Google seems the best search engine, in terms of both the number of pages it has surveyed and its ability to deliver first the most relevant pages.
|To search within your results, add words to your query. Syntax: " ", +, -, OR, ( ), %, *|
|Select a source||Simple Search|||||Power Search|
Syntax: " ", +, -, *
37 Search Engines (for the despairing ...) Return to Demo or HTML Guide or <@--a href="moreengines.html">types of engines
DOE search engine; 21 publishers and 1000 journals.
and also ResearchIndex (NEC free search engine of science, esp., computer science. literature)