Perhaps you should try some spelling variations:
"multiple vaccines research : july 2009" » "multiple access research : july 2009", "multiple crises research : july 2009", "multiple faces research : july 2009", "multiple vaccine research : july 2009", "multiple practices research : july 2009", "multiple accidents research : july 2009", "multiple vaccines research : july 2008", "multiple vaccines research : july 2007", "multiple vaccines research : july 2019"
"multi factor research : july 2013" » "multi factors research : july 2013", "multi sector research : july 2013", "multi actors research : july 2013", "multi actor research : july 2013", "_ multifactor 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: (("multiple vaccines research : july 2009") OR ("multi factor research : july 2013"))~.
• Removing quotes may allow a broader search: (( multiple vaccines research : july 2009 ) or ( multi factor research : july 2013 ))~.
• Adding a wildcard symbol may retrieve word variants: (("multiple vaccines research : july 2009") or ("multi factor research : july 2013"))*.