@article{shields_koo_kron_1989, 
  title={Faint quasi-stellar-object candidates in selected areas 28 and 68 identified from multicolor photometry}, 
  volume={101}, 
  DOI={10.1086/132440}, 
  publisher={IOP Publishing}, 
  author={Shields and Koo and Kron}, 
  year={1989}
  }