• In 1981, US scientists fielded nearly 40 percent of research papers in the most influential journals, by 2009, that figure was down to 29 percent.
• The US demonstrates heavy output in health and biomedical research, in line with the nation’s investment focus, with a significant skew away from previous focal strengths in physical sciences and engineering
• Though total volume output has not risen as quickly as Europe and Asia, average influence of research papers remains high at 40 percent above the world average 
• The structure of the US research base may be a contributing factor to its current position. The 61 US members of the Association of American Universities (AAU), for example, now account for 56 percent of US output in the five-year period to 2009
• Though the US is still a dominant force in the global scientific research landscape, this prominence is being significantly challenged by increased competition from Europe and Asia

http://researchanalytics.thomsonreuters.com/grr/