Perhaps you should try some spelling variations:
22composite materials » composite materials, biocomposite materials, composites materials
2f congresses » _ congresses, 1 congresses, 16 congresses
6 congresses » _ congresses, 600 congresses, 6 congress

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• The words AND, OR and NOT may confuse the search; try adding quotes: "%22composite materials %((2f congresses) OR (6 congresses))%22".
• Adding a wildcard symbol may retrieve word variants: %22composite materials %((2f congresses) OR (6 congresses))%22*.