The sources of prior art are usually divided into "patent literature" and "non-patent literature". Patent literature can be found in public databases of patent offices like the European Patent Office (EPO) or the United States Patent and Trademark Office (USPTO).
Non-patent literature (NPL) is defined as any "technical document that is neither a patent nor a patent application and that is submitted by a party — such as an applicant, an opponent, or a third party — or cited by an examiner during patent prosecution."
Part of the NPL are scientific and technical articles. In 2015 the number of scientific and technical articles published worldwide was almost 80% of the number of patent applications and nearly double the number of granted patents:
Data (patent applications):
Data (granted patents):
Data (scientific and technical articles):