: This is a specific international standard regarding Water quality — Determination of the dissolved fraction of selected active pharmaceutical ingredients . If your topic is environmental science, the ISO 21676 standard is the definitive "paper" on this topic.
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It is possible the string is part of a DOI (Digital Object Identifier) or a specific database ID. For example: : This is a specific international standard regarding
: Search for "H.264/AVC" or "H.265/HEVC" efficiency if the number refers to a specific bitrate or resolution setting. 2. Specific Technical Documents 21676mp4