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   350篇
  免费   15篇
化学   233篇
晶体学   8篇
力学   9篇
数学   15篇
物理学   100篇
  2022年   3篇
  2020年   2篇
  2019年   2篇
  2018年   3篇
  2017年   3篇
  2016年   10篇
  2015年   13篇
  2014年   4篇
  2013年   9篇
  2012年   23篇
  2011年   11篇
  2010年   12篇
  2009年   8篇
  2008年   19篇
  2007年   17篇
  2006年   24篇
  2005年   15篇
  2004年   13篇
  2003年   17篇
  2002年   12篇
  2001年   7篇
  2000年   9篇
  1999年   7篇
  1997年   6篇
  1996年   7篇
  1995年   6篇
  1994年   8篇
  1993年   12篇
  1992年   9篇
  1991年   2篇
  1989年   2篇
  1988年   7篇
  1987年   2篇
  1986年   3篇
  1985年   3篇
  1984年   5篇
  1983年   3篇
  1982年   6篇
  1981年   3篇
  1980年   6篇
  1979年   4篇
  1977年   3篇
  1976年   5篇
  1975年   2篇
  1973年   3篇
  1970年   2篇
  1969年   1篇
  1944年   2篇
  1941年   2篇
  1909年   1篇
排序方式: 共有365条查询结果,搜索用时 0 毫秒
101.
Kinetics of the hydroprocessing of anisole, a compound representative of lignin‐derived bio‐oils, catalyzed by a commercial sulfided CoMo/Al2O3, was determined at 8–20 bar pressure and 573–673 K with a once‐through flow reactor. The catalyst was sulfided in an atmosphere of H2 + H2S prior to the measurement of its performance. Selectivity‐conversion data were used as a basis for determining an approximate, partially quantified reaction network showing that hydrodeoxygenation (HDO), hydrogenolysis, and alkylation reactions take place simultaneously. The data indicate that these reactions can be stopped at the point where HDO is virtually completed and hydrogenation reactions (and thus H2 consumption) are minimized. Phenol was the major product of the reactions, with direct deoxygenation of anisole to give benzene being kinetically almost insignificant under our conditions. We infer that the scission of the Cmethyl–O bond is more facile than the scission of the Caromatic–O bond, so that the HDO of anisole likely proceeds substantially through the reactive intermediate phenol to give transalkylation products such as 2‐methylphenol. The data determine rates of formation of the major primary products. The data show that if oxygen removal is the main processing goal, higher temperatures and lower pressures are favored.  相似文献   
102.
103.
104.
Application of matrix-assisted laser desorption/ionization (MALDI) to the analysis of dextran and dextrin derivatives, specifically glucose saccharides, by time-of-flight (TOF) mass spectrometry has been reported. MALDI-TOF analysis was carried out on alpha-, beta- and gamma-cyclodextrin, two O-methylated-beta-cyclodextrins of differing degrees of substitution (DS) and dextrans (a linear glucose saccharide), as pure and doped solutions and as mixtures of two or more of these. Doping was carried out with trace amounts of inorganic salts. The purpose of the analysis of the cyclodextrins was to determine whether they would form inclusion complexes with the various cations added, or whether less specific cation addition/exchange was occurring either prior to desorption or in the gas phase.  相似文献   
105.
Abstract

The limits of cyclopentadienyl ring-tilting in [l]ferrocenophanes are explored with the incorporation of group 16 elements and a first row element. In this paper the synthesis and ring-opening polymerisation (ROP) behaviour of highly strained chalcogen-and boron- bridged [l]ferrocenophanes will be described.  相似文献   
106.
107.
108.
109.
110.
Multiple periodic solutions for a nonlinear suspension bridge equation   总被引:1,自引:0,他引:1  
We investigate nonlinear oscillations in a fourth-order partialdifferential equation which models a suspension bridge. Previouswork establishes multiple periodic solutions when a parameterexceeds a certain eigenvalue. In this paper, we use Leray-Schauderdegree theory to prove that if the parameter is increased further,beyond a second eigenvalue, then additional solutions are created.  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