Perhaps you should try some spelling variations:
"multiple vaccines research : july 2007" » "multiple access research : july 2007", "multiple crises research : july 2007", "multiple faces research : july 2007", "multiple vaccine research : july 2007", "multiple practices research : july 2007", "multiple accidents research : july 2007", "multiple vaccines research : july 2008", "multiple vaccines research : july 2013", "multiple vaccines research : july 2012"
"multi class research : july 2007" » "multi crops research : july 2007", "multi classroom research : july 2007", "multiclass _ research : july 2007", "multi class research : july 2008", "multi class research : july 2013", "multi class research : july 2012"

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 class research : july 2007") OR ("multiple vaccines research : july 2007"))~.
• Removing quotes may allow a broader search: (( multi class research : july 2007 ) or ( multiple vaccines research : july 2007 ))~.
• Adding a wildcard symbol may retrieve word variants: (("multi class research : july 2007") or ("multiple vaccines research : july 2007"))*.