Not all scientific information can be neatly found in handbooks, encyclopedias or published articles. Please look at the gray literature sections (preprints, standards, patents, etc.) for ideas on how to track down harder-to-find materials.
This diagram, "Scientific Literature" by K. Subramanyam (p.394) originated from Encyclopedia of Library and Information Science (New York, 1979, Allan Kent and Harold Lancour, eds.). A copy of the diagram can be found at http://www.unm.edu/~unmvclib/handouts/scienceresearchpublication.jpeg
