Perhaps you should try some spelling variations:
income distributions » income distribution, income redistribution, discrete distributions
time distributions » time distribution, size distributions, stable distributions
72 developing » 7.2 developing, 762 developing, 2 developing

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 distributions) OR (time distributions)) %72 developing countries%22.
• Adding a wildcard symbol may retrieve word variants: %((income distributions) or (time distributions)) %72 developing countries%22*.