With Scitopia.org you can search over 3.5 million documents, plus patents and government data from the following societies:
Acoustical Society of America, American Geophysical Union, American Institute of Physics, American Physical Society, American Society of Civil Engineers, American Society of Mechanical Engineers, Audio Engineering Society, AVS, ECS, IEEE, Institute of Physics, IUCR Crystallography Journals Online, Optical Society of America, Professional Engineering Publishing, Royal Society, Society for Industrial & Applied Mathematics, SPIE, The Society for Information Display, DTIC Science & Technology, European Patents, Information Bridge, Japanese Patents, NSF Publications Database, US Patent & Trademark Office Database
This search engine is free and on the open Internet, like Google Scholar, but with less noise. It's not full-text, so in most cases you'll still have to depend on your dear old library to provide you with the content, but this looks like a great search engine to use when you're beginning your research.
According to Library Journal, its content "...includes such significant scientific papers as Isaac Newton's invention of the reflecting telescope and the first research paper published by Stephen Hawking." (Those links will open as PDFs.)