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   148篇
  国内免费   26篇
  完全免费   76篇
  地质学   250篇
  2022年   1篇
  2021年   1篇
  2020年   2篇
  2019年   5篇
  2018年   5篇
  2017年   11篇
  2016年   8篇
  2015年   8篇
  2014年   10篇
  2013年   17篇
  2012年   14篇
  2011年   21篇
  2010年   14篇
  2009年   19篇
  2008年   17篇
  2007年   13篇
  2006年   18篇
  2005年   12篇
  2004年   8篇
  2003年   8篇
  2002年   5篇
  2001年   5篇
  2000年   3篇
  1999年   5篇
  1998年   4篇
  1996年   4篇
  1995年   3篇
  1993年   2篇
  1992年   1篇
  1990年   1篇
  1989年   2篇
  1988年   2篇
  1986年   1篇
排序方式: 共有250条查询结果,搜索用时 156 毫秒
1.
原油二次裂解气——天然气重要的生成途径   总被引:41,自引:3,他引:38       下载免费PDF全文
赵孟军  卢双舫 《地质论评》2000,46(6):645-650
本文通过模拟实验,结合塔里木盆地塔中北斜坡地区包括有机质成油、有机质成气及原油二次裂解成气在内的生烃剖面,说明原油二次裂解成气的门限深于干酪根初次裂解成气门限。原油二次裂解生成的天然气与干酪根初次裂解生成的天然气在组分特征和碳同位素特征上存在明显的差异。一些以原油二次裂解气为主要气源所形成气藏的实例,表明原油二次裂解气可以作为特殊的重要的天然气来源。  相似文献
2.
湖南土地资源可持续利用的生态安全评价   总被引:39,自引:0,他引:39  
张建新  邢旭东 《湖南地质》2002,21(2):119-121
生态安全是土地可持续利用的基础,土地生态安全评价是土地可持续利用研究的前沿课题。以湖南省14个地州市为样本,从1999年社会经济和土地生态环境压力、土地生态环境质量、土地生态环境保护和整治能力等方面的运行数据中选取人口密度、城镇化水平、人均耕地等24个指标,采用均方差客观赋权,从各指标的统计特征值及全国的平均值出发,确定本省的生态安全评价阈值S,计算各地市多指标加权综合评价值,试图对本省土地生态安全进行客观综合评价。  相似文献
3.
浙江省滑坡灾害预警预报的降雨阀值研究   总被引:28,自引:0,他引:28  
根据浙江省降雨的特点,将降雨分为台风降雨和非台风降雨,采用统计方法研究了区域性滑坡灾害与台风区和非台风区降雨量及降雨强度的相关性,通过相关性分析确定了有效降雨量模型;得到了浙江省区域性滑坡发生的临界降雨量和降雨强度阀值,为实时时间预警提供了定量依据;将滑坡灾害的空间易发性与降雨量和降雨强度相结合确定了滑坡灾害的空间预警区划指标和等级;最后初步研究了滑坡发生的滞后时间。  相似文献
4.
Regionalization of rainfall thresholds: an aid to landslide hazard evaluation   总被引:25,自引:2,他引:23  
 Rainfall, soil properties, and morphology are major factors controlling shallow landsliding. A series of meteorological events that triggered soil slips in northern Italy were studied to define rainfall thresholds and to evaluate a possible regionalization. Soil properties, triggering rainfall, and local lithological and morphometrical settings of different sites were used as input to an infiltration model. The approach allows the recognition of several triggering conditions in the Piedmont, Pre-Alpine and Alpine regions. This suggests the need for different rainfall thresholds with respect to those derived with other methods. Intensity versus rainfall duration relationships become particularly important when related to soil permeability and thickness, and demonstrate the role of antecedent precipitation. Events with exceptional water discharge from obstructed road culverts reveal the role played by anthropic structures in triggering such phenomena. Different approaches to slope stability analysis are shown, taking into account bedrock lithology, topography, seepage, and local saturation conditions. Received: 23 October 1997 · Accepted: 25 June 1997  相似文献
5.
A warning system for rainfall-induced shallow failures   总被引:22,自引:0,他引:22  
Pietro Aleotti   《Engineering Geology》2004,73(3-4):247-265
It is widely recognised that soil slips and debris flows are triggered by short intense storms. Owing its geologic, geomorphologic and climatic settings, the Piedmont Region (NW Italy) is highly prone to the occurrence of this kind of landslides. In the last two centuries, in fact, a total of 105 severe meteoric events which triggered shallow failures occurred and, of these, 18 events took place from 1990 to 2002. A fair number of rainfall thresholds have been proposed in the literature, defined both on empirical or on physical bases. Empirical thresholds are defined collecting rainfall data for landslide meteoric events and for events without landslides, while physical thresholds are based on numerical models that consider the relation between rainfall, pore pressure and slope stability. The main objective of this paper is the identification of the empirical triggering thresholds for the Piedmont Region. Four meteoric events were selected and analysed (November 4–5, 1994; July 7–8, 1996; April 27–30, 2000; October 13–16, 2000) because they supply a wide range of variation for both rainfall parameters (duration, intensity, cumulative rainfalls) and the number of induced landslides. In the intensity–duration plot, the critical limit is described by the equation: I=19D−0.50 (where I=rainfall intensity expressed in mm/h and D=rainfall duration expressed in hours). Such a limit is traced to envelop 90% of the points on the graph. In the NI–D diagram the triggering thresholds are given by the equations NI=0.76D−0.33 and NI=4.62D−0.79 (where NI=normalised intensity with respect to the annual precipitation, MAP, expressed in %, [(mm/h)/PMA]×100). In the article the different meaning of these thresholds is discussed. Finally, the diagram NI–NCR is proposed; the triggering threshold is given by the expression: NI=−0.09ln[NCR]+0.54 (where NCR is the normalised cumulative critical rainfall, [mm/PMA]×100). The application of the triggering thresholds as a fundamental element in a warning system dedicated to the safeguarding of population in landslide-prone areas is discussed. In detail an operating procedure which is presently being verified and tested in the studied area is described.  相似文献
6.
