Perhaps you should try some spelling variations:
research instruments » research instrument, research instrumentation, research environments
research documents » search document, research arguments, research comments
research elements » research experiments, research effects, research students
online model » online medien, online media
online range » online change, nonlinear range, online ratings
online ring » online during, online rating, online racing

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: (( online model research documents ) OR ( ((online range) OR (online ring)) ((research elements) OR (research instruments)) )).
• Adding a wildcard symbol may retrieve word variants: (( online model research documents ) or ( ((online range) or (online ring)) ((research elements) or (research instruments)) ))*.