when you have a partial resistance, it doesn't seem to change anything. i.e. _every_ hit to/by acid creature does -1 on equipment, and you're allways feared/conf/paralysed for a _long_ time when hit by a spell.
So, what's the use of a partial res in those attack/spell types ?
I /think/ they stop the attacks in question working, certainly +70% acid resistance is enough for me to not have to worry about getting hit by acid particularly (but then I use lots of spells and scarcely ever attack directly...)