How do I test the significance of my correlation coefficients for various regressions

Hi, I have a set of 25 points and I used a TI-84 calculator to calculate the linear, quadratic, logistic, exponential, and power regression models for this data set. I have, likewise, obtained the r^2 value for each of these regressions. Some of these r^2 values appear to be quite similar. For example, r^2 for quadratic is 0.822 and r^2 for logistic is 0.82.

How do I test the significance of these correlations? To put it in drastically simplified terms, is there something equivalent to a "p-value" for each of these regressions (especially the nonlinear ones) that I can use? Thank you!