Which database you use depends on what your subject is and what type of materials (journals, proceedings, book chapters, etc.) you hope to find. In addition to the specialized journal collections and subject indexes included in this guide, the Library also has multidisciplinary databases such as Academic Search Complete (an EBSCO database), ScienceDirect, SpringerLink, and Wiley Online Library. See this guide: Finding Scholarly Articles for guidance on searching these databases. You should strongly consider trying these especially if your topic is at all interdisciplinary in nature - as many Engineering topics can be.
See below for databases specific to subject areas.