I want scientific articles on biofuels.
Your best bet is EBSCO Academic Search Complete. If you are off campus, you'll need your COM ID. Just search on the word biofuels and thousands of articles will come up. To save some time, first try limiting to full text under the Limit Your Results box. Next, click on Subject and Subject: Thesaurus term under the Narrow Results by box. Look for the closest fit to your topic and you'll have fewer articles to look through, and they will all be closer to what you want.