Perhaps you should try some spelling variations:
transactional costs » transaction costs, transactions costs, transitional costs
firms transactional » minds transactional, moores transactional, towards transactional
firms sanitation » firms organization, rural sanitation, site sanitation
harold firms » held firms, harold adams, harold sir
head firms » held firms, lead firms, dead firms

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: (( head firms sanitation (services. OR series.) ) OR ( harold firms transactional costs. ))~.
• Adding a wildcard symbol may retrieve word variants: (( head firms sanitation (services. or series.) ) or ( harold firms transactional costs. ))*.