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Last Updated: Aug 05, 2016     Views: 59

The AMA Manual of Style states in Chapter 3.15.1 Online Journals:

When the DOI is provided, it is preferable to cite it rather than the URL. 

Note: The DOI is provided immediately after ‘‘doi:’’ and is set closed up to it, per convention. No accessed date is required for the DOI, making it the last item in the reference.