Perhaps you should try some spelling variations:
"multi vaccine research : july 2006" » "multi medicine research : july 2006", "anti vaccine research : july 2006", "multiple vaccines research : july 2006", "multi vaccine research : july 2008", "multi vaccine research : july 2007", "multi vaccine research : july 2013"
"multi option research : july 2009" » "multi opinion research : july 2009", "multi action research : july 2009", "multi optics research : july 2009", "multi location research : july 2009", "multi population research : july 2009", "multi ratios research : july 2009", "multi option research : july 2008", "multi option research : july 2007", "multi option research : july 2019"

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 vaccine research : july 2006") or ("multi option research : july 2009"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("multi vaccine research : july 2006") OR ("multi option research : july 2009")).
• Removing quotes may allow a broader search: (( multi vaccine research : july 2006 ) or ( multi option research : july 2009 )).
• Adding a wildcard symbol may retrieve word variants: (("multi vaccine research : july 2006") or ("multi option research : july 2009"))*.