[ Eq(Derivative(x1, t), ((-1)*k1*x1*k2 + 1*k3*x2*k1)/k1),
  Eq(Derivative(x2, t), (1*k1*x1*k2 + (-1)*k3*x2*k1 + (-1)*k1*k13*x2)/k1),
  Eq(Derivative(x3, t), ((-1)*x3*k4*x2*k1 + 1*k5*x4*k1)/k1),
  Eq(Derivative(x4, t), (1*x3*k4*x2*k1 + (-1)*k5*x4*k1)/k1),
  Eq(Derivative(x5, t), (-1)*x5*k6*x4*k1/k1),
  Eq(Derivative(x6, t), (1*x5*k6*x4*k1 + (-1)*x6*k7*x7*k1)/k1),
  Eq(Derivative(x7, t), (-1)*k8*x7*k14*k1/k1),
  Eq(Derivative(x8, t), (1*x6*k7*x7*k1 + 1*k1*k9/(1 + x11**3) + (-1)*k11*x8*k1)/k1),
  Eq(Derivative(x9, t), 0),
  Eq(Derivative(x10, t), 1*k8*x7*k14*k1/k1),
  Eq(Derivative(x11, t), (1*k1*k10/(1 + x8**3) + (-1)*k1*x11*k12)/k1),
  Eq(Derivative(x12, t), 1*k1*k13*x2/k1) ]