首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   410篇
  免费   74篇
  国内免费   77篇
测绘学   22篇
大气科学   4篇
地球物理   61篇
地质学   397篇
海洋学   35篇
天文学   1篇
综合类   27篇
自然地理   14篇
  2023年   4篇
  2022年   13篇
  2021年   7篇
  2020年   20篇
  2019年   17篇
  2018年   7篇
  2017年   12篇
  2016年   23篇
  2015年   11篇
  2014年   29篇
  2013年   11篇
  2012年   23篇
  2011年   23篇
  2010年   28篇
  2009年   33篇
  2008年   27篇
  2007年   27篇
  2006年   29篇
  2005年   26篇
  2004年   31篇
  2003年   21篇
  2002年   17篇
  2001年   14篇
  2000年   15篇
  1999年   12篇
  1998年   12篇
  1997年   15篇
  1996年   12篇
  1995年   6篇
  1994年   4篇
  1993年   6篇
  1992年   4篇
  1990年   2篇
  1989年   4篇
  1988年   1篇
  1986年   3篇
  1985年   6篇
  1984年   5篇
  1979年   1篇
排序方式: 共有561条查询结果,搜索用时 31 毫秒
11.
影响新生界"底含"发育的因素及含水层参数修正   总被引:5,自引:1,他引:5  
分析了“底含”发育的主要影响因素,并以祁东煤矿为例,利用地下水动力学方法重新计算了“底含”的有关参数,对以往抽水试验参数进行修正,并成功地运用到邻近矿井。该研究表明,在富水性较强的古河道发育位置,要合理留设防水煤岩柱,才能保证煤矿安全生产。  相似文献   
12.
海州式磷矿床地质特征及其成矿模式   总被引:2,自引:0,他引:2  
熊先孝  姚超美 《矿床地质》1996,15(2):171-181
海州式磷矿成矿物质有多种来源。磷元素在地壳发展过程中,随着磷矿成矿作用不同阶段物化条件等改变而变化,将成矿划分为沉积、变质及改造三阶段。中元古代早期海州群锦屏组,肥东群双山 ,宿松群柳坪组和虎踏石组及红安群七角山组下段为其“源”,磷块岩形成后,由于变质、混合岩化交代和风化淋滤作用,使磷质活化,在一定的空间富集成矿。  相似文献   
13.
超基性岩体在金川矿区露采边坡稳定性评价中占有重要地位, 它是整体边坡的支撑体。本文研究了该岩体的物质组成、赋存环境、物理力学性质、岩体结构特征等。在此基础上, 对超基性岩体质量进行了评价。  相似文献   
14.
疏降地下水引起地面塌陷浅析--以淮南煤矿区为例   总被引:4,自引:0,他引:4  
以淮南西部矿区为例,介绍了该地区自20世纪60年代开采煤矿以来,由于疏降地下水,引起的地面塌陷。为了研究灰岩水动力场规律,先后在该区进行多时段、多水平放水试验。研究表明,覆盖粘土层、岩溶及人工疏降地下水,是该地区岩溶塌陷形成的基本条件。通过对粘土盖层性质、疏降地下水岩溶塌陷演化过程及塌陷机理与对应阶段过程综合分析,结合区域地质条件,掌握了塌陷点的分布规律。对目前西部地区塌陷“复活”、整治及未来城市规划,提出了建设性建议。  相似文献   
15.
The preliminary study of streams and rivers from the Roşia Montană area revealed that the concntration of heavy metals— Cd, Mn, Cu, Pb, and Zn—are above accepted limits. The gold extraction method is based on flotation. The most important pollution sources are mine tailings. The determinations were performed for samples collected in: April 2004, July 2004, September 2004, November 2004, February 2005 and May 2005. The highest concentrations were found for cadmium in September 2004: 0.17 mg/L; for copper in September 2004: 1.38 mg/L; for manganese in July 2004: 239.4 mg/L; for lead in May 2005: 0.54 mg/L; and for zinc in September 2004: 35.37 mg/L;. This study involved three small rivers (streams) that flow into the Mureş River and finally into the Danube River, having a great impact on human health and environmental stability in the area. In May 2005, a sample of drinking water from the mining district was also collected.  相似文献   
16.
