Perhaps you should try some spelling variations:
"world board working paper" » "world word working paper", "world hard working paper", "world world working paper", "world toward working paper", "works board working paper", "world born working paper", "world board working papers"
"world bank working paper" » "world band working paper", "world black working paper", "world manko working paper", "world bank working papers"
"world bond working paper" » "world bonds working paper", "world band working paper", "world bone working paper", "world beyond working paper", "world blind working paper", "world blood working paper", "world bond working papers"
"world bold working paper" » "world cold working paper", "world bolt working paper", "world gold working paper", "world old working paper", "world bold working papers"

Try widening your search to All Fields.

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

• If you are trying to use Boolean operators, they must be ALL CAPS: (((("world board working paper") OR ("world bank working paper"))) OR ((("world bond working paper") OR ("world bold working paper")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"world board working paper\") or (\"world bank working paper\"))) or (((\"world bond working paper\") OR (\"world bold working paper\"))))".
• Removing quotes may allow a broader search: (((( world board working paper ) or ( world bank working paper ))) or ((( world bond working paper ) OR ( world bold working paper )))).
• Adding a wildcard symbol may retrieve word variants: (((("world board working paper") or ("world bank working paper"))) or ((("world bond working paper") OR ("world bold working paper"))))*.