Some of the relevant Library of Congress subject headings to use in an Advanced search or a Subject search of the Library's traditional catalogue include
Use * to say "I don't care how this word ends" e.g. ethnograph* retrieves ethnography, ethnographic, ethnographer(s)
" " to keep the words in a phrase together
OR to combine alternate terms or spellings for the same concept group, e.g. fieldwork OR "field work" OR "participant observ*"
AND to combine different concepts, e.g.
(fieldwork OR "field work" OR "participant observ*") AND ethnograph* AND "semi-structured interview*"
Finding too much?
Finding too little?
For better searching, think of multiple ways to describe your topic