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   8055篇
  免费   1084篇
  国内免费   1094篇
测绘学   2650篇
大气科学   315篇
地球物理   1190篇
地质学   3919篇
海洋学   489篇
天文学   53篇
综合类   738篇
自然地理   879篇
  2024年   16篇
  2023年   74篇
  2022年   212篇
  2021年   291篇
  2020年   269篇
  2019年   320篇
  2018年   203篇
  2017年   367篇
  2016年   325篇
  2015年   379篇
  2014年   489篇
  2013年   599篇
  2012年   605篇
  2011年   592篇
  2010年   474篇
  2009年   524篇
  2008年   573篇
  2007年   561篇
  2006年   574篇
  2005年   489篇
  2004年   451篇
  2003年   393篇
  2002年   306篇
  2001年   254篇
  2000年   235篇
  1999年   127篇
  1998年   121篇
  1997年   86篇
  1996年   69篇
  1995年   55篇
  1994年   41篇
  1993年   36篇
  1992年   23篇
  1991年   28篇
  1990年   15篇
  1989年   15篇
  1988年   12篇
  1987年   8篇
  1986年   6篇
  1985年   7篇
  1984年   2篇
  1983年   4篇
  1980年   1篇
  1979年   1篇
  1954年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
As a legacy of the centrally planned economy, the economies in transition of Central and Eastern Europe (CEE) have a unique potential to reduce their greenhouse gas emissions through the improvement in their high energy intensities. Since much of this `low-hanging fruit' in energy-efficiency improvements can be highly cost-effective, many developed countries facing difficulties in meeting their greenhouse gas (GHG) emission targets domestically are eager to find such opportunities in the CEE region. Therefore, studies analysing the potentials and costs of carbon dioxide reduction through technology improvement in the region have come into the limelight. While there are a few excellent studies in the region aimed at analysing climate change abatement potentials, they all embark on different assumptions, methodologies and boundary conditions. It is hence difficult, if not impossible, to compare and analyse the results of these studies across different authors, countries or time horizons. Consequently, the purpose of this paper is to place four leading studies on GHG mitigation through technology improvement from the CEE region into an internationally comparable framework. Four studies were selected from three countries, Poland, Hungary and Estonia, which are all the results of major national and international efforts to assess costs and potentials of GHG reduction. The paper places their assumptions, methods and final results into a framework which enables policy-makers and project designers to compare these across geographical and technological boundaries. Since other studies from around the globe have been analysed in this framework in the literature, this paper provides a vehicle for the findings of these four studies to be compared to others worldwide. In addition, the paper highlights a few areas where similar studies to be completed in the future in the region may be enhanced by incorporating features used in GHG mitigation research in other parts of the world. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
132.
Giant landslides are significant hazards associated with many active volcanic edifices. We describe a similar feature on ancient (>4 Ma) volcanic deposits subject to active tectonism. The landslide is approximately 3 km long by 1 km wide, with an estimated depth of 400 m. Side margins are straight and parallel, mimicking regional structure; narrow valleys incised down these margins provide low-strength side-release surfaces. Between these is a giant slump consisting of at least four, largely intact, discrete blocks that have moved down-dip a distance of >500 m. A series of flows with areal extents ranging from 0.01 to 0.5 km2 extends from the front of the failure. The materials represent an eroded sequence of andesite flows on the flanks of a stratovolcano. These have undergone two phases of hydrothermal alteration, and are deeply weathered to low-density (1040±80 kg m−3) silt (59%) and clay (35%) materials with strength properties typical of weathered silts (c=26±3 kN m−2; φ=42±8°). The size and location of this landslide preclude detailed geotechnical investigation of the failure. The worth of numerical stability analysis as an alternative technique in assessing the nature of the failure and hence the risk it poses to nearby communities is investigated. Sensitivity analysis identified likely conditions under which initial failure may have occurred: analyses for sensitivity to strength and earthquake acceleration needed conversion to critical combinations (F=1.0) of water table and strength/acceleration to remove the overriding influence of water table fluctuations. Failure was likely initiated either by a high water table level (83-84%), or some combination of intensity VII-IX earthquake waves together with water table heights of 40-80%. A general hazard assessment indicates that the risk associated with creep and catastrophic failure of the main mass is small, whereas the risk from flow failures near the toe of the landslide may be high. Important parameters (hydrological regime, flow failure morphology, age of initiation, and rates of movement) requiring closer investigation are identified. Development of a model is crucial to assessing the hazard associated with a feature such as that described here. With limited resources, a detailed stability analysis is a powerful tool as an initial stage in hazard analysis.  相似文献   
133.
本文以 1∶5万里庄幅为例 ,阐述了运用GIS系统对区调过程中各种资料的处理与编辑方法 ,并介绍了数字制图方法及工艺流程 ,提出了GIS系统在 1∶5万区调工作中的应用前景  相似文献   
134.
人工值守台数字化地震仪标定原理   总被引:1,自引:0,他引:1  
张海  张艺 《四川地震》2002,(3):45-48
推导了人工台数字化地震仪的分段标定公式,提出数字化记录系统的微分近似标定和拾震器阻尼衰减法标定的方法,并提供了不同短周期地震仪与数字化地震仪并行的藕合方式和标定计算公式。  相似文献   
135.
