Wow, I was not expecting so many to be biology and chemistry. Good reminder that computer science isn't the whole world. Nice to see EM, simulated annealing, and Levenberg Marquardt in the bottom 50.
Some fields cite more and publish more than other fields. It doesn't really make any sense to compare citation counts between fields. Moreover, Google's ranking removes review articles and many other things - it purely looks for 'new research' articles. Those get cited much less frequently than reviews or methods papers.
I naively thought that it is a simple thing and someone have that "collection of best articles".
Things are going to more like "this is hard problem"