Perhaps you should try some spelling variations:
multiple natural » multiple integral, multiple data, multiple capital
natural research » namura research, national research, cultural research
action research » national research
multi action » multi actor, multi option, multi location
july 2011 » july 2013, july 2015, july 2019
july 2012 » july 2013

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: (( multiple natural research : july 2011 ) OR ( multi action research : july 2012 ))~.
• Adding a wildcard symbol may retrieve word variants: (( multiple natural research : july 2011 ) or ( multi action research : july 2012 ))*.