In the SpringerLink search function, when no search operators like "AND" or quotes are used, all results that include any of the terms are returned, and those that contain all terms the greatest number of times in important fields display at the top. The total number of results does not affect the relevance of the ones shown at the top: '"AND"ed results display higher than '"OR"ed results. Using quotes and Boolean operators will alter which items are considered most relevant.
For further information and tips on making searches: see here.
For information on using the advanced search form: see here.