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.
Description format of references: 1, name of journal author [J]. Title, year of publication, volume (issue): page number.
2. Monograph author. Title [M] edition (the first edition is not recorded). Place of publication: publisher, year of publication: page numbers.
3. Title of the author of the anthology [C] Name of the editor's anthology, place of publication: publishing house, year of publication: starting and ending page numbers.
4. Title of dissertation author [D]. Save location Save unit year.
5. Title of the patent document [P]. Country. Types and patent numbers of patent documents. Date of publication.
6. Standard number. Standard name.
7. Title of newspaper author. Newspaper name. Publication date (version).
8. Title of the report author [R]. The year when this place was preserved.
9. Title of electronic document author [electronic document and carrier type identification]. The source and date of the document.