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   291826篇
  免费   25610篇
  国内免费   17698篇
化学   159078篇
晶体学   4324篇
力学   14656篇
综合类   26篇
数学   35848篇
物理学   121202篇
  2021年   2330篇
  2020年   2748篇
  2019年   3556篇
  2018年   4190篇
  2017年   4721篇
  2016年   6180篇
  2015年   4851篇
  2014年   6090篇
  2013年   14041篇
  2012年   12223篇
  2011年   15342篇
  2010年   14849篇
  2009年   14842篇
  2008年   12126篇
  2007年   11848篇
  2006年   11206篇
  2005年   10735篇
  2004年   11023篇
  2003年   9376篇
  2002年   9050篇
  2001年   9608篇
  2000年   7312篇
  1999年   6326篇
  1998年   5261篇
  1997年   5124篇
  1996年   5233篇
  1995年   5329篇
  1994年   5296篇
  1993年   5233篇
  1992年   5151篇
  1991年   4780篇
  1990年   4354篇
  1989年   4315篇
  1988年   4357篇
  1987年   3668篇
  1986年   3542篇
  1985年   4056篇
  1984年   4441篇
  1983年   3249篇
  1982年   3979篇
  1981年   3765篇
  1980年   3633篇
  1979年   3474篇
  1978年   3595篇
  1977年   3642篇
  1976年   4061篇
  1975年   3080篇
  1974年   3043篇
  1973年   3371篇
  1972年   2350篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Understanding and control of the surface properties such as molecular orientations are of great importance in numerous applications of ionic liquids. However, there remain discrepancies among the previous experimental and theoretical studies on the surface orientation and structures of room temperature ionic liquids(RTIL) systems. In this article, the orientation of 1-butyl-3-methylimidazolium([bmin]) cation at the air/liquid interface of a characteristic RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate([bmim][PF6]), was investigated by the sum frequency generation vibrational spectroscopy(SFG-VS). Detailed polarization and experimental configuration analyses of the SFG-VS spectra showed the possibility of a small spectral splitting in the CH3 symmetric stretching region, which can be further attributed to the probable existence of multiple orientations for the interfacial [bmim] cations. In addition, the(N)–CH3 vibrations were absent, ruling out the prediction by several recent molecular dynamics simulations which state that portions of the [bmim] cations orient with a standing-up(N)–CH3 group at the ionic liquid surface. Hence, new realistic theoretical models have to be developed to reflect the complex nature of the ionic liquid surface.  相似文献   
92.
93.
94.
95.
Radiophysics and Quantum Electronics - We present the results of comparing the total electron content measurements based on GLONASS satellite signals and the EISCAT UHF incoherent scatter radar...  相似文献   
96.
Thin films (monolayer and bilayer) of cylinder forming polystyrene‐block‐polydimethylsiloxane (PS‐b‐PDMS) were shear aligned by the swelling and deswelling of a crosslinked PDMS pad that was physically adhered to the film during solvent vapor annealing. The nanostructures formed by self‐assembly were exposed to ultraviolet‐ozone to partially oxidize the PDMS, followed by calcination in air at 500 °C. In this process, the PS segments were fully decomposed, while the PDMS yielded silica nanostructures. The highly aligned PDMS cylinders were thus deposited as silica nanolines on the silicon substrate. Using a bilayer film, the center‐to‐center distance of these features were effectively halved from 38 to 19 nm. Similarly, by sequential shear‐alignment of two distinct layers, a rhombic array of silica nanolines was fabricated. This methodology provides a facile route to fabricating complex topographically patterned nanostructures. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1058–1064  相似文献   
97.
98.
Algebras and Representation Theory - We would like to correct two errors in our paper Involutions of type G2 over a field of characteristic 2 [2].  相似文献   
99.
Methods for phase stabilization of ammonium nitrate were sought for in order to considerably expand the application area of this oxidizing agent in various-purpose self-combustible formulations, including that in a new generation of gas-generating formulations for automobile air bags. New methods for stabilization of ammonium nitrate were studied and, in particular, a search was made for organic compounds that can stabilize ammonium nitrate even at their low content. The mechanism of phase state stabilization of ammonium nitrate by compounds of this kind was examined.  相似文献   
100.
Summary Carbon deposits on the surface ofRu/Fe2O3 catalysts used in the water-gas shift reaction have been investigated by Auger Electron Spectrometry. A correlation has been found between the thickness of the carbon deposit and the catalytic activity in WGSR. The carbon deposit covers the metallic active centers and blocks their contact with reagents. The dotting of the iron oxide support with sodium has been found to reduce the amount of carbon deposit. .   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