My experience is the exact opposite. I've regularly pulled data/observations/ideas from 1920's-1960's era articles and cited them. (Heck, I've used depth soun

My experience is the exact opposite. I've regularly pulled data/observations/ideas from 1920's-1960's era articles and cited them. (Heck, I've used depth soundings from Capitan Cook's expeditions in the 1700's as data when making detailed bathymetric maps -- it was the only thing available in the area.) You can't be a researcher in a field and only read articles from the last 20 years. I've lost count of the number of times I've been struggling with a problem, come up with a partial solution, then found a nice, complete, well-thought-out solution in some random engineering journal from the 40's. Use the literature. Never, ever, ignore papers just because they're from a few years back. You may need to filter the ideas through a few paradigm shifts, but the underlying observations and methods can be very useful. Textbooks can be wonderful overviews and great ways to learn, but they only scratch the surface of topics. Furthermore, in most cases, you can't directly cite textbooks. Only original research is citeable. Review papers, most textbooks, and other compendiums are not citeable in any field I've been involved with. The exceptions are textbooks that have original research in them, which are very common, but are more akin to special editions of a journal than most textbooks.