This is an attempt to provide a starting point for your research for your work, including research on historical periods, settings, styles of clothing, etc.
Note that looking at Ort Library's other online reference guides and subject guides can be helpful too. However, coming into the library may work the best.
Vallar is a historical fiction writer who has assembled this insanely-thorough list of historical resources; topics include costume history, food and drink, the history of science, in addition to more basic information about various countries in various periods.
This online version of the popular print source won't take you into topics in great detail, but is good if you need to know what crops are grown in a country, the name of a city's pro basketball team, etc.
Arbor Day Foundation's Guide to more than a thousand U.S. trees. Linked here is the page for Eastern and Central U.S.--use the menu on the left for more.
Digital access to the large collection owned by the Henry Ford Museum--it's searchable and includes both photos and thorough descriptions of the included gowns, hats, shoes, etc.
Full digital access to Facts On File's book; conveniently organized alphabetically rather than under headings; if your allusion is "Belshazzar," simply look under "B."