Question: Find out the send dates of the documents with the grant amount of more than 5000 which were granted by organisation type described research.
SQL: SELECT T1.sent_date FROM documents AS T1 JOIN Grants AS T2 ON T1.grant_id  =  T2.grant_id JOIN Organisations AS T3 ON T2.organisation_id  =  T3.organisation_id JOIN organisation_Types AS T4 ON T3.organisation_type  =  T4.organisation_type WHERE T2.grant_amount  >  5000 AND T4.organisation_type_description  =  'Research'