题干

下列关于硝酸的认识中,正确的是(    )

A:浓、稀硝酸光照和受热都会分解

B:浓硝酸与金属反应不放出氢气,而稀硝酸与金属反应可置换出氢气

C:常温下,因为铝和铁不与浓硝酸反应,所以浓硝酸可盛放在铝制或铁制容器中

D:铜分别与浓硝酸、稀硝酸反应生成NO2和NO,故稀硝酸的氧化性大于浓硝酸

上一题 下一题 0.0难度 选择题 更新时间:2018-12-07 01:42:58

答案(点此获取答案解析)

A

同类题1

阅读下面说明文,完成1-5题。


科学家揭开变色龙变色之谜

①长期以来,人们一直对变色龙通过变色吸引同伴,吓退情敌、迷惑捕猎者的原理着迷。

②今天,科研人员宣布他们揭开了变色龙变色的秘密,而这一发现让他们大为震惊。

③科研人员发现,变色龙不是通过色素来改变颜色的,而是靠调节皮肤表面的纳米晶体,通过改变光的折射而变色的。

④日内瓦大学的生物学家米歇尔·米林科维奇说:“我们十分惊讶,人们曾认为它们是通过色素来变色的,但真正的原理完全不同。”

⑤雄性变色龙变色,可以让自己的外表更加华丽,以吸引异性、吓退情敌;或是让自己的外表更加不起眼,从而躲过捕食者。

⑥大多数其他种类的变色动物通过黑色素在载黑素细胞内聚集和发散来调整颜色的明暗程度,它们改变的是颜色的亮度而不是色调。   

⑦研究团队称,此前人们也一直用该原理解释变色龙的变色过程。但这个说法,现在被证明是错误的。

⑨对变色龙皮肤的分析显示,变色龙的变色是由透明的被称为“光子晶体”的纳米物质控制的,光子晶体位于虹细胞层,在变色龙的色素细胞之下。

⑨日内瓦大学在一份报告中说,变色龙可通过“调节”虹细胞内的纳米晶体结构来改变光线的折射。“当变色龙状态平静时,纳米晶体呈密集网状分布,折射出蓝光。而当变色龙兴奋时,纳米晶体结构会变得松散,因此折射的光线呈黄色或红色等其他颜色。

⑩他们发现变色龙还有更深一层的虹细胞.这些细胞包括“体积更大、更不规律”的晶体,可折射强光,实质上是一层智能隔热板。

⑪研究团队说:“虹细胞呈两层分布是进化的新特点。这令变色龙可以迅速在有效保护色和鲜艳颜色间转换,同时提供被动热防护。”其他爬行动物体内只有一种无法变色的虹细胞。

                    (选自2015年3月12日《参考消息》)

同类题5

阅读理解

B

    Most of us have ever imagined the life on a desert island. We sometimes imagine a desert island to be a sort of paradise(天堂) where the sun always shines. “Ripe fruit falls from the trees and you are free to sit around without any work. This is really a beautiful picture, isn't it? However, the other side of the picture is quite the opposite. Life on a desert island is awful. You either starve to death or live like Robinson Crusoe, waiting for a boat which never comes.

    Perhaps there is some truth in both these pictures, but few of us have had the chance to find out. We can only experience it in the story like the following.

    Many years ago, two men spent five days on a coral island and they wished that they could stay there longer. They were driving a badly damaged boat from the Virgin Islands to Miami to have it repaired. During the journey, their boat began to sink(下沉). They quickly put food, matches, and cans of beer into a rubber dinghy(救生筏) and rowed for a few miles across the Caribbean until they arrived at a tiny coral island.

    There were hardly any trees on the island and there was no water, but this did not seem to be a problem. The men collected rainwater in the rubber dinghy. As they had brought a gun with them, they had plenty to eat. They caught lobster and fish every day, and they thought they lived just like a king. Five days later, a tank passed by and saved them. However, they felt sorry that they had to leave