sources of information

Main information: letters, oral interviews.

Second-hand materials: textbooks, encyclopedias, yearbooks, reviews and series of articles.

Indexes, abstracts, catalogues and bibliographies.

1, printed materials. Printed materials refer to materials that can only be read intuitively through printing procedures. Their types include: printed books, serial publications, periodicals, manuscripts, brochures, publicity materials, leaflets, sales catalog clippings, etc.

2. Non-printed materials

Non-printed materials, also known as "non-book materials", refer to materials that are not produced and presented by printing; Multimedia data is a part of it, such as records, slides, micro data and other data learned by hearing or vision.

Its types are:

Picture (picture)

Microform (microform)

Movies and slides (movies and slides)

Video tape (video tape)

record

Computer software (computer software)

Artifacts, teaching AIDS (teaching AIDS), etc.