本文介绍了数字化射线照相技术对轻物质进行判断的方法。经实践证明,该方法是合理和有效的,可大大增强对轻物质的识别能力,是一种非常可行的识别技术。  相似文献   
136.
To evaluate techniques for assessing earthquake-triggeredlandslide hazard in the Southern Apennines (Italy), a GIS-based analysis was used to modelseismically induced slope deformations. Geological, geotechnical, geomorphological and seismologicaldata were integrated into a standard earthquake slope stability model. The model assessed thelandslide potential that existed during the 1980 Irpinian earthquake in the Upper Sele river Valley.The standard Newmark displacement analysis, widely used for predicting the location of shallowunstable slopes, does not take into account errors and/or uncertainties in the input parameters.Therefore, a probabilistic Newmark displacement analysis technique has been used. Probabilistictechniques allow, e.g., an estimation of the probability that a slope will exceed a certain criticalvalue of Newmark displacement. In our probabilistic method, a Monte-Carlo based simulation modelis used in conjunction with a GIS. The random variability of geotechnical data is modelled by probabilitydensity functions (pdfs), while for the seismic input three different regression laws wereconsidered. Input probability distributions are sampled and the resulting values input into empiricalrelations for estimating Newmark displacement. The outcome is a map in which to each siteis related a spatial probability distribution for the expected displacement in response to seismic loading.Results of the experiments show a high grade of uncertainty in the application of the Newmarkanalysis both for the deterministic and probabilistic approach in a complex geological setting suchas the high Sele valley, quite common in the Southern Apennines. They show a strong dependence onthe reliability of the spatial data used in input, so that, when the model is used at basin scale,results are strongly influenced by local environmental condition (e.g., topography, lithology, groundwatercondition) and decrease the model performance.  相似文献   
137.
Post-earthquake field investigations of landslide occurrence have provided a basis for understanding, evaluating, and mapping the hazard and risk associated withearthquake-induced landslides. This paper traces thehistorical development of knowledge derived from these investigations. Before 1783, historical accounts of the occurrence of landslides in earthquakes are typically so incomplete and vague that conclusions based on these accounts are of limited usefulness. For example, the number of landslides triggered by a given event is almost always greatly underestimated. The first formal, scientific post-earthquake investigation that included systematic documentation of the landslides was undertaken in the Calabria region of Italy after the 1783 earthquake swarm. From then until the mid-twentieth century, the best information on earthquake-induced landslides came from a succession ofpost-earthquake investigations largely carried out by formal commissions that undertook extensive ground-based field studies. Beginning in the mid-twentieth century, when the use of aerial photography became widespread, comprehensive inventories of landslide occurrence have been made for several earthquakes in the United States, Peru, Guatemala, Italy, El Salvador, Japan, and Taiwan. Techniques have also been developed for performing ``retrospective' analyses years or decades after an earthquake that attempt to reconstruct the distribution of landslides triggered by the event. The additional use of Geographic Information System (GIS) processing and digital mapping since about 1989 has greatly facilitated the level of analysis that can applied to mapped distributions of landslides. Beginning in 1984, syntheses of worldwide and national data on earthquake-induced landslides have defined their general characteristics and relations between their occurrence and various geologic and seismic parameters. However, the number of comprehensive post-earthquake studies of landslides is still relatively small, and one of the most pressing needs in this area of research is for the complete documentation of landslides triggered by many more earthquakes in a wider variety of environments.  相似文献   
138.
地球物理技术在我国考古和文物保护工作中的应用   总被引:3,自引:6,他引:3  
20世纪80年代以来,我国考古及文物保护工作者和地球物理工作者越来越认识到地球物理技术在考古和方物保护方面可以发挥作用,在古幕探查、大型古建筑地下遗存现状、古遗迹断代等方面,地球物理技术都找到了发挥作用的机会,本文通过地球物理技术在云冈石窟、龙门石窟、克孜尔石窟、北京故宫紫禁城、嵩岳寺塔、古泗州城遗址、风阳明中都等的物理探查实例,以及查找古幕、古遗迹断代等方面的工作,介绍了我国在考古和文物保护领域应用地球物理技术的进展,并指出了物探在用于考古和文保时的特点和展望。  相似文献   
139.
基于DEM的分布式水文模型构建方法   总被引:52,自引:4,他引:52  
基于 DEM的分布式水文模型是现代水文学同高科技 (如计算机技术、 3S技术等 )相结合的产物 ,是研究变化环境下水文循环与水资源演化规律的理想工具 ,代表了水文模型的最新发展方向。从 DEM的特性出发 ,本文探讨并总结了分布式水文模型的特点、建模思路和模型基本结构框图。在流域离散化方面 ,重点介绍了分布式水文模型常用的三种单元划分方法 ;最后 ,针对分布式水文模型构建问题 ,从“输入模块”、“单元水文模型”、“河网汇流模型”三方面 ,阐述了分布式水文模型微结构构建方法。  相似文献   
140.
徐君亮  江璐明 《热带地理》2002,22(3):236-240
广东省经济和旅游业发展位于全国榜首,人多地少全国最为突出,但乡村旅游建设相对滞后,文中通过潮州市郊鹤陇山农业科技园与观光农园规划设计,论述了发展高新技术农业是新世纪广东农业必由之路,提出结合农业科技园建设,叠加农业观光园,把生态农业建设与旅游文化结合起来,是广东乡村旅游发展的主要途径。  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