1. A computer implemented method for selecting external corpora to integrate into primary internet search engine results in response to a query, comprising: receiving a query, at least one server computer, from a client computer over a network; storing an offline model probability in memory; processing said query by: computing a first probabilistic estimate of relevance of external corpora to said query from offline query-related data from said offline model probability; combining said offline query-related data with user feedback data to determine a second probabilistic estimate of relevance of said external corpora to said query; selecting said external corpora to integrate into a response to said query based on said second probabilistic estimate of relevance of said external corpora to said query; and transmitting over said network, for display on said client computer search results for said query that include said external corpora selected.