Perhaps you should try some spelling variations:
"country population research : july 2006" » "city population research : july 2006", "young population research : july 2006", "country population research : july 2008", "country population research : july 2007", "country population research : july 2009"
"multi vaccine research : july 2013" » "multi medicine research : july 2013", "anti vaccine research : july 2013", "multiple vaccines research : 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: (("multi vaccine research : july 2013") OR ("country population research : july 2006"))~.
• Removing quotes may allow a broader search: (( multi vaccine research : july 2013 ) or ( country population research : july 2006 ))~.
• Adding a wildcard symbol may retrieve word variants: (("multi vaccine research : july 2013") or ("country population research : july 2006"))*.