Sharpness should always be applied and evaluated at 1:1 (100% view).
When you compare the original (viewed at 1:1 in Lightroom) with the exported image (also at 1:1), do you still see a difference?
What are your export settings?
How big (pixels) is the image to start with?
Are you resizing the image?
What program are you using to view the exported JPG?
Can you show us examples?
Whatever number is entered in the resolution box has no effect on sharpness or quality in general.
It only comes into play when printing,