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        검색결과 1,895

        1327.
        1991.12 KCI 등재 구독 인증기관 무료, 개인회원 유료
        지리산 국립공원의 화엄사입구에서 노고단 정상에 이르는 화엄사 계곡 및 성삼재에서 노고단에 이르는 등산로 주변에 출현하는 관속식물을 파악하고자, 1991년 5월 5일-7일, 7월 10일-13일 및 9월 28일-30일 사이에 본 조사를 수행한 바, 2강 31목 83과 175속, 216종, 24변종 및 7품종으로 조사되었다.
        4,000원
        1328.
        1991.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        4,000원
        1332.
        1991.06 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The reactions of semicarbazide hydrochloride with aliphatic and alicyclic ketones were studied kinetically at 15, 25, 35 and 45℃ in 20% ethanol solution buffered at pH 2.9. The rate of cyclohexanone semicarbazone formation is 5.5 times as fast as that of cyclopentanone semicarbazone, while 3-pentanone semicarbazone is 4.7 times as slow as that of 2-pentanone, The activation energy of cyclohexanone, 2-pentanone, 2 hexanone, cyclopentanone, 4-methyl-2-pentanone and 3-pentanone semicarbazone formation are calculated 5.08, 7.52, 8.79, 9.59, 9.49, 11.59, respectively. It is concluded from the effect of ionic strength that the reaction is affected by not ion but neutral molecules being progressed hydrogen bond between oxygen atom of carbonyl group and hydrogen atom of acid-catalyst and concerted nucleophilic attack of free base on the carbonly compound. Dependence on pH of the rate of 2-pentanone semicarbozone formation is linear relationship below pH 4.60 and above pH 5.60. As a result of studing citric acid catalysis, second order constants increase linearly with citric acid concentration. As the catalyst concentration is varied from 0.025 to 0.10 mol/1 at pH 2.90, the rate constants increase 1.4 times, but slight increase is observed at pH 5.60. Conclusively, the rate-determining step is formation of tetrahedral interemediate below pH 4.65 and dehydration between pH 5.60 and pH 7.11. It is concluded that the formation reaction of cyclohexanone semicarbazone is faster than cyclopentanone semicarbazone due to the steric strain in the process of forming tetrahedral intermediate.
        4,000원
        1340.
        1990.12 KCI 등재 구독 인증기관 무료, 개인회원 유료
        4,000원