Sources are considered primary, secondary, or tertiary depending on the originality of the information presented and their proximity or how close they are to the source of information. In the sciences, research findings may be communicated informally between researchers through email, presented at conferences (primary source), and then, possibly, published as a journal article or technical report (primary source). Once published, the information may be commented on by other researchers (secondary sources), and/or professionally indexed in a database (secondary sources). Later the information may be summarized into an encyclopedic or reference book format (tertiary sources).
Information taken from University of Minnesota Libraries Bio-Medical Library: Primary, Secondary & Tertiary Sources in the Health Sciences (2010). http://hsl.lib.umn.edu/sites/default/files/Primary%20Sources%202010.pdf
Primary sources are original materials/information on which other research is based. #primarysource
Journals or periodicals: main type of publication in which scientific research is reported. May be published by learned societies or by commercial publishers.
Theses: detailed accounts of research conducted for the awarding of higher academic degrees. The research is assessed by external examiners before the degree is awarded.
Conferences: an important avenue for reporting new research or developments. Conference papers can be: not published at all, published only in abstract form, published in advance of the conference as a preprint, published in book form, or as a special issue of a journal.
Reports: individual publications reporting research. They may report internal research within an organization, or research done by an individual or organization under contract to a client. Many governmental reports (full-text) are now being made available via the Internet.
Patents: provides research information on new products or processes. Once published, patent information is freely available, but rarely republished in journal articles.
Secondary sources analyses, evaluates, interprets, re-packages, summarizes or reorganizes information reported by researchers in the primary literature. #secondarysource
Review Journals: These generally start with Annual Review of ..., Advances in ..., Current Opinion in ...
Literature/Article Reviews: Articles that summarize the current literature on a specific topic.
Data compilations: Statistical databases (SEERS),Vital & Health Statistics, etc.
Article indexes/databases: These can be abstracting or citation (e.g. Biological Abstracts/MEDLINE)