Proceedings of the National Academy of Sciences

The Proceedings of the National Academy of Sciences of the United States of America, usually referred to as PNAS, is the official journal of the United States National Academy of Sciences. PNAS is an important scientific journal that printed its first issue in 1915 and continues to publish cutting-edge research reports, commentaries, reviews , perspectives , colloquium papers , and actions of the Academy. Coverage in PNAS spans the biological, physical, and social sciences. Although most of the papers published in the journal are in the biomedical sciences, PNAS recruits papers and publishes special features in the physical and social sciences and in mathematics. PNAS (abbreviated Proc Natl Acad Sci USA for referencing and indexing purposes) is published weekly in print, and daily online in PNAS Early Edition.

Impact
PNAS is widely read by researchers, particularly those involved in basic sciences, around the world. The journal is notable for its policy of making research articles freely available online to everyone 6 months after publication or immediately if authors have chosen the "open access" option. Immediate online access (without the 6-month delay) is available in more than 140 developing countries and for some categories of papers such as colloquia. Abstracts and tables of contents are free.

Because PNAS is self-sustaining and receives no direct funding from the government or the National Academy of Sciences, the journal charges authors publication fees to help offset the cost of the editorial and publication process. PNAS is abstracted and/or indexed in: Index Medicus, PubMed Central, Current Contents, Medline, SPIN, JSTOR, ISI Web of Science, and BIOSIS.

The journal's impact factor for 2004 was 10.452 (as measured by Thomson ISI). PNAS is also the second most cited scientific journal with 1,338,191 articles from 1994-2004 (the Journal of Biological Chemistry is the most cited journal over this period with 1,740,902 citations in total).