JSTOR provides online access to thousand academic journals and over 1 million images, letters, and other primary sources. Designed for the academic community, 7,000 institutions in 159 countries are members, they presently have a beta test whereby independent researchers can register to gain limited free access to images of articles in their collection.
I discovered this facility in connection with my 24 July posting on Probability in Genealogy, which attracted more comments than most. In response I pointed to an interesting study using probabilities, the case of Thomas Jefferson as the father of Sally Hemmings' children which uses Monte Carlo techniques and Bayes Theorem. It's Coincidence or Causal Connection? The Relationship between Thomas Jefferson's Visits to Monticello and Sally Hemings's Conceptions, by Fraser D. Neiman, is published in The William and Mary Quarterly,Third Series, Vol. 57, No. 1 (Jan., 2000), pp. 198-210.
That article is one of the million you can view free through JSTOR and although there is no download facility you can capture images of partial pages and read those off-line.