Perhaps you should try some spelling variations:
"international efforts economics series" » "international airports economics series", "international energy economics series", "international airport economics series", "international effects economics series", "international sports economic series", "international forest economics series"
"international ship economy series" » "international shipping economy series", "international series economy series", "international social economy series", "international ship economics series", "international china economy series", "international share economy series"

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

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