This study was designed to investigate the developmental principle and characteristics of pencil grasps in preschool children by mean of their drawing circles.

以握笔画圆为测查任务，考察了学龄前儿童握笔姿势的发展趋势及特点。

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This review summarizes the fundamental principle of ion mobility spectrometry (IMS). New progress is presented and commented in detail. Furthermore, t he developmental trend of IMS is also discussed.

本文简要介绍了离子迁移谱的基本原理，对近年来离子迁移谱技术的最新进展进行了较为详细的评述，并对未来的发展趋势作了展望。

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The basic principle of atmospheric ozone layer destruction hy polyurethane blowing agent CFC-11, and various way, developmental trend and economic feature of substitution for CFC-11 were reviewed.

简述了CFC - 11对大气臭氧层破坏的基本原理，介绍了聚氨酯cfc - 11替代的不同途径及发展趋势，评价了CFC - 11替代的经济特性。

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