前言：介绍管道三层结构聚烯烃防腐技术的基本特点和技术要求，以及该技术在国内外的应用情况。
This article introduces the characteristics and technical demands of the "three_layer_structure" polyolefin anticorrosive technology of pipeline and its application.
第三为不饱和烯烃；
本文简要介绍用几种方法立体选择性合成三和四取代烯烃。
This paper reports briefly stereoselective synthesis of tri and tetra-substituted ethylenes by some methods.
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