Free DOI lookup

If you have bibliographic data for a item and would like to find the DOI, or if you only have an article title and author or the text of a bibliographic reference, try CrossRef for individual DOI retrieval. CrossRef is a collaborative reference linking service that functions as a sort of digital switchboard. It holds no full text content, but rather effects linkages through CrossRef Digital Object Identifiers (CrossRef DOI), which are tagged to article metadata supplied by the participating publishers. The end result is an efficient, scalable linking system through which a researcher can click on a reference citation in a journal and access the cited article. (Source: CrossRef, accessed on 06/01/2011)