According to GB3469- 83 "File Type and File Carrier Code", it is identified by a single letter:
M 1 monograph (including historical records in ancient books).
Prose collection.
Newspaper articles.
Journal articles.
A paper.
R- research report.
S standard
Patents.
Precipitating documents in monographs and papers.
Z- Other unspecified literature types.
Electronic document types are identified by two letters:
DB-a database.
Computer program.
Electronic bulletin.
For electronic documents with non-paper carriers, the carrier type shall be indicated in the reference mark:
DB/OL- an online database.
DB/MT-a tape database.
M/CD- CD books.
Disk software.
J/OL- online journal.
Online electronic bulletin.
Specific arrangement of sequential coding system
References are continuously coded with Arabic numerals in the order in which they appear in the text, and the serial numbers are placed in square brackets. If the file is referenced repeatedly, it is marked with the same serial number in the text. Generally speaking, the page number (or page number range) of a document cited once is listed in the following references.
The format is "publication year" of the work or "year, volume (issue)"+":page number (or page number range)" of the periodical. For documents cited many times, list the page number or page number range of each reference in the serial number tag (some publications also regard the information that can indicate the location of the cited documents as page numbers) and put them in square brackets (only numbers are listed, without words and characters such as "P" or "page"; The line in the middle of the page number range is a half-word line) and marked with superscript.
If the serial number of a reference appearing as text needs to be followed by a page number or a page number range, the page number or page number range should also be superscript. Authors and editors need to carefully check the serial numbers of references under the sequential coding system, so that the serial numbers are consistent with the list of references after the marked documents are exactly the same. In addition, the page number or page number range of references should also be accurate.
Reference to the above content: Baidu Encyclopedia-References