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   253篇
  免费   36篇
  国内免费   38篇
测绘学   97篇
大气科学   15篇
地球物理   125篇
地质学   59篇
海洋学   21篇
天文学   2篇
综合类   4篇
自然地理   4篇
  2023年   5篇
  2022年   14篇
  2021年   18篇
  2020年   7篇
  2019年   3篇
  2018年   9篇
  2017年   4篇
  2016年   12篇
  2015年   15篇
  2014年   9篇
  2013年   12篇
  2012年   8篇
  2011年   10篇
  2010年   13篇
  2009年   12篇
  2008年   22篇
  2007年   9篇
  2006年   12篇
  2005年   18篇
  2004年   11篇
  2003年   13篇
  2002年   13篇
  2001年   9篇
  2000年   10篇
  1999年   17篇
  1998年   7篇
  1997年   4篇
  1996年   7篇
  1995年   3篇
  1994年   7篇
  1993年   3篇
  1992年   8篇
  1988年   1篇
  1984年   2篇
排序方式: 共有327条查询结果,搜索用时 78 毫秒
51.
基于ArcGIS Engine的地质灾害信息管理与应用   总被引:1,自引:0,他引:1  
以地质灾害风险信息管理与应用为例,运用AE技术实现多源灾害信息统一管理、快速提取、专题图输出,揭示了GIS技术在此领域应用的可行性和广阔前景。  相似文献   
52.
To reveal the effect of shale reservoir characteristics on the movability of shale oil and its action mechanism in the lower third member of the Shahejie Formation(Es3l), samples with different features were selected and analyzed using N2 adsorption, high-pressure mercury injection capillary pressure(MICP), nuclear magnetic resonance(NMR), high-speed centrifugation, and displacement image techniques. The results show that shale pore structure characteristics control shale oil movability directly. Movable oil saturation has a positive relationship with pore volume for radius > 2 μm, as larger pores often have higher movable oil saturation, indicating that movable oil is present in relatively larger pores. The main reasons for this are as follows. The relatively smaller pores often have oil-wetting properties because of organic matter, which has an unfavorable effect on the flow of oil, while the relatively larger pores are often wetted by water, which is helpful to shale oil movability. The rich surface provided by the relatively smaller pores is beneficial to the adsorption of immovable oil. Meanwhile, the relatively larger pores create significant pore volume for movable oil. Moreover, the larger pores often have good pore connectivity. Pores and fractures are interconnected to form a complex fracture network, which provides a good permeability channel for shale oil flow. The smaller pores are mostly distributed separately;thus, they are not conducive to the flow of shale oil. The mineral composition and fabric macroscopically affect the movability of shale oil. Calcite plays an active role in shale oil movability by increasing the brittleness of shale and is more likely to form micro-cracks under the same stress background. Clay does not utilize shale oil flow because of its large specific surface area and its block effect. The bedding structure increases the large-scale storage space and improves the connectivity of pores at different scales, which is conducive to the movability of shale oil.  相似文献   
53.
54.
55.
中国数字地震台网的现状和近期发展   总被引:7,自引:0,他引:7       下载免费PDF全文
中国数字地震台网(CDSN)自20世纪80年代建成并投入运行以来, 有力地促进了我国的数字地震学研究, 扩大并加深了我们对地壳、 地球内部构造和地震震源过程的认识, 从而有助于地震预报和减轻地震灾害的研究工作. 随着世界科学技术的发展, 中美双方于1992年~2001年,对CDSN进行了二期技术改造.本文综述了CDSN二期技术改造的目标和技术内容;ldquo;新一代rdquo;CDSN的技术特性和运行状况;基于CDSN二期技术改造建立的CDSN数据通信系统,研发CDSN数字地震实时分析系统的进展.   相似文献   
56.
概述了微卫星的特点和发展应用概况,简述了微卫星借助单个磁强计完成三轴姿态确定的原理;并以WMM2010模型为研究对象,介绍了确定卫星姿态的统计性方法;分析了几种不同截断阶数的地磁模型与地磁场真值的差异,指出对于定姿精度要求不高的中低轨道(数百千米)卫星,可将低阶模型作为磁场真值存储在卫星处理器中,有助于提高卫星定姿的实时性。  相似文献   
57.
