Plot3D[(Sqrt[1 - (x^2) - (y^2)]), {x, -1, 1}, {y, -1, 1}, 
      PlotPoints -> 60]

Plot3D[(Sqrt[(x^2) + (y^2)]), {x, -1, 1}, {y, -1, 1}, 
      PlotPoints -> 60]

Plot3D[
      (Sqrt[-(x^2) - (y^2) + (Sqrt[(x^2) + (y^2)])]), {x, -1, 1}, {y, -1, 
        1}, PlotPoints -> 60]

Plot3D[(Sqrt[-(x^2) + (Sqrt[(x^2)])]), {x, -1, 1}, {y, -1, 1}, 
      PlotPoints -> 60]

Plot3D[(Sqrt[(x^2) + (y^2)]) -  .25, {x, -1, 1}, {y, -1, 1}, 
      PlotPoints -> 60]

⁃  Graphics  ⁃

Plot3D[
      (Sqrt[-(x^2) - (y^2) + (Sqrt[(x^2) + (y^2)]) -  .24]), {x, -1, 1}, {y, 
        -1, 1}, PlotPoints -> 60]