全文获取类型
| 收费全文 | 95篇 |
| 免费 | 19篇 |
| 国内免费 | 12篇 |
专业分类
| 测绘学 | 2篇 |
| 大气科学 | 13篇 |
| 地球物理 | 55篇 |
| 地质学 | 19篇 |
| 天文学 | 1篇 |
| 综合类 | 2篇 |
| 自然地理 | 34篇 |
出版年
| 2024年 | 1篇 |
| 2022年 | 2篇 |
| 2021年 | 9篇 |
| 2020年 | 7篇 |
| 2019年 | 9篇 |
| 2018年 | 1篇 |
| 2017年 | 3篇 |
| 2016年 | 3篇 |
| 2015年 | 6篇 |
| 2014年 | 5篇 |
| 2013年 | 5篇 |
| 2012年 | 5篇 |
| 2011年 | 4篇 |
| 2010年 | 6篇 |
| 2009年 | 4篇 |
| 2008年 | 6篇 |
| 2007年 | 8篇 |
| 2006年 | 5篇 |
| 2005年 | 5篇 |
| 2004年 | 6篇 |
| 2003年 | 3篇 |
| 2001年 | 2篇 |
| 2000年 | 2篇 |
| 1999年 | 5篇 |
| 1998年 | 3篇 |
| 1997年 | 6篇 |
| 1995年 | 2篇 |
| 1994年 | 1篇 |
| 1992年 | 2篇 |
排序方式： 共有126条查询结果，搜索用时 203 毫秒
11.
Land surface actual evapotranspiration is an important process that influences the Earth's energy and water cycles and determines the water and heat transfer in the soil-vegetation-atmosphere system. Meanwhile, the cryosphere's hydrological process is receiving extensive attention, and its water problem needs to be understood from multiple perspectives. As the main part of the Chinese cryosphere, the Tibetan Plateau faces significant climate and environmental change. There are active interaction and pronounced feedback between the environment and ETa in the cryosphere. This article mainly focuses on the research progress of ETa in the Tibetan Plateau. It first reviews the ETa process, characteristics, and impact factors of typical underlying surfaces in the Tibetan Plateau (alpine meadows, alpine steppes, alpine wetlands, alpine forests, lakes). Then it compares the temporal and spatial variations of ETa at different scales. In addition, considering the current greening of cryosphere vegetation due to climate change, it discusses the relationship between vegetation greening and transpiration to help clarify how vegetation activities are related to the regional water cycle and surface energy budget. 相似文献
12.
Vegetation has a major influence on the water and energy balance of the earth's surface. In the last century, human activities have modified land use, inducing a consequent change in albedo and potential evapotranspiration. Linear vegetation structures (hedgerows, shelterbelts, open woodland, etc) were particularly abundant but have declined considerably over the past several decades. In this context, it is important to quantify their effect on water and energy balance both on a global scale (climate change and weather prediction) and on a local scale (soil column, hillslope and watershed). The main objective of this study was to quantify the effect of hedgerows on the water cycle by evaluating spatial and temporal variations of water balance components of a hillslope crossed by a hedgerow. Water flow simulation was performed using Hydrus‐2D to emphasize the importance of transpiration in the water balance and to evaluate water extraction from groundwater. Model validation was performed by comparing simulated and observed soil matrix potentials and groundwater levels. Hedgerow transpiration was calculated from sap flow measurements of four trees. Water balance components calculated with a one‐dimensional water balance equation were compared with simulations. Simulation runs with and without tree root uptake underlined the effect of hedgerow transpiration, increasing capillary rise and decreasing drainage. Results demonstrated that the spatial and temporal variability of water balance components was related to the hedgerow presence as well as to the meteorological context. The relations between transpiration, groundwater proximity and soil‐water availability determined the way in which water balance components were affected. Increased capillary rise and decreased drainage near hedges were related to the high transpiration of trees identified in this study. Transpiration reached twice the potential evapotranspiration when groundwater level and precipitation amounts were high. Water balance analysis showed that transpiration was a substantial component, representing 40% of total water output. These results may offer support for improving hydrological models by including the effect of land use and land cover on hydrological processes. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
13.