Aquatic ecosystems have been identified as a globally significant source of nitrous oxide (N2O) due to continuous active nitrogen involvement, but the processes and influencing factors that control N2O production are still poorly understood, especially in reservoirs. For that, monthly N2O variations were monitored in Dongfeng reservoir (DFR) with a mesotrophic condition. The dissolved N2O concentration in DFR displayed a distinct spatial–temporal pattern but lower than that in the eutrophic reservoirs. During the whole sampling year, N2O saturation ranging from 144% to 640%, indicating that reservoir acted as source of atmospheric N2O. N2O production is induced by the introduction of nitrogen (NO3 ?, NH4 +) in mesotrophic reservoirs, and is also affected by oxygen level and water temperature. Nitrification was the predominate process for N2O production in DFR due to well-oxygenated longitudinal water layers. Mean values of estimated N2O flux from the air–water interface averaged 0.19 µmol m?2 h?1 with a range of 0.01–0.61 µmol m?2 h?1. DFR exhibited less N2O emission flux than that reported in a nearby eutrophic reservoir, but still acted as a moderate N2O source compared with other reservoirs and lakes worldwide. Annual emissions from the water–air interface of DFR were estimated to be 0.32 × 105 mol N–N2O, while N2O degassing from releasing water behind the dam during power generation was nearly five times greater. Hence, N2O degassing behind the dam should be taken into account for estimation of N2O emissions from artificial reservoirs, an omission that historically has probably resulted in underestimates. IPCC methodology should consider more specifically N2O emission estimation in aquatic ecosystems, especially in reservoirs, the default EF5 model will lead to an overestimation.  相似文献   
58.
真实地震情况下人群疏散特征与模拟演练的差异是应急疏散的统计物理研究中的一个关键问题.本文通过互联网收集和分析了2008年5月12日汶川MS8.0地震中一些记录到地震时人群疏散的监控录像.这些监控录像不仅为真实地震情况下人员疏散行为的研究提供了目前仍十分稀缺的实例.而且可用于约束紧急情况下人群疏散的统计物理模型.对条件相似的真实地震情况下和模拟演练情况下的疏散人数一疏散时间进行研究,发现出口处的疏散人数和疏散时间呈显著的非线性关系,这与通过模拟演练所得出的线性关系具有明显的差异.  相似文献   
59.
This paper presents a new methodology for slope reliability analysis by integrating the technologies of updated support vector machine (SVM) and Monte Carlo simulation (MCS). MCS is a powerful tool that may be used to solve a broad range of reliability problems and has therefore become widely used in slope reliability analysis. However, MCS often involves a great number of slope stability analysis computations, a process that requires excessive time consumption. The updated SVM is introduced in order to build the relationship between factor of safety and random variables of slope, contributing to reducing a large number of normal computing tasks and enlarging the problem scale and sample size of MCS. In the algorithm of the updated SVM, the particle swarm optimization method is adopted in order to seek the optimal SVM parameters, enhancing the performance of SVM for solving complex problems in slope stability analysis. Finally, the integrating method is applied to a classic slope for addressing the problem of reliability analysis. The results of this study indicate that the new methodology is capable of obtaining positive results that are consistent with the results of classic solutions; therefore, the methodology is proven to be a powerful and effective tool in slope reliability analysis.  相似文献   
60.
作为一个中长期地震预测方法,基于复杂系统统计物理的图象信息学PI算法近年来广受关注.针对7级以上强震成组和突发交替的川滇地区,考虑将与其构造和地震活动关系密切,且强震频发的安达曼-苏门答腊地区作为统一的强震预测研究区,使用PI算法进行MW7.0及以上预测ldquo;目标震级rdquo;的地震危险性分析.计算中使用了1973年以来的NEIC目录,采用10年尺度的地震活动ldquo;异常学习rdquo;时段和3年尺度ldquo;预测时间窗rdquo;,对预测效果进行了ROC检验.回溯性研究显示,PI预测效果较好,表明将川滇-安达曼-苏门答腊地区作为统一的7以上强震PI预测研究区在统计上具有合理性.从统计物理角度,研究区组合前后的各态遍历性曲线显示,组合后的研究区对PI的适用程度虽不优于单独考虑川滇地区,但优于安达曼-苏门答腊地区.PI图象显示,2008震前可能存在中长期尺度的ldquo;前兆性rdquo;地震活动异常.   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