Perhaps you should try some spelling variations:
workers volunteers » horse volunteers, older volunteers, women volunteers
infants treatment » its treatment, effects treatment, agents treatment
worker volunteer » words volunteer, brother volunteer, coerced volunteer
new workers » new yorker, new markers, line workers
new worker » new yorker, new work, new marker

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: (( 7th new workers volunteers ((infants treatment) OR (implants treatment)) ) OR ( 7th new worker volunteer ((infants treatment) OR (implants treatment)) )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( 7th new workers volunteers ((infants treatment) OR (implants treatment)) ) or ( 7th new worker volunteer ((infants treatment) OR (implants treatment)) ))".
• Adding a wildcard symbol may retrieve word variants: (( 7th new workers volunteers ((infants treatment) OR (implants treatment)) ) or ( 7th new worker volunteer ((infants treatment) OR (implants treatment)) ))*.