Perhaps you should try some spelling variations:
"world black working paper" » "world pack working paper", "world flask working paper", "world stack working paper", "worlds black working paper", "world back working paper", "world lack working paper"
"world black working papers" » "world pack working papers", "world flask working papers", "world stack working papers", "worlds black working papers", "world back working papers", "world lack working papers"
"world flick working papers" » "world fick working papers", "world flink working papers", "world flask working papers", "world alice working papers", "world nick working papers", "world policy 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 black working paper") OR ((("world black working papers") OR ("world flick working papers")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"world black working paper\") or (((\"world black working papers\") OR (\"world flick working papers\"))))".
• Removing quotes may allow a broader search: (( world black working paper ) or ((( world black working papers ) OR ( world flick working papers )))).
• Adding a wildcard symbol may retrieve word variants: (("world black working paper") or ((("world black working papers") OR ("world flick working papers"))))*.