intermittently       
adverb uk/ˌɪn.təˈmɪt.ənt.li/ us/ˌɪn.t̬ɚˈmɪt.ənt.li/
 间歇地,断断续续地
in a way that does not happen regularly or continuously; in a way that stops and starts repeatedly or with periods in between
  We've discussed this problem intermittently, but so far we've failed to come up with a solution. 我们断断续续地讨论过这个问题,但目前还没有找到解决方案。 
 Lightning flashed intermittently in an otherwise clear sky. 闪电在原本晴朗的天空中断断续续地闪现。 
 See: intermittent
 - More examples
 - Wind energy supplies power only intermittently - when the wind blows.
 - The group has met intermittently for several years in an attempt to devise a long-term plan.
 - In the war-torn city, electricity is available only intermittently.