TY JOUR TI Customs services: essence, procedure of provision and quality problems KW economy KW export KW trade KW foreign trade activity KW customs service KW service KW integration KW barriers KW intellectual property KW market KW services KW customs institutions KW fiscal function KW international cooperation KW efficiency KW service JO Russian Journal of Management AU Zybenko, S.V. PY 2021 IS 9 PB Publishing Center RIOR