Doi consists of two parts: prefix and suffix, separated by "/". The basic structure of doi coding is as follows: doi:10.3969/j.issn.xxxx-xxxx.yyyy.nn.zzz, where nn is the issue number. The doi of extended data includes two parts: prefix and suffix, separated by "/". The prefix consists of two parts, one is the directory code, and all doi directories are "10". , that is, all Dior codes start with "10". The other is the registration agency code. Any organization or unit that wants to register doi can apply for registration agency code from IDF. Suffixes are unique. The suffix under a specific prefix is assigned by the registration authority to ensure its uniqueness. The suffix can be any alphanumeric code, and its coding scheme is completely specified by the registration agency itself. The suffix can be machine code or existing specification code, such as ISBN number or ISSN number. The basic structure of the doi code of the cooperative periodical papers of Wan Fang Data Company is as follows: doi:10.3969/j.issn.xxxx-xxxx.yyyy.nn.zzz, where nn refers to the issue number. For example:10.3969/j.issn.1004-3810.2008+0.00438+0. The issue number here is "0 1".