The style used by the journal Proceedings of the National Academy of Sciences. This is a numbered style. Proper formatting of references in PNAS style is described on page vi of these instructions for authors (see the section on References).
Reference managers (also called citation managers or bibliographic management software) offer a way to save, organize and manage references. Many work with word processing software to format in-text citations and bibliographies for papers and theses, allow you to share references, and enable you to attach or link PDFs to a citation record.