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   542421篇
  免费   11943篇
  国内免费   5521篇
化学   279841篇
晶体学   6974篇
力学   26506篇
综合类   298篇
数学   74620篇
物理学   171646篇
  2021年   4881篇
  2020年   5622篇
  2019年   5878篇
  2018年   13590篇
  2017年   14029篇
  2016年   13584篇
  2015年   7855篇
  2014年   10682篇
  2013年   22839篇
  2012年   22018篇
  2011年   31879篇
  2010年   21302篇
  2009年   21169篇
  2008年   28229篇
  2007年   30484篇
  2006年   18446篇
  2005年   21369篇
  2004年   17439篇
  2003年   15654篇
  2002年   13848篇
  2001年   14329篇
  2000年   11149篇
  1999年   8729篇
  1998年   7317篇
  1997年   6991篇
  1996年   6399篇
  1995年   5998篇
  1994年   5874篇
  1993年   5560篇
  1992年   6163篇
  1991年   6179篇
  1990年   5906篇
  1989年   5657篇
  1988年   5656篇
  1987年   5535篇
  1986年   5191篇
  1985年   6703篇
  1984年   6801篇
  1983年   5379篇
  1982年   5458篇
  1981年   5416篇
  1980年   4972篇
  1979年   5405篇
  1978年   5534篇
  1977年   5376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 312 毫秒
51.
Xu  Mengtao  Li  Changyou  Sun  Yang  Yang  Tianzhi  Zhang  Hongzhuang  Liu  Zhendong  Liu  Haiyang  Li  Zhenyuan  Zhang  Yimin 《Nonlinear dynamics》2021,105(4):3061-3092
Nonlinear Dynamics - Investigation of the dynamic characteristics of linear guideway is essential for enhancing structural performance of machine tools. However, few mechanical models are...  相似文献   
52.
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   
53.
Du  Zhong  Xu  Tao  Ren  Shuai 《Nonlinear dynamics》2021,104(1):683-689
Nonlinear Dynamics - In this paper, we investigate the interactions of the vector breathers for the coupled Hirota system with $$4\times 4$$ Lax pair. Firstly, we give the first-order breather...  相似文献   
54.
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   
55.
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   
56.
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   
57.
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   
58.
59.
60.
An electromechanical integrated electrostatic harmonic actuator is promising for the miniaturization of electromechanical devices. As the dimensions of the actuator decrease, the effects of the van der Waals force become obvious. In this study, by considering the nonlinearity of electrostatic and van der Waals forces, nonlinear vibration equations of the flexible ring of an electrostatic harmonic actuator are deduced. Using these equations, the nonlinear free vibration and nonlinear forced response of the actuator are investigated. The effects of the van der Waals force on the nonlinear vibration of the flexible ring are analyzed. Results show that these effects of the van der Waals force are relatively obvious under some conditions and should be considered.  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