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   99篇
  免费   9篇
  国内免费   30篇
测绘学   1篇
大气科学   23篇
地球物理   21篇
地质学   33篇
海洋学   13篇
天文学   9篇
综合类   8篇
自然地理   30篇
  2023年   2篇
  2022年   2篇
  2021年   4篇
  2020年   1篇
  2019年   3篇
  2018年   3篇
  2017年   2篇
  2016年   3篇
  2014年   8篇
  2013年   4篇
  2012年   5篇
  2011年   3篇
  2010年   2篇
  2009年   5篇
  2008年   5篇
  2007年   6篇
  2006年   5篇
  2005年   5篇
  2004年   4篇
  2003年   3篇
  2002年   2篇
  2001年   1篇
  2000年   12篇
  1999年   2篇
  1998年   3篇
  1996年   4篇
  1994年   2篇
  1993年   7篇
  1992年   4篇
  1991年   1篇
  1990年   3篇
  1989年   2篇
  1988年   6篇
  1987年   2篇
  1986年   4篇
  1985年   2篇
  1984年   1篇
  1983年   1篇
  1982年   2篇
  1981年   1篇
  1978年   1篇
排序方式: 共有138条查询结果,搜索用时 15 毫秒
1.
The grid DEM(digital elevation model) generation can be from any of a number of sources:for instance,analogue to digital conversion of contour maps followed by application of the TIN model,or direct elevation point modelling via digital photogrammetry applied to airborne images or satellite images.Currently,apart from the deployment of point-clouds from LiDAR data acquisition,the generally favoured approach refers to applications of digital photogrammetry.One of the most important steps in such deployment i...  相似文献   
2.
辽宁省是全国水资源短缺的省份之一,海岸带地区作为辽宁省经济发展的龙头,水资源已成为其经济可持续发展的主要瓶颈。通过研究海岸带地区淡水资源量和质,对于海岸带地区水资源的可持续利用、区域的可持续发展具有重大意义。  相似文献   
3.
The Abor volcanics outcroping in the core of the Siang window in the Eastern Himalaya comprise voluminous mafic volcanics (47%-56% w(SiO2)),with subordinate felsic volcanics (67%-75% w(SiO2)).The felsi...  相似文献   
4.
目前,辽宁省海洋经济迅速发展,但海洋经济发展的同时也导致海洋环境的破坏.制约了海洋经济的可持续发展.本文从辽宁省海洋经济和海洋环境的现状出发.分析其各自存在的问题及二者之间互相制约的关系,提出保护海洋环境促进海洋经济可持续发展的对策.  相似文献   
5.
【Title】

