Perhaps you should try some spelling variations:
"world black working paper" » "world pack working paper", "world flask working paper", "world flick working paper", "worlds black working paper", "world back working paper", "world lack working paper", "world black working papers"
"world bank working paper" » "world manko working paper", "world pack working paper", "world book working paper", "world bank working papers"
"world band working paper" » "world bandes working paper", "world board working paper", "world based working paper", "world brand working paper", "world bond working paper", "world hand working paper", "world band 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 bank working paper") OR ("world band working paper"))) OR ("world black working paper")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"world bank working paper\") OR (\"world band working paper\"))) or (\"world black working paper\"))".
• Removing quotes may allow a broader search: (((( world bank working paper ) OR ( world band working paper ))) or ( world black working paper )).
• Adding a wildcard symbol may retrieve word variants: (((("world bank working paper") OR ("world band working paper"))) or ("world black working paper"))*.