Primary Sources
These sources are the original accounts of scientific research. Primary sources are how researchers communicate their findings to the engineering scholarly and professional community.
Research articles are typically published in academic journals and have most likely been through a peer-review process. They function as primary reports of research: engineers publish papers to share the results of their work. The language in articles is usually highly technical and assumes the reader is experienced in the field.
Preprints are early versions of research articles which have not yet been peer-reviewed. Engineers may choose to disseminate their research as preprints before submitting to an academic journal, which can make the research reported very cutting edge, but should be read critically as it has not yet been reviewed by other experts.
Technical reports are structured like case studies, or "how I solved this problem." They typically cite research articles as the basis for methods chosen. They serve as a project report to the funding source, which may be a federal, state, or local government agency. Technical reports are not always available to the public - they may be kept proprietary, especially if client is a non-governmental corporation.
Proceedings papers are usually works in progress that are presented as lectures or posters at academic conferences. Depending on the organization, proceedings papers may or may not be peer-reviewed. It is common for a conference presentation to be later published as a full research article.
Dissertations and theses are detailed accounts of research by graduate students. These documents are reviewed by a committee of university faculty before a degree is awarded. In many fields, the chapters will be also published as a journal article in a more concise form.
A patent for an invention grants intellectual property rights to the inventor. In order to obtain a patent, scientists must file technical information about the new invention, which is publicly disclosed for everyone to read.
Secondary Sources
These sources analyze, evaluate, interpret, or otherwise discuss information originally presented elsewhere.
A review article is a peer-reviewed report which analyzes a body of research articles. They are usually narrow in focus and have extensive bibliographies. Review articles examine trends, replication of results, and future directions of the field. While reviews are written for a technical audience, they can be helpful for readers who are new to the subject because they condense a lot of previous research.
Trade publications are frequently called magazines or journals. They serve to keep practitioners up to date about products, meetings, and research summaries. They are structured informally, and they contain lots of advertising and news. Articles are brief and usually do not have references at the end.
There is a wide scope of engineering books, ranging from broad overviews to narrowly focused. Scholarly books are useful for learning the foundations of the field; they often include a lot of detail that is omitted from research articles. Books can range from specialized to easily accessible for non-experts.
Tertiary Sources
Complied works that list, index, or organize primary and secondary resources for reference. These types of sources are not usually credited to any particular author.
Encyclopedias and dictionaries are organized compilations of information that are usually broad in scope and written by a large number of authors. These resources are a good place to look up quick facts, key concepts, and unfamiliar definitions of terms.
Data are first reported in the primary literature. Later, book editors and database providers compile these data into tables and charts for easy reference. Many of these resources are now digital.
Databases are indexes of the contents of thousands of scholarly journals. When searching for a research article, using a database enables readers to refine search queries and locate articles of interest. Databases typically only index journal articles, meaning that the full text of the paper itself is located in the journal.
