浅说化学式

一、化学式表示的意义用元素符号表示物质组成的式子叫做化学式.以CuSO4·5H2O为例,从宏观意义上说:a.它表示胆矾这种物质.b.表示胆矾由铜、硫、氧、氢四种元素组成;c.胆矾中各元素质量比为m(Cu):m(S):m(O):m(H)=64:32:9×16:10×1=32:16:72:5;d.它的式量是64+32+9×16+10×1=250;e.从微观意义上说,它可表示一个胆矾分子;f.一个胆矾分子中Cu:S:O:H原子个数比1:l:9:10.     

数字宝塔

形体各异、千姿百态的宝塔,是我国古代文明的瑰宝.十分有趣的是,在数学里也有这种“数字宝塔”.例如,1×8+1=912×8+2=98123×8+3=9871234×8+4=987612345×8+5=98765123456×8+6=9876541234567×8+7=987654312345678×8+8=98765432123456789×8+9=987654321法国数学家路伽,对“数字宝塔”特别感兴趣.他收集和研究了大量的例子,下面列举的只是其中的两例:1×9+2=1112×9+3=111123×9+4=11111234×9+5=1111112345×9+6=111111123456×9+7=11111111234567×9+8=1111111112345678×9+9=111111111123456789×9+10=11111111110×9+8=89×9+7=8898…     

负压下隔音毡阻气性能的测定

阐述了汽车隔音毡阻气性能的测定和数据处理方法,通过在负压下针对700 g/m2×9 mm、1000 g/m2×15 mm、1400 g/m2×20 mm这3种规格隔音毡阻气性能的测定,发现隔音毡的两侧压差与流量间存在一定联系,并可以用幂函数方程式表示出隔音毡阻气率与两侧压差(或流量)之间的关系,为新产品的开发提供了理论上的引导。     

有关溶质质量分数的计算复习导引

一、复习要求有关溶质质量分数的计算 ,应该在掌握溶液、溶质、溶剂和溶质质量分数等概念的区别与联系的基础上 ,熟练掌握 :(1 )应用溶质质量分数概念进行计算 .(2 )有关溶质质量分数的综合计算 .二、知识结构溶质质量分数的计算1 基本计算 :溶质质量分数 (p) =溶质质量溶液质量× 10 0 %　　　　　　 =溶质质量溶质质量 +溶剂质量 × 10 0 %2 溶液稀释的计算 :　m浓 ×p浓 =(m浓 +m水)×p稀3 溶液浓缩的计算 :　m稀 ×p稀 =(m稀 -m水)×p浓4 溶液混合的计算 :　m浓 ×p浓 +m稀 ×p稀 =(m浓 +m稀)×p混5 溶质质量分数与化学方程式的综合…     

一题多解小议

有这样一道例题:“小学生排队做操,每行8人,可以排9行。如果每行站6人,可以排成几行?”学生读题后,教师组织了以下的师生活动。师:这道题怎样列式解答? 生甲:先求出总人数(8×9=72),再除以每行6人,就得到所求的行数(72÷6=12)。师:除了这种解法外,还有其它的解法吗? 生乙:可以列式为8×9÷6=12(行)。生丙:也可看成每列9人,排了8列,这样就有9×8÷6=12(行)。生丁:一行是两个半行,一行8人,半行4人,于是有4×2×9=72(人),72÷6=12(行)。师:刚才同学们积极动脑,发言踊跃,很快找到4种解法,课后大家有兴趣,还可找出更多的解法。在这里,教师不是从不同角度、不同侧面启发学生对题目的数量关系进行分析,从而求得多解,而是把同种解法的不同列式看成不同解法,即在同一层次上进     

“9的乘法口诀”教学实录

一、复习准备 　　口算下面各题。 3× 4= 8× 3= 5× 4= 8× 4= 7× 6= 5× 8= 6× 5= 8× 7= 4× 6= 8× 2= 3× 6= 5× 7=　　二、揭示课题 　　前面同学们已经学习了 1～ 8的乘法口诀,这节课学习 9的乘法口诀。 (板书课题 )　　看到课题,你们能想到什么 ?　　(想到 9的乘法口诀共有 9句,每句口诀的第二个字都是九,第一个字从一排到九, 9的乘法口诀得数一个比一个多 9…… )　　三、教学新课 　　1推导 9的乘法口诀 (教准备题及例 1)　　(1)学生自编 9的乘法口诀 　　师：刚才同学们说 9的乘法口诀的前半句是从“一九”到“九九…     

