Perhaps you should try some spelling variations:
"population ; space economical" » "population ; espace economique", "population ; space economy", "population ; socio economical"
"population ; peace economic" » "population ; france economic", "population ; science economic", "population ; disease economic"

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

• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"population ; space economical\") OR (\"population ; peace economic\"))".
• Removing quotes may allow a broader search: (( population ; space economical ) OR ( population ; peace economic )).
• Adding a wildcard symbol may retrieve word variants: (("population ; space economical") OR ("population ; peace economic"))*.