Science.gov - USA.gov for science - is a gateway to government science information and research results. Currently in its fifth generation, Science.gov provides a search of over 40 scientific databases, 200 million pages of science information, and 1,950+ scientific websites. Search the site for certain terms, or browse the site by topic.
Also, don't forget to check out the featured search, which is currently alternative fuels.
Register for a free account in order to set up alerts for various subject areas and databases, including the NASA Technical Report Server (NTRS), the NASA Astrophysics Data System (ADS), and the NASA website.