All of the titles listed are peer-reviewed. Browsing through tables of contents is a recognized research technique. Most e-journals also have a 'search' feature. It may not be very sophisticated, but it will usually work for a single term or a phrase. Use interlibrary loan to request any articles outside the date ranges listed for these publications.
1. Look for leading theorists and innovators in your textbooks and class readings.
2. Skim encyclopedia articles on adult education, adult learners, nontraditional students, e.g.:
Encyclopedia of Education; call number REF LB15 .E47 2003
Encyclopedia of Educational Psychology; call number REF LB1050.9 .E63 2008
International Encyclopedia of Adult Education; call number REF LC5211 .I56 2005
21st Century Education: A Reference Handbook; call number REF LA210 .A15 2008
3. Look for early articles/books in book and article bibliographies. Search for works by those authors.
4. Many results lists will include a 'cited by [#]' link. The number of times cited may provide an indication of the importance of the item.
5. Try Web of Science. Enter a topic, e.g., "adult learning", sort results by 'Times Cited.' Also try a 'cited reference' search when you have a known reference – Enter the last name and first initial of the author, the journal name, and date of publication. Select the likely citations and click on Finish Search. You will have a list of articles citing your reference.
[Be aware: Web of Science is noted more for science than social science]