When you buy resources from neighbor do you take the card or just get access to the resources you need?
Just the resources.
The rules on page 4 define things pretty well.
Cards are called "structures", the brown ones can generate "resources"
In red, there is a notice:
Obviously if you were to take the card, the production of the city would be reduced and this is prohibited.
No, you do not take the card. The neighbor retains the card; you are simply allowed to use your neighbor's cards, for a fee of course.
You can also buy the resource from the top corner of the civilization cards as well. It doesn't need to be a "card".