The most cited paper in physics (and/or chemistry) is, last I heard, by Walter Kohn. In fact, if I recall correctly he wrote the top two: Hohenberg & Kohn and Kohn & Sham.
I hear that one of his favourite observations, though, is that you're not really famous until they stop citing you. I mean, who cites Newton?
Yeah, the top four are the four key papers of Density Functional Theory. After that it gets a little more diverse.
I've met a couple of the people on that list. One of 'em is a nice guy. Another is a complete jerk. And that's all I'll say in my state of only partial anonymity.
Misleading headline (exposing a science bias). The article states "This paper, which is featured here as a JBC Classic, is the most highly cited paper in science." I don't happen to know if it is still the most cited paper ever, but this article can't actually make that claim without doing the bibliometrics for all of academia.
Both the title of the article (headline) and the statement you highlighted, are valid guesses. The number of citations of that paper was 275,669 as of January 2004; quite possibly over 300K by now. For comparison, the most cited article in CS, Rubin's paper on EM, has about 12K citations in ISI. What additional fields of academia (outside of science) did you have in mind?
I'd be incredibly surprised if it weren't. The (slow) rate at which papers are produced in the humanities, and the (small) number of citations on each, means you're awfully unlikely to find one with 300,000 citations.
I hear that one of his favourite observations, though, is that you're not really famous until they stop citing you. I mean, who cites Newton?