全文获取类型
| 收费全文 | 128篇 |
| 免费 | 3篇 |
| 国内免费 | 7篇 |
专业分类
| 测绘学 | 1篇 |
| 大气科学 | 6篇 |
| 地球物理 | 33篇 |
| 地质学 | 44篇 |
| 海洋学 | 3篇 |
| 天文学 | 1篇 |
| 综合类 | 9篇 |
| 自然地理 | 41篇 |
出版年
| 2021年 | 3篇 |
| 2020年 | 4篇 |
| 2019年 | 4篇 |
| 2018年 | 1篇 |
| 2017年 | 2篇 |
| 2016年 | 3篇 |
| 2015年 | 2篇 |
| 2014年 | 7篇 |
| 2013年 | 4篇 |
| 2012年 | 7篇 |
| 2011年 | 6篇 |
| 2010年 | 5篇 |
| 2009年 | 10篇 |
| 2008年 | 7篇 |
| 2007年 | 9篇 |
| 2006年 | 18篇 |
| 2005年 | 9篇 |
| 2004年 | 6篇 |
| 2003年 | 3篇 |
| 2002年 | 2篇 |
| 2001年 | 3篇 |
| 2000年 | 4篇 |
| 1999年 | 3篇 |
| 1998年 | 2篇 |
| 1997年 | 1篇 |
| 1995年 | 2篇 |
| 1994年 | 4篇 |
| 1993年 | 2篇 |
| 1990年 | 1篇 |
| 1989年 | 1篇 |
| 1988年 | 1篇 |
| 1986年 | 1篇 |
| 1984年 | 1篇 |
排序方式： 共有138条查询结果，搜索用时 62 毫秒
101.
Spatial and temporal variations in alpine vegetation cover have been analyzed between 1982 and 2001 in the source regions of the Yangtze and Yellow Rivers on the Tibetan Plateau. The analysis was done using a calibrated-NDVI (Normalized Difference Vegetative Index) temporal series from NOAA-AVHRR images. The spatial and temporal resolutions of images are 8 km and 10 days, respectively. In general, there was no significant trend in alpine vegetation over this time period, although it continued to degrade severely in certain local areas around Zhaling and Eling Lakes, in areas north of these lakes, along the northern foot of Bayankala Mountain in the headwaters of the Yellow River, in small areas in the Geladandong region, in a few places between TuoTuohe and WuDaoliang, and in the QuMalai and Zhiduo belts in the headwaters of the Yangtze River. Degradation behaves as vegetation coverage reduced, soil was uncovered in local areas, and over-ground biomass decreased in grassland. The extent of degradation ranges from 0 to 20%. Areas of 3×3 pixels centered on Wudaoliang, TuoTuohe, QuMalai, MaDuo, and DaRi meteorological stations were selected for statistical analysis. The authors obtained simple correlations between air temperature, precipitation, ground temperature and NDVI in these areas and constructed multivariate statistical models, including and excluding the effect of ground temperature. The results show that vegetation cover is sensitive to variations in temperature, and especially in the ground temperature at depths of ∼40 cm. Permafrost is distributed widely in the study area. The resulting freezing and thawing are related to ground temperature change, and also affect the soil moisture content. Thus, degradation of permafrost directly influences alpine vegetation growth in the study area. 相似文献
102.
During uplift of the Tibetan plateau and surrounding ranges, tectonic processes have interacted with climatic change and with local random effects (such as landslides) to determine the development of the major river systems of Asia. Rivers draining northward from the Pamir syntaxis have three distinctive patterns that are controlled by different tectonic and climatic regimes. West of the Pamir, the rivers have moderate but irregular gradients and drain northwards to disappear into arid depressions. Relatively steady uplift of the Hindu Kush in northern Afghanistan allowed rivers to cut across the rising ranges, modified by the shear along the Harirud fault zone, local faulting, and by increasing rain-shadow effects from the rising Makran. In the transition to the Pamir the rivers have steeper but more even gradients suggesting more even flow and downcutting during uplift, possibly related to larger glacial sources. In the central Pamir, only one antecedent river, the Pyandzh appears to have kept its northward course with compression and uplift of the indenter, and its course strangely corresponds with a major geophysical boundary (a distorted subducted slab) but not a geological boundary: the other rivers are subsequent rivers developed along deformation fronts during development and northward displacements of the Pamir structural units. The above areas have sources north of the Cretaceous Karakorum–South Pamir Andean margin. On the eastern flank of the Pamir, in the Kunlun and northern Tibetan plateau, the rivers rise similarly north of the Cretaceous Andean margin of southern Tibet, but then flow with low gradients across the plateau, before cutting and plunging steeply down across the Kunlun to disappear into the arid Tarim. These steep profiles are the result of late Neogene uplift of the northern Tibetan plateau and Kunlun possibly modified by glacial diversion and river capture. The drainage history of the Pamir indenter can be reconstructed by restoring the gross movements of the plates and the tectonic displacements, uplift, and erosion of individual tectonic units. Most important changes in drainage took place in the last 10 million years, late Miocene to Quaternary times, as the Pamir syntaxis developed. 相似文献
103.
