Are you asking if it's possible to adjust your status to a non-immigrant employment-based visa after entering on a B2 tourist visa? Generally yes, but you have the issue that your stay will probably end before your petition is processed. If you're talking H1B and time permits, you can consider premium processing. I don't much care to guess as to the circumstances or type of visa you're asking about, so if you need more information please share the relevant details.