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   631451篇
  免费   6593篇
  国内免费   1605篇
化学   318744篇
晶体学   9408篇
力学   31464篇
综合类   22篇
数学   86137篇
物理学   193874篇
  2021年   5004篇
  2020年   5411篇
  2019年   6134篇
  2018年   13300篇
  2017年   13616篇
  2016年   14388篇
  2015年   7583篇
  2014年   11432篇
  2013年   26141篇
  2012年   22781篇
  2011年   31944篇
  2010年   22206篇
  2009年   22304篇
  2008年   29324篇
  2007年   31207篇
  2006年   20789篇
  2005年   22372篇
  2004年   19178篇
  2003年   17486篇
  2002年   16175篇
  2001年   17042篇
  2000年   13042篇
  1999年   10046篇
  1998年   8323篇
  1997年   8166篇
  1996年   7937篇
  1995年   7104篇
  1994年   7073篇
  1993年   6817篇
  1992年   7622篇
  1991年   7800篇
  1990年   7430篇
  1989年   7313篇
  1988年   7284篇
  1987年   7153篇
  1986年   6761篇
  1985年   8737篇
  1984年   8961篇
  1983年   7210篇
  1982年   7302篇
  1981年   7224篇
  1980年   6702篇
  1979年   7364篇
  1978年   7498篇
  1977年   7477篇
  1976年   7446篇
  1975年   6870篇
  1974年   6772篇
  1973年   6952篇
  1972年   5010篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
61.
Physics of the Solid State - The external factors which influence the ferromagnetic resonance (FMR) line width in bilayer (ferromagnet/antiferromagnet) exchange-biased systems are studied. The...  相似文献   
62.
Crystallography Reports - The orientation of grains and the special boundaries formed by them in multicrystalline silicon has been studied by electron backscattered diffraction. It is found that...  相似文献   
63.
Theoretical and Mathematical Physics - The fractional derivative method is used to take wave dispersion into account in the wave equation when describing the propagation of gravitational soliton...  相似文献   
64.
Crystallography Reports - The specific features of the formation of crystallites in gallium arsenide crystals grown by the Czochralski method have been investigated. The crystallites are found to...  相似文献   
65.
A facile biosynthesis route was followed to prepare zinc oxide nanoparticles (ZnO NPs) using Euphorbia milii (E. milii) leaf constituents. The SEM images exhibited presence of spherical ZnO NPs and the corresponding TEM images disclosed monodisperse nature of the ZnO NPs with diameter ranges between 12 and 20 nm. The Brunauer–Emmett–Teller (BET) analysis revealed that the ZnO NPs have specific surface area of 20.46 m2/g with pore diameter of 2 nm–10 nm and pore volume of 0.908 cm3/g. The EDAX spectrum exemplified the existence of Zn and O elements and non-appearance of impurities that confirmed pristine nature of the ZnO NPs. The XRD pattern indicated crystalline peaks corresponding to hexagonal wurtzite structured ZnO with an average crystallite size of 16.11 nm. The FTIR spectrum displayed strong absorption bands at 512 and 534 cm?1 related to ZnO. The photocatalytic action of ZnO NPs exhibited noteworthy degradation of methylene blue dye under natural sunlight illumination. The maximum degradation efficiency achieved was 98.17% at an illumination period of 50 min. The reusability study proved considerable photostability of the ZnO NPs during photocatalytic experiments. These findings suggest that the E. milii leaf constituents can be utilized as suitable biological source to synthesis ZnO NPs for photocatalytic applications.  相似文献   
66.
67.
Journal of Applied and Industrial Mathematics - We study the problem of optimal location of the ambulance fleet at the base stations. The objective is to minimize the average waiting time for...  相似文献   
68.
69.
70.
Triene 6π electrocyclization, wherein a conjugated triene undergoes a concerted stereospecific cycloisomerization to a cyclohexadiene, is a reaction of great historical and practical significance. In order to circumvent limitations imposed by the normally harsh reaction conditions, chemists have long sought to develop catalytic variants based upon the activating power of metal–alkene coordination. Herein, we demonstrate the first successful implementation of such a strategy by utilizing [(C5H5)Ru(NCMe)3]PF6 as a precatalyst for the disrotatory 6π electrocyclization of highly substituted trienes that are resistant to thermal cyclization. Mechanistic and computational studies implicate hexahapto transition-metal coordination as responsible for lowering the energetic barrier to ring closure. This work establishes a foundation for the development of new catalysts for stereoselective electrocyclizations.  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