Ten science search engines is actually a list of nine – you are invited to submit suggestions for the tenth via the comments section. The nine are:Scirus, Scitopia.org, Science.gov, ScienceResearch.com, Scitation, WorldWideScience.org, Science Accelerator, TechXtra, and search.optics.org. They all have different coverage and emphasis and none are comprehensive. Which one will work for you depends very much on the subject area. The three I regularly use in this list are Elsevier’s Scirus, TechXtra for engineering (ICBL and Heriot-Watt University) and WorldWideScience.org. Conspicuous by its absence is Google Scholar!