Are there OpenGL functions that are only available for specific platforms?

Question

I want to load the OpenGL functions for my project myself. Are there any specific functions besides wglGetSwapIntervalEXT that require me to query the spec for its availability? And if there are, where can I find a list of them or somthing? E.G.

bool IsFunctionAvailable(char *string) { ... }

main.cpp:
if(IsFunctionAvailable("glActiveTexture"))
{
    LoadFunction("glActiveTexture");
}