共查询到20条相似文献，搜索用时 102 毫秒
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在一水合硫酸氢钠存在下 ,由氯乙酸和正丁醇合成了氯乙酸正丁酯 .当氯乙酸、正丁醇和硫酸氢钠的物质的量比为 1 :2 :0 .0 72 ,回流分水 1h ,酯收率达 85 .7% ,同时该催化剂能够重复使用 . 相似文献
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评述了利用对甲苯磺酸、六水三氯化铁、十二水合硫酸铁铵,一水硫酸氢钠和杂多酸催化制备苯甲酸正丁酯的方法 相似文献
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硫酸氢钠催化合成氯乙酸正丁酯 总被引：6，自引：0，他引：6
在一水合硫酸氢钠存在下，由氯乙酸和正丁醇合成了氯乙酸正丁酯。当氯乙酸、正丁醇和硫酸氢钠的物质的量比为1：2：0．072，回流分水1h，酯收率达85．7％，同时该催化剂能够重复使用。 相似文献
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评述了利用对甲苯磺酸、六水三氯化铁、十二水合硫酸铁铵、十八水硫酸铝、一水硫酸氢钠和杂多酸催化剂催化制备苯甲酸异戊酯的方法。 相似文献
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对文献中关于浓硫酸与饱和盐溶液作用的解释提出了疑问.从反应机理、热力学判据及实验现象等多重角度,探讨了不同浓度的硫酸对水合盐的吸水作用,兼论了不同用量下浓硫酸与饱和盐溶液反应的产物.并在此基础上,提出了相关的教学建议. 相似文献
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评述了利用对甲苯磺酸，六水三氯化铁，十二水合硫酸铁铵，一水硫酸氢钠和杂多酸化制备苯甲酸正丁酯的方法。 相似文献
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二乙酸乙二醇酯的合成 总被引：1，自引：0，他引：1
论述了利用相转移催化剂、对甲苯磺酸、强酸性阳离子交换树脂、六水三氯化铁、十二水合硫酸铁铵、硫酸铁、一水硫酸氢钠和载铁分子筛等催化剂制备二乙酸乙二醇酯的方法． 相似文献
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罗艳萍 《读与写:教育教学刊》2008,5(6)
The communication of people partially is the communication of cultures. Culture has a direct effect on international commercial activities in all aspects. Different conceptions about time, space, equality, law and the like, lead people to deal with things in different ways. So to know cultures of the counterpart is to facil-itate our enterprises so as to have a smooth and successful communication in commercial activity. 相似文献
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Richard Denner 《海外英语》2007,(4):14-15
Rosco and I wait for the fishermen to return.I sit at a wooden bench near the store at Mt.Baker Resort and watch the clouds change shape. Rosco has my belt around his neck and an eight foot tow chain hooked to a tree. Dogs must be on a leash. Ducks and rabbits are loose. 相似文献
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Given a graph G,a subgraph C is called a clique of G if C is a complete subgraph of G maximal under inclusion and |C|≥2. A clique-transversal set S of G is a set of vertices of G such that S meets all cliques of G. The clique-transversal number, denoted as TC (G), is the minimum cardinality of a clique-transversal set in G. The clique-graph of G, denoted as K (G), is the graph obtained by taking the cliques of G as vertices, and two vertices are adjacent if and only if the corresponding cliques in G have nonempty intersection. Let F be a class of graphs G such that F={G|K(G) is a tree}. In this paper the graphs in F having independent clique-transversal sets are shown and thus TC (G)/|G|≤1/2 for all G ∈ F. 相似文献
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《海外英语》2007,(5):10-11
Many college freshmen arrive woefully unprepared to do college work, and as disadvantaged populations continue to grow, the share of the American work force that has made it through college is expected to plummet. Many experts blame that educational failure not just on high schools but also on colleges. School & College, a special report by The Chronicle, looks at efforts to fix the system. What reforms would better prepare students for college? What should schools and colleges be doing differently? How should state and federal officials help? 相似文献
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陈美曦 《山东教育学院学报》2008,23(2):103-107
Different nations have different social cultures, and the social culture of every nation is developing with the development of the nation, language is greatly influenced by social culture, which enables language to possess national and historical characteristics. Word is the smallest, independent, meaningful linguistic unit of language. It can well reflect the national and historical characteristics. From synchronic aspect, the social and cultural influence on word meaning is mainly embodied in conceptual and associative meanings of word. The incorrespondence of word meaning is a phenomenon that exists in both conceptual and associative meanings of word among different languages. From diachronic aspect, the development of social culture causes some changes of word meaning to some extent. Therefore, social culture plays a key role in vocabulary learning and mastery of a language. 相似文献
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邱崇丙 《唐山师范学院学报》2014,(1):21-23
汉字的六书,《说文》对“转注”一类,语焉不详。后世学者提及转注,也仅限于许慎所举出的例字。《汉字例说》一文,作者从转注的角度综合考虑,对部分现代常用字作了分析,跟传统的解释有所不同。希望能抛砖引玉,互相切磋,以推进学术研究。 相似文献
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《海外英语》2007,(4):36
There are numbers of crossroads on our long and unpredictable life journey where we totally have no idea about which direction to choose. No matter what our decision is, we should not turn back, but face the music and go ahead instead. I am this kind of girl who always does try without regretting, one example is how I dealt with my love. 相似文献