I’ve found a couple of great technical research sites and both offer full content PDF downloads for free. The first is from Penn State CiteSeerx alpha here’s the opening description from their about page.
CiteSeerx is a scientific literature digital library and search engine that focuses primarily on the literature in computer and information science. CiteSeerx aims to improve the dissemination of scientific literature and to provide improvements in functionality, usability, availability, cost, comprehensiveness, efficiency, and timeliness in the access of scientific and scholarly knowledge.
Tip of the hat to f5r5e5d for sending me there to get a great old PSRR op-amp paper.
The other research site is Google Patents here’s a quote from their about page:
Google Patent Search covers the entire collection of issued patents and millions of patent application made available by the USPTOfrom patents issued in the 1790s through those most recently issued in the past few months. We don’t currently include international patents, but we look forward to expanding our coverage in the future.
IMO, Google’s system to be the easiest to use complete patent search around.