Especially useful if you are not sure where to start with a topic. Or set your browser to use the UNC Charlotte Proxy server. The Gale group of reference works provides a comprehensive source for biographical and critical information on authors. The various volumes in the series cover Antiquity to the present. Entries are several pages long.
Articles are fairly long.
Selected volumes of the Dictionary of Literary Biography deal with authors of specific literary movements and genres. An ongoing series. The cumulative author index in the back of the newest volume will direct you to the correct volume of Poetry Criticism for your poet as well as other titles in the Gale Literary Criticism Series. Entries are several pages long. There is a Story Title Index and a Cumulative Index which cross references to the entire Gale series.