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   1459506篇
  免费   26047篇
  国内免费   7875篇
化学   745013篇
晶体学   20831篇
力学   77116篇
综合类   107篇
数学   250279篇
物理学   400082篇
  2021年   13686篇
  2020年   16079篇
  2019年   16197篇
  2018年   15751篇
  2017年   14089篇
  2016年   29481篇
  2015年   21278篇
  2014年   30753篇
  2013年   74980篇
  2012年   44347篇
  2011年   46241篇
  2010年   40887篇
  2009年   42200篇
  2008年   43594篇
  2007年   40559篇
  2006年   43202篇
  2005年   37125篇
  2004年   36468篇
  2003年   33391篇
  2002年   33577篇
  2001年   34290篇
  2000年   28456篇
  1999年   24305篇
  1998年   21735篇
  1997年   21615篇
  1996年   21515篇
  1995年   19533篇
  1994年   18992篇
  1993年   18611篇
  1992年   19269篇
  1991年   19438篇
  1990年   18623篇
  1989年   18615篇
  1988年   18172篇
  1987年   18057篇
  1986年   17024篇
  1985年   23389篇
  1984年   24348篇
  1983年   20368篇
  1982年   21939篇
  1981年   21123篇
  1980年   20476篇
  1979年   20973篇
  1978年   22042篇
  1977年   21727篇
  1976年   21559篇
  1975年   20265篇
  1974年   19970篇
  1973年   20394篇
  1972年   14861篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
The Clauser–Horne approach used to derive experimentally measurable quantities for performing experiments on EPR paradox based on Type-I Spontaneous Parametric Down Conversion (SPDC) sources is discussed. It is proved that in this case the deduced Bell's type inequality does not correctly express separability and causality. A deeper analysis of the problem shows that the Clauser–Horne hypothesis of factorizability of joint detection probability cannot be considered so general as to describe this physical situation.  相似文献   
992.
The spectrum and the spatial distribution of the emission of scattered particles upon bombardment of Be, Ti, Ta, and W with H and He ions were studied. The quantum yield and the velocity and angular distributions of the scattered excited particles were measured. Computer simulation of the scattering of H ions and He ions from the metals under study was performed with the use of the program TRIM-95. Agreement is observed between the calculated and experimentally measured angular distributions of the scattered particles.  相似文献   
993.
The results of investigations of the rheological characteristics and electrical resistance of the suspensions of carbon black in vaseline oil under the effects of shear and vibration were presented. The investigations are carried out on an original unit that allowed one to simultaneously subject the suspensions to shear deformation and orthogonal vibration. The electrical resistance was also measured in an ac pulsed low-voltage mode. Possible mechanisms of the suspension conductivity were considered depending on the regime of dynamic action.  相似文献   
994.
995.
Feel like writing a review for The Mathematical Intelligencer? You are welcome to submit an unsolicited review of a book of your choice; or, if you would welcome being assigned a book to review, please write us, telling us your expertise and your predilections.  相似文献   
996.
997.
Relationships between Gaussian beams and geometry are considered in the paper. We show that the main properties of the Gaussian beam solutions are determined by the natural geometry related to the problem under consideration. The geometry is determined by the Hamilton-Jacobi equation and the corresponding Hamiltonian. In particular, we find a geometric interpretation of the Riccati equation for the quadratic form of the phase function corresponding to a Gaussian beam in the case of Finsler geometry. Bibliography: 2 titles.__________Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 297, 2003, pp. 66–92.  相似文献   
998.
There is growing interest in the use of lidar for remote sensing of vegetation owing to the emergence of reliable and rugged lasers and highly sensitive detectors. Lidar remote sensing has a distinct advantage over conventional techniques in vegetation remote sensing due to its capability for three-dimensional characterization of vegetative targets. The Multiwavelength Airborne Polarimetric Lidar (MAPL) system was developed primarily for vegetation remote sensing applications from an airborne platform of up to 1,000 -m altitude. The lidar system has full waveform capture and polarimetric measurement capability at two wavelengths in the near-infrared (1064 nm) and the green (532 nm) spectral regions. This study presents preliminary ground-based lidar reflectance measurements on a variety of deciduous and coniferous trees under fully foliated conditions with a view towards tree species discrimination. Variations in the reflectance characteristics of selected deciduous trees under unfoliated and fully foliated conditions were also investigated. Our study reveals distinct differences in the reflectance characteristics of various trees.  相似文献   
999.
The time average holography measurements of the vibrating microelectromechanical switch (MEMS) were performed in this study. Experimental measurement results exhibit good agreement with computer generated holographic interferogram analysis. The validation of experimental investigations versus numerical analysis provides the necessary background to analyze the dynamical characteristics of micromechanical systems in virtual numerical environments. Direct application of fringe counting techniques for reconstruction of motion from time average holograms cannot be straightforward if the analyzed micromechanical systems contain motion limiters. Modifications of a classical time average holographic technique enable qualitative analysis of MEMS and can be applied for investigation of dynamical properties of much broader classes of MEMS systems.  相似文献   
1000.
The anisotropic g-values of defects in hydrogenated microcrystalline silicon prepared by hot-wire chemical vapour deposition have been measured as a function of crystalline volume fraction at room temperature. The defect has been identified as a silicon-dangling bond existing on the surface of crystalline grain. Their anisotropic g-values are discussed in the light of theoretical calculations by Ishii et al. and Ishii and Shimizu. The defect density is also discussed as a function of crystalline volume fraction.  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