Lesson 16　Plastics

Plasticsaresyntheticorman-madematerialswhichhaveuniqueandremarkableproperties.Manydifferentplasticsmaybeobtainedbymanipulatingthemoleculesandchangingthechemicalcombinations.Plasticshaveimportantrolesinagriculture,appliances,clothing,construction,electroni ......（本文共 7326 字 , 2 张图）     [阅读本文] >>