In the sciences, there is a strong preference for journals and conference papers over books; informal communication that is as important as formal research; publications that are international; the use of technical language that is not always understandable to the lay person.
Primary scientific literature has several characterisitics:
1. They often have a "Materials and Methods" section and "Results" section.
2. Authors may use "We" or "I" to describe what was done.
3. They are usually very specific: mentioning particular places, organisms, etc.
4. Papers usually start with an introduction-- an overview to set the stage for the research. A very explicit description of what was done follows: the materials or methods used and/or the exact location and sampling procedures. A discussion section will attempt to place the work in a larger theoretical context and may suggest further research to follow and extend the conclusions.
Secondary scientific literature is generally contained in works such as books, chapters or review articles. Primary scientific papers may be difficult to read if the general subject is not well understood. Reading secondary resources first may help to place the research in context. They are sometimes referred to as literature reviews.