Perhaps you should try some spelling variations:
income distributional » income distribution1.3, more distributional, income distributive
income distributions » time distributions, discrete distributions, stable distributions
size distributions » size distribution
2f developing » f developing, 2.1 developing, self developing

Try widening your search to All Fields.

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• If you are trying to use Boolean operators, they must be ALL CAPS: %((income distributional) OR (((((income redistribution) OR (((income distributions) OR (size distributions))))) OR (income distribution)))) %2f developing countries%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%((income distributional) or (((((income redistribution) or (((income distributions) OR (size distributions))))) or (income distribution)))) %2f developing countries%22".
• Adding a wildcard symbol may retrieve word variants: %((income distributional) or (((((income redistribution) or (((income distributions) OR (size distributions))))) or (income distribution)))) %2f developing countries%22*.