Perhaps you should try some spelling variations:
"population resource development countries." » "population resource developed countries.", "population resource development congresses.", "population resource development agencies.", "population research development countries.", "population pressure development countries.", "population pressures development countries."
"population resource developing countries." » "population research developing countries.", "population pressure developing countries.", "population pressures developing countries.", "population resources developing countries.", "population sources developing countries."

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (("population resource development countries.") OR ("population resource developing countries."))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"population resource development countries.\") OR (\"population resource developing countries.\"))".
• Removing quotes may allow a broader search: (( population resource development countries. ) OR ( population resource developing countries. )).
• Adding a wildcard symbol may retrieve word variants: (("population resource development countries.") OR ("population resource developing countries."))*.