为了满足可地浸砂岩铀矿的开采工艺要求,研制了HXY-800QT型拖车钻机。介绍了该钻机的设计思想、性能特点、主要部件的结构设计及生产使用情况。  相似文献   
17.
Tooeleite, nominally Fe63+(As3+O3)4(SO4)(OH)4·4H2O, is a relatively uncommon mineral of some acid-mine drainage systems. Yet, if it does occur, it does so in large quantities, indicating that some specific conditions favor the formation of this mineral in the system Fe-As-S-O-H. In this contribution, we report the thermodynamic properties of synthetic tooeleite. The sample was characterized by powder X-ray diffraction, scanning electron microscopy, extended X-ray absorption fine-structure spectroscopy, and Mössbauer spectroscopy. These methods confirmed that the sample is pure, devoid of amorphous impurities of iron oxides, and that the oxidation state of arsenic is 3+. Using acid-solution calorimetry, the enthalpy of formation of this mineral from the elements at the standard conditions was determined as −6196.6 ± 8.6 kJ mol−1. The entropy of tooeleite, calculated from low-temperature heat capacity data measured by relaxation calorimetry, is 899.0 ± 10.8 J mol−1 K−1. The calculated standard Gibbs free energy of formation is −5396.3 ± 9.3 kJ mol−1. The log Ksp value, calculated for the reaction Fe6(AsO3)4(SO4)(OH)4·4H2O + 16H+ = 6Fe3+ + 4H3AsO3 + SO42− + 8H2O, is −17.25 ± 1.80. Tooeleite has stability field only at very high activities of aqueous sulfate and arsenate. As such, it does not appear to be a good candidate for arsenic immobilization at polluted sites. An inspection of speciation diagrams shows that the predominance field of Fe3+ and As3+ overlap only at strongly basic conditions. The formation of tooeleite, therefore, requires strictly selective oxidation of Fe2+ to Fe3+ and, at the same time, firm conservation of the trivalent oxidation state of arsenic. Such conditions can be realized only by biological systems (microorganisms) which can selectively oxidize one redox-active element but leave the other ones untouched. Hence, tooeleite is the first example of an “obligatory” biomineral under the conditions prevailing at or near the Earth's surface because its formation under these conditions necessitates the action of microorganisms.  相似文献   
18.
Hematite is a thermodynamically stable iron oxide under the aerobic conditions present in most natural surface soils and sediments. Most studies to date have focused on the capacity of hematite to adsorb trace metals and metalloids, but structural incorporation of trace metals within hematite is less recognized. This study assessed the incorporation of molybdenum within the structure of hematite during the phase transformation of 2-line ferrihydrite under alkaline conditions (pH ∼10). Extended X-ray absorption fine structure analyses show molybdenum incorporated into hematite, with two Mo-O shells having a coordination number (CN) of 3 and average bond distances of 1.78 ± 0.01 and 2.08 ± 0.02 Å, respectively, as well as two Mo-Fe shells with a CN of 3 and average bond distances of 3.10 ± 0.02 Å and 3.44 ± 0.02 Å, respectively. This observation suggests the tetrahedrally-coordinated Mo in the molybdate that adsorbs onto the 2-line ferrihydrite changes to an octahedrally-coordinated Mo within the hematite with Mo possibly substituting for Fe in the hematite structure. Our findings suggest that molybdenum partitioning (low concentrations) to iron oxides in the environment can occur due to structural incorporation as well as adsorption.  相似文献   
19.
针对地下盐矿在开采过程中,随时可能会因为溶通状况的改变而发生坍塌地质灾害,本文利用矿山数字管理软件Quanty Mine,确定昆明盐矿的三维模型,以期监控盐矿开采不同阶段溶通的变化规律,为避免盐矿过度开采导致地质灾害的发生。  相似文献   
20.
南召县石鼓金矿地质特征及成因探讨   总被引:1,自引:0,他引:1  
石鼓金矿位于北秦岭复杂褶皱带东段,乔端-瓦穴子断裂南侧,牧虎顶花岗岩体之北侧,矿脉的产出受断裂构造控制.矿脉数量多,规模大小不一,成矿与构造岩浆活动等关系密切.矿床类型为石英脉型.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号