google一下会大致有数。

http://www.forbes.com/sites/jonbruner/2011/10/05/nobel-prizes-and-american-leadership-in-science-infographic/

"The United States is also unique in the scale on which it attracts human capital: of the 314 laureates who won their Nobel prize while working in the U.S., 102 (or 32%) were foreign born, including 15 Germans, 12 Canadians, 10 British, six Russians and six Chinese . "

三分之一是国外出生的。在国外读大学的估计小于这个比例。