"Pick this up" vs. "Pick up this"

I read a grammar book. In the chapter on phrasal verb, it says that if the object is a pronoun that should be put between the (transitive) verb and the adverb. I believed that is also true for such objects as something, anything, this, that, etc. and that the sentence like "Pick up this" wouldn't be grammatical.
But.. I saw this today on Wikipedia(href="http://en.wikipedia.org/wiki/Determiner (linguistics)" style="cursor: pointer; color: rgb(58, 88, 151); text-decoration: none; ">http://en.wikipedia.org/wiki/Determiner_(linguistics) ):
In phrasal verbs, pronouns must appear between the verb and particle. Determiners may occur after the particle.

1. pick it up
2. *pick up it
3. pick this up
4. pick up this

I don't understand how 'pick up this', not 'pick this up', could be correct. If 'this' in 'pick up this' is a determiner, a noun sholud be followed, shouldn't it? Hmm... Is a noun left off there? =/
If "pick up this" stands alone, please tell me how it could be.