@article{Velinov:2017Hk,
  author = "Velinov, Peter I. Y.  and  Mishev, A.",
  title = "{Long term ionization effect during several GLE events of solar cycle 23 - comparative analysis}",
  doi = "10.22323/1.301.0074",
  journal = "PoS",
  year = 2017,
  volume = "ICRC2017",
  pages = "074"
}