共查询到20条相似文献，搜索用时 109 毫秒
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以K-Nb-H2O三元体系为研究系统,在Lencka-Riman热力学模型的框架内,对水热法合成KNbO3粉体进行了理论设计,得到了体系稳定产出相图和优化的合成条件包括反应温度、反应物浓度和溶液的pH控制等重要信息.研究结果表明,前驱物浓度和pH调节(矿化剂KOH浓度)是形成纯相KNbO3必需的条件.在此基础上,利用简单的五氧化二铌和KOH做前驱物,在523K反应温度,高强碱性溶液条件下,常规水热法成功合成了纯相的KNbO3粉体.实验研究和理论设计十分吻合. 相似文献
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以K2S2O8-NaHSO3氧化还原体系为引发剂,合成了羧甲基纤维素（CMC）-丙烯酰胺（AM）-壳聚糖（CTS）接枝共聚物.研究了单体浓度、引发剂用量、反应温度、反应时间以及壳聚糖用量对接枝共聚反应的影响.采用红外光谱（FI-IR）对接枝聚合物进行了结构表征.结果表明：当AM=1.00 mol.L-1,引发剂（K2S2O8/NaHSO3=1∶1）浓度为5 mmol.L-1,mCTS/mCMC=1/5,反应温度55℃,反应时间3 h时,AM的转化率和接枝效率可分别达到76%和91%. 相似文献
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本文以KOH／Al1O3为催化剂，研究了正己醛和苯甲醛交叉缩合a-丁基肉桂醛的反应，重点考察了反应温度、反应时间、反应原料摩尔配比(己醛／苯甲醛)、溶剂用量、催化剂用量、催化剂负载量诸因素对目标产物α-丁基肉桂醛产率的影响，确定了制备α-丁基肉桂醛的优化反应条件：温度70℃、时间1．5h、己醛／苯甲醛10mmol／12mmol、溶剂苯乙醇5ml、催化剂KOH／Al2O3 0．84g、催化剂负载量11．9mmol／g，得己醛的转化率为100％，α-丁基肉桂醛的选择性为83．24％，即α-丁基肉桂醛的收率为83．24％。 相似文献
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本文研究了以TiO2-Sb2O3/SO42-为催化剂,催化假性紫罗兰酮合成紫罗兰酮.探索了反应温度、反应时间、催化剂用量、溶剂用量等因素对环化反应的影响.最佳合成条件:6mL假性紫罗兰酮,催化剂用量为1.8g,溶剂用量为6mL,环化反应温度为30℃,反应时间为3.0h,紫罗兰酮产率约为70%. 相似文献
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纳米KNbO3粉体的水热合成及表征 总被引：2，自引：0，他引：2
给出了一个在Nb-K-H2O三元体系中水热合成KNbO3的新的工艺条件；讨论了水热反应温度、溶液初始浓度及反应时间对合成产物的组分及形态等的影响；采用水热合成方法，在KOH浓度3M以上、反应温度为250℃、反应时间24h时，成功合成了钙钛矿结构KNbO3纳米陶瓷粉体；X射线衍射（XRD）、透射扫描电子（TEM）分析表明，水热合成的KNbO3晶粒发育完整，平均粒径为40nm；FT-IR、FT-Raman光谱等测试结果表明，纳米尺度KNbO3晶粒的Nb-O特征振动吸收带和拉曼位移分别出现了宽化和蓝移现象． 相似文献
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以细铁丝为阳极,铂片为阴极,KOH溶液为电解液电解合成高铁酸钾,在KOH溶液浓度12mol dm-3,电流密度2mA·cm~(-2),温度25℃电解1．5h条件下,获得最佳合成效率54．2％． 相似文献
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本文研究了以TiO2-Sb2O3/SO4^2-为催化剂,催化假性紫罗兰酮合成紫罗兰酮。探索了反应温度、反应时间、催化剂用量、溶剂用量等因素对环化反应的影响。最佳合成条件：6mL假性紫罗兰酮,催化剂用量为1.8g,溶剂用量为6mL,环化反应温度为30℃,反应时间为3.0h,紫罗兰酮产率约为70%。 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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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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《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
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Sister Carrie is one of the most controversial characters in American literature.Thought as a "fallen woman" firstly,she was defined as a "new woman" by some critics later. However, by digging into the motivaton behind the whole process of Carrie's "success", the relationship between Carrie and her creator (the author), the social conditions of then American, it can be found that Carrie has never been free-standing on her thought and she has never found her real-sdf even after becoming a famous actress. In a society dominated by mass consumerism Carrie is only an adherent of her own desires. She also is a representative of all those country girls flooded into cities, a symbol and a sacrifice of the urbanization of America in a time countryside was overcome by cities. 相似文献
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RUZBEHANI Mohsen 《重庆大学学报(英文版)》2004,3(1):20-25
1.IntroductionOne-cyclecontrolmethod,whichwasproposedaboutonedecadeago[1],hasbecomeanattractivemethodinspecialfieldssuchaspowerfactorcorrection[2-6],switchingamplifiers[7,8],etc.Themainideaofthiscontrollerisbasedonintegrationofdiodevoltageinone-cycleandforcesittobeexactlyequaltothereferencevalue.Themainadvantageofthiscontrollerisitsrealtimeabilitytorejectthevariationofinputvoltage[1].Despitethisgreatability,ithasnogoodperformancesinrejectingofloaddisturbanceandfollowingreferencecommands.Espec… 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