Perhaps you should try some spelling variations:
"multiple population research : july 2007" » "multitude population research : july 2007", "multiple imputation research : july 2007", "multi population research : july 2007", "multiple population research : july 2008", "multiple population research : july 2012", "multiple population research : july 2020"
"multi action research : july 2013" » "multi national research : july 2013", "multi actor research : july 2013", "multi option research : july 2013", "multi location research : july 2013"

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("multiple population research : july 2007") OR ("multi action research : july 2013"))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"multiple population research : july 2007\") OR (\"multi action research : july 2013\"))".
• Removing quotes may allow a broader search: (( multiple population research : july 2007 ) OR ( multi action research : july 2013 )).
• Adding a wildcard symbol may retrieve word variants: (("multiple population research : july 2007") OR ("multi action research : july 2013"))*.