Hi Herve,
No, it's not possible - although if you turn off the 'book now' function, you get to choose who to prioritise as long as you respond to the first person who requests to book within 24 hours.
Having said that, anyone who emails to ask if the room is available when it clearly is, is probably emailing several hosts and is not necessarily serious about booking with you. You are probably better off taking a definite booking over an enquiry. In my experience, unless an enquiry is about something specific about the room or house rules that they want to double check, they are unlikely to book.
Regards
Bob