11. A processor-implemented method comprising the steps of: detecting a reference citation in a first electronic document; processing the reference citation to determine a plurality of links to a second electronic document identified by the reference citation, each of the plurality of links comprising a uniform resource identifier (URI) for directly accessing the second electronic document; selecting at least one of the plurality of links based on preference information; and displaying the selected at least one link and at least a portion of the first electronic document; wherein processing the reference citation to determine the plurality of links comprises: formulating a search query based on the reference citation; identifying a plurality of document portals, the plurality of document portals comprising a first subset of document portals for which a particular user is known to have a valid subscription and a second subset of document portals for which a particular user is not known to have a valid subscription; restricting the search query to the first subset of the plurality of document portals; executing the restricted search query; and in the event that executing the restricted search query fails, executing an unrestricted search query to search the second subset of the plurality of document portals.
17. The method of claim 11 wherein at least one of the restricted search query and the unrestricted search query is limited to a particular designated document format and a given one of the determined links is a link to an electronic document having that designated document format.