3D HNCA out-and-back:HN->N(t)->Co(t2)->N->HN(t3) 分L DIPSI-2 12N 1t1 15N GARP 2HN Ny 2N.Ca 2HN N 3C0 2N,Coy 13C sin4(π1JN.Hw△)exp(-2△WT2Hw) sin2(JCa.N 2t)cos2(n 2JCa.N 2t)exp(-4t/T2N) cos(n Jca.cB t2)exp(-tz/T2ca)