There are also "papers" and some "monographs", which are identified by single letters according to GB3469-83 "Document Types and Document Carrier Codes":
M- Monographs (including works on history and chronicles in ancient books)
Essays
Newspaper articles
Journal articles
Doctoral dissertation
R- research report
S standard
patent
A—— Precipitated documents in monographs and papers.
Z—— Other unspecified literature types
Electronic document types are identified by two letters:
database
computer program
Electronic bulletin