ScirusScirus is a search engine devoted to science subjects. On the advanced search page, you can limit your search to articles. If you also uncheck the "All journal sources" box, you will get only web based materials, including many full text articles in institutional repositories, such as University of Toronto's T-Space. (To search the journal literature covered by the "All journal sources", log in to the SCSU database ScienceDirect with a lot of full text available by our subscription.)