Perhaps you should try some spelling variations:
"multi accident research : july 2006" » "multi current research : july 2006", "multi recent research : july 2006", "multi vaccine research : july 2006", "multi client research : july 2006", "multi accident research : july 2008", "multi accident research : july 2007", "multi accident research : july 2009"
"multiple vaccines research : july 2013" » "multiple access research : july 2013", "multiple crises research : july 2013", "multiple faces research : july 2013", "multiple vaccine research : july 2013", "multiple practices research : july 2013", "multiple accidents research : july 2013"

Try widening your search to All Fields.

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("multi accident research : july 2006") or ("multiple vaccines research : july 2013"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("multi accident research : july 2006") OR ("multiple vaccines research : july 2013")).
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• Adding a wildcard symbol may retrieve word variants: (("multi accident research : july 2006") or ("multiple vaccines research : july 2013"))*.