共查询到20条相似文献，搜索用时 78 毫秒
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电学实验中仪器的选择是一项综合性指标,既要对仪器不造成损害,又要使测量的误差尽可能的小,并不是量程不小于待测量值和实际值不大于额定值即可。怎样选择仪器呢? 一、电表的选择指针式电压表、电流表的“允差”(最大可能误差)为±(量程×等级÷100),例如某一2.5级电压表量程0～3伏,允差ΔU=±3×2.5％=±0.075伏。因此,用同一量程时,电表不同示数的绝对误差相同,但相对误差不同。当上述电压表读数U=2.5伏时,则相对误差仍为ΔU/U=±0.075/2.5=±3％,而当读数U=0.50伏时、相对误差却增大为ΔU/U=±0.075/0.50=±15％。由此可见,选择电表量程时,应使指针的偏 相似文献
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《中国远程教育(综合版)》1985,(6)
〔习题3-1〕(1)算术平均误差:δ_Ⅰ=3.6、δ_Ⅱ=3.6;(2)标准偏差:σ_Ⅰ=3.9、σ_Ⅱ=6.2。〔习题3-2〕无周期性系统误差,无累进性系统误差。〔习题3-3〕(1)串联总电阻:R_串=5000Ω、绝对误差±5Ω,相对误差0.1％;(2)并联总电阻:R_并=200Ω,绝对误差±0.2Ω,相对误差0.1％。〔习题3-4〕相对误差3.2％。〔简解〕(1)测50mV时,毫伏表的基本误差为:γ_1=仪表满量程示值/测量值×仪表引用误差=100/50×1.5=3％;(2)温度附加误差: 相似文献
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在小学阶段,有些几何图形的面积引导学生用分数方法解答既简便,又利于学生掌握,而且突出了图形之间的相互关系,培养了学生良好的思维品质。下面举例说明。在教学中,我们可以发现:圆心角是90°的扇形面积是以它的半径为边长的正方形面积的78.5％。(π取3.14) 证明:圆心角是90°的扇形的半径为r,则面积是πr~2×(90)/(360)=πr~2/4。边长为a的正方形面积为a~2。当a=r时,则a~2=r~2,扇形面积是正方形面积的(πr~2)/(4/a~2),当π取3.14时,则π/4=0.785=78.5％还可以得出图中阴影部分面积为1-78.5％= 相似文献
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食品或饲料中三聚氰胺和三聚氰酸经乙腈水萃取、提纯后,采用高效液相色谱(HPLC)法测定,外标法定量.对色谱分离条件进行了优化,三聚氰胺在0.1156～11.56 mg/L范围内线性良好,复相关系数r2=0.9997,平均加标回收率在95.59％～105.97％之间,相对标准偏差为0.14％～0.29％,检出限(S/N=3)为0.012 mg/L.三聚氰酸0.1020～10.20mg/L范围内线性良好,复相关系数为r2=0.9995,平均加标回收率在77.44％～88.77％之间,相对标准偏差为0.32％～0.86％,检出限(S/N=3)为0.051 mg/L.该法能满足食品或饲料中三聚氰胺和三聚氰酸检验工作的需要. 相似文献
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例 1将溶质质量分数为 3p％的某溶液与 p％的该溶液等体积混和后,其溶质质量分数小于 2p％,则这种物质可能是 A H2SO4 B氨水 C NaOH D C2H5OH 解析： 设 3p％的密度为ρ 1, p％的密度为ρ 2,体积均为 V,混和溶液的密度为ρ,则混和溶液溶质质量分数： =× 100％ =％ =％ =2p％＋ p％ 由上式可知,当浓度与溶液的密度成正变关系时,ρ 1－ρ 2>0,则混合后溶质质量分数大于其算术平均值;若浓度与溶液的密度正反变关系时,ρ 1－ρ 2 大家知道,已知溶液的溶质质量分数为 a％,密度为ρ g/cm3,则其物质的量浓度为： … 相似文献
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姚翠荣 《四川教育学院学报》2010,26(7):34-36
目的探讨海洛因依赖者的时间管理倾向与自我价值感的特点及二者的关系。方法运用时间管理倾向量表和自我价值感量表对150名海洛因依赖者进行问卷调查。运用均值差异性检验、方差差异分析、相关分析及多元逐步回归分析。结果 1.海洛因依赖者的时间管理倾向显著低于大学生;2.海洛因依赖者自我价值感高于常模群体;3.海洛因依赖者时间管理倾向和自我价值感有显著正相关;4.时间价值感和时间监控观对自我价值感有预测作用,但未发现时间效能感对自我价值感有预测作用,表现出特殊性。结论海洛因依赖者的时间管理倾向、自我价值感同常模有差异,海洛因依赖者的时间管理倾向与自我价值感呈显著正相关。 相似文献
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不少小学数学教师在教学的实践中,发现一个奇怪又极为普遍的现象:不同学校,甚至不同年代的学生,在学习数学的某一阶段出现的一些错误,几乎是完全相同的。比如:0.5小时=50分,80×0=80,3/4+3/4=6/8,0.8999>0.9,7-3(1/2)=4(1/2),100增加10％,再减少10％,仍然是100,等等。这些错误一般发生在那些对知识不求甚解的学生身上,而且很不容易纠正。 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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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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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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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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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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《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