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On the Preferences page, look under the "PubMed Preferences" section and click the Outside Tool link to configure Outside Tool Preferences.
"Select an institution to activate their Outside Tool. You may select up to five institutions. Please contact your institution for an explanation of its service."
Tick a box for a single institution, then scroll down to the bottom of the list and click the link to return to the preferences page.
Repeat steps 4-6 for each institution, i.e.
a. Fred Hutchinson Cancer Ctr Arnold Library
b. Seattle Children's Library & Information Commons
c. University of Washington Check for full-text