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   506499篇
  免费   5529篇
  国内免费   1244篇
化学   254599篇
晶体学   6480篇
力学   24156篇
综合类   13篇
数学   70275篇
物理学   157749篇
  2021年   3683篇
  2020年   4184篇
  2019年   4519篇
  2018年   12402篇
  2017年   12932篇
  2016年   11901篇
  2015年   6201篇
  2014年   8641篇
  2013年   20279篇
  2012年   18924篇
  2011年   28657篇
  2010年   19067篇
  2009年   18979篇
  2008年   25863篇
  2007年   28380篇
  2006年   16405篇
  2005年   19814篇
  2004年   16187篇
  2003年   14597篇
  2002年   12873篇
  2001年   13562篇
  2000年   10330篇
  1999年   7944篇
  1998年   6561篇
  1997年   5902篇
  1996年   5750篇
  1995年   5396篇
  1994年   5359篇
  1993年   5142篇
  1992年   5757篇
  1991年   5862篇
  1990年   5612篇
  1989年   5424篇
  1988年   5454篇
  1987年   5368篇
  1986年   5043篇
  1985年   6556篇
  1984年   6702篇
  1983年   5309篇
  1982年   5400篇
  1981年   5380篇
  1980年   4956篇
  1979年   5395篇
  1978年   5534篇
  1977年   5374篇
  1976年   5354篇
  1975年   4923篇
  1974年   4893篇
  1973年   4932篇
  1972年   3469篇
排序方式: 共有10000条查询结果,搜索用时 68 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