Rainbow crosswalk, Washington DC (2017). More info here. Source:Ted Eytan, Flickr. Licence.
Summon is usually the best starting point for finding articles, books and dissertations.
You may also want to run supplementary searches in these databases:
It is worth joining the British Library, which offers a greater range of relevant databases. Most can only be accessed from the the Library's own PCs, but, once you have joined, you can access the excellent LGBTQ+ Source with Full Text from any location. MA students should also join Senate House Library which has an even wider range of relevant databases. See the other libraries section of this guide for more info about both these libraries.
For introductory articles:
Reference sources for LGBTQ+ vocabulary: