The kind of open-access materials most widely used on Wikimedia projects is figures from scholarly articles. This extends to historic publications, e.g. the benzeneformulae from Kekulé's original article that depict the molecule's two resonance structures.[1] However, chemical formulae are nowadays preferentially rendered in editable vector graphics formats like SVG.
A page from the lab notebook underlying the experiments described in Lang & Botstein (2011).[2]
Different kinds of media are being posted within articles or their supplements.