全文获取类型
收费全文 | 492篇 |
免费 | 81篇 |
国内免费 | 86篇 |
专业分类
测绘学 | 66篇 |
大气科学 | 78篇 |
地球物理 | 136篇 |
地质学 | 198篇 |
海洋学 | 16篇 |
天文学 | 3篇 |
综合类 | 52篇 |
自然地理 | 110篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 26篇 |
2021年 | 11篇 |
2020年 | 23篇 |
2019年 | 39篇 |
2018年 | 22篇 |
2017年 | 22篇 |
2016年 | 30篇 |
2015年 | 26篇 |
2014年 | 36篇 |
2013年 | 39篇 |
2012年 | 49篇 |
2011年 | 53篇 |
2010年 | 25篇 |
2009年 | 38篇 |
2008年 | 31篇 |
2007年 | 28篇 |
2006年 | 28篇 |
2005年 | 19篇 |
2004年 | 19篇 |
2003年 | 14篇 |
2002年 | 10篇 |
2001年 | 11篇 |
2000年 | 6篇 |
1999年 | 16篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 9篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 5篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1983年 | 1篇 |
排序方式: 共有659条查询结果,搜索用时 280 毫秒
291.
292.
针对目前利用CORS观测数据进行地面变形和参考站点位稳定性分析时缺乏具有较好通用性的数据处理与分析一般流程和策略的问题,该文在对地面变形和参考站点位稳定性分析需要考虑的影响因素进行分析的基础上,提出了一种数据处理与分析的一般流程和策略,并针对大范围地面变形(或地壳板块运动)分析与小范围(局部)地面变形分析以及CORS参考站点位稳定性分析的不同特点,提出了相应的变形分析基准的合理选择与统一方法。实验结果表明:所提出的流程、策略以及基准选择与统一方法能够获得精确、可靠的地面变形和参考站点位稳定性分析成果。 相似文献
293.
294.
孙玉兵 《测绘与空间地理信息》2016,(4):173-174,177
通过以GPS载波相位差分定位技术和回声测深仪等组成的三维数据自动采集系统,按照规定的测线,快速准确地采集高密度、高精度水下地形数据,获取水底测点平面和深度信息,利用以ArcGIS为平台的数据处理编辑软件,制作水下地形图、计算库容、生成库容曲线,并与初设库容曲线进行复核分析,为探查泥沙淤积对库容的影响、节能增效提供详实可靠的基础数据。 相似文献
295.
Characterization of sub‐daily thermal regime in alpine rivers: quantification of alterations induced by hydropeaking
下载免费PDF全文
![点击此处可从《水文研究》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The thermal regime of rivers is threatened by anthropogenic stresses at a large variety of timescales. We focus on sub‐daily thermal alterations induced by the release of hypolimnetic water for hydropower production (thermopeaking). We analyse the thermal signal focusing on the following characteristics that are potentially affected by hypolimnetic releases: (i) sub‐daily thermal rate of change and (ii) oscillation frequencies contained in the thermal signal. Through a proper scaling, we derive two dimensionless at‐a‐station indicators to compare alterations among stations with different locations and physiographic characteristics of the basins. Then we analyse the data from two different thermal datasets (Italy/Switzerland) for a total of 48 stations with 10 min time resolution of temperature data. The stations are grouped according to the absence of upstream hydropeaking releases (29 stations, reference group) and the existence of upstream hydropeaking, hence potentially impacted by thermopeaking (19 stations, altered group). Using a simple statistical approach, based on a non‐parametric definition of outliers, we identify the range of variability of the two indicators for the reference, unaltered group. This range measures the ‘natural’ sub‐daily thermal variability of the proposed indicators. Finally, we investigate the seasonality effects on the two proposed indicators and it results, that sub‐daily alterations mostly occur during summer. The two indicators represent a novel tool for the assessment of river thermal regime alterations and can be easily included in existing methodologies to assess river quality. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
296.
In water-deficient rivers, environmental flows (e-flows) are usually sustained via inter-basin water transfer projects from water-sufficient rivers, but these projects incur tremendous costs and may lead to many negative ecological effects, such as ecological invasion. This research proposed to transfer hydropower instead of water from water-sufficient rivers, because hydropower could substitute for water to promote economic development and reduce water withdrawal from water-deficient rivers (conserved water). In addition, based on the analysis of eco-hydrological processes, the flow regime alteration plays an important role in restoring riverine ecosystem. With the goal of minimum flow regime alternation, we set up two scenarios to distribute the annual conserved water, and determined the optimal amount of transferred hydropower and the optimal use of conserved water, which could effectively sustain the e-flows. Accordingly, this paper established a computable general equilibrium model to analyse the substitution of hydropower for water in a water-deficient river basin, and determined the water withdrawal volume that could be reduced. We adopted a range-of-variability approach to measure the degree of flow regime alteration, and optimized the flow regime management scheme. The Luanhe River Basin was adopted as a study case. The results showed that: the water-hydropower equivalent decreased as the transferred hydropower into the Luanhe River Basin increased; a transferred hydropower amount of 22.46 kWh/s, equivalent to 18.30 m3/s conserved water, was optimal for the river basin; the conserved water should be distributed to the Luanhe River in the proportions of 0.55:0.1:0.35 during the wet, normal and dry seasons, respectively, which is the optimal scheme to sustain the hydrological processes of the river. 相似文献
297.
Flow regulation is widely known to modify the thermal regime of rivers. Here, we examine the sensitivity of an empirical approach, the Equilibrium Temperature Concept (ETC), to detect both the effects of hydraulic infrastructures on the annual thermal cycle and the recovery of the thermal equilibrium with the atmosphere. Analysis was undertaken in a Pyrenean river (the Noguera Pallaresa, Ebro basin) affected by a series of reservoirs and hydropower plants. Equilibrium temperature (Te) is defined as the water temperature (Tw) at which the sum of all heat fluxes is zero. Based on the assumption of a linear relationship between Te and Tw, we identified changes in the Te–Tw regression slope, used as an indicator of a thermal alteration in river flow. We also assessed the magnitude of the alteration by examining the regression slope and its statistical significance. Variations in the regression parameters were used as indicators of the influence of factors other than atmospheric conditions on water temperature. Observed Tw showed a linear relationship with Te at all river stations. However, the slopes of the Te–Tw relationship appeared to be lower in the reaches downstream from hydraulic infrastructures, particularly below large dams. A seasonal analysis indicated that Te–Tw relationships had higher slopes and lower p‐values during autumn, while no significant differences were found at other seasons. Although thermal characteristics did not strongly depend on atmospheric conditions downstream of hydraulic infrastructures, the river recovered to pre‐alteration conditions with distance downstream, indicating the natural tendency of water to attain thermal equilibrium with the atmosphere. Accepting associated uncertainties, mostly because of the quality of the data and the lack of consideration of other factors influencing the thermal regime (e.g. discharge), ETC appears to be a simple and effective method to identify thermal alterations in regulated rivers. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
298.
Abstract The French national project IMAGINE2030 aims to assess future water availability in the Garonne River basin (southwest France) by taking account of changes in both climate and water management in the 2030s. Within this project, two mountainous drainage basins located in the Pyrenees were examined to assess the specific impact of climate change on reservoir management. The Salat River basin at Roquefort, is considered as a proxy (representative of a natural basin), whereas the Ariège River at Foix is influenced by hydropower production in winter and by water releases to sustain low flows in summer. The Cequeau rainfall–runoff model, combined with a simplified model of reservoir management operations, was calibrated on present-day conditions and forced with climate projections derived from the IPCC AR4 report. The results show that a warming climate over the basins induces a decrease in mean annual runoff, a shift to earlier snow melting in mountainous areas and more severe low-flow conditions. The simulations show a decrease in electricity generation. Under two water management scenarios (one “business-as-usual” and the other incorporating an increased downstream water demand in compliance with requirements for increased minimum flow), simulations for the Ariège River basin suggest an earlier filling of the reservoir is necessary in winter to anticipate the increased release from reservoirs in summer to support minimum flow farther downstream. Editor Z.W. Kundzewicz; Associate editor D. Hughes Citation Hendrickx, F. and Sauquet, E., 2013. Impact of warming climate on water management for the Ariège River basin (France). Hydrological Sciences Journal, 58 (5), 976–993. 相似文献
299.
对龙胜县洪水河水电站的地质环境特征进行了调查研究,同时进行了地质灾害现状和预测的评估,在分析各种影响因素的基础上对存在的地质灾害和隐患提出了防治措施和建议,可为水电站建设过程中和建成运营后的地质灾害防治工作提供一定的理论依据。 相似文献
300.