Welcome to the Airtable community!
You could have users enter the two parts of the scientific number in two different fields. Then use a formula field to calculate the decimal.
IF(
AND(
{significand (m)} & "",
{significand (m)} < 10,
{significand (m)} > -10,
{exponent (n)} & ""
),
{significand (m)} * POWER(10, {exponent (n)})
)
You can see a writeup on my website here, including a working demo where you can enter your own numbers.