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   219篇
  免费   40篇
  国内免费   26篇
测绘学   76篇
大气科学   15篇
地球物理   35篇
地质学   110篇
海洋学   13篇
天文学   2篇
综合类   14篇
自然地理   20篇
  2023年   1篇
  2022年   4篇
  2020年   3篇
  2019年   9篇
  2018年   8篇
  2017年   9篇
  2016年   12篇
  2015年   9篇
  2014年   16篇
  2013年   11篇
  2012年   12篇
  2011年   10篇
  2010年   10篇
  2009年   8篇
  2008年   11篇
  2007年   10篇
  2006年   20篇
  2005年   19篇
  2004年   7篇
  2003年   13篇
  2002年   10篇
  2001年   24篇
  2000年   10篇
  1999年   15篇
  1998年   9篇
  1997年   2篇
  1996年   7篇
  1995年   1篇
  1994年   3篇
  1993年   1篇
  1990年   1篇
排序方式: 共有285条查询结果,搜索用时 15 毫秒
121.
This research aims to evaluate the geographical knowledge of nine teachers in the region of Valparaiso, Chile. An interpretive case study was conducted with data collected through classroom observations, interviews, and questionnaires, and these data were then analyzed through triangulation. The findings showed that these teachers, who are the most qualified within the region's context, consider geography to be marginal knowledge in the school curriculum, although they also consider it relevant to the education of their pupils. Both elements provided evidence of the fragility of their geographical knowledge, which fell within a spectrum that combines expert knowledge and lay knowledge.  相似文献   
122.
 There exist many sites with contaminated groundwater because of inappropriate handling or disposal of hazardous materials or wastes. Health risk assessment is an important tool to evaluate the potential environmental and health impacts of these contaminated sites. It is also becoming an important basis for determining whether risk reduction is needed and what actions should be initiated. However, in research related to groundwater risk assessment and management, consideration of multimedia risk assessment and the separation of the uncertainty due to lack of knowledge and the variability due to natural heterogeneity are rare. This study presents a multimedia risk assessment framework with the integration of multimedia transfer and multi-pathway exposure of groundwater contaminants, and investigates whether multimedia risk assessment and the separation of uncertainty and variability can provide a better basis for risk management decisions. The results of the case study show that a decision based on multimedia risk assessment may differ from one based on risk resulting from groundwater only. In particular, the transfer from groundwater to air imposes a health threat to some degree. By using a methodology that combines Monte Carlo simulation, a rank correlation coefficient, and an explicit decision criterion to identify information important to the decision, the results obtained when uncertainty and variability are separate differ from the ones without such separation. In particular, when higher percentiles of uncertainty and variability distributions are considered, the method separating uncertainty and variability identifies TCE concentration as the single most important input parameter, while the method that does not distinguish the two identifies four input parameters as the important information that would influence a decision on risk reduction.  相似文献   
123.
白垩系是西昆仑山前地区最重要的储层,受区域构造演化控制,其岩性与分布在纵、横向上均发生变化。下白垩统为冲积扇辫状河相沉积的红色砾岩、砂岩夹泥岩;上白垩统英吉沙群在研究区西部为一套海相碳酸盐岩地层。白垩系在喀什凹陷最厚,往西、往东、往北均逐渐变薄,并发生相变与尖灭,控制储层发育。本文在研究区域首次通过地震相研究,根据白垩系反射特征精细追踪对比其层位,确定尖灭位置,进而确定白垩系分布范围。研究认为,地震相能在区域上宏观地反映白垩系的沉积特征与分布范围,进而指导油气勘探,具有很重要的现实意义。  相似文献   
124.
地块—海槽边缘带成油成气新概念   总被引:1,自引:0,他引:1  
对准噶尔,塔里木等盆地沉积环境的研究表明,古生代时,中国西北区海相沉积,沉积盆地的基底是一些离散的古老结晶地块,其上海水侵浸,地块之间为大洋或窄大洋的海槽,地块之间的海槽或地块与海槽过渡的边缘带盆地是油气形成的有利地带。  相似文献   
125.
云南省应用地球化学勘查已有50年历史,积累丰富的地球化学资料,取得突出成果,在矿产勘查中发挥了重要作用,也为成矿预测、基础地质研究提供可靠资料,并运用于环境、农业等领域。  相似文献   
126.
The seismic assessment of the local failure modes in existing masonry buildings is currently based on the identification of the so‐called local mechanisms, often associated with the out‐of‐plane wall behavior, whose stability is evaluated by static force‐based approaches and, more recently, by some displacement‐based proposals. Local mechanisms consist of kinematic chains of masonry portions, often regarded as rigid bodies, with geometric nonlinearity and concentrated nonlinearity in predefined contact regions (unilateral no‐tension behavior, possible sliding with friction). In this work, the dynamic behavior of local mechanisms is simulated through multi‐body dynamics, to obtain the nonlinear response with efficient time history analyses that directly take into account the characteristics of the ground motion. The amplification/filtering effects of the structure are considered within the input motion. The proposed approach is validated with experimental results of two full‐scale shaking‐table tests on stone masonry buildings: a sacco‐stone masonry façade tested at Laboratório Nacional de Engenharia Civil and a two‐storey double‐leaf masonry building tested at European Centre for Training and Research in Earthquake Engineering (EUCENTRE). Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
127.
128.
为监测公网盲区地质灾害,提出采用无线信号将前端传感器采集的数据传输到主站,然后使用公网信号再将数据传输到后端指挥中心.对珠峰保护区泥石流沟公网盲区泥石流的监测实验表明,该方法是可行的.  相似文献   
129.
GPS偏心观测及其精度分析   总被引:3,自引:0,他引:3  
由于种种条件的限制,在很多情况下GPS天线都无法实现真正的对中,在某些特殊情况下,例如观测站必须与VLBI站或SLR站重合,而又无法在这些站的标志中心安设接收机天线,这就要求进行GPS偏心观测。本文将着重对GPS偏心观测归心元素的测定方法、归心改正数的计算以及归心元素的测定精度进行讨论和分析。  相似文献   
130.
通过对利用网络RTK控制点进行放线测量的现有作业模式的总结,提出了一些质量控制技术的改进。通过测量手簿的集成和基于PDA的放线测量程序的二次开发,实现了由PDA放线测量程序对GZCORS-RTK数据进行质量控制。与以前的作业模式的比较,质量得到有效控制,效率得到提高。  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