Google's advanced search allows you to search by domain name (on bottom line of the advanced search form).
Entering .edu or .gov into this line will only return results from educational or US government sites, which tend to contain more reliable scholarly or factual information. You will still have to evaluate the sites for authority, accuracy, currency, and objectivity.
There are many Internet gateways and resources that provide high quality management information. Some of the ones we recommend are: