Have a look at File Menu > Export Page.
...or are you referring to something else.
If you are referring to "publish" when you say "export", and you only want to publish some pages and not others in a pub, you could simply divide your pub up into relevant Chapters. (Dividing a pub up into Chapters has no effect on the publication's performance) Then when it comes to publish time, just temporarily delete the not required Chapter/s when you publish, then restore them after publishing.
Plus at publish time, you can go to 'Settings' and choose to publish each page separately.
I hope all this covers what you mean.