The R-groups give the amino acids their physical-chemical characteristics such as polarity (hydrophobic or hydrophilic) and charge (acidic or positive versus basic or negative).
R基团赋予氨基酸物理化学特性，例如极性（亲水性和疏水性）以及电荷（酸性或正电荷，碱性或负电荷）。
2
In the process of formation, the material must have received an environmental signal that reflects a change in climate and that can be deciphered by modern physical or chemical means.
在形成的过程中，材料必须接收到环境信号，反映气候变化，并能被现代物理或化学手段破译。
3
Various proposals were put forth to arrange the elements into groups based on similarities in chemical and physical properties.