Then, based on retrospectivelaw introduced systematic study of the wisdom of the content and features of beer, a retrospective study of the role of law in the system;
然后，介绍了基于回溯法的智能排课系统研究的内涵及特征，研究了回溯法在系统中的作用；
2
Methods: By epidemic retrospective study, we have investigated the occurrence and distributive law of occupational injury from 1980 to 1999 in a non-ferrous metal company.