The letter represents the type of document cited, such as [J] indicating that the cited document comes from a journal.
Common reference letter types represent:
1. Monograph [M], Proceedings [C], Newspaper Article [N], Journal Article [J], Dissertation [D], report [R], standard [S], patent [P], extracted literature in thesis collection [A];
2. Electronic document types: database [DB], computer [ CP], electronic bulletin [EB];
3. The carrier type of electronic documents: Internet [OL], optical disk [CD], magnetic tape [MT], disk [DK].
Reference description format
1. Journal author. Title〔J〕. Journal title, year of publication, volume (issue): starting and ending page numbers
2. Author of the monograph. Book title〔M〕. Edition (the first edition is not described). Place of publication: publisher, year of publication: starting and ending page numbers
3. Author of the collection of papers. Title〔C〕． editor. Name of thesis collection, place of publication: publisher, year of publication: starting and ending page numbers
4. Author of thesis. Title〔D〕. Save location. Save the unit. Year
5. Patent document title [P]. Country. Types of patent documents. Patent number. Publication date
6. Standard number. Standard name [S]
7. Newspaper author. Title〔N〕． Newspaper name. Publication date (edition)
8. Report author. Title〔R〕． Save location. Year
9. Author of electronic documents. Title [Electronic document and carrier type identification]. Document source, date