Problem with .htaccess file

Hi, i have a website and i would like to replace links such as:
http://www.xxx.est/viewsomething.php?id_fls=152
with
http://www.xxx.est/something_152.php
in order to do this i have tried this code into the .htaccess file:
RewriteEngine on
RewriteRule ^viewricetta\.php?id_fls=(.*)$ /ricetta_$1.php [L,R]

this is wrong... i have also read the guide but i didn't realized the right
code. can someone help me please?
Thx