There is a newish science specific search engine - WorldWideScience.

It is similar to Google Scholar and Scirus, but is based on multilateral partnerships to enable federated searching of national and international scientific databases and portals, with approaching 100 participants. In Advanced Search you can turn on or off databases. In search results you can choose format tabs (papers, data, multimedia), or topic and other options to refine results. Not all results are open access resources and UQ Library subscriptions are not recognised, as they may be in Google Scholar and Scirus (when you set up your preferences to do so).