When can I claim an asset if part was paid in a previous year and part in the current year?

If I put a down payment on a business asset in 2018 but pay the balance on the bill and receive the item in 2019, how do I list it as a business asset?  Can I claim the whole thing in 2018?  Do I wait and claim the whole thing in 2019 (even though part was paid for in 2018)?