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   634篇
  免费   44篇
  国内免费   83篇
化学   325篇
晶体学   7篇
力学   44篇
数学   38篇
物理学   148篇
综合类   199篇
  2023年   8篇
  2022年   11篇
  2021年   9篇
  2020年   24篇
  2019年   12篇
  2018年   13篇
  2017年   6篇
  2016年   17篇
  2015年   21篇
  2014年   26篇
  2013年   26篇
  2012年   37篇
  2011年   56篇
  2010年   28篇
  2009年   29篇
  2008年   34篇
  2007年   25篇
  2006年   24篇
  2005年   31篇
  2004年   26篇
  2003年   21篇
  2002年   32篇
  2001年   30篇
  2000年   19篇
  1999年   16篇
  1998年   18篇
  1997年   15篇
  1996年   24篇
  1995年   12篇
  1994年   7篇
  1993年   13篇
  1992年   11篇
  1991年   6篇
  1990年   11篇
  1989年   14篇
  1988年   13篇
  1987年   11篇
  1986年   7篇
  1985年   4篇
  1984年   1篇
  1983年   3篇
  1982年   2篇
  1981年   1篇
  1979年   2篇
  1977年   3篇
  1975年   1篇
  1969年   1篇
排序方式: 共有761条查询结果,搜索用时 125 毫秒
51.
In this paper we analyse the vibrations of an N-stepped Rayleigh bar with sections of complex geometry, supported by end lumped masses and springs. Equations of motion and boundary conditions are derived from the Hamilton’s variational principal. The solutions for tapered and exponential sections are given. Two types of orthogonality for the eigenfunctions are obtained. The analytic solution to the N-stepped Rayleigh model is constructed in terms of Green function.  相似文献   
52.
盖明媚 《科技信息》2008,(21):57-57
介绍了FAST公司研制推广使用的企业搜索技术、相关搜索技术及其在不同企业的应用。FASTESP向用户安全提供了结构、非结构与多媒体数据检索点.为新的智能检索建立新的标准。所具备的上下文识别、可测量性和制订解决方案的超级性能极大程度地改变着公司从事贸易的活动方式,同时也改变了用户的搜索信息方式。  相似文献   
53.
The optimum operating parameters of miniature OPFIRL was studied theoretically and experimentally. The theoretical results were in pretty good agreement with experimental results except for 1.5cm laser. The transverse feedback effect plays an important role in the miniature OPFIRL. it's worthv to be funther studied.  相似文献   
54.
An effective solvothermal reaction route has been developed for large-scale synthesis of CdS nanowires. L-cysteine was used as both sulfur source and capping reagent. The nanowires obtained were characterized by XRD, SEM, TEM, HRTEM, UV-Vis and PL. On the basis of time-resolved experiments, a possible growth mechanism was proposed. FTIR analysis confirmed the formation of Cd-cysteine complex and peptide during the reaction. The mechanism was further supported by comparative experiments with other sulfur sources. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users. PACS 81.05.Bx; 81.07.-b; 81.07.BC; 81.07.Vb; 81.10.Dn  相似文献   
55.
The degradation of azobenzene (AO) by a gaseous plasma is reported. The plasma was generated in a localized zone between an electrolytic solution and a tip of an anode in contact with the surface of solution by means of contact glow discharge electrolysis. There is an optimum pH for the degradation of AO. Iron (II) had a remarkable catalytic action on it. Furthermore, the degradation followed the first‐order kinetic law. Some of the intermediate products of the degradation process were detected by HPLC.  相似文献   
56.
中文文本压缩的LZW算法   总被引:8,自引:0,他引:8  
本文报告两个关于中文信息处理研究的结果:(1)采用Cover的方法,猜估中文信息熵,实验表明,中文信良熵不大于4.1bits/字。(2)根据中文的结构特性,选择Welch型的Lemple-Ziv数据压缩算法,把它移植、扩展于中文文本压缩上。应用该算法于不同类型的中文文本,本文获得一些中文文本压缩实际性能值。  相似文献   
57.
58.
<正>Tetracycline selective electrode using molecularly imprinted polymer particles as quasi-ionophore was constructed the first time, and its performance was carefully characterized.Due to the specific recognition of tetracycline by the particles,the selectivity coefficients for routine interferences were less than 10~(-4).Benefited from the absence of tetracycline in the sensitive membrane and the optimized composition of the inner filling solution,the limit of detection of the electrode was reduced to about 2.5×10~(-8) mol/ L.It exhibited a good electrode slope 57.6 mV/decade near the theoretical Nernstian one,with a wide linear working range from 6.0×10~(-8) to 1.0×10~(-3) mol/L.The fabricated electrode should be used in pH 2-4,response time of which was less than 200 s when the concentration of tetracycline was higher than 1.0×10~(-6) mol/L and no more than 30 min at the concentration of 1.0×10~(-8) mol/L.  相似文献   
59.
Generation of short-wavelength radiation by a free-electron laser using up-frequency conversion of an electron bunch density modulation is currently an area of active research. We propose a new scheme for producing the longitudinal electron bunch density modulation similar to the recently proposed echo-enabled harmonic generation but based on an emittance exchange beam line and a multislit mask. Beam line analysis and start-to-end simulation are presented.  相似文献   
60.
In strongly correlated electronic systems, the global transport behavior depends sensitively on spin ordering. We show that spin ordering in manganites can be controlled by depositing isolated ferromagnetic nanodots at the surface. The exchange field at the interface is tunable with nanodot density and makes it possible to overcome dimensionality and strain effects in frustrated systems to greatly increasing the metal-insulator transition and magnetoresistance. These findings indicate that electronic phase separation can be controlled by the presence of magnetic nanodots.  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