SE) generated on nonresonant excitation of an inhomogeneously broadened two-level system by a radio-frequency pulse (RFP), against the background of which a magnetic video pulse (MVP) of certain length has been switched on, have been described analytically. It is established that under the conditions of such excitation several SE signals are formed whose generation moments are determined by the duration and amplitudes of the RFP and MVP. The amplitudes of some of these signals depend on the Rabi frequency according to a quadratic law, and the amplitudes of others depend on this frequency according to a biquadratic law. It has been established that the mechanism underlying the appearance of these signals is associated with zero beats arising as a result of superposition of the magnetization fluctuations at variable frequencies and at a frequency of detuning from resonance. It is shown that in the limiting case, where the RFP duration considerably exceeds the duration of the MVP or is comparable with it, the number of SE signals decreases to two. Theoretical results on the formation of SE and the dependence of the amplitude of these signals on the MVP amplitude agree with the experimental data on NMR pulsed signals in ferromagnetic materials.  相似文献   
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