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   562827篇
  免费   5840篇
  国内免费   1600篇
化学   270515篇
晶体学   6904篇
力学   29084篇
综合类   13篇
数学   95632篇
物理学   168119篇
  2021年   3725篇
  2020年   4185篇
  2019年   4522篇
  2018年   20251篇
  2017年   20524篇
  2016年   16448篇
  2015年   6833篇
  2014年   8874篇
  2013年   20498篇
  2012年   21480篇
  2011年   35899篇
  2010年   23059篇
  2009年   23338篇
  2008年   30412篇
  2007年   34374篇
  2006年   16559篇
  2005年   20703篇
  2004年   17301篇
  2003年   16097篇
  2002年   13633篇
  2001年   13738篇
  2000年   10544篇
  1999年   8058篇
  1998年   6750篇
  1997年   6329篇
  1996年   5876篇
  1995年   5484篇
  1994年   5414篇
  1993年   5212篇
  1992年   5795篇
  1991年   5906篇
  1990年   5647篇
  1989年   5463篇
  1988年   5498篇
  1987年   5410篇
  1986年   5085篇
  1985年   6592篇
  1984年   6729篇
  1983年   5342篇
  1982年   5436篇
  1981年   5409篇
  1980年   4993篇
  1979年   5422篇
  1978年   5560篇
  1977年   5391篇
  1976年   5363篇
  1975年   4934篇
  1974年   4899篇
  1973年   4946篇
  1972年   3484篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Crystallography Reports - Electron backscattered diffraction (EBSD) has been used to analyze structures of natural minerals and artificial compounds for almost three decades. In recent years, it is...  相似文献   
42.
Optical and Quantum Electronics - Classification of hyperspectral image (HSI) is widely used for the study of remotely sensed images. Convolutional Neural Networks (CNNs) are one of the most...  相似文献   
43.
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   
44.
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   
45.
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   
46.
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   
47.
48.
49.
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   
50.
Russian Physics Journal - A relationship between the structural-morphological and physical-mechanical properties of macro-porous calcium phosphate (CaP) coatings on the surface of titanium implants...  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