Measurements of sap flow, meteorological parameters, soil water content and tension were made for 4 months in a young cashew (Anacardium occidentale L.) plantation during the 2002 rainy season in Ejura, Ghana. This experiment was part of a sustainable water management project in West Africa. The Granier system was used to measure half‐hourly whole‐tree sap flow. Weather variables were observed with an automatic weather station, whereas soil moisture and tension were measured with a Delta‐T profile probe and tensiometers respectively. Clearness index (CI), a measure of the sky condition, was significantly correlated with tree transpiration (r2 = 0·73) and potential evaporation (r2 = 0·86). Both diurnal and daily stomata conductance were poorly correlated with the climatic variables. Estimated daily canopy conductance gc ranged from 4·0 to 21·2 mm s−1, with a mean value of 8·0 ± 3·3 mm s−1. Water flux variation was related to a range of environmental variables: soil water content, air temperature, solar radiation, relative humidity and vapour pressure deficit. Linear and non‐linear regression models, as well as a modified Priestley–Taylor formula, were fitted with transpiration, and the well‐correlated variables, using half‐hourly measurements. Measured and predicted transpiration using these regression models were in good agreement, with r2 ranging from 0·71 to 0·84. The computed measure of accuracy δ indicated that a non‐linear model is better than its corresponding linear one. Furthermore, solar radiation, CI, clouds and rain were found to influence tree water flux. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
14.
15.
16.
渭干河灌区的水土环境及水文地质条件在克孜尔水库建成后发生了一定的变化,本文结合灌区12年来的水盐监测资料,对灌区地下水的埋深变化规律、水质演变趋势、灌区的排水效果及目前存在的问题进行了分析与探讨,并为今后灌区排水措施和保持水土环境的良性发展提出了建议. 相似文献
17.
C3植物光合作用日变化的模拟 总被引：28，自引：1，他引：27
对前人光合作用-气孔导度耦合模型进行了修正,建立了光合作用-蒸腾作用-气孔导度的耦合模型,它概括了叶片上各主要物理过程和生理过程之间的相互联系和制约关系。 用数值方法研究了不同环境因子（太阳辐射、温度、湿度和风速等）对光合作用、蒸腾作用和气孔导度的日变化及中午降低（midday depression）的影响。 主要结果是:（1）当边界层导度减小时,光合“午睡”加剧,蒸腾作用减弱,但作为反馈调节,气孔导度增加。 （2）气孔导度的最适温度最低,光合作用次之,蒸腾作用最适温度最高。当光合作用中午受到高温的胁迫时,气孔导度下降的幅度最大,光合作用次之,蒸腾作用的降幅最小。一天中,气孔导度降低的持续时间最长,蒸腾作用降低的持续时间最短。（3）空气绝对湿度越低,气孔导度越低,光合午睡越明显。蒸腾作用则决定于饱和水汽压差(Vpd)和气孔导度两个因素的相反的作用。蒸腾作用随Vpd增加而增大,但Vpd超过一定值后,反而使蒸腾作用下降。 （4）当温度在光合最适温度以上时,太阳辐射的增加使叶温增加,引起光合“午睡”的加剧和气孔导度的降低。（5）ci/cs在中午的降低表明气孔的关闭是光合作用“午睡”现象的原因。 相似文献
18.
