Many search engines provide specialized types of Internet search
functionality, focusing on certain types of data. The following sites provide
lists of specialized search engines:
Deep web. The following index provides information
about access to online databases and other information not easily accessible
by normal
search
engines:
Meta-search. Meta-search engines allow
you to submit a search query to several engines at once, and then return
the results in
a single listing. The
advantage of meta-search engines is that they perform multiple searches for only
one query entry. The disadvantage is that you can't use all of the features
that you
can on specific search engines. Most meta search engines will preserve boolean
searches using AND, OR, and NOT, and some will preserve phrases
in quotes. The following sites index meta-search engines: