全文获取类型
收费全文 | 734篇 |
免费 | 193篇 |
国内免费 | 146篇 |
专业分类
测绘学 | 27篇 |
大气科学 | 70篇 |
地球物理 | 152篇 |
地质学 | 577篇 |
海洋学 | 151篇 |
综合类 | 34篇 |
自然地理 | 62篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 16篇 |
2021年 | 22篇 |
2020年 | 31篇 |
2019年 | 38篇 |
2018年 | 26篇 |
2017年 | 79篇 |
2016年 | 102篇 |
2015年 | 33篇 |
2014年 | 75篇 |
2013年 | 54篇 |
2012年 | 52篇 |
2011年 | 60篇 |
2010年 | 45篇 |
2009年 | 50篇 |
2008年 | 38篇 |
2007年 | 55篇 |
2006年 | 37篇 |
2005年 | 28篇 |
2004年 | 21篇 |
2003年 | 23篇 |
2002年 | 25篇 |
2001年 | 15篇 |
2000年 | 20篇 |
1999年 | 19篇 |
1998年 | 15篇 |
1997年 | 18篇 |
1996年 | 15篇 |
1995年 | 13篇 |
1994年 | 8篇 |
1993年 | 12篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1986年 | 5篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1978年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有1073条查询结果,搜索用时 187 毫秒
1.
Socio-economic and Environmental Implications of the Hydroelectric Projects in Uttarakhand Himalaya, India 总被引:1,自引:1,他引:0
This paper deals with detailed analysis of the fiasco created by the Tehri High Dam in Uttarakhand, India, particularly in terms of resettlement and rehabilitation of the local inhabitants. Aspects pertaining to the environmental issues are also discussed. Currently, the river valleys in Uttarakhand state of India are the targets of increasing hydroelectric projects. Virtually all rivers are being exploited for generating environmental friendly power. Having being learned the hard lesson from Tehri Dam, it has been decided to opt for such schemes in which comparatively little submergence and tempering with the fragile eco-systems is involved.However, our observations suggest that even in such schemes if due care is not taken they may turn out to be a failure. 相似文献
2.
Huijun Jin Zhi Wei Shaoling Wang Qihao Yu Lanzhi Lü Qingbai Wu Yanjun Ji 《Engineering Geology》2008,101(3-4):96-109
The Qinghai–Tibet Highway and Railway (the Corridor) across the Qinghai–Tibet Plateau traverses 670 km of permafrost and seasonally frozen-ground in the interior of the Plateau, which is sensitive to climatic and anthropogenic environmental changes. The frozen-ground conditions for engineering geology along the Corridor is complicated by the variability in the near-surface lithology, and the mosaic presence of warm permafrost and talik in a periglacial environment. Differential settlement is the major frost-effect problem encountered over permafrost areas. The traditional classification of frozen ground based on the areal distribution of permafrost is too generalized for engineering purposes and a more refined classification is necessary for engineering design and construction. A proposed classification of 51 zones, sub-zones, and sections of frozen ground has been widely adopted for the design and construction of foundations in the portion of the Corridor studied. The mean annual ground temperature (MAGT), near-surface soil types and moisture content, and active faults and topography are most commonly the primary controlling factors in this classification. However, other factors, such as local microreliefs, drainage conditions, and snow and vegetation covers also exert important influences on the features of frozen ground. About 60% of the total length of the Corridor studied possesses reasonably good frozen-ground conditions, which do not need special mitigative measures for frost hazards. However, other sections, such as warm and ice-rich or -saturated permafrost, particularly in the sections in wetlands, ground improvement measures such as elevated land bridges and passive or proactive cooling techniques need to be applied to ensure the long-term stability of thermally unstable, thick permafrost subsoils, and/or refill with non-frost-susceptible soils. Due to the long-history of the construction and management of the Corridor by various government departments, adverse impacts of construction and operation on the permafrost environment have been resulted. It is recommended that an integrated, executable plan for the routing of major construction projects within this transportation corridor be established and long-term monitoring networks installed for evaluating and mitigating the impact from anthropogenic and climatic changes in frozen-ground conditions. 相似文献
3.
遥感在滑坡灾害研究中的应用进展 总被引:9,自引:1,他引:8
在对常用的光学遥感卫星影像、InSAR,LiDAR等遥感技术方法介绍的基础上,综述了这些方法在滑坡研究中的最新应用进展,从滑坡风险评估中的基础地形数据获取、滑坡编录与制图、监测、滑坡因素制图、承灾体制图等5个方面阐述遥感技术在滑坡风险中的支撑技术作用与应用前景。从遥感影像在滑坡风险评估中的作用、解译能力、影响解译的因素、精度评价和遥感数据源选择等角度阐述了常用遥感技术在滑坡风险评估应用中存在的问题,认为: ① 遥感技术在滑坡风险评估中的主要作用为数据、信息的获取与更新;② 滑坡的遥感影像解译能力取决于影像空间分辨率与待识别滑坡大小的相对关系,影像的时间分辨率、滑坡与其周边环境的对比度、立体影像的获取能力是利用遥感影像开展滑坡探测、识别与制图的关键要素;解译方法和解译员的专业素质是滑坡遥感解译的重要影响因素;③ 遥感影像与GIS空间分析、3D可视化的综合可有效增强滑坡识别与制图的效率和精度;④ 对于遥感解译滑坡的精度评价应针对具体影像的可解译性从有效解译,错误解译和遗漏解译三个方面予以客观评价;⑤ 滑坡风险评估应针对具体应用,从成本效益比的角度,本着“够用为止”原则合理选用遥感数据源。 相似文献
4.
通过对尚家—太平川地区构造演化、烃源岩特征、沉积特征、储盖组合、油水关系及油藏类型和油气成藏特征的分析,研究了本区的石油地质条件,认为烃源岩具有较好的生、排烃能力,分流河道砂体为油气聚集提供较好的沉积环境,良好的储盖组合有利于油气的聚集与保存。研究区没有统一油水界面,尚家地区以岩性—构造油藏为主,太平川地区以构造—岩性油藏为主。区内扶余—杨大城子油层油气成藏受有效性圈闭、优势运移通道、过剩压力、储集条件和构造诱导作用控制。据上述认识确定了研究区下一步的勘探方向,并已在指导勘探实践中取得了较好的效果。 相似文献
5.
The Eastern Flank Hydrocarbon Province borders the southeastern edge of the South Oman Salt Basin in the southern part of Oman. An intensive exploration programme by PDO over the past seven years has led to the discovery of almost 2 × 109 m3 of oil with current production of some 15000 m3/d from six fields.In stark contrast to other oil habitats of the Arabian Peninsula, the main play involves rock units and geological events ranging in age from Late Precambrian to Quaternary Times, while trap development and charging are closely related to syn-tectonic salt dissolution.The principal reservoirs and seals are poorly consolidated, Palaeozoic clastics which drape, due to salt dissolution, over residual ‘cores’ principally composed of either Lower Palaeozoic sandstones (Haima Group), or Late Proterozoic carbonates (Huqf Group), or some combination of these. Oils have been geochemically correlated with algal source rocks of the Huqf Eastern Flank. Structures are considered to have been ‘charged’ from Late Mesozoic times onwards in conjunction with progressive subsurface salt removal and the onset of maturation of local source rocks. The effectiveness of ‘charging’ along the retreating salt edge is indicated by the small percentage of dry wells.Major oil zones are found in both anticlinal and truncation traps which are commonly developed around sandstone (Haima Group) cores. Oils show a wide range of characteristics but are typically heavy, early expulsion crudes, high sulphur with little associated gas. Bacterial transformation is not uncommon.Producing reservoirs mainly occur at relatively shallow depths (600–1200 m). Primary recovery factors of around 7% reflect the high density and viscosity of the Eastern Flank crudes and have initiated interest in Enhanced Oil Recovery (EOR) techniques. Two such pilot projects, involving steam and polymer flooding, are due to commence in 1984 and, if successful, will substantially increase the reserve base of these fields. 相似文献
6.
7.
Deep sea drilling in the Central Gulf of California, a young and active spreading centre, shows that the high heat flow typical of these regions causes extensive alteration of sediment organic matter, especially near sills and above magma chambers where hydrothermal activity is concentrated. Even on the nearby passive margin, where there are no sills, heat flow is moderately high and hydrocarbon generation has begun in immature sequences. Migrating light hydrocarbons are detected especially where hydrothermal activity is concentrated. Thermogenic methane is more widespread, though not in the passive margin bordering the spreading centre. Despite the incidence of hydrocarbon generation and migration, the amounts of hydrocarbons involved are relatively small and apparently do not lead to commercially significant accumulations of petroleum.The organic matter in these sediments is mostly marine because the Gulf of California generally has low runoff from land and highly productive surface waters. Turbidites rich in terrigenous organic material are locally abundant in the mainly pelagic section in the Guaymas Basin. The highest concentrations of organic matter are found in laminated diatomites deposited on the Guaymas passive margin within the oxygen minimum zone. 相似文献
8.
Integrated fishery assessments are intended to take an integrated and wholistic view of fisheries management, to provide comprehensive systems-based evaluations of the sustainability of individual fisheries and their products. Using guidance derived from decision theory and management science, we develop 18 criteria to evaluate the likely effectiveness of nine integrated fishery assessment systems. The assessment systems do not consistently consider four key criteria: the socio-economic impacts of fisheries, the provision of food security, the local relevance of the assessment to the fishery under assessment, and the independent peer review of assessment outcomes. Other important areas of weakness include the lack of appropriate consultation processes relating to both the design of the assessment system and the outcomes of fishery assessments, and limitations in the quality of data and information used in assessments. Improvements will be needed in these areas across all the systems we evaluated if fishers, consumers, managers and other stakeholders are to be provided with consistently reliable assessment outcomes, and an assurance of the sustainability of capture fisheries. 相似文献
9.
10.