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   595篇
  免费   13篇
化学   269篇
力学   14篇
数学   125篇
物理学   200篇
  2022年   3篇
  2021年   5篇
  2020年   4篇
  2019年   4篇
  2018年   5篇
  2017年   4篇
  2016年   4篇
  2015年   14篇
  2014年   11篇
  2013年   22篇
  2012年   26篇
  2011年   35篇
  2010年   24篇
  2009年   20篇
  2008年   22篇
  2007年   23篇
  2006年   29篇
  2005年   35篇
  2004年   29篇
  2003年   16篇
  2002年   23篇
  2001年   16篇
  2000年   25篇
  1999年   11篇
  1998年   9篇
  1997年   10篇
  1996年   15篇
  1995年   9篇
  1994年   16篇
  1993年   14篇
  1992年   11篇
  1991年   3篇
  1990年   4篇
  1989年   3篇
  1987年   8篇
  1985年   10篇
  1984年   7篇
  1982年   6篇
  1981年   8篇
  1980年   6篇
  1979年   5篇
  1978年   14篇
  1977年   8篇
  1976年   4篇
  1975年   3篇
  1974年   5篇
  1973年   3篇
  1972年   3篇
  1970年   3篇
  1968年   3篇
排序方式: 共有608条查询结果,搜索用时 125 毫秒
1.
Using the symbolic computation program MAPLE, we compute several terms of an asymptotic expansion for the distribution function of the logistic midrange.  相似文献   
2.
The European Physical Journal C - We discuss possible searches for the new particles predicted by Little Higgs Models at the LHC. By using a simulation of the ATLAS detector, we demonstrate how the...  相似文献   
3.
This article describes a professional development course intended to improve the content understanding of middle school mathematics teachers. The design of the course included three professional learning strategies: problem solving, examination of student thinking, and discussion of research. The concepts studied in the course included multi‐digit subtraction, multi‐digit multiplication, operations with fractions, and concepts of area and perimeter. Results from pre‐ and post‐tests administered to the nineteen participants indicate a significant increase in the mean score for each concept and document growth in the teachers' content understanding. In particular, their solutions moved from primarily procedural to more conceptual. Responses to an open‐ended survey indicate other important aspects of the professional development. Examples of teachers' work and comments are included.  相似文献   
4.
The reaction of various alcohols with N-fluorodibenzenesulfonimide and triphenylphosphine leads to the corresponding dibenzenesulfonylated amines in high yields.  相似文献   
5.
The local structure of Tm3+ ions incorporated into GaN epilayers was studied by means of Extended X-ray Absorption Fine Structure. The samples were doped either in situ during growth by Molecular Beam Epitaxy or by ion implantation of layers grown by Metal Organic Chemical Vapour Deposition. The implantation was done at ion energy of 300 keV and different nominal fluences of 3×1015, 4×1015 cm−2 and 5×1015 cm−2. The concentration of Tm in the samples studied was measured by Wavelength Dispersive X-ray analysis. For the in situ doped sample with concentration of 0.5%, and for all of the implanted samples, Tm was found on the Ga site in GaN. The ion implanted sample and an in situ doped sample with a similar concentration of Tm showed the same local structure, which suggests that the lattice site occupied by Tm does not depend on the doping method. When the average Tm concentration for in situ doped samples is increased to 1.2% and 2.0%, Tm is found to occupy the Ga substitutional site and the presence of a substantial number of Tm ions in the second coordination sphere indicates dopant clustering in the films. The formation of pure TmN clusters was found in an in situ doped sample with a dopant concentration of 3.4%.  相似文献   
6.
We have studied the optical properties of Eu doped GaN thin films. We have grown high quality Eu doped GaN thin films by using Gas Source Molecular Beam Epitaxy (GSMBE), with 1.4% Eu concentration. The Full Width at Half Maximum (FWHM) of the X-ray diffraction in an omega scan was found to be 288 arcsecs. Low Eu concentration (0.08%) doped GaN thin films were grown, where Eu-related photoluminescence at 622 and 613 nm was detected using above band-gap excitation at 2 K. For high Eu concentration of 30% GaN:Eu crystal photoluminescence (PL) and cathodoluminescence (CL) spectra show strong and intense transitions at 622 and 664 nm, but also at 593 nm for CL spectra, with a similar transition observed from the low Eu concentration sample.  相似文献   
7.
8.
9.
We report simultaneous observation of coherent resonance Raman scattering and incoherently broadened resonance fluorescence following excitation of cytochrome c in the α(0, 0) region. The influence of incoherent broadening processes on resonance Raman scattering experiments is considered.  相似文献   
10.
[reaction: see text] The Cp(2)TiCl-mediated deoxygenation of leurosine (1) afforded anhydrovinblastine (4) in good yield. Furthermore, as the reaction proceeded via a carbon-centered radical intermediate, this transient was also trapped by a hydrogen-atom donor to afford selectively reduced alkaloid 10.  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