npm安装依赖包报错?报错

我在安装npm依赖包时，比如npm install express -g，他会显示安装错误，错误信息为：

C:\Windows\system32>npm install express -g
npm ERR! Windows_NT 6.1.7601
npm ERR! argv "D:\\Program Files\\nodejs\\node.exe" "D:\\Program Files\\nodejs\\
node_modules\\npm\\bin\\npm-cli.js" "install" "express" "-g"
npm ERR! node v5.6.0
npm ERR! npm  v3.6.0
npm ERR! code ECONNRESET

npm ERR! network tunneling socket could not be established, cause=write EPROTO 1
01057795:error:140770FC:SSL routines:SSL23_GET_SERVER_HELLO:unknown protocol:ope
nssl\ssl\s23_clnt.c:794:
npm ERR! network
npm ERR! network This is most likely not a problem with npm itself
npm ERR! network and is related to network connectivity.
npm ERR! network In most cases you are behind a proxy or have bad network settin
gs.
npm ERR! network
npm ERR! network If you are behind a proxy, please make sure that the
npm ERR! network 'proxy' config is set properly.  See: 'npm help config'

npm ERR! Please include the following file with any support request:
npm ERR!     C:\Windows\system32\npm-debug.log