Si it possible to not let the visitors not see the source codes?

See this thread

If it's an intranet site, ask the administrator to set the NoViewSource Internet Explorer Restriction for all users

Yes their are java scripts that do this but its used by amatures and in 99% of cases it causes people generally not to return to your site.

yes and there are many ways to get passed the javascript, so its really kind of useless..

be careful because their are some scripts that will actually disable the users toolbar (back,forward, reload,stop buttons) also it is very unprofessional and I have never returned to a site that implimented such tatics, but yes you can do it to answer your question you might find something on hotscripts.com