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   31030篇
  免费   5572篇
  国内免费   3263篇
化学   21964篇
晶体学   349篇
力学   1801篇
综合类   136篇
数学   2983篇
物理学   12632篇
  2024年   135篇
  2023年   692篇
  2022年   1202篇
  2021年   1372篇
  2020年   1392篇
  2019年   1373篇
  2018年   1165篇
  2017年   1047篇
  2016年   1593篇
  2015年   1514篇
  2014年   1946篇
  2013年   2390篇
  2012年   2857篇
  2011年   2867篇
  2010年   1868篇
  2009年   1780篇
  2008年   1992篇
  2007年   1736篇
  2006年   1624篇
  2005年   1278篇
  2004年   974篇
  2003年   763篇
  2002年   756篇
  2001年   587篇
  2000年   467篇
  1999年   592篇
  1998年   511篇
  1997年   498篇
  1996年   491篇
  1995年   426篇
  1994年   342篇
  1993年   281篇
  1992年   279篇
  1991年   224篇
  1990年   202篇
  1989年   151篇
  1988年   92篇
  1987年   79篇
  1986年   104篇
  1985年   74篇
  1984年   37篇
  1983年   44篇
  1982年   28篇
  1981年   22篇
  1980年   7篇
  1979年   4篇
  1976年   1篇
  1975年   1篇
  1957年   4篇
  1923年   1篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
861.
Ping Zhao  Bo Xu  Mei Yang 《代数通讯》2013,41(3):1116-1121
Both maximal idempotent-generated subsemigroups and maximal idempotent-generated regular subsemigroups of O n were studied by Yang [10 Yang , X. , Lu , C. ( 2000 ). Maximal properties of some subsemigroups in finite order-preserving transformation semigroups . Communications in Algebra 28 : 31253135 .[Taylor &; Francis Online], [Web of Science ®] [Google Scholar]]. The purpose of this article is to simplify the results of Yang [10 Yang , X. , Lu , C. ( 2000 ). Maximal properties of some subsemigroups in finite order-preserving transformation semigroups . Communications in Algebra 28 : 31253135 .[Taylor &; Francis Online], [Web of Science ®] [Google Scholar]].  相似文献   
862.
Channel noise is often assumed to be Gaussian in most of the existing channel equalization algorithms. The performance of these algorithms will degrade seriously when the noise is non-Gaussian. This paper deals with the problem of blind channel equalization in impulsive noise environment that is modeled as α-stable process. A modified adaptive error-constrained constant modulus algorithm (MAECCMA) is proposed by soft-limiting the amplitude of the equalizer input and transforming the error signal of the original adaptive error-constrained constant modulus algorithm (AECCMA) nonlinearly to suppress the influence of α-stable noise. Computer simulation results of two underwater acoustic channels show that, MAECCMA has almost the same performance as AECCMA and they both have faster convergence rate than constant modulus algorithm (CMA) and normalized least mean absolute deviation (NLMAD) algorithm in Gaussian noise, while MAECCMA provides the best performance of those four algorithms in α-stable noise.  相似文献   
863.
We describe a protocol for generation of remote multi-photon entanglement using Einstein-Podolsky-Rosen (EPR) photon pairs via entanglement swapping. According to the requests of users, Quantum Switch (QS) can prepare three-photon W entangled states or Greenberger-Horne-Zeilinger (GHZ) states based on independent, spatially separated EPR pairs among three distant users. Only Bell states measurement (BSM) is needed utilizing a CPHASE gate and PAs. This protocol can also generate remote N-photon GHZ entangled states.  相似文献   
864.
Laser conditioning effects of the dielectric mirror coatings in vacuum environments were investigated. The laser-induced damage thresholds (LIDT) in vacuum environments before and after laser conditioning were compared. It is found that laser conditioning in vacuum environments decrease the LIDT of the component. Laser conditioning effects in vacuum and atmosphere environments were also compared and investigated. The negative effects of laser conditioning in vacuum environments were discussed and analyzed with defect statistical model, energy dispersive X-ray analysis and absorption measurements.  相似文献   
865.
High spin states of the odd-odd162Lu nucleus have been studied via147Sm(19F,4nγ)162Lu reaction at 95 MeV beam energy. Level scheme for yrast band based onπ[h11/2 v[i13/2] quasiparticle configuration was established up to I π = (23?) for the first time. This band shows the signature inversion in energy before backbending generally appeared in this mass region. It is stressed that the signature splitting in162Lu is larger than that in the160Tm nucleus.  相似文献   
866.
This paper is concerned with the traveling waves for a class of delayed reaction-diffusion equations with crossing-monostability. In the previous papers, we established the existence and uniqueness of traveling waves which may not be monotone. However, the stability of such traveling waves remains open. In this paper, by means of the (technical) weighted energy method, we prove that the traveling wave is exponentially stable, when the initial perturbation around the wave is relatively small in a weighted norm. As applications, we consider the delayed diffusive Nicholson??s blowflies equation in population dynamics and Mackey?CGlass model in physiology.  相似文献   
867.
周忠祥  万秋玉 《光学学报》1997,17(6):10-716
应用微扰展开法了“跳跃模型”给出了空间电荷场前三阶分量随时间,外加电场等变化的解析表达式,同时讨论了外加电场对各阶空间电荷场建立的影响,当扩散与外加电场可比拟时,外加电场对空间电荷场的影响不大,随着空间电荷场阶数的提高,其达到最大饱和值所需的外加电磁越小,在外加电场作用下,空间电荷场各阶分量随时间呈振荡衰减,直到达到饱和,外加是场越大,振荡越强烈,周期越短,在考虑高阶分量的贡献后,空间电荷场的振荡  相似文献   
868.
线性啁啾光纤光栅的数值分析   总被引:1,自引:2,他引:1  
李智红  杨秀峰 《光子学报》1997,26(10):911-914
本文利用耦合模方程对线性啾光纤光栅的反射谱进行了计算,并讨论了方程中各参数对计算结果的影响.  相似文献   
869.
本文利用毫微秒技术在ns秒量级测量了不同浓度组分的LaOBr:Ce3+,Tb3+中Ce3+发射带的衰减常数τCe值和时间分辨光谱,确立了Ce3到Tb3+能量传递过程模型,建立了动力学方程和导出能量传递的计算公式。据此计算出Ce3+到Tb3+的能量传递几率和效率,得出Ce3+,Tb3+的最佳浓度。  相似文献   
870.
Since the classical example of complex system is the quantum system which is one of the foci of ongoing research, in this paper, the issue of controllability and observability for a class of time-varying impulsive systems defined in complex fields, to be brief, complex time-varying impulsive systems, is addressed. Several sufficient and necessary conditions for state controllability and observability of such systems are established. Meanwhile, corresponding criteria for complex linear time-invariant impulsive systems are also obtained.  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