全文获取类型
收费全文 | 40234篇 |
免费 | 10359篇 |
国内免费 | 14600篇 |
专业分类
测绘学 | 7352篇 |
大气科学 | 4983篇 |
地球物理 | 7608篇 |
地质学 | 27452篇 |
海洋学 | 7706篇 |
天文学 | 496篇 |
综合类 | 3475篇 |
自然地理 | 6121篇 |
出版年
2024年 | 281篇 |
2023年 | 919篇 |
2022年 | 2506篇 |
2021年 | 3072篇 |
2020年 | 2422篇 |
2019年 | 2784篇 |
2018年 | 2584篇 |
2017年 | 2436篇 |
2016年 | 2339篇 |
2015年 | 2943篇 |
2014年 | 2892篇 |
2013年 | 3531篇 |
2012年 | 3761篇 |
2011年 | 3789篇 |
2010年 | 3660篇 |
2009年 | 3455篇 |
2008年 | 3487篇 |
2007年 | 3311篇 |
2006年 | 3193篇 |
2005年 | 2709篇 |
2004年 | 2048篇 |
2003年 | 1400篇 |
2002年 | 1483篇 |
2001年 | 1305篇 |
2000年 | 1088篇 |
1999年 | 473篇 |
1998年 | 220篇 |
1997年 | 177篇 |
1996年 | 170篇 |
1995年 | 106篇 |
1994年 | 94篇 |
1993年 | 70篇 |
1992年 | 75篇 |
1991年 | 33篇 |
1990年 | 64篇 |
1989年 | 38篇 |
1988年 | 23篇 |
1987年 | 25篇 |
1986年 | 25篇 |
1985年 | 21篇 |
1984年 | 20篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1979年 | 20篇 |
1978年 | 6篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1957年 | 15篇 |
1954年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
121.
Maggie Cusack Yannicke Dauphin Jean-Pierre Cuif Murielle Salom Andy Freer Huabing Yin 《Chemical Geology》2008,253(3-4):172-179
Biominerals are natural composite materials comprising organic and inorganic components. Detailed knowledge of the nature and distribution of both components is a crucial requirement in order to advance our understanding of biomineral formation, their material properties and preservation potential as well as the interpretation of environmental data. Detailed chemical data are essential for our understanding of the nature and distribution of such components. Micro-XANES mapping at the sulphur K-edge reveals that, in the brachiopod Terebratulina retusa, the sulphate concentration is higher in the outer (primary) layer than in the calcite fibres of the secondary layer. This is co-incident with a higher magnesium concentration. In contrast, the sheaths surrounding the calcite fibres contain sulphur as thiol, confirming the presence of protein while, the sulphur within the fibres themselves, occurs as sulphate. Micro-XANES analysis of the insoluble organic extract from T. retusa indicates the presence of organic sulphate while Micro-Raman spectroscopy confirms that structurally substituted sulphate (SSS) is also present although semi-quantitative Raman spectroscopy carried out in this spectral region (wavenumbers 900–1200) indicates that the sulphate present is at the threshold of detection by Raman spectroscopy. The distribution of phosphorus in the shell of T. retusa correlates well with that of protein indicating the presence of phosphorylated proteins in the periostracum, the sheaths surrounding the calcite fibres and the interface between the primary and secondary layer. 相似文献
122.
西天山达巴特矿区火山岩的形成时代、构造背景及对斑岩型矿化的制约 总被引:9,自引:0,他引:9
本文通过对西天山地区比较典型的达巴特斑岩铜钼矿床矿区范围内出露的英安岩和花岗斑岩进行了系统的岩石地球化学分析,对流纹斑岩和花岗斑岩中的锆石进行了SHRIMPU—Pb定年研究,分别获得了315.9±5.9Ma和278.7±5.7Ma。岩石化学、微量以及稀土元素特征表明从英安岩到花岗斑岩,岩体具有明显的分异演化特征和很好的继承性。火山岩和次火山岩的精确定年为准确厘定火山岩形成的时限和地球动力学背景提供了依据。结合已有的Re-Os法获得的矿化年龄,表明晚石炭世末-早二叠世初(278.7±5.7Ma),西天山地区进入板块碰撞-板内伸展阶段,由于深源岩浆侵位,在达巴特矿区形成了由花岗斑岩、流纹斑岩和流纹质角砾熔结凝灰岩组成的椭圆形火山机构,并导致相关矿床的形成。 相似文献
123.
124.
Controlling of landsides safely and economically is a great challenge to mine operators because landslides are major geological
problems especially in open-pit mines. In this paper, a case history at Panluo open-pit mine is presented in detail to share
the experiences and lessons with mine operators. Panluo open-pit mine is located in the southwestern Fujian province of China.
It is the largest open-pit iron mine in the Fujian province and was planned in 1965 and is in full operation from 1978. In
July 1990, an earthquake of magnitude 5.3 in Taiwan Strait and big rainstorms impacted the mine slope, causing tension cracks
and rather large-scale failures, and forming a U-shaped landslide. Total potential volume was estimated to be up to 1.0 × 106 m3. This directly threatened the mine production. In order to protect the mine production and the dwellers’ safety around, a
dynamic comprehensive method was implemented including geotechnical investigations, in-situ testing and monitoring, stability
analysis, and many mitigation and preventive measures. These measures slowed down the development and further occurrence of
the landslide. The results showed that the landslides were still active, it was slowed with the control measures and moved
rapidly with rainfall and mining down. However, no catastrophic accidents occurred and the pit mining was continued till it
was closed at the elevation of 887 m in 2000. As a successful case of landslide control at an open-pit mine for 10 years,
this paper reports the controlling measures in details. These experiences of landslide control may be beneficial to other
similar mines for landslide control. 相似文献
125.
126.
127.
128.
129.
130.
云南罗平中三叠世安尼期生物群的发现及其意义 总被引:15,自引:0,他引:15
本文介绍了云南罗平地区新发现的罗平生物群的产出层位、生物面貌、保存特征、古地理位置及其研究意义。该生物群产于关岭组二段薄层泥晶灰岩中,地层对比和化石鉴定表明其时代为中三叠世安尼期,以鱼类为主,伴生有爬行类、两栖类(?)、棘皮动物、节肢动物(甲壳类、昆虫等)、双壳类、腹足类以及植物化石;化石保存完好,分布广泛,埋藏方式独特。罗平生物群无论在丰度、分异度及化石保存上都极为罕见和独特,对研究埋藏学、古生态学、古地理以及三叠纪海洋生物尤其是海生爬行类都具有极为重要的意义。 相似文献