For every search, limit to Peer-Reviewed articles and limit by date to after 2009
Workplace Ageism (also try employment ageism OR ageism organizations)
Human Factors/Ergonomics (try ergonomics)
Drug testing (use "drug usage screening")
Sexual harassment in the workplace (try sexual harassment workplace )
A primary research article is a journal article in which the author/s have conducted a research experiment of their own, they are not reporting on research done by others or giving their opinion or arguing for a particular policy.
Look for: a METHODS section