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   63篇
  免费   14篇
  国内免费   27篇
测绘学   6篇
大气科学   5篇
地球物理   19篇
地质学   64篇
海洋学   1篇
天文学   1篇
综合类   5篇
自然地理   3篇
  2022年   2篇
  2019年   1篇
  2017年   2篇
  2016年   3篇
  2015年   2篇
  2014年   2篇
  2013年   2篇
  2011年   11篇
  2010年   3篇
  2009年   7篇
  2008年   1篇
  2007年   3篇
  2006年   2篇
  2005年   7篇
  2004年   10篇
  2003年   17篇
  2002年   6篇
  2001年   3篇
  2000年   4篇
  1999年   2篇
  1998年   1篇
  1997年   1篇
  1996年   1篇
  1994年   1篇
  1993年   7篇
  1989年   1篇
  1987年   1篇
  1986年   1篇
排序方式: 共有104条查询结果,搜索用时 31 毫秒
81.
西藏日土岩基三宫岩石序列地球化学、年代学及构造意义   总被引:1,自引:2,他引:1  
西藏日土岩基三宫岩石序列由花岗闪长岩、英云闪长岩、石英闪长岩组成,富含包体,包体由砂板岩捕掳体、角闪石析离体和镁铁质暗色深源包体组成。寄主岩的地球化学性质显示高硅、铝不饱和-弱饱和、钙碱性-高钾钙碱性、富集轻稀土、弱-中等的铕异常,寄主岩地球化学协和图指示岩浆来源为壳幔混源,花岗闪长岩锆石~(206)Pb/~(238)U年龄为115.5±0.4Ma,该混源花岗岩序列与狮泉河带闭合过程中岛弧与班戈地体的碰撞有关。  相似文献   
82.
内蒙古赤峰浩布高铅锌矿床大地构造位置位于大兴安岭地区南段,属黄岗梁—甘珠尔庙褶皱成矿带.对浩布高铅锌矿床小罕山岩体进行了详细的岩石学、年代学、岩石地球化学和Hf同位素研究.结果显示:小罕山岩体主要岩石类型为二长花岗岩,形成于(143.9±1.1)Ma,属于早白垩世;地球化学组成上表现出高硅(SiO2=66.96% ~6...  相似文献   
83.
The study applies the improved cloud‐free moderate resolution imaging spectral radiometer daily snow cover product (MODMYD_MC) to investigate the snow cover variations from snow hydrologic year (HY) HY2000 to HY2013 in the Amur River basin (ARB), Northeast Asia. The fractions of forest cover were 38%, 63%, and 47% in 2009 in China (the southern ARB), Russia (the northern ARB), and ARB, respectively. Validation results show that MODMYD_MC has a snow agreement of 88% against in situ snow depth (SD) observations (SD ≥ 4 cm). The agreement is about 10% lower at the forested stations than at the nonforested stations. Snow cover durations (SCDs) from MODMYD_MC are 20 days shorter than ground observations (SD ≥ 1 cm) at the forested stations, whereas they are just 8 days shorter than ground observations (SD ≥ 1 cm) at the nonforested stations. Annual mean SCDs from MODMYD_MC in the forested areas are 21 days shorter than those in the nearby farmland in the Sanjiang Plain. This indicates forest has a complex influence on the snow accumulation and melting processes and even on optical satellite snow cover mapping. Meanwhile, SCD and mean snow cover are negatively correlated with air temperature in ARB, especially in the snow melting season, when mean air temperature in March and April can explain 86% and 74% of the mean snow cover variations in China ARB and Russia ARB, respectively. From 1961 to 2015, the annual mean air temperature presented an increased trend by 0.33 °C/decade in both China ARB and Russia ARB, whereas it had a decrease trend from HY2000 to HY2013. The decrease of air temperature led to an increase of snow cover, which is different from the global decrease trend of snow cover variations. SCD and snow cover had larger increase rates in China ARB than in Russia ARB, and they were larger in the forested areas than in the nearby farmland in the Sanjiang Plain.  相似文献   
84.
针对山区地形复杂,高程变化较大的特点,利用6S辐射传输模型建立查找表,结合研究区DEM对影像进行了大气校正。试验结果表明,校正后的影像清晰度、对比度提高了,消除了大气对NDVI的负面影响。  相似文献   
85.
