With a Media Query an artboard is made visible when it’s minimum width is available.
If you have a 3 artboards that are 100px, 500px and 800px wide then the smallest artboard will be visible until the browser window is 500px wide.
The 500px artboard will be shown from 500px to 800px (800px is the size of the next artboard).
From 800px and on the last artboard will be shown.
When Exporting select Single Page (show by size).