共查询到20条相似文献，搜索用时 187 毫秒
1.
在固体酸S04^2-/ZrO2-MoO3催化下，由马来酸酐和甲醇催化合成富马酸二甲酯(DMF)。探讨了催化剂用量，原料配比，反应时间对DMF产率的影响，确定了最佳反应条件为：醇酸摩尔比为6：1，反应时间3h，催化剂用量1．5％，该条件下，产物收率达93％以上。 相似文献
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固体超强酸SO4^2-／TiO2-Fe2O3催化合成丁酸丁酯的试验研究 总被引：3，自引：0，他引：3
王良 《咸阳师范学院学报》2005,20(4):29-30
利用正交试验找到用SO4^2-／TiO2-Fe2O3固体超强酸催化合成丁酸丁酯的最佳应条件。即反应时间4．0h，催化剂用量为酸质量的1．4％，酸醇比1．2：1，验证实验产率为97．6％。且该实验反应时间相对短，无腐蚀无污染，催化剂可回收可重复使用。 相似文献
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研究了用硫酸氢钠催化合成乳酸正丁酯的反应，探讨了催化剂用量、酸醇比、反应时间及催化剂重复使用次数等因素对反应的影响。在酸醇体积比为1：3，催化剂为1．5％（w)，反应时间为2h，反应温度为120℃时，乳酸酯化率达97．2％。结果表明，在实验条件下，该催化剂具有较好的活性。 相似文献
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以固体十六烷基三甲基溴化铵为相转移催化剂，冰醋酸和正己醇为原料合成乙酸正己酯，考察了催化剂用量，反应时间，酸醇犀尔比对酯产率的影响。结果表明：催化剂用量为物料总用量的5％，反应时间为120min，酸醇摩尔比为1．4：1，反应温度为109～120℃时，产率可达82．90％。 相似文献
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首次报道了以固载杂多酸盐TiSiW12O40/TiO2为多相催化剂，通过氯乙酸和丙醇反应合成了氯乙酸丙酯，并探讨了诸因素对产率的影响。实验表明：TiSiW12O40/TiO2是合成氯乙酸丙酯的良好催化剂，最佳反应条件为：醇酸物质的量比为1．4：1，催化剂用量为反应物料总量的2．0％，反应时间2．0h，反应温度95－110℃。上述条件下，氯乙酸丙酯的产率可达77．14％。 相似文献
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实验制备了三种Keggin型钼钒磷杂多酸催化刘,并将其应用于催化H2O2氧化蒽制备蒽醌,考察了各种因素对蒽醌产率的影响,以H5PMo10V2O40为催化剂,催化H2O2氧化葸制蒽醌的最佳条件为：正丁醇为溶剂,催化剂用量为反应物的6％,蒽：H2O2物质的量比为1：16,反应温度70℃,反应时间2h,产率可达90％以上。 相似文献
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钨硅酸催化合成乙酸辛酯 总被引：3，自引：2，他引：3
以钨硅酸为催化剂，通过乙酸和辛醇反应合成了乙酸辛酯。探讨了酸醇物质的量比、催化剂用量以及反应时间对酯化率的影响。实验结果表明：钨硅酸催化合成乙酸辛酯的最佳条件为：酸醇物质的量比1．3：1，催化剂用量0．2g／0．1mol(辛醇)，带水剂(环己烷)10mL，反应时间1h．温度100～118℃．在此条件下其酯化率可达99．30％。 相似文献
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首次以固载杂多酸盐TiSiW12O40／TiO2为多相催化剂。通过己二酸和乙醇反应合成了己二酸二乙酯，并探讨了诸因素对产率的影响。正交实验结果表明：TiSiW12O40/TiO2具有良好的催化活性，醇酸物质的量比为4．0：1，催化剂用量为反应物料总量的1．5％，反应时间1．5h。反应温度66--118℃，酯收率可达79％。 相似文献
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以H3PW12O40／TiO2为催化剂催化合成了环己酮1，2-丙二醇缩酮，探讨了H3PW12O40／TiO2对缩酮反应的催化活性，较系统地研究了酮醇物质的量比，催化剂用量，反应时间诸因素对产品收率的影响．实验表明：H3PW12O40／TiO2是合成环己酮1，2-丙二醇缩酮的良好催化剂，在n（环己酮）：n（1，2-丙二醇）=1：1．7，催化剂用量为反应物料总质量的0．5％，环己烷为带水剂，反应时间1．0h的优化条件下，环己酮1，2-丙二醇缩酮的收率可达83．7％． 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
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Migration occurs behind a variety of reasons and has a great effect on the whole world. People may migrate in order to improve their economic situation, or in order to escape civil strife, persecution, and environmental disasters. The impact of migration is complex, bringing both benefits anddisadvantages. This paper briefly talks about the causes of migration, the allocation of benefits, and the ways in which individual countries and the international community deal with this important subject. 相似文献