Rellich - Necas identity

I am looking for a book/paper which has the proof of the Rellich-Nicas identity.

[EDIT by Yemon Choi] It seems that what was meant is "the Rellich-Necas identity", although the original poster hasn't really clarified or expanded on the request.

I am looking for a book/paper which has the proof of the Rellich-Nicas identity.

                                                             Rellich - Necas identity