Perhaps you should try some spelling variations:
research theories » research theory, research themes, research topics
residue research » residues research, residual research, rescue research
research studies » research study
research series » research services, research service, research summaries

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (( rescue ((research series) OR (research theories)) ) OR ( residue research studies )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( rescue ((research series) OR (research theories)) ) or ( residue research studies ))".
• Adding a wildcard symbol may retrieve word variants: (( rescue ((research series) OR (research theories)) ) or ( residue research studies ))*.