I recently read that Yahoo was shutting down Alta vista, they must have bought them a while ago.
http://www.scirus.com/
http://www.scinet.cc/
http://www.athenus.com/
I can’t tell you if they are any good I just googled “best search engine for science”.
Goodsearch.com is the engine I use. It’s a very good search engine, and you can name a “charity” when you sign up. GS gives a donation to the charity you name. Second Amendment Sisters is a named “chairty” on the site, and we get a few pennies every time someone names us. As we are a non-profit org, we appreciated the couple of hundred dollars we got from them last year.