原子吸收光谱法测定铅蓄电池板栅中锡、钙和铝

通过先加酒石酸、硝酸溶解样品,用氧化镧、EDTA联合掩蔽铝来测定钙,盐酸沉淀铅后测锡、铝的试验,采用火焰原子吸收光谱法测定锡、钙和铝.     

用构造法证明对称不等式

《中学生数学》2005年3月(上)刊登的“寻找‘零件不等式’证明对称不等式”一文,读后受益匪浅.笔者研读后发现,文中的4道竞赛题还可用构造法统一证明,而且方法独特,提供了一种新的解题途径.下面仍用原文例子加以介绍,供同学们参考。     

不等式a~2+b~2≥2ab的几个推论及应用

不等式a2+b2≥2ab(*)在数学中有着广泛的应用,但有时直接用这个不等式解题,往往很难凑效.本文给出(*)的几个推论及应用,以加深同学们对(*)式潜在的应用价值的理解和掌握.     

一道竞赛题的分析与证明

2004年中国西部数学竞赛题第4题为： 求证：对任意正实数a,b,c,都有     

《数学通报》1830号问题的换元证法

《数学通报》2010年第1期刊登的1830号问题如下:     

寡聚(亚硅基二炔基蒽)电子结构和光谱性质的密度泛函理论研究

Poly(silanylenediethynylanthracene) (PSDEA) exhibits a hole-transporting ability experi-mentally. In order to simulate the property of PSDEA, a series of silanylenediethynylan-thracene oligomers were designed. The structures of these oligomers were optimized by using density function theory at B3LYP/6-31G(d) level. The energy gaps of the oligomers decrease with the increase in the chain length. The energy gaps of the oligomers also de-crease in the presence of the electron-withdrawing group on the anthracene ring. The ¹³C chemical shifts and nucleus independent chemical shifts (NICS) at the anthracene ring center in the oligomers were calculated at B3LYP/6-31G level. The chemical shifts of the carbon atoms connected with the nitryl group changed upfield, compared with those of the carbon atoms without the nitryl group. The aromaticity at the anthracene ring center decreases in the presence of the electron-withdrawing group, whereas increases with the increase in the number of the silanylene units. The most sensitive location for calculating the NICS values is 0.1 nm above the anthracene plane.     

优美不等式中的三姐妹

文[1]、文[2]分别给出了如下两个优美的不等式： 命题1 设a,b,c∈R＋且a＋b＋c=1,则     

一个数学问题的再探究

对如下一个数学问题：在锐角△ABC中，求证：