Focus on why you want to (want to) read them - what about it interests you? If you can try to boil that interest down to a few questions, that'll give you something to be on the lookout for, which might help you stay alert.

Be "mindful": if you feel your attention slipping, just sort of "notice" that it's happened, without emotion or judgment, acknowledge what distracted you and then go back to it.

Try to make a specific effort to "do something" with the text you're reading - read out loud, visualize or sketch, rephrase/summarize when writing notes, mindmap... whatever works and might engage some different parts of the brain.