Perhaps you should try some spelling variations:
investment series » investment services, investment barriers, investment treaties
fixed investment » direct investment
investment rate » investment climate
test based » text based, trust based, test case
rest based » forest based, result based, trust based
road fixed » head fixed

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( h. ((test based) OR (rest based)) investment rate ) or ( h. road fixed investment series ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( h. ((test based) OR (rest based)) investment rate ) OR ( h. road fixed investment series )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( h. ((test based) OR (rest based)) investment rate ) or ( h. road fixed investment series ))".
• Adding a wildcard symbol may retrieve word variants: (( h. ((test based) OR (rest based)) investment rate ) or ( h. road fixed investment series ))*.