<a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Digital_object_identifier" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Digital_object_identifier</a><p><i>A digital object identifier (DOI) is a serial code used to uniquely identify objects. The DOI system is particularly used for electronic documents such as journal articles.</i>