6.
对于定义域为\(R\)的函数\(f(x)\),若满足\(①f(0)=0\);\(②\)当\(x∈R\),且 \(x\neq 0\)时,都有\(xf{{"}}(x) > 0\);\(③\)当\(x_{1} < 0 < x_{2}\),且\(|x_{1}|=|x_{2}|\)时,都有\(f(x_{1}) < f(x_{2})\),则称\(f(x)\)为“偏 对称函致”\(.\)现给出四个函数:\(f_{1}(x)=x\sin x\);\(f_{2}(x)=\ln ( \sqrt {x^{2}+1}-x)\);\(f_{3}(x)= \begin{cases} \overset{e^{x}-1,x\geqslant 0}{-x,x < 0}\end{cases}\);\(f_{4}(x)=e^{2x}-e^{x}-x\);则其中是“偏对称函数”的函数个数为\((\) \()\)