PMC includes some journals published by US government agencies that make their articles
available under a Creative Commons CC0 (public domain) license. Some other journals also
apply a CC0 license to selected articles in PMC. All these articles may be used and
reproduced without special permission. However, anyone using the material is requested to
properly cite and acknowledge the source.
You may now search for CC0 articles by using special filters in both PMC (cc0 license[filter]) and PubMed (pmc cc0 license[filter]). These filters
are based on license information that is provided to PMC by publishers and encoded as
machine-readable identifiers in the source XML of each article. For more information, see
the Open Access Subset page.
Please bear in mind that these articles, although made available under a CC0 license, may
still contain photographs or illustrations copyrighted by other commercial organizations or
individuals that may not be used without obtaining prior approval from the holder of the