二年级上学期期末数学(人教版)测试题

智慧乐园1.在○里填上“>”“<”或“=”。35-16○208×9○804×4○153×6○6+6+66×6○9×42.填上合适的单位。铅笔长18()大树高6()小学生高1()12()3.在对称的图形下面画“√”()()()4.中有()条线段,()个直角。5.水果下面藏着什么数?+=×=12同学们,一个学期的学习要结束了,老师知道你学的很棒,试试吧!你一定会取得好成绩!神机妙算1.直接写得数。6×8=5×9=5×6=7×4=9×9=8×7=9×4=3×8=6×9=7×5=8×9=5×8=7×6=8×4=9×7=15+30=36-15=55-40=21+36=48-9=2.用竖式计算。37+2876-3690-593.笔算下面各题。39+60-7594-56+37心灵手巧1.画一条…     

因式分解的妙用

在计算或证明题中 ,如能巧妙利用因式分解 ,则能使问题由复杂变得简单 ,下面就介绍它的几种妙用。一、进行有理数计算例 1.计算 :62 12 - 72 9× 373-1482 。解 :62 12 - 72 9× 373- 1482=( 62 1 148) ( 62 1- 148) - 72 9× 373=769× 4 73- 72 9× 373=( 72 9 40 )× 4 73- 72 9× ( 4 73- 10 0 )=72 9× 4 73 40× 4 73- 72 9×4 73 72 9× 10 0=4 0× 4 73 72 9× 10 0=9182 0。二、计算代数式的值例 2 .已知 a2 a- 1=0 ,求 a3 2 a2 1998的值。解 :a3 2 a2 1998=( a3 a2 - a) ( a2 a) 1998,∵ a2 a- 1=0 ,则 a2 a=1。　　∴原式…     

以3排头的自然数序列——自然数的萨尔可夫斯基序

自然数从它诞生的时候起,就是从小到大排序的:1,2,3,4,5,….1964年,前苏联数学家萨尔可夫斯基在《乌克兰数学杂志》发表了一篇不太引人注目的论文《线段连续自映射的各周期共存》,文中把自然数重新排序为:3,5,7,9,11,…6,10,14,18,22,…12,20,28,36,44,…为了便于理解,我们把上面的排序在形式上稍作改动,即是:3×20,5×20,7×20,9×20,11×20,…3×21,5×21,7×21,9×21,11×21,…3×22,5×22,7×22,9×22,11×22,…3×2n,5×2n,7×2n,9×2n,11×2n,…2m,…,25,24,23,22,21,20.…,32,16,8,4,2,1.通过这样一改动,我们可发现这种排序的构成方…     

神奇的12345679

数字世界里充满了神奇的数字,上次我们提到了神奇的6174,今天再来看看神奇的12345679。乍一看这个数字,是有一点点特殊,从1到9,中间只少了一个8,那么它有什么神奇呢?我们动手做做就知道了。我们用12345679去分别乘以9、18、27……的9的倍数,看看,得到了什么结果。12345679×9=11111111112345679×18=22222222212345679×27=33333333312345679×36=44444444412345679×45=55555555512345679×54=66666666612345679×63=77777777712345679×72=88888888812345679×81=999999999很神奇吧?得到的9个9位数,各个数位上的数字全部是一样的。这是中…     

卡思卡特城堡

It is worthy of noting that, whilst Crookston Castle witnessed the earlier and happier portion of Mary's variegated life,     

不同的吃喝玩乐

一、吃和喝吃苹果 eat an apple, 吃药 take medicine,吃糖 have some sweets,吃饭 have one's meals,吃馆子 dine out,吃惊 be surprised/     

漏洞百出的教育

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?     

Western and Eastern culture differences in commercial field

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.     

只要努力,不要后悔

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.     

浅谈移民问题

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.     

Sister Carrie, an Adherent of Desires

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.     

Improvement of one-cycle controller by use of proportional integral differential controller

1.IntroductionOne-cyclecontrolmethod,whichwasproposedaboutonedecadeago[1],hasbecomeanattractivemethodinspecialfieldssuchaspowerfactorcorrection[2-6],switchingamplifiers[7,8],etc.Themainideaofthiscontrollerisbasedonintegrationofdiodevoltageinone-cycleandforcesittobeexactlyequaltothereferencevalue.Themainadvantageofthiscontrollerisitsrealtimeabilitytorejectthevariationofinputvoltage[1].Despitethisgreatability,ithasnogoodperformancesinrejectingofloaddisturbanceandfollowingreferencecommands.Espec…     

风的曲线

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.