【Author】

【Addresses】1

The tree root distribution pattern and biomass of seventeen year old trees of Grewia optiva, Morus alba, Celtis australis, Bauhinia variegata and Robinia pseudoacacia were studied by excavation method. B. variegata roots penetrated to a maximum depth of 4.78 m, whereas, M. alba roots were found down to 1.48 m depth. Lateral spread was minimum in B. variegata (1.10 m)and maximum inR. pseudoacacia (7.33 m). Maximum root biomass of 6.30 kg was found in R. pseudoacacia and minimum (2.43 kg) was found in M. alba. For four species viz.,G. optiva, M. alba, C. australis andR. pseudoacacia, 68%-87% root biomass occurred within top 0-30 cm soil depth, but forB. variegata this was only45%. The soil binding factor was maximum in G. optiva and minimum in B. variegata. Soil physico-chemical properties also showed wide variation. The study suggests thatB. variegata with a deep root system is the most suitable species for plantation under agroforestry systems. R. pseudoacacia and G. optiva with deep root systems, more lateral spread and high soil binding factor are suitable for plantation on degraded lands for soil conservation.  相似文献   
6.
With the rapid development of the marine economy industry, human exploitation of marine resources is increasing, which is contributing to the growing trend of eutrophication and frequent occurrence of red tide. Accordingly, investigations of seawater quality have attracted a great deal of attention. This study was conducted to construct a seawater environmental quality assessment model based on the variable fuzzy recognition model. The uncertainty and ambiguity of the seawater quality assessment were then considered, combining the monitoring values of evaluation indicators with the standard values of seawater quality. Laizhou Bay was subsequently selected for a case study. In this study, the correct variable model for different parameters was obtained according to the linear and nonlinear features of evaluation objects. Application of the variable fuzzy recognition model for Laizhou Bay, water quality evaluation and comparison with performance obtained using other approaches revealed that the generated model is more reliable than traditional methods, can more reasonably determine the water quality of various samples, and is more suitable for evaluation of a multi-index, multi-level, nonlinear marine environment system; accordingly, the generated model will be an effective tool for seawater quality evaluation.  相似文献   
7.
A new locality bearing ichnofossils of the Cruziana Assemblage Zone-Ⅲ from the Mussoorie syncline,Lesser Himalaya,is located in rocks of Member-B of the Dhaulagiri Formation,Tal Group,exposed along the Maldewta-Chhimoli fresh road cut section.The site yielded ichnofossils Bergaueria perata,Cochlichnus anguineus,?Diplocraterion isp.,Dimorphichnus obliquus,diplichnitiform Cruziana bonariensis,Diplichnites gouldi,Glockeria isp.,Helminthopsis isp.,Monomorphichnus lineatus,Phycodes palmatum,Palaeophycus striatus,Planolites beverleyensis,Planolites montanus,Treptichnus cf.T.pedum,scratch marks and an undetermined worm impression.An Early Cambrian age (Cambrian Series 2) is assigned to the ichnofossil-bearing strata based on the stratigraphic position between the Drepanuroides and Palaeoolenus trilobite zones.A revised Cambrian ichnofossil zonation is presented for the Tal Group of the Mussoorie syncline.Together with their occurrence on rippled surfaces,and the lateral displacement of some trackways (due to current action),a sub-aqueous shallow-marine depositional setting is proposed for the rocks of Member-B.  相似文献   
8.
盖美  岳鹏  徐晶晶  徐玉梅 《地理研究》2023,(10):2605-2621
作为实现海岸带可持续发展的有效测度手段,韧性研究为海岸带地区自然环境和人类活动的风险评估提供了全新视角。基于人地系统视角提出海岸带韧性的概念,从海岸带韧性分析框架、概念内涵、指标构成出发,构建海岸带韧性HNS-PSR评价体系,并以中国海岸带为例进行测度。研究表明:(1)现有海岸带韧性研究大多囿于单一要素,缺乏整体性,对于海岸带交互强烈的人地属性、人地冲突为核心的人地关系关注较少,亟待基于人地系统视角对海岸带韧性底层逻辑、分析框架进行架构,构建全视角、多角度的海岸带韧性评价体系。(2)在海岸带韧性HNS-PSR评价体系中,“人”聚焦于人口数量及质量的功能发挥和以“人”为载体而物化的经济社会文化属性;“地”既是对陆或海单一区域“地”要素的继承,又着重强调海陆交互作用属性,并为人类活动提供空间场所和资源要素支撑;“人地关系”则侧重对海陆间交互作用协调的纽带作用及感知海岸带抵御、适应、更新能力产生的适应行为和结果。(3) 2005—2019年间,中国海岸带韧性呈波动上升趋势,省际差异明显,且仍以压力韧性为主导。其中,广东、上海、天津海岸带韧性位居前三位,广西、河北、海南位于后三位。研究为海岸带...  相似文献   
9.
Continuous and accurate monitoring of earth surface changes over rugged terrain Himalayas is important to manage natural resources and mitigate natural hazards.Conventional techniques generally focus on per-pixel based processing and overlook the sub-pixel variations occurring especially in case of low or moderate resolution remotely sensed data.However,the existing subpixel-based change detection(SCD)models are less effective to detect the mixed pixel information at its complexity level especially over rugged terrain regions.To overcome such issues,a topographically controlled SCD model has been proposed which is an improved version of widely used per-pixel based change vector analysis(CVA)and hence,named as a subpixel-based change vector analysis(SCVA).This study has been conducted over a part of the Western Himalayas using the advanced wide-field sensor(AWiFS)and Landsat-8 datasets.To check the effectiveness of the proposed SCVA,the cross-validation of the results has been done with the existing neural network-based SCD(NN-SCD)and per-pixel based models such as fuzzybasedCVA(FCVA)andpost-classification comparison(PCC).The results have shown that SCVA offered robust performance(85.6%-86.4%)as comparedtoNN-SCD(81.6%-82.4%),PCC(79.2%-80.4%),and FCVA(81.2%-83.6%).We concluded that SCVA helps in reducing the detection of spurious pixels and improve the efficacy of generating change maps.This study is beneficial for the accurate monitoring of glacier retreat and snow cover variability over rugged terrain regions using moderate resolution remotely sensed datasets.  相似文献   
10.
The counter-gradient terms in the computations of turbulent fluxes of heat and moisture have been included in the PBL parameterization of a regional model for monsoon prediction. Results show that inclusion of counter-gradient terms has a marginal impact in the prediction of large scale monsoon circulation and rainfall rates.  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