在收集河南省及邻省地磁台的核旋绝对观测资料基础上,应用最小二乘法原理进行线性空间相关分析和精度检验。结果表明,三类地磁台核旋观测资料精度较高,F总强度不仅精度高且稳定性好。尤其是郑州-信阳台间各项精度指标均名列前茅,显示出内在质量的优越性。  相似文献   
86.
金强  张晋仁 《地质论评》1993,39(4):316-321
盆地分析与油藏描述代表了当代石油地质科学研究的发展方向,它们以高度综合性和定量化为显著标志,大大推进了油气勘探与开发。作者连续几年对三春集等地区先后作了盆地构造岩相分析和精细油藏描述,通过前者建立了该区构造岩相模式,指出了油气富集规律,指导了勘探布置;通过后者建立了油藏地质模型,具体地提出了精细勘探和改善开发效果的建议。最后指出盆地构造相分析法和油藏描述技术应大力推广。  相似文献   
87.
分析对比了多种岩土钻探工程大口径钻头的优缺点,设计了适应不同地层的大口径钻头。  相似文献   
88.
Drilling fluid is a common flushing medium used in pile foundation, geological drilling and petroleum drilling. Study on ultrasonic propagation properties in drilling fluid is of vital importance, not only for developing equipments to non-contact measuring concrete casting level for bored pile, but also for developing equip- ments considering drilling fluid as signal channel. The existence of clay particles makes the ultrasonic propagation and attenuation in drilling fluid much different from pure water. In order to know the relation among ultrasound frequency, slun-y density and depth, a series of laboratory experiments about ultrasound propagation in water-based bentonite slurry were finished. Wavelet method was adopted to process the gained original waves of ultrasonic propagation in slurry, so we knew the velocity and attenuation coefficient of ultrasound propagated in different drilling fluids with different density. The first group experiments shows that with density of drilling fluid increase, ultrasonic velocity will decrease but attenuation coefficient will increase if ultrasonic frequency keep constant. The second group experiments shows that the power of ultrasound will intensify in small bore hole, the attenuation coefficient is much smaller than theoretical value.  相似文献   
89.
Concentrations of seventeen hazardous trace elements including As, Pb, Hg, Se, Cd, Cr, Co, Mo, Mn, Ni, U, V, Th, Be, Sb, Br and Zn in the No.ll coal seam, Antaibao surface mine, Shanxi Province were determined using Instrumental Neutron Activation Analysis (INAA), Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES), Cold-Vapor Atomic Absorption Spectrometry (CV-AAS) and Graphite Furnace Atomic Absorption Spectrometry (GF-AAS). Comparisons with average concentrations of trace elements in Chinese coal show that the concentrations of Hg and Cd in the No. 11 coal seam, Antaibao surface mine are much higher. They may be harmful to the environment in the process of utilization. The variations of the trace elements contents and pyritic suffur in vertical section indicated that: (a) the concentrations of As, Pb, Mn, and pyritic sulfur decrease from roof to floor; (b) the concentrations of Cr, Zn and Mo are higher in roof, floor and lower in coal seam; (c) the concentration of Br, Sb, and Hg are higher in coal seam and lower in roof and floor; (d) the concentrations of Mo, V, Th and AI vary consistently with the ash yield. Cluster analysis of trace elements, pyritic sulfur, ash yield and major elements, such as AI, Fe, P, Ca shows that: (a) pyritic sulfur, Fe, As, Mn, Ni, Be are closely associated and reflect the influence of pyrite; (b) Mo, Se, Pb, Cr, Th, Co, Ca and A! are related to clay mineral, which is the main source of ash; (c) U, Zn, V, Na, P maybe controlled by phosphate or halite; (d) Hg, Br, Sb and Cd may be mainly organic-associated elements which fall outside the three main groups. The concentration distribution characteristics of trace elements in coal seam and the cluster analysis of major and trace elements showed that the contents of trace elements in the No. 11 coal seam, Antaibao surface mine, are mainly controlled by detrital input and migration from roof and floor.  相似文献   
90.
本文对发现于河南毛堂金矿田氧化矿石中的含锡自然铜进行了矿物学研究。该矿物属等轴晶系,O_h~5-F_(m3m),a_0=3.655?,Z=4。化学成分中Cu 90.38(wt)%,Sn 9.38(wt)%,分子式Cu_(18)Sn。含锡自然铜相当于Cu_(18)Sn合金中的a相,在自然界属首次发现。  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