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   113篇
  免费   0篇
化学   99篇
数学   2篇
物理学   12篇
  2019年   1篇
  2016年   1篇
  2015年   1篇
  2014年   1篇
  2013年   5篇
  2012年   5篇
  2011年   3篇
  2010年   4篇
  2009年   4篇
  2008年   2篇
  2007年   1篇
  2006年   5篇
  2005年   1篇
  2004年   7篇
  2003年   2篇
  2002年   6篇
  2000年   4篇
  1999年   3篇
  1998年   5篇
  1997年   3篇
  1996年   6篇
  1995年   6篇
  1994年   6篇
  1993年   5篇
  1992年   1篇
  1987年   1篇
  1985年   2篇
  1984年   2篇
  1982年   3篇
  1981年   3篇
  1980年   2篇
  1979年   1篇
  1976年   2篇
  1974年   2篇
  1973年   2篇
  1972年   3篇
  1971年   1篇
  1970年   1篇
排序方式: 共有113条查询结果,搜索用时 15 毫秒
51.
The title adduct (1) was synthesized, and its conformationally and configurationally rigid chiral structure in solution and in the crystal was established by NMR spectroscopy and by X-ray structural analysis. Atropoenantiomers of1 were observed by the1H NMR method in the presence of a chiral shift reagent. A barrier to their interconversïon was determined, Gx > Z5 kcal mol–1 (200 °C).Translated fromItvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1796–1799, July, 1996.  相似文献   
52.
The possibility of tranferring chirality from nitrogen to carbon by a three-step transformation of racemic dimethyl 1-methoxyaziridine-2,2-dicarboxylate into 3-amino-2-chloromethyl-2-methoxyaminopropan-1-ol was demonstrated. The first representative of 1-silyloxyaziridines,viz., dimethyl 1-(tert-butyldimethylsilyloxy)aziridine-2,2-dicarboxylate, was synthesized by acidolysis or thermolysis of triazoline, obtained by the reaction oftert-butyldimethylsilyloxime of dimethy mesoxalate with CH2N2  相似文献   
53.
Comparative investigations of the mass spectra of eEH2, Me2EH, Et2EH(E = N, P); Me3E, Et3E(E = N, P, As, Sb, Bi). (n-Pr)3E(E = Sb, Bi); (n-Bu)3E(E = P, As); (n-C5H11)3As and (n-C6H13)3As as well as Et2AsBr have been carried out. Deuteroanalogues, metastable transitions and low voltage spectra were used for elucidation of the fragmentation paths. The mass spectra of MeN(CH2)2 and CD3N(CH2)2 were studied to analyse the structure of the fragments. The main degradation path of amines, i.e. α-cleavage, was shown to be untypical for P, As, Sb and Bi derivatives.  相似文献   
54.
Alkoxyamines with tertiary N-alkyl substituents were chlorinated to N-chloro-N-alkoxyamines whose reaction with alcohols enabled synthesis of N,N-dialkoxyamines. The DNMR method was used to determine the barriers of inversion of these compounds. Alkaline hydrolysis (13) followed by subsequent reactions with R-(+)- and S-(?)-α-phenylethylamine yielded diastereomeric salts (+29 and ?29) whose crystallization and subsequent esterification resulted in optically active acyclic amines (?13 and +13) with the asymmetric center only at the N atom in the open chain.  相似文献   
55.
The behaviour of compounds I to XII under electron-impact (electron voltages 30 and 12 eV) was investigated. The abundance of the ions characteristic of amines was shown to decrease drastically with an increase of chain branching in alkylphosphines. Comparison of the spectra of VII and X led to the conclusion that the unshared electron pair of phosphorus does not affect the fragmentation. The main peaks in the spectra of phosphines corresponded to hydrocarbon fragments. The origins of the main fragment ions were confirmed by metastable peaks.  相似文献   
56.
57.
Diastereoselective transformations of Leakadine were discovered: dimerization during melting or heating in CHCl3 with the formation of one diastereomer. The obtained dimer reacts with methyl isocyanate under mild conditions with the formation of an N-methylcarbamoyl derivative – also in the form of one diastereomer. In the diastereoselective reaction of Leakadine with dimethyl formamide dimethyl acetal, 2-dimethylamino-1,3-diazabicyclo[3.1.0]hexan-4-one was obtained. The reaction of Leakadine with perfluoroisobutylene was studied.  相似文献   
58.
A loopQ is said to be left conjugacy closed (LCC) if the left translations form a set of permutations that is closed under conjugation. This papers investigates those LCC loops where the group generated by left translations is normal in the group generated by both left and right translations.  相似文献   
59.
60.
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