Perhaps you should try some spelling variations:
options research » operations research, action research, opinion research
vaccine research » action research
multi vaccine » anti vaccine
mali options » call options, making options, scale options
july 2007 » july 2013
july 2012 » july 2013

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (( multi vaccine research : july 2007 ) or ( mali options research : july 2012 ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( multi vaccine research : july 2007 ) OR ( mali options research : july 2012 )).
• Adding a wildcard symbol may retrieve word variants: (( multi vaccine research : july 2007 ) or ( mali options research : july 2012 ))*.