首页 | 官方网站   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   2939篇
  免费   6篇
  国内免费   239篇
数理化   3184篇
  2023年   3篇
  2022年   2篇
  2021年   1篇
  2018年   2篇
  2017年   2篇
  2016年   5篇
  2015年   3篇
  2014年   8篇
  2013年   1篇
  2012年   258篇
  2011年   325篇
  2010年   42篇
  2009年   125篇
  2008年   428篇
  2007年   300篇
  2006年   351篇
  2005年   349篇
  2004年   244篇
  2003年   186篇
  2002年   139篇
  2001年   87篇
  2000年   107篇
  1999年   35篇
  1998年   13篇
  1997年   8篇
  1996年   37篇
  1995年   19篇
  1994年   20篇
  1993年   46篇
  1992年   24篇
  1991年   4篇
  1989年   3篇
  1988年   3篇
  1986年   3篇
  1979年   1篇
排序方式: 共有3184条查询结果,搜索用时 234 毫秒
991.
本文报道了以光学活性乳酸为手性元对目标化合物的所有可能的四个异构体所进行的合成。根据合成样品与天然产物的核磁及旋光数据比较,标题化合物的相对及绝对构型都得以完全确立,其完整结构定为(2S,3S)-4,6-庚二炔-2,3-二醇。  相似文献   
992.
SHOCKCOMPRESSIONBEHAVIOROFBROMOFORMPengShangqianga,b,cJingFuqiana,bHuJinbiaoa,bGouQingquanba.LabforShockWaveandDetonationPhy...  相似文献   
993.
994.
Foreword     
Garcı́a-Campaña AM 《Talanta》2003,60(2-3):223-224
  相似文献   
995.
1 INTRODUCTION Although the incorrect assignment of the space groups of crystal structures has been addressed in a number of reports, instances of crystal structures refined in incorrect symmetry turn up even in the recent literature[1~4]. A simple method of space group revision makes use of the published atomic coordinates and temperature factors to simulate the diffraction intensities; the structure is then 搒olved?in the correct space group from the simulated hkl-F2 data[5] and an O…  相似文献   
996.
1 INTRODUCTION Nitronyl nitroxide radicals (NITR), stable organic radicals, have played an important role in the design and synthesis of molecular magnetic materials[1, 2]. However, nitronyl nitroxide radicals are poor elec- tron-donor ligands and their coordination ability is limited. Recently, it has led to the development of functionalized nitronyl nitroxide radicals in which a strong coligand is incorporated. Due to the strong coordinate ability of nitrogen atom from pryidinyl ring,…  相似文献   
997.
1 INTRODUCTION The determination of structures of adsorbed cya- nide (CN) and cyanate (OCN) on transition metal surfaces is important for understanding their bon- ding and reactivity in catalysis and other surface phenomena[1~4]. During the past decade, the adsorp- tion of CN and CN-containing on transition metal surfaces has received a great deal of attention in both experimental[5~20] and theoretical[1~5, 13, 20~33] inves-tigations, and the previous work about the adsorp- tion of…  相似文献   
998.
1 INTRODUCTION Macrocyclic[1~5] and macrobicyclic[6~11] com- pounds and their derivatives are great interesting ligand systems because they are good hosts for metal anions, neutral molecules and organic cation guests. Recently, many ligands in these fields have been rapidly developed and studied. Herein we will report the synthesis, crystal structure and characteri- zation of a novel 42-membered [2+2] macrocyclic compound obtained by the condensation of diethyl- lenetriamine with 4,4-d…  相似文献   
999.
1 INTRODUCTION Since Bedard et al. reported microporous tin(IV) sulfides synthesized by hydrothermal method in the presence of organic amine in 1989[1, 2], a number of thiostannates have been synthesized using hydro- or solvothermal techniques with organic amines as tem- plates. The structures of the resulting tin(IV) sulfi- des are related to the types of organic amines. Two- dimensional polyanions of the types of [Sn3S7]2- and [Sn4S9]2-, which are denoted as SnS-1 and SnS-3, respe…  相似文献   
1000.
1 INTRODUCTION even three-dimensional (3-D) extended solid frame- works in appropriate ways is a major challenge in The syntheses and characterizations of novel po- POMs chemistry. Based on the fact that POMs fra- lyoxometalates (POMs) have currently attached in- meworks with high electronic density can act as un- creasing interest owing to not only enormous variety usually effective ligands to coordinate second tran- of intriguing structural topologies, but also their fas- sition meta…  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-23

京公网安备 11010802026262号