Perhaps you should try some spelling variations:
income distributions » income redistribution, time distributions, size distributions
self developing » relief developing, self development, level developing
f developing » 7 developing, turf developing, f development

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: %((income distribution) OR (((income distributions) OR (discrete distributions)))) %((self developing) OR (f developing)) countries%22.
• Adding a wildcard symbol may retrieve word variants: %((income distribution) or (((income distributions) or (discrete distributions)))) %((self developing) or (f developing)) countries%22*.