They are very short and the only way of getting a bit more details is to read the whole article. It should zoom smoothly.
For some reason authors tend to withhold something important from the abstract. If they write what they did, they don't tell what they got; if they tell the result, no clues on how they figured it out.
I don't know about other fields, but math papers have an abstract, then a section called "Introduction" which has some background and motivation and ends with an overview of the rest of the paper, and then the remainder has the details.
They are very short and the only way of getting a bit more details is to read the whole article. It should zoom smoothly. For some reason authors tend to withhold something important from the abstract. If they write what they did, they don't tell what they got; if they tell the result, no clues on how they figured it out.