Perhaps you should try some spelling variations:
"nato science theories 2:, physics" » "nato science theory 2:, physics", "nato science three 2:, physics", "radio science theories 2:, physics", "nato science theories 4:, physics", "nato science theories 1:, physics"
"national science theories 2:, physics" » "national science theory 2:, physics", "national science three 2:, physics", "natural science theories 2:, physics", "spatial science theories 2:, physics", "animal science theories 2:, physics", "national science theories 4:, physics", "national science theories 1:, physics"
"nato science theories 3:, physics" » "nato science theory 3:, physics", "nato science three 3:, physics", "radio science theories 3:, physics"

Try widening your search to All Fields.

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• If you are trying to use Boolean operators, they must be ALL CAPS: (((("nato science theories 2:, physics") OR ("national science theories 2:, physics"))) OR ("nato science theories 3:, physics")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"nato science theories 2:, physics\") OR (\"national science theories 2:, physics\"))) or (\"nato science theories 3:, physics\"))".
• Removing quotes may allow a broader search: (((( nato science theories 2:, physics ) OR ( national science theories 2:, physics ))) or ( nato science theories 3:, physics )).
• Adding a wildcard symbol may retrieve word variants: (((("nato science theories 2:, physics") OR ("national science theories 2:, physics"))) or ("nato science theories 3:, physics"))*.