Chloride is a major anion in soil water and its concentration rises essentially as a function of evapotranspiration. Compared to herbaceous vegetation, high transpiration rates are measured for isolated trees, shelterbelts or hedgerows. This article deals with the influence of a tree hedge on the soil and groundwater Cl? concentrations and the possibility of using Cl? as an indicator of transpiration and water movements near the tree rows. Cl? concentrations were measured over 1 year at different depths in the unsaturated zone and in the groundwater along a transect intersecting a bottomland oak hedge. We observed a strong spatial heterogeneity of Cl? concentrations, with very high values up to 2 g l?1 in the unsaturated zone and 1·2 g l?1 in the upper part of the groundwater. This contrasts with the low and homogeneous concentrations (60–70 mg l?1) in the deeper part of the groundwater. Cl? accumulation in the unsaturated zone at the end of the vegetation season allows us to identify the active root zone extension of trees. In winter, upslope of the tree row, downwards leaching partly renews the soil solution in the root zone, while the slow water movement under the trees or farther downslope results in Cl? accumulation and leads to a salinization of the soil and groundwater. This salinization is of the same order as experimental conditions produce negative effects on oak seedlings. The measurement of Cl? concentrations in the unsaturated zone under tree rows at the end of the vegetation season would indicate whether certain topographic, pedological or climatic conditions are likely to favour a strong salinization of the soil, as observed in the present study. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
19.
作为计算太阳总辐射(Rs)的主要公式,Angstrom公式参数(a、b)的合理取值是计算参照腾发量(ET0)的重要前提。针对FAO所提出的a、b建议值(a=0.25、b=0.5)在中国无辐射观测资料地区被大量使用,而其合理性尚未得到系统评价的情况,基于中国104个地面站的观测数据,在逐月时间尺度上,讨论了a、b变化对ET0的影响,分析了a、b的地区分布规律,评价了FAO建议值所导致的ET0计算误差,进而阐明了该建议值在中国7个区域的适用性。提出了无辐射资料情况下a、b的地区综合取值方法。主要研究结论是:①参数a、b偏差对ET0的计算有重要影响,在中国无资料地区采用FAO建议值将导致较大的太阳总辐射(Rs)和ET0计算误差。②大多数站点,a的率定值较FAO建议值明显偏小,而b的率定值明显偏大。新疆地区和华南地区a、b率定值分布比较集中,而在其它区域比较分散。③FAO建议参数值在东北、西北和新疆3个区域计算ET0的适用性较好,而在西南和华南两个区域的适用性很差,计算的ET0偏高较大。④提出的地区综合取值方法,能使Rs和ET0的计算精度较FAO建议值显著提高。 相似文献
20.
蒸散发是地表陆气水分交换的纽带,准确量化蒸散发的时空演变格局对于水资源规划与管理至关重要。本文基于GLEAM模型的蒸散发及其组分数据集,借助7个通量观测站数据、120个流域的流域水量平衡及PML_V2蒸散发产品,在中国九大流域系统评估了GLEAM-ET产品,分析了植被恢复背景下,蒸散发（ET）及其组分（植被蒸腾Ec,截留蒸发Ei,土壤蒸发Es）在1980—2020年的时空演变格局。本文主要得到以下结论：① GLEAM-ET产品在中国九大流域具有较好的适用性,其性能与气候类型有关,干旱区效果优于湿润区。此外,GLEAM与PML_V2模型在九大流域相关性较好（R>0.7）,分布格局与变化趋势整体保持一致。② 全国尺度上,ET均值为416.88 mm,增长速率为1.21 mm/a。Ec与ET均呈自东南向西北递减的分布格局,而Es与其相反。Ec、ET在九大流域均呈显著增加趋势（p<0.001）。Ei、Es在季风区流域分别呈显著增加和显著减小趋势;在内陆区流域呈不显著减小（p>0.05）和显著增加趋势。③在植被恢复背景下,ET组分比例发生了变化。Ec占比变化存在南北差异,南方流域Ec占比均减小,北方流域均增加。Ei占比在各流域均增加,Es占比均减小。黄河流域ET组分对植被恢复的响应最为明显,Ec占比增加了5.21%,Es占比减小了5.56%。 相似文献