Q:

Make API query to only one Stack Exchange site

Is there a way to limit a /search or a /similar query to a specific site or sites?

A:

By definition all /search and /similar queries are made on one specific site. There is currently no way to search more than one site.
Example:

http://api.stackoverflow.com/1.1/search?intitle=linq

This example will search only Stack Overflow for the term linq.

