@misc{1155656,
  author = {A S Risley},
  title = {The physical basis of atomic frequency standards:},
  year = {1969},
  month = {1969-01-01 05:01:00},
  publisher = {, National Institute of Standards and Technology, Gaithersburg, MD},
  doi = {https://doi.org/10.6028/NBS.TN.399},
  language = {en},
}