Press Load Next 100
in the results footer for large results set to extend the listing with the next 100 results. Each time this is done the listing is expanded to include all the previous results, and a vertical scroll bar will appear to the right of the results panel to allow the list to be scrolled.
Ad-hoc selections are preserved when the next 100 results are loaded, so selections can be added from throughout the entire results set if needed (although a better strategy might be to refine the search query to get a smaller results set).