In 2000 back issues of this scholarly journal were made available to researchers through JSTOR (Journal Storage). JSTOR offers online access to numerous scholarly journals on a "moving wall" basis -- in which users may download the full text and figures of each article that is at least three-years-old. Currently, JSTOR coverage includes Proceedings of the National Academy of Sciences of the United States of America, Vols. 77-97, 1980-2000. Newer articles are continually added on a moving wall basis. Access is limited to participating institutions.