You can hyperlink DOI numbers to doi.org. However, some
publishers have elected to use nasty characters in their DOI
numbering scheme ('<', '>', '_' and ';' have all been spotted).
This will either upset (La)TeX, or your PDF reader. This
package contains a single user-level command \doi{}, which
takes a DOI number, and creates a correct hyperlink to the
target of the DOI.