The Laws of Prayer /The Blessings of the Shema (57)

1. One who recites the Shema without its accompanying blessings (e.g. he recited it before praying so as not to miss the final time for its recital) has fulfilled his obligation to recite the Shema. He may nevertheless recite the blessings by themselves, without saying the Shema. (Shulchan Aruch 60)

2. However, it is good if he could return and recite the Shema with the blessings, so that he can stand to say the Amidah immediately after having learned Torah, and the recital of the Shema when there is no obligation, is considered like learning Torah. (Shulchan Aruch and Mishne Berurah ibid)