说明：  郑君里的《信号与系统》，非常经典的一本书。是研究确定性信号经线性时不变系统传输与处理的基本概念和基本分析方法。
(Zheng Junli's signals and systems, a very classic book. It is the basic concept and basic analysis method for the transmission and processing of invariable system when determining the longitude of deterministic signal.)