SCITOPIA: a new search engine for Science!
I gave up with the idea to mention every search engine which appear each month! But this one is worth investigating.
Queries are searched against 25 sources, 18 scientific society sources and 7 government information sources, including Patents free sources. Some of these sources are not common on usual databases. Of course it is frustrating to get only abstracts, full-text content is mostly reserved to society members.
Anyway, the interface is efficient and intuitive, offering clustering options that everybody now claims (associated topics, top authors, top journals, etc.)
SciTopia can be good to complete traditional sources like PubMed, Scopus and WoS… especialy for technology and engineering topics.