Scientists say the compound is likely to cause cancer but have no hard scientific proof.

科学家们称这种化合物可能致癌，但是并没有确凿的科学依据。

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Other parapsychologists believe the field is on the brink of collapse, having tried to produce definitive scientific proof and failed.

其他前卫的心理学家则认为，该学科曾试图提出明确的科学论证，但却失败了，因此该学科正处于瓦解的边缘。

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L There is no scientific proof that any ET life form has ever visited the Earth.

l还没有任何科学证据可以证明外星生命曾经访问过地球。

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It also provides an invaluable scientific proof of concept, opening up new avenues for cancer therapy.

FORBES: Genentech's Rite Of Spring

Lacking so far is direct scientific proof that wearing ultraviolet-blocking contact lenses will prevent long-term eye issues.

WSJ: Contacts Lenses That Let In Sun, But Block UV Rays

And although we've known that for years, this is the first big scientific proof of that relationship.

CNN: Simple test may determine smokers' lung cancer risk