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   1327篇
  免费   44篇
  国内免费   11篇
化学   778篇
晶体学   50篇
力学   21篇
数学   67篇
物理学   277篇
无线电   189篇
  2023年   13篇
  2022年   35篇
  2021年   44篇
  2020年   41篇
  2019年   39篇
  2018年   39篇
  2017年   26篇
  2016年   47篇
  2015年   30篇
  2014年   44篇
  2013年   95篇
  2012年   78篇
  2011年   72篇
  2010年   55篇
  2009年   54篇
  2008年   79篇
  2007年   65篇
  2006年   40篇
  2005年   40篇
  2004年   35篇
  2003年   31篇
  2002年   26篇
  2001年   30篇
  2000年   47篇
  1999年   58篇
  1998年   15篇
  1997年   9篇
  1996年   10篇
  1995年   8篇
  1994年   8篇
  1993年   10篇
  1992年   7篇
  1991年   9篇
  1990年   6篇
  1989年   7篇
  1987年   5篇
  1986年   8篇
  1985年   15篇
  1984年   10篇
  1983年   5篇
  1982年   7篇
  1980年   9篇
  1979年   11篇
  1978年   3篇
  1977年   13篇
  1976年   6篇
  1975年   4篇
  1974年   5篇
  1973年   4篇
  1972年   4篇
排序方式: 共有1382条查询结果,搜索用时 203 毫秒
61.
62.
This paper presents an analysis of diffraction effects taking place at different Schlieren diffracting elements. Two types of diffraction effects are prominent in the Schlieren schemes. One is diffraction of direct light (source image) at the Schlieren element, which limits the sensitivity and resolution of Schlieren systems. The second type is the diffraction of light deflected from the test object at the Schlieren-diffracting element. This second type of diffraction degrades the quality of Schlieren results. Experimental results showing the effect of diffraction of light deflected from the test object at a phase knife-edge, corner of a square phase aperture and an optical fiber tip as Schlieren diffracting elements have been presented and discussed.   相似文献   
63.
We study spectral distortions of diffuse ultra-high energy (UHE) neutrino flavour fluxes resulting due to physics beyond the Standard Model (SM). Even large spectral differences between flavours at the source are massaged into a common shape at earth by SM oscillations, thus, any significant observed spectral differences are an indicator of new physics present in the oscillation probability during propagation. Lorentz symmetry violation (LV) and neutrino decay are examples, and result in significant distortion of the fluxes and of the well-known bounds on them, which may allow UHE detectors to probe LV parameters, lifetimes and the mass hierarchy over a broad range.  相似文献   
64.
65.
66.
Base free Fe(CO)5 catalyzed one-pot synthesis of E/Z alkyl 3-formyl-3-alkyl/aryl/ferrocenyl-2-propenoates (retinoid esters) was achieved by the photolysis of alcoholic solution of terminal acetylenes and carbon monoxide. 8–10 Mol% of ironpentacarbonyl was used as a catalyst for significant transformations of retinoid esters. During the photolysis, alkynes reduced by the simultaneous double functionalization esterification and formylation and resulted in regioselective E/Z isomers of alkyl 3-formyl-3-alkyl/aryl/ferrocenyl-2-propenoates. The bi-functionalization of acetylene is quite unusual and is not observed frequently. The highest yield of the retinoid esters was achieved with 3° alcohols (96%, for E and Z isomers) while the least yield was observed with 1° alcohols (25%, for E and Z isomers). All retinoid esters are regiospecific and have exceptional biological significance to serve as key structural motifs in drug and pharmaceutical applications.  相似文献   
67.
68.
A bibliography on research work related to nullors and their applications in circuit analysis, synthesis and design, covering the period 1961–2000, is given.  相似文献   
69.
We provide experimental evidence for stretching and collapse of neutral polymer layers, already adsorbed at an oil-in-water interface, due to its interaction with surfactants. Upon stretching, the first interaction length (2L(0)) follows a power law dependence on surfactant concentration ( proportional, variant C(x)(s), where x approximately 0.5 for cationic surfactants) and collapses in the presence of salt, as a relatively weak power law (C(-y)(s), where y=0.17), in good agreement with brush length decay for polyelectrolyte brushes.  相似文献   
70.
Summary A random coefficient model in which means of random coefficients are subject to a set of linear stochastic constraints is considered and estimators for the means of coefficients are proposed. Their asymptotic properties are presented and some remarks on efficiency are placed.  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