Regional landslide-hazard assessment for Seattle, Washington, USA   总被引:19,自引:6,他引:13  
Landslides are a widespread, frequent, and costly hazard in Seattle and the Puget Sound area of Washington State, USA. Shallow earth slides triggered by heavy rainfall are the most common type of landslide in the area; many transform into debris flows and cause significant property damage or disrupt transportation. Large rotational and translational slides, though less common, also cause serious property damage. The hundreds of landslides that occurred during the winters of 1995–96 and 1996–97 stimulated renewed interest by Puget Sound communities in identifying landslide-prone areas and taking actions to reduce future landslide losses. Informal partnerships between the U.S. Geological Survey (USGS), the City of Seattle, and private consultants are focusing on the problem of identifying and mapping areas of landslide hazard as well as characterizing temporal aspects of the hazard. We have developed GIS-based methods to map the probability of landslide occurrence as well as empirical rainfall thresholds and physically based methods to forecast times of landslide occurrence. Our methods for mapping landslide hazard zones began with field studies and physically based models to assess relative slope stability, including the effects of material properties, seasonal groundwater levels, and rainfall infiltration. We have analyzed the correlation between historic landslide occurrence and relative slope stability to map the degree of landslide hazard. The City of Seattle is using results of the USGS studies in storm preparedness planning for emergency access and response, planning for development or redevelopment of hillsides, and municipal facility planning and prioritization. Methods we have developed could be applied elsewhere to suit local needs and available data.  相似文献
7.
排烃门限存在的地质地球化学证据及其应用   总被引:17,自引:0,他引:17  
排烃门限概念的提出为有效源岩的判识奠定了理论基础 ,它在油气勘探与资源评价中具有重要意义 .采用地球化学的方法论证了排烃门限的客观存在 .研究表明 ,源岩进入排烃门限后 ,其反映生烃潜能的指标 (S1+S2 ) /TOC、氢指数以及反映烃源岩残留烃量的指标氯仿沥青“A”都开始明显降低 ;烃源岩中可溶有机质的化学成分、生物标志物的含量与分布特征也都发生明显的变化 ,没有进入排烃门限的源岩可溶有机质与原油差别大 ,进入门限后的源岩可溶有机质开始与原油组分较为一致 .渤海湾盆地东营凹陷沙四段泥岩和页岩的排烃门限分别为 2 2 0 0m和 2 0 0 0m左右 ,排烃强度分别为 0~110 0kg/m2 和 0~ 15 0kg/m2 ,累积排出烃量为 7.36 5× 10 8t和 1.4 35× 10 8t.  相似文献
8.
门限控烃作用及其在有效烃源岩判别研究中的应用   总被引:16,自引:2,他引:14  
姜振学  庞雄奇 《地球科学》2002,27(6):689-695
油气在生排运聚成藏过程中需经历生烃门限、排烃门限、成藏门限和资源门限。某一确定的油气运聚成藏系统进入任一门限都将损耗一部分烃量,实际地质条件下源岩生成的烃量只有超过进入各个门限时损耗烃量之和后才能大规模聚集成藏,构成油气勘探的远景区;只有提供的油气满足成藏过程中各种油气损耗形成工业油气聚集的源岩才称为有效烃源岩。阐明了各门限地质含义、判别标准和控油气作用机理,并将门限控烃作用在塔里木盆地台盆区古生界碳酸盐岩源岩评价中进行了应用。研究表明,不存在一个放之四海而皆准的最小有机质丰度下限,最小有机质丰度下限受源岩自身条件及成藏地质条件的共同影响。  相似文献
9.
The paper deals with the validation and evaluation of mathematical models in natural hazard analysis, with a special focus on establishing their predictive power. Although most of the tools and statistics available are common to general classification models, some peculiarities arise in the case of hazard assessment. This is due to the fact that the target for validation, the propensity to develop a dangerous characteristic, is not really known and must be estimated from a (usually) very small sample. This implies that the two types of errors (false positives and false negatives) should be given different meanings. Related to this, a very frequent situation is the presence of prevalence (different proportion of positive and negative cases) in the sample. It is shown that sample prevalence can have a dramatic effect in some very common validation statistics, like the confusion matrix and model efficiency. Here some statistics based on the confusion matrix are presented and discussed, and the use of threshold-independent approaches (especially the ROC plot) is shown. The ROC plot is also proposed as a convenient tool for decision-taking in a risk management context. A general scheme for hazard predictive modeling is finally proposed.  相似文献
10.
成矿流体研究的若干进展与动态   总被引:15,自引:2,他引:13       下载免费PDF全文
近年成矿流体研究在大规模流体的存在与运移、巨型矿床与流体的关系、成矿流体输运动力学、建立热液成矿反应体系及成矿流体分测试技术等方面取得了重要进展;今后成矿流体研究在流体的运移路径与成矿预测、超临界流体与金属矿产巨量堆积的关系及成矿流体的计算机模拟等方面走势明显。  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