本文给出了严格对角占优周期三对角矩阵逆元素上界和下界的估计，改进了一些学者近期的研究结果。
In this paper, we give the estimates for the upper and lower bounds on the inverse elements of strictly diagonally dominant periodic tridiagonal matrices, and improve the latest findings.
镉是重金属有毒元素，其环境污染一直是众多学者研究的焦点。
The environmental pollution caused by cadmium, a heavy metal toxic element, has aroused geologists' attention.
在工程制图课程学习中，几何元素点、线、面的投影问题是学习形体投影的基础，也是初学者刚开始接触制图知识，学习中容易感觉困难的部分。
In engineering drawing courses, the projection of point, line and surface is the basis of learning physical projection, which is often difficult for beginners to learn.
目前，化学者已发现了一百多种元素。
More than one hundred elements have been found by chemical workers at present.
目前，化学者已发现了一百多种元素。
More than one hundred elements have been found by chemical workers at present.
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