Perhaps you should try some spelling variations:
"international prices economic theories" » "international best economic theories", "international banks economic theories", "international prices economic theory", "international crisis economic theories", "international brief economic theories", "international africa's economic theories"
"national poverty economic studies" » "national policy economic studies", "national energy economic studies", "national poverty economic status", "national poverty economic surveys"

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("international prices economic theories") or ("national poverty economic studies"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("international prices economic theories") OR ("national poverty economic studies")).
• Removing quotes may allow a broader search: (( international prices economic theories ) or ( national poverty economic studies )).
• Adding a wildcard symbol may retrieve word variants: (("international prices economic theories") or ("national poverty economic studies"))*.