I like to visit Xiamen for a week in autumn. Is there possibility to buy a some days ticket or prepaid-Ticketcard for allcity- busses, airport-bus, taxis etc ?
The short answer to your question is, no. Prepaid transportation cards are only sparsely used in a couple of the major cities (Beijing & Shanghai), but even there the amount of services that use is it very small so it would probably be a waste of money.