Can "some" be a noun and a subject?

What is the noun in this sentence:

Some of our greatest innovations were launched during tough times.

I know that of our greatest innovations is a prepositional phrase and as such cannot contain the subject of the sentence. Some just doesn't strike me as a noun—or is it?

If it is, what is the easy way to recognize these type of nouns?

Solution 1:

The full subject is some of our greatest innovations. The head of the noun phrase is some, which is an adjective used as a noun with a plural meaning. Most adjectives can be used as nouns in certain situations: some like it hot; red is ugly; the weak will perish; the lowest of the low, etc. If an adjective is modified by a prepositonal phrase, it is usually used as a noun.