首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 62 毫秒
1.
人类进入 2 1世纪 ,科学已经非常发达 ,技术也已经非常先进 ,但许多最基本的问题仍然没有找到答案。比如 ,元素是如何形成的 ?宇宙是怎样开始的 ?大脑是如何工作的 ?生命是如何起源的 ?从某种意义上说 ,这些谜底都与元素本身有一定的关联。  现在的周期表中的元素已经扩展到 1 1 6号 (其间的 1 1 3和 1 1 5号尚未合成成功 ) ,其中有2 3种人造元素。除Tc、Pm外 ,从 93号元素 (Np)到 1 0 3号元素 (Lr)共 1 1种称为“锕系的超铀元素”(Transactinideelements) ;另外 1 1种称为“锕系后元素”(Transura…  相似文献   

2.
1 INTRODUCTIONTheα ,α ,α′,α′ tetraaryl 1 ,3 dioxolane 4,5 dimethanols (TADDOLS)diolswhicharereadilyavailablefromalkyltartrates ,havebeenwidelyusedaschiralligandsinenantioselectiveadditionreactionsofcarbon centerednucleophilestoaldehy des[1 ] ,in [2 +2 ]cycloadditions[2 ] …  相似文献   

3.
1 INTRODUCTIONStudiesofthecoordinationchemistryofzinc(II)havearousedmoreandmoreinterestinlastdecadeinviewoftheirbiologicalmodelingapplica tions[1 ,2 ] andsolid statematerials[3 ,4] .WehavebeeninterestedinthestudyoftransitionmetalcomplexesofN oxopyridine 2 thiol(…  相似文献   

4.
Ferricoxide(αFe2O3),chromicoxide(αCr2O3)andtheirmixedcompoundshaveimportantapplicationinmanyfields.Forinstance,theycanbeusedascatalystsforhightemperaturewatergasshiftreaction[1]andreductionofNOxbyNH3[2],asrefractorymaterials[3]andsensingmaterials[4,5],andsoon.Sinc…  相似文献   

5.
IntroductionInorganiclightemittingdiode(OLED) ,somemetalswithlowworkfunction ,suchasalloyofmag nesiumandsilver(Mg∶Ag) [1] andaluminium[2 ] ,areusedastheelectroninjectioncathodes .InMg∶Agal loysilverisusedtoprotectmagnesiumfromthereac tionofmagnesiumwithoxygenand…  相似文献   

6.
IntroductionSingle walledcarbonnanotubes(SWNTs)havebeensynthesisedbyusingvariousmethods[1— 3] andthechemicalvapourdeposition (CVD )methodhasbeenconsideredasa promisingmethodto produceSWNTsonanindustrialscale[3— 5] .However ,alltheSWNT productssynthesisedtodateco…  相似文献   

7.
1 INTRODUCTIONOneofourcurrentinterestsfocusesonthedesignandsynthesesofpolyazamacrocyclicligands,andthestabilitiesofcorrespondingmetalcomplexes.Twopolyazadiphenolmacrocycles,R(babp) 2 (dfc) 2 andR (bac) 2 (dfp) 2 ;[1 ]oneoctaaza macrocycle,BPBD ;[2 ,3]andseveralhexaazama…  相似文献   

8.
IntroductionSeveralplantsofgenusAnaphalis(Compositae)havebeenphytochemicallystudied ,fromwhichflavanoids[1,2 ] ,helipyrone[3] ,chloroacetyleniccompoundswithadihydropyranorfuranring[4] andphthalideshavebeenreported[5 ] .A .sinicaHance ,distributedinChinaandalsofound…  相似文献   

9.
HuperzineA(HupA),analkaloidisolatedfromChineseherbHuperziaserrataThunb[1],isapotentreversibleacetylcholinesterase(AChE)inhibitor[2]withhighefficacyandlowtoxicity(fig.1).Acetylcholine(ACh)isachemicalsubstance,whichcantransmitthesignalofnerveimpulse.Therearemany…  相似文献   

10.
日本大学分析化学教育现状简介与借鉴   总被引:10,自引:0,他引:10  
王秋泉 《大学化学》2002,17(5):57-61
科学技术的飞速发展使分析化学发展到了分析科学阶段[1] 。大学 (理工学科 )的分析化学教育应适应这一需要进行适当的调整 ,使原本有学科交叉性质的分析化学 (科学 )具有更丰富的内涵[2 ,3] ;世界范围内的分析化学教育改革正在进行[4~ 9] ,改变原有的老师“教”(Teach ing)、学生“学”(Learning)的传统教学模式 ,使学生带着问题学习 (PBL ,ProblemBasedLearn ing)、带着课题实践 (PBA ,ProjectBasedApproach) ,以提高他们的学习兴趣 ,提供培养创新能力的氛围 ;同时利用多…  相似文献   

11.
12.
13.
HEPT类化合物的QSAR研究   总被引:3,自引:0,他引:3  
章文军  许禄 《应用化学》2001,18(9):717-0
为定量结构/活性相关性研究提取了量子化学参数,拓扑指数Am,分子连接性指数^mxt及疏水性常数,同时应用正交变换和最佳变量子集算法(Leaps-and-Bonds)进行了变量压缩和选择,进而实施了多元回归分析,并由此结果进行了HEPT类化合物(1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)-thymine derivatives)的结构/活性关系的理论解释,进行了人工神经网络法对于该类化合物的活性预测,其结构明显好于多元回归法。  相似文献   

14.
15.
The dependence of the chemical shifts of the ring protons on the pH of the medium for a number of 4-hydroxyquinoline derivatives was studied by means of PMR spectroscopy. The dipolar and uncharged hydroxy forms exist in equilibrium in aqueous solutions. The effect of intramolecular hydrogen bonding on the character of the dependence of the chemical shift on the pH of the medium in the case of 3-piperidinomethyl-4-hydroxyisoquinoline was investigated. The possibility of the separate protonation of the ring nitrogen and the side-chain nitrogen in 3-piperidinomethyl-4-hydroxyisoquinoline was established. The distribution of the -electron density in 4-hydroxyisoquinoline is in good agreement with its chemical behavior.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1546–1549, November, 1971  相似文献   

16.
The dependence of the chemical shift of the ring protons on the pH of the medium for a number of 3-hydroxyquinoline derivatives was studied by PMR spectroscopy. The regions of ionization of the molecules, which correspond to the ranges of acidic, neutral, and alkaline media, were found. In D2O, 3-hydroxyquinoline is present only in the uncharged hydroxy form. The presence of intramolecular hydrogen bonding in 4-dimethylaminomethyl-3-hydroxyquinoline has a substantial effect on the character of the dependence of the chemical shift on the pH of the medium; the existence of separate protonation of the nitrogen atoms of the ring and the side chain of 4-dimethylaminomethyl-3-hydroxyquinoline was established. The distribution of the -electron density in the 3-hydroxyquinoline molecule is in good agreement with its chemical behavior during electrophilic substitution.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1540–1545, November, 1971.  相似文献   

17.
18.
19.
20.
Sweden's famous warship, Vasa, sank on her maiden voyage in August 1628, and remained on the bottom of Stockholm harbour for 333 years. Raised in 1961, she became the first large-scale wooden object to be treated with polyethylene glycol (PEG). In the summer of 2000 a number of acidic salt precipitations were noticed on the surface of the ship and on wooden artefacts in the storerooms. An international research project has been established to look into the causes of this problem and suggest possible re-treatments. Meanwhile projects are underway to monitor movements in the ship, to build a better support system, and to replace the thousands of iron bolts holding the structure together, while a sophisticated new climate system has recently been installed in the museum.  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