共查询到20条相似文献，搜索用时 93 毫秒
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1，2：5，6-双-0-异丙叉基-3-C-（1-甲氧羰基）-乙基-α-D-呋喃阿洛糖是由D-葡萄糖衍生的一种重要支链糖。系通过以下途径制得，将D-葡萄糖羟基进行部分保护，在酸性条件下与过量丙酮进行缩合反应得二丙酮葡萄糖；然后将3位羟基进行PCC氧化得中间体二丙酮-3-已酮糖；再将中间体与-α-溴代丙酸甲酯进行亲核加成反应即得目标物，总收率为79.6%。目标物结构经核磁共振谱，红外光谱，元素分析表征。 相似文献
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2—氨基—4，6—二甲氧基嘧啶的合成研究 总被引：1，自引：0，他引：1
吕成学 《沈阳教育学院学报》2000,2(3):115-117
2－氨基－4,6－二甲氧基嘧啶系高效除草剂的重要中间体之一。它有多种合成方法,经过文献检索,我们选择了环化、氯化、醚化的合成路线。环化收率为95％,氯化收率为78％,醚化收率为75％。成品有效含量可达90％以上。 相似文献
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用肌苷与苯甲酰氯反应制得三苯甲酰肌苷（2）,在浓H2SO4存在下,用乙酐／乙酸混合液处理化合物（2）,得到1－O－乙酰基－2,3,－5－三－O－苯甲酰基－β－D－呋喃糖（1）,总产率约33％。 相似文献
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袁先友 《郴州师范高等专科学校学报》2002,23(5):38-40
以十二醛为二羧甲基丙二酸二乙酯为原料反应，然后用氢氧化钠皂化，合成了2－正十一烷基－1，3－二氧杂环己烷－5，5－二羧酸二钠盐，并对它的临界胶束浓度（CMC）进行了测定。 相似文献
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2，3－二甲基－5，6－二氢吡嗪在氢氧化钠的乙醇溶液中与乙醛反应，合成了2，3－二甲基－5－乙基吡嗪。 相似文献
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袁先友 《零陵师范高等专科学校学报》2001,22(3):4-6
研究了以1－十八醇和丙二酸二乙酯为原料合成二正十八烷基丙二酸二乙酯，然后用LiAlH4还原得到2，2－二正十八烷基－1，3－丙二醇，再对甲苯磺酸催化与β-溴丙醛缩合得5，5－二正十八烷基－2－－（2－溴乙基）－1，30－二氧六环，并对产物的重结晶条件进行了研究，产物经元素分析，IR和1HNMR光谱表征。 相似文献
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合成了两种新型兼有植物生长调节剂和除草剂功效的N硝基－N－氨基（取代）甲酰－2，4，6－三氯苯氨类化合物，并经元素分析、红外光谱等证实了它们的结构。 相似文献
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本报道了用2,3－－二甲吡嗪和正己酸在自由基引发剂引发下合成5－－戊基－－2,3－－二甲吡嗪的新合成方法研究,并对合成条件进行了探索。用元素分析、红外光谱、氢核磁共振谱表征了目标物结构。 相似文献
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本报道了用2，3－二甲吡嗪和正庚酸在自由基引发剂引发下合成5－己基－2，3－二甲吡嗪的新合成方法研究，并对合成条件进行了探索。实验表明：该方法具有产率高、路线短、分离精制简单等优点，是合成5－己基－2，3－二甲吡嗪的有效方法。 相似文献
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本文介绍了弱酸艳红１０Ｂ的中间体２．４－二（２－甲基－苯氧基）硝基苯的合成新工艺,该工艺的产物收率为９７．４％,所用溶剂的回收率为８７．４％。 相似文献
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王秀燕 《聊城师范学院学报》2010,(2):285-287
在我国,中间业务没有得到应有的重视,中间业务收费标准偏低,收入占银行总收入的比重低,收费管理不规范,收费市场秩序混乱,严重影响了中间业务的发展。从我国商业银行中闯业务的收费问题现状入手,分析制约我国银行中间业务收入水平的因素,并就如何开展商业银行中间业务收费问题提出了相关的对策和建议。 相似文献
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Indira N. Z. Day F. M. van Blankenstein P. Michiel Westenberg W. F. Admiraal 《Educational studies》2018,44(4):449-467
Universities introduce intermediate assessment because it is understood to have positive effects on student behaviour and achievement. Yet, how intermediate assessment is perceived might be conditional for its success. The current study investigates both teachers’ and students’ perceptions of intermediate assessment. Teachers and students were interviewed and Student Evaluations of Teaching were examined. Results indicate that both teachers and students had generally positive perceptions of intermediate assessment. However, the two groups provided different reasons for their positive perceptions. Teachers and students agreed that intermediate assessment helps students to keep up with their study work. Moreover, teachers mentioned that they could assess various knowledge and skills with intermediate assessment, whereas students preferred intermediate assessments to test the same knowledge and skills as the final exam. This finding suggests that teachers and students in our study had different goals for intermediate assessment. 相似文献
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刘润辉 《株洲师范高等专科学校学报》2005,10(5):42-43,47
