References
- NLM: the story of NLM historical collections [Internet]. Bethesda: U.S. National Library of Medicine; c2004-2012 [cited 2012 Jun 01]. Available from: http://www.nlm.nih.gov/hmd/about/collectionhistory.html.
- Introducing the new NEJM iPad edition [Internet]. Waltham: Massachusetts Medical Society [cited 2012 Jun 01]. Available from: http://cdf.nejm.org/campaigns/genericlp.aspx?cpc=GMAAALLE0311C&querry=nejmbanner.
- The DOI System [Internet]. DE: International DOI Foundation [cited 2012 Jun 01]. Available from: http://doi.org.
- Crossref.org [Internet]. Lynnfield: Publishers International Linking Association (PILA) [cited 2012 Jun 01]. Available from: http://www.crossref.org.