Try the following:
Ty1 = {11, 13, 19, 22, 27, 30, 41};
Tm1 = {0.4125, 0.42, 0.4933, 0.525, 0.539, 0.575, 0.52};
Tx2 = {20, 18, 35, 37, 38, 44, 57};
Tm2 = {0.5625, 0.47, 0.58, 0.59, 0.57, 0.6, 0.58};
Tx3 = {9, 12, 19, 21, 24, 27, 32};
Tm3 = {1.044, 1.234, 0.874, 0.811, 0.82, 0.708, 0.828};
data = Table[{Tx2[[i]], Tm1[[i]], Tx2[[i]], Tm2[[i]], Tx3[[i]],
Tm3[[i]], Ty1[[i]]}, {i, 7}];
nlm = NonlinearModelFit[data,
k1*x2*m1^a + k2*x2*m2^b + k3*x3*m3^c + d, {k1, k2, k3, a, b, c,
d}, {x1, m1, x2, m2, x3, m3}, MaxIterations -> Infinity]
As output, you will get something like this

What is the meaning of <<18>> or <<19>>,and how to handle it?
<<or<<...>>. So unless you know already that it is calledSkeletonthe available answer is unreachable. – halirutan Apr 07 '15 at 10:12