Admission is by invitation only.

凭请柬入场。

《牛津词典》

Entry to this competition is by invitation only.

此次竞赛的参赛只凭邀请函。

《柯林斯英汉双解大词典》

To get a sense of current economist opinion, we turned to the experts at Economics by invitation.

为了获得当下经济学家们的观点，我们向经济学界的专家们发出了邀请。

youdao

It has similarly failed to respond to an invitation by European Union Foreign Policy chief Javier Solana for a new round of talks on its nuclear program with the five permanent U.N.Security Council member countries and Germany,the P5+1.

VOA: standard.2009.06.24

They've got the gardens open by invitation.

他们有花园，对受邀者开放。

快乐的休息日下午 - SpeakingMax英语口语达人

you could leave your response to the invitation slightly open-ended by saying you're not sure.

你可以表示你不确定，开放性地回复这个邀请。

I don't know 课堂 - SpeakingMax英语口语达人

IR Peter Drucker's comments on financial services (By invitation, September 25th) dismiss derivative products much too quickly.

ECONOMIST: Letters

Participation in the OnStar Family Link pilot is by invitation only and will include approximately 10, 000 active U.S. OnStar subscribers.

ENGADGET: OnStar Family Link brings loved ones closer together through vehicle tracking

Exclusive parties erupt around the Monterey Peninsula throughout the week, accessible only by invitation from the likes of Bentley and Mercedes-Benz.

FORBES: Magazine Article