发布时间:2025-01-20 19:21:27
PVC是不可以用于食品包装的,PVC是聚氯乙烯,这种物质会对人体产生有害作用,所以不能用于食品包装,用于食品包装的材料一般用PE或者PP,或者PET
电容器当u不变时 为什么电容与正对面积无关 而当q不变时与正对面积有关
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