共查询到20条相似文献，搜索用时 93 毫秒
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采用一种腐蚀阴极尖端的新方法,对阴极常用金属材料W,Mo,Ir,Ta制作的阴极尖端进行腐蚀.在1.2×10-6Pa的真空下,对金属材料W,Mo,Ir,Ta尖端阴极的热发射束流稳定性进行了实验研究,得到每小时束流稳定度△I/I<1%的结果.实验表明,采用新方法对阴极尖端进行腐蚀后得到的尖端阴极,同样可保证热发射束流的稳定性要求. 相似文献
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在 1.2× 10 - 6 Pa的真空下 ,对多晶钼尖端阴极的热发射特性进行了实验研究 ,在工作温度 1.8～ 2 .2×10 3K ,亮度可达 10 4 A/cm2 ·sr .实验表明 ,用多晶钼代替单晶钼 ,同样可保证热发射特性的要求 相似文献
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鉴于教材中"验证牺牲阳极的阴极保护法"实验,在铁电极附近滴入K3[Fe(CN)6]溶液,出现溶液变蓝色的异常现象,不能证明铁未被腐蚀。分析了该实验中产生Fe2+离子的原因,通过实验改进,完善了牺牲阳极的阴极保护法实验。 相似文献
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过去中学教材在介绍金属的电化学腐蚀与防护这一内容时,主要是以叙述的方式介绍电化学腐蚀所涉及到的一些概念,如金属腐蚀、化学腐蚀、电化学腐蚀等概念,重点分析析氢腐蚀、吸氧腐蚀、牺牲阳极的阴极保护法和外加电流的阴极保护法这些内容及其相应的4张示意图,从未用实验来介绍这些内容。 相似文献
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为了搞清BaC12溶液与NaHCO3溶液怎样反应的问题,我们组织了一次化学课外活动专门来研究它．首先,我们查阅了有关资料．查出了20℃时的溶解度：BaC1235．7g;NaHCO39．6g其次,准确配制物质的量浓度为1摩／升的氯化钡溶液和碳酸氢钠溶液．用稀释法又配制出浓度分别为0．1、0．95、0．02、0．01、0．005、0．002、0．001、0．0002的氯化钡和碳酸氢钠溶液．然后把化学兴趣小组分为10个实验组,每组2人,把配制的试剂分到10个小组去．令每组务必洗净实验仪器,特别是试剂瓶、试管、滴管．每次必须洗净再做．把试管编上号码（或贴上写有反… 相似文献
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“在使用两种液体配制溶液时，可以用其中一种液体的体积分数来表示．医疗上使用的酒精溶液，就可以用70体积的酒精和30体积的水配制而成，该溶液酒精的体积分数为70％”·（三年制初级中学课本，第145页）这种表述方法，容易对学生造成误导，两种液体混合后溶液的总体积等于两液体体积之和．实际上两种液体混合后溶液的密度一般都发生变化，混合后溶液的体积不等于两种液体体积之和．为了中学教材的科学性、严密性，建议：溶质的体积分数表述使用“国标”，即溶质的体积分数为：“溶液中溶质域溶剂）的体积与溶液体积之比”．例如，乙醇体… 相似文献
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在指导学生做配制一定物质的量浓度的某溶液实验时，我们遇到了这样一个问题：我们要求学生用250ml的容量瓶配制250ml0．4mol/L的NaCl溶液。 相似文献
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三年制中等师范学校《生物学》教科书中，渗透作用演示实验用蔗糖溶液存在不足：由于蔗糖溶液是无色透明的．实验演示时．距离稍远的学生就看不清液面位置，观察不到液面高度变化，影响学生对渗透作用的理解。为此，我们用高锰酸钾—蔗糖溶液替代蔗糖溶液。溶液的配制方法是：取清水置于大烧坏中，向里面分别加入蔗糖和2～3粒高锰酸钾颗粒。充分搅拌、静置，等高锰酸钾完全溶解后即制成紫红色的高锰酸钾一蔗糖溶液。这种改进的优点：由于实验用烧杯和长颈漏斗中的溶液都取自大烧杯中，两者浓度相等，是等渗溶液，不会影响实验效果。而该替代… 相似文献
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李永常 《天津教育学院学报(自然科学版)》1995,(2):39-41
介绍了氢阴极超电势产生的机理，机理共有四步，其中第二步电荷迁越电极金属／溶液相界面的放电反应是控制步骤，举例介绍了氢阴极超电势在科研和生产中的有利与不利作用，以及影响氢电势的主要因素。 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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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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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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Rachel Zupek 《海外英语》2007,(11):40-41
我们绝大部分人都同意一件事情——我们喜欢金钱。但是你对金钱的喜欢之情足够到让你创立一份事业么?.财富通常被人忽视,主要在于人们不能真正了 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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YANGShiguo 《重庆大学学报(英文版)》2004,3(1):86-88
The problem on the geometrc inequalities involving an n-dimensional simplex and its inscribed simplex is studied. Aninequality is established, which reveals that the difference between the squared circumradius of the n-dimensional simplex andthe squared distance between its circumcenter and barycenter times the squared circumradius of its inscribed simplex is not lessthan the 2(n-1)th power of n times its squared inradius, and is equal to when the simplex is regular and its inscribed siplex is atangent point one. Deduction from this inequality reaches a generalization of n-dimensional Euler inequality indicating that thecircumradius of the simplex is not less than the n-fold inradius. Another inequality is derived to present the relationship betweenthe circumradius of the n-dimensional simplex and the circumradius and inradius of its pedal simplex. 相似文献