The phrase "at intervals of three weeks" is correct and usable in written English.
You can use it to describe a recurring event or action that takes place every three weeks.
Example: "The team meets at intervals of three weeks to discuss project updates and progress."
Alternatives: "every three weeks" or "once every three weeks".
There were three holiday episodes—"Pinkeye", "Starvin' Marvin" and "Mr. Hankey, the Christmas Poo which aired at intervals of three weeks, while the remaining four aired later in February 1998.
Non-respondents received two postal reminders at intervals of three weeks.
To increase participation in the study non-respondents were sent up to two reminder letters and a new copy of the questionnaire at intervals of three weeks.
To produce anti-sera, mice were immunized subcutaneously with 20 µg recombinant protein in complete Freund's adjuvant as primary immunisation, and given 3 boost immunisations at intervals of two weeks with the same quantity of protein emulsified with incomplete Freund's adjuvant.
The aftercare coordination consists of six phone contacts at intervals of two weeks that are performed by therapists in the inpatient units.
See Table 4. Non-randomized controlled studies: These studies administered MDA at intervals of two weeks to 10 weeks for between eight and 23 rounds, alongside IRS.
After the inpatient treatment, the patients in the intervention group will receive six aftercare coordination phone contacts at intervals of two weeks that will be performed by their inpatient treatment therapists for 12 weeks.
A self -administered questionnaire that had been specially developed and pretested was posted to nurses in September 2006 and non-responders were sent questionnaires up to two more times at intervals of four weeks.
During the implementation phase two workshops (each 2 days with 720 min duration) at intervals of eight weeks will take place together with all BET-therapists from both rehabilitation centres.
The practice nurses were trained to deliver five telephone coaching sessions at intervals of six weeks in the first six months, telephone coaching sessions at months 8 and 10, a face to face coaching session at 12 months, and a final telephone coaching session at 15 months.
Blood was collected from the lateral saphenous vein of a hind limb of 5 mice per group one day prior to each immunization and at intervals of two weeks after inoculation.Sera were separated and stored at -20°C until analyzed for specific antibodies.