Cauchy中值定理统一了微积分中值定理各种形式，从而建立了微分中值定理和积分中值定理之间的内在联系,以Rolle中值定理为基础，借助不同形式辅助函数可对其它几个中值定理作出多种形式的统一证明；利用Taylor公式可以进一步导出微积分中值定理的推广形式。 相似文献
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孔子中庸思想中的现实性是一个重要的内容,特别是中庸的“用中”思想中最能体现中庸的现实性。在现在这样一个现代化的社会中,我们不仅仅要努力发挥孔子的“中”的思想,还需要发挥孔子“用中”的思想。 相似文献
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Indira N. Z. Day Floris M. van Blankenstein Michiel Westenberg Wilfried Admiraal 《Assessment & Evaluation in Higher Education》2018,43(6):908-929
In-course assessment, such as midterms, quizzes or presentations, is often an integral part of higher education courses. These so-called intermediate assessments influence students’ final grades. The current review investigates which characteristics of intermediate assessment relate to these grades. In total, 88 articles were reviewed that examined the relationship between intermediate assessment and student grades. Four main characteristics were identified: the use of feedback, whether the assessment is mandatory, who is the assessor, and the reward students get for participating. Results indicate that corrective feedback leads to the most positive results, but elaborate feedback may benefit lower achieving groups. No difference in results was found for mandatory versus voluntary intermediate assessments. Peer assessment seemed to be beneficial, and rewarding students with course credit improves grades more than other rewards. Three scenarios are presented on how teachers can combine the different characteristics to optimise their intermediate assessment. 相似文献
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有机化学反应中 ,活性中间体的稳定性大小与该分子的反应活性有很大的关系 .活性中间体越稳定 ,其越容易形成 ,反应活性就越大 .本文仅就一些常见的活性中间体稳定性的分析 ,得出了稳定性与反应活性的关系 相似文献
18.
Cognitive load and mental rotation: structuring orthographic projection for learning and problem solving 总被引：1，自引：0，他引：1
Hitendra K. Pillay 《Instructional Science》1994,22(2):91-113
Cognitive load theory was used to generate a series of three experiments to investigate the effects of various worked example formats on learning orthographic projection. Experiments 1 and 2 investigated the benefits of presenting problems, conventional worked examples incorporating the final 2-D and 3-D representations only, and modified worked examples with several intermediate stages of rotation between the 2-D and 3-D representations. Modified worked examples proved superior to conventional worked examples without intermediate stages while conventional worked examples were, in turn, superior to problems. Experiment 3 investigated the consequences of varying the number and location of intermediate stages in the rotation trajectory and found three stages to be superior to one. A single intermediate stage was superior when nearer the 2-D than the 3-D end of the trajectory. It was concluded that (a) orthographic projection is learned best using worked examples with several intermediate stages and that (b) a linear relation between angle of rotation and problem difficulty did not hold for orthographic projection material. Cognitive load theory could be used to suggest the ideal location of the intermediate stages. 相似文献
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藏淑芹 《青岛职业技术学院学报》2010,23(1):82-85
随着经济危机蔓延深入,建立何种货币政策中介目标以实现国民经济复苏发展是世界各国经济学家不断探究的重要课题。我国货币政策中介目标的选择从货币供应量逐步演变为利率,基于本国实际,利率作为货币政策的中介目标还存在一些障碍,需要一些配套条件。 相似文献
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