Perhaps you should try some spelling variations:
research documents » search document, research arguments, research comments
research elements » research experiments, research effects, research developments
research contents » research content, research context, research concepts
research students » research studies, research instruments, research study
panel research » channel research, model research, level research
online panel » nonlinear panel, online channel, online packet
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 panel research documents ) OR ( ((online range) OR (online ring)) ((((research elements) OR (research contents))) OR (research students)) )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( online panel research documents ) or ( ((online range) or (online ring)) ((((research elements) OR (research contents))) or (research students)) ))".
• Adding a wildcard symbol may retrieve word variants: (( online panel research documents ) or ( ((online range) or (online ring)) ((((research elements) OR (research contents))) or (research students)) ))*.