Perhaps you should try some spelling variations:
"colloques, congres et conferences sur le xxe siecle" » "colloques, congres _ conference sur le xxe siecle" (Expand Search), "colloques, congres a conference sur le xxe siecle" (Expand Search), "colloques, congres et conferences sur la xxe siecle" (Expand Search)
"colloque, congres et conferences sur le xxe siecle" » "colloque, congres _ conference sur le xxe siecle" (Expand Search), "colloque, congres a conference sur le xxe siecle" (Expand Search), "colloque, congres et conferences sur la xxe siecle" (Expand Search)

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• Performing a fuzzy search may retrieve terms with similar spellings: (("colloques, congres et conferences sur le xxe siecle") OR ("colloque, congres et conferences sur le xxe siecle"))~.
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• Adding a wildcard symbol may retrieve word variants: (("colloques, congres et conferences sur le xxe siecle") OR ("colloque, congres et conferences sur le xxe siecle"))*.