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   7423篇
  免费   605篇
  国内免费   983篇
化学   2133篇
晶体学   35篇
力学   586篇
综合类   76篇
数学   404篇
物理学   1718篇
无线电   4059篇
  2024年   2篇
  2023年   3篇
  2022年   2篇
  2021年   1篇
  2020年   1篇
  2018年   20篇
  2017年   4篇
  2016年   4篇
  2015年   2篇
  2014年   396篇
  2013年   43篇
  2012年   4篇
  2011年   13篇
  2010年   2篇
  2009年   7篇
  2008年   3篇
  2007年   4篇
  2006年   2篇
  2005年   1篇
  2003年   614篇
  2002年   2523篇
  2001年   2730篇
  2000年   530篇
  1999年   410篇
  1998年   323篇
  1997年   95篇
  1996年   167篇
  1995年   204篇
  1994年   144篇
  1993年   183篇
  1992年   132篇
  1991年   142篇
  1990年   163篇
  1989年   129篇
  1985年   1篇
  1982年   1篇
  1980年   1篇
  1965年   5篇
排序方式: 共有9011条查询结果,搜索用时 0 毫秒
111.
采用浸渍法、溶胶-凝胶过程与普通干燥、超临界干燥过程相结合的方法制备了具有不同结构特点的NiO-CeO2-Al2O3催化剂,分别为浸渍型催化剂(iNCA)、干凝胶催化剂(xNCA)和气凝胶催化剂(aNCA),利用BET、TEM、XRD、TPR、NH3-TPD、H2-TPD等方法对各催化剂样品的物化化质进行了考察。研究结果表明,经823K焙烧后,镍含量为9%的各催化剂样品中镍物种分散良好;与iNCA相比,以溶胶-凝胶法为基础制备的xNCA和aNCA中镍物种与载体的相互作用用强并且存在状态均一;三种催化剂中,气凝胶样品具有比表面积高、堆密度低、表面酸中心数多及表面镍分散度高的特点。  相似文献   
112.
陈锡华  林晨升 《结构化学》2001,20(5):369-380
1 INTRODUCTIONWith the invention of lasers[1] and the observation of second-harmonic generation in quartz[2], nonlinear optics(NLO), as a cornerstone of photonics, has been booming since 1960's. And intense interest has been aroused to search materials exhibiting appropriate nonlinear optical properties suitable for the construction of practical optical devices for the important techniques such as frequency converting, signal processing and optical computing[3~6]. In order to determine …  相似文献   
113.
潘国华  庄伯涛 《结构化学》2001,20(5):384-386
1 INTRODUCTION In 1984, thiolate ligand was successfully introduced into molybdenum carbonyl compound by the reaction of Mo(CO)6 with [Et4N]SR( R = C6H5, But) in a moderate condition[1]. From then on, a series of dinuclear molybdenum(0) carbonyl thiolate compounds have been synthesized and characterized by using a variety of thiolate ligands in our research group. It was found that a planar Mo2S2 unit is in the compound [Et4N]2[Mo2(CO)8(SC6H4-CH_3-p)2][2] (2) and a "butterfly" t…  相似文献   
114.
屠树江  周建峰 《结构化学》2001,20(6):459-461
1 INTRODUCTION Since the discovery of the pharmacological effects of 1,4-dihydropridines(1,4-DHPs) as calcium channel blocks[1], a great deal of work has been directed towards synthesis of the novel 1,4-DHPs acting as calcium antagonists[2, 3]. In fact, it is well-established that slightly modified structures on the DHP exhibit a calcium agents effect[4, 5] ; however, two fused rings have been less well-studied. By refluxing equivalent amounts of dimedone, aromatic aldehyde Meldrum抯 …  相似文献   
115.
CHO  Iwhan  PYUN  Kwang-Soo 《应用化学》2001,18(5):296-300
In recent years certain new technologies demand optically transparent high Tgpolymer materials.Some aliphatic polymers containing cyclic structure are in the marketalready and have been applied to manufacture various devices in optics industry.However,these polymers are usually of nonpolar character and their difficulties inadhesion and solubility in solvents limited their applicability in many technologies[1 ,2 ] .The polymerization of polar group-containing internal cyclic olefins by transit…  相似文献   
116.
注射用生物可降解胰岛素纳米微球的制备   总被引:10,自引:1,他引:10  
共聚物;药剂释放体系;注射用生物可降解胰岛素纳米微球的制备  相似文献   
117.
118.
119.
Aromatic amine compounds and their derivatives are important intermediates of fine chemicals like dye and medicine.The former hydrogenation catalyst has many problems,such as environment pollution caused by old technology,strict reaction condtion,complicated equipment,bad property of catalyst and so on.Holy ^[1] firstly reported the hydrogenation of nitrobenzene on modified polystyrene Pd catalyst.But how to improve the activity,selectivity and stability of the polymer suppoorter catalyst needs to studyfurther.We prepared a series of polymer supported catalysts by the methods of adsorption and mechanical mixting ,selected a high active catalyst Pd-Ah-1 by observing the hydrogenation of nitrobenzene.  相似文献   
120.
Disclosed is a method of preparing hypophosphorous acid comprising contacting an insoluble anode with an aqueous solution of hypophosphite anions and applying a direct current through the insoluble anode to a cathode in electrical contact with the equeous solution to generate H^+ ions in the aqueous solution thereby forming a hypophosphorous acid solution.The process is simple,low cost and high efficient,which can be tied into an existing process for producing sodium hypophosphite wherein the product of sodium hypophosphite process is used as a starting material in the hypop[hosphorous acid process.  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