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   693896篇
  免费   8764篇
  国内免费   2467篇
化学   367729篇
晶体学   10464篇
力学   32114篇
综合类   19篇
数学   84784篇
物理学   210017篇
  2021年   5390篇
  2020年   6087篇
  2019年   6624篇
  2018年   8359篇
  2017年   8178篇
  2016年   12805篇
  2015年   8361篇
  2014年   12700篇
  2013年   31902篇
  2012年   24264篇
  2011年   30152篇
  2010年   20814篇
  2009年   20699篇
  2008年   27401篇
  2007年   27319篇
  2006年   25610篇
  2005年   23116篇
  2004年   21338篇
  2003年   18703篇
  2002年   18603篇
  2001年   20589篇
  2000年   15758篇
  1999年   12436篇
  1998年   10301篇
  1997年   10061篇
  1996年   9755篇
  1995年   8841篇
  1994年   8596篇
  1993年   8454篇
  1992年   9274篇
  1991年   9376篇
  1990年   8915篇
  1989年   8759篇
  1988年   8772篇
  1987年   8557篇
  1986年   8081篇
  1985年   10826篇
  1984年   11147篇
  1983年   8966篇
  1982年   9327篇
  1981年   9163篇
  1980年   8653篇
  1979年   9176篇
  1978年   9423篇
  1977年   9277篇
  1976年   9259篇
  1975年   8649篇
  1974年   8609篇
  1973年   8674篇
  1972年   6011篇
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
61.
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   
62.
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   
63.
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   
64.
Crystallography Reports - Some questions related to the establishment, development, and prospects of physical studies using inelastic thermal-neutron scattering are briefly reviewed. The directions...  相似文献   
65.
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   
66.
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   
67.
Crystallography Reports - Methods of coherent X-ray diffraction imaging of the spatial structure of noncrystalline objects and nanocrystals (nanostructures) are considered. Particular attention is...  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