[经] harvest theory of the trade cycle

shāng yè zhōu qī de shōu chéng lùn ㄕㄤ ㄧㄝˋ ㄓㄡ ㄑㄧ ㄉㄜ˙ ㄕㄡ ㄔㄥˊ ㄌㄨㄣˋ