Perhaps you should try some spelling variations:
"resources research studies" » "research research studies", "resources research study"
"residues research studies" » "residents research studies", "resins research studies", "issues research studies", "residues research study"

Try widening your search to All Fields.

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• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"residues research studies\") OR (\"resources research studies\"))".
• Removing quotes may allow a broader search: (( residues research studies ) OR ( resources research studies )).
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