John P. A. Ioannidis et al. have published "Estimates of the Continuously Publishing Core in the Scientific Workforce" in PLOS ONE.
Here's an excerpt:
The proportion of the scientific workforce that maintains a continuous uninterrupted stream of publications each and every year over many years is very limited, but it accounts for the lion's share of researchers with high citation impact. This finding may have implications for the structure, stability and vulnerability of the scientific workforce.