晝夜節律 （英語：circadian rhythm ）又稱日夜節律 、概日節律 、日變週期 、生理時鐘 （physiological clock），是一種生理現象，以內源性 、持續的，呈現以約24小時為週期的變動；由日變時鐘 （circadian clock）所驅動。包括植物、動物、真菌等，都被觀察到有類似生理變化。英語 circadian 源自拉丁語 circa，為大約、大概的意思；拉丁語 diem 是一天、一日之意。合起來，在字面上的意思，是大約一天。
晝夜振盪器 （circadian oscillator）則是驅動晝夜節律的中樞機制，使生物的生理節律與晝夜週期相一致，以近24小時為週期而振盪的節律，由基因產物 作用於基因啟動子 所組成的反饋迴路 或其他反饋迴路。
2017年來自美國的三位遺傳學家傑弗理·霍爾 （Jeffrey Hall）、麥可·羅斯巴希 （Michael Rosbash）和麥可·揚 （Michael Young）因發現控制晝夜節律的分子機制而共同贏得了諾貝爾生理醫學獎 。
延伸閱讀 [ 編輯 ]
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. PMID 11707566. doi:10.1073/pnas.181484498.
