Create an entry based on an ID such as DOI or ISBN.
For other identifiers, choose Library → New entry, or click on the New entry button, or use the keyboard shortcut CTRL + N. In the lower part of the window, there are two boxes : "ID type" and "ID". In the field "ID type", you can select the desired identifier, e.g. "ISBN" (it works also for DOI). Then enter the identifier in the textbox below and press Enter. That will generate an entry based on the given ID (you can also click on "Generate"). The entry is added to your library and opened in the entry editor. In case an error occurs, a popup is shown.
ArXiv is a repository of scientific preprints in the fields of mathematics, physics, astronomy, computer science, quantitative biology, statistics, and quantitative finance (Wikipedia).
ID search is carried out using the ArXiv identifier.
Crossref is an official Digital Object Identifier (DOI) Registration Agency of the International DOI Foundation.
ID search is carried out using the DOI.
First, eBook.de's API is used to fetch bibliographic information based on the ISBN. If no entry is found, the JabRef tries OttoBib to get data.
ID search is carried out using the International Standard Book Number.
DiVA (Digitala Vetenskapliga Arkivet) is a database with publications from about 40 Swedish universities and research institutions.
ID search is carried out using the DiVA id (diva2).
JabRef uses http://dx.doi.org/ (provided by http://crossref.org/) to convert the given DOI to a new entry.
ID search is carried out using the DOI.
If JabRef cannot find the reference of your DOI using this ID type, please, try the same DOI with the ID type "mEDRA". The ID type mEDRA looks for the reference corresponding to a DOI too, but using another registration agency.
The International Association for Cryptologic Research maintains an eprint archive to which anyone can submit papers and technical reports. These eprints are given IDs based on the year of submission, e.g. the 10th submission in 2018 gets the ID "2018/10". To get the ID, you may want to use their web search form at https://eprint.iacr.org/search.html.
ID search is carried out using the Cryptology ePrint ID.
The Library of Congress is the research library that officially serves the United States Congress and is the de facto national library of the United States (wikipedia).
ID search is carried out using the Library of Congress Control Number (LCCN).
MathSciNet is a searchable online bibliographic database. It contains all of the contents of the journal Mathematical Reviews (MR) since 1940 along with an extensive author database, links to other MR entries, citations, full journal entries, and links to original articles. It contains almost 3 million items and over 1.7 million links to original articles (Wikipedia).
ID search is carried out using the MR number.
ID search is carried out using the DOI.
Based on the title of your publication, JabRef call Crossref, which return the corresponding DOI. Then JabRef fetches the reference based on this DOI.
To return a reference, the publication needs to have a DOI.
IETF (Internet Engineering Task Force) Datatracker is a database that "contains data about the documents, working groups, meetings, agendas, minutes, presentations, and more, of the IETF." It used to be available at https://datatracker.ietf.org/ (currently down).
ID search is carried out using the (Request for Comments number) (RFC) of the IETF database.
ID search is carried out using the Zbl number.