I think you've already got it (provided the number is exactly that):
library(tidyverse)
df <- data.frame(col1 = c(1.03e-06, 0.00000103))
df %>%
filter(col1 == 1.03e-06) #should return both rows
You need to be careful when dealing with floating point numbers though, so you should use a function like all.equal() In such cases.