Decoding temporal and spatial patterns of fault uplift using transient river long profiles 总被引：2，自引：1，他引：1
Alexander C. Whittaker Mikaël Attal Patience A. Cowie Gregory E. Tucker Gerald Roberts 《Geomorphology》2008,100(3-4):506-526
We present detailed observations of rivers crossing active normal faults in the Central Apennines, Italy, where excellent constraints exist on the temporal and spatial history of fault movement. We demonstrate that rivers with drainage areas > 10 km2 and crossing faults that have undergone an increase in throw rate within the last 1 My, have significant long-profile convexities. In contrast, channels that cross faults that have had a constant-slip rate for 3 My have concave-up profiles and have similar concavities and steepness indices to rivers that do not cross any active fault structures. This trend is consistent across the Central Apennines and cannot be explained by appeal to lithology or regional base level change. The data challenge the belief that active faulting must always be reflected in river profiles; instead, the long-profile convexities are best explained as a transient response of the river system to a change in tectonic uplift rate. Moreover, for these rivers we demonstrate that the height of the profile convexity, as measured from the fault, scales with the magnitude of the uplift rate increase on the fault; and we establish that this relationship holds for throw rate variation along strike for the same fault segment, as well as between faults. These findings are shown to be consistent with predictions of channel response to changing uplift rate rates using a detachment-limited fluvial erosion model, and they illustrate that analysis of the magnitude of profile convexities has considerable predictive potential for extracting tectonic information. We also demonstrate that the migration rate of the profile convexities varies from 1.5–10 mm/y, and is a function of the slip rate increase as well as the drainage area. This is consistent with n > 1 for the slope exponent in a classical detachment-limited stream-power erosion law, but could potentially be explained by incorporating an erosion threshold or an explicit role for sediment in enhancing erosion rates. Finally, we show that for rivers in extensional settings, where the response times to tectonic perturbation are long (in this case > 1 My), attempts to extract tectonic uplift rates from normalised steepness indices are likely to be flawed because topographic steady state has not yet been achieved. 相似文献
104.
AbstractRiver managers worldwide are increasingly addressing flow needs for ecosystem processes and services in their management plans for dams and reservoirs. However, while planning and scientific assessments have advanced substantially, successful re-operation of infrastructure to achieve environmental benefits has been more limited. The Sustainable Rivers Project (SRP) was formalized in 2002, as a national partnership between the United States Army Corps of Engineers and The Nature Conservancy to define and implement environmental flows through adaptive reservoir management. The project has focused on eight demonstration basins containing 36 Corps dams, but is designed to direct the collective experience from these sites to help guide agency-wide operational changes for as many as 600 dams to benefit up to 80 000 river kilometres and tens of thousands of hectares of related floodplain and estuarine habitat. This article summarizes the progress to date on defining and implementing environmental flows through the SRP, and evaluates the technical, social, legal, and institutional factors that act as dominant enabling conditions and constraints to implementation.
Editor Z.W. Kundzewicz; Guest editor M. Acreman 相似文献
105.
《国际泥沙研究》2016,(2):159-163
Roughened horizontal aprons are bed covering scour countermeasures constructed downstream of stilling basins and other places where scour hole may develop. In these cases scour occurs at the edge of the apron which can lead to failure of the apron. In the present study, 24 experimental tests were carried out on four different aprons with (2, 5, 10 and 14.28 mm) roughness heights and two different bed material sizes of 0.8 and 1.4 mm under different flow conditions. The results indicated that as the roughness height of apron increases, a significant reduction in the scour depth occurs. 相似文献
106.
《Geoforum》2017
The paper intends to consider how territorial, political and legal culture dominant within mid-19th century Iberian Peninsula influenced boundary-making state practices, and to what extent a complex understanding of natural border areas -and particularly of river boundaries- emerged during this demarcation process. We draw on recent insights about, on the one hand, the important link between territory, nature and law within territorialization processes and state-making and, on the other, intrinsic problems of modern legal categories and juridical practices concerning river boundaries which are argued to be part of territorial ideologies associated with modern states.Within this framework, the paper initially addresses main practices and discourses about territory in this particular Iberian context, regarding both the enduring relevance of theory of natural boundaries within European history of modern state-making and legal codification of river boundaries delimitation by Spanish and Portuguese law internationalists. The following part of the paper presents main historical problems and territorial border disputes along the Minho River which the 1864 Spanish-Portuguese Boundary Treaty attempted to settle. Discussions and negotiations taking place within the Joint Boundary Commissions in charge of examining, delimiting and demarcating this stretch of the border are analysed as to consider how diverging interest and competing discourses about this fluvial space were displayed and related eventually to the solutions adopted by the Boundary Treaty. In that sense, state-driven boundary-making proved to be an important tool for territorial management of this border space. 相似文献
107.
The study of the transport processes in the riparian environment is currently a subject of great interest. In this context, the evaluation of longitudinal dispersion is a fundamental issue. Although it plays an important role in the transport of chemicals, nutrients, and wood debris, few works have studied the effects of riparian vegetation on the dispersion coefficient in transversally non-uniform streams. Here, a quasi two-dimensional model is proposed to evaluate the transverse profile of the depth-averaged velocity in the presence of any vegetation distribution along the riparian transect. Once velocity profile is obtained, the dispersion coefficient is evaluated and the remarkable role of vegetation is shown. Both the velocity profile and the dispersion coefficient have been validated using our new experimental results and literature data. The work highlights the importance of taking into account the presence of vegetation along river banks. The estimation of the longitudinal dispersion in vegetated rivers can be affected by as much as 70–100% compared to the case without vegetation. 相似文献
108.
Diatom assemblages of surface sediments in 46 billabongs from four river floodplains in the southeast Murray-Darling Basin,
Australia were sampled to investigate drivers of species distribution. The principal purpose of the study was to derive information
to aid interpretation of diatom-based palaeoecological studies of these systems and of floodplain lakes more generally. Patterns
in billabong diatom assemblages in relation to river reach, hydrology and farming intensity on surrounding land were examined,
as were correlations with water quality variables. Seasonal variation in billabong water quality was high relative to spatial
variation, and spatial patterns in billabong water quality were weak. In contrast, strong patterns were evident in diatom
assemblages. Three main patterns were observed: (1) a distinction between billabongs dominated by planktonic diatoms from
those dominated by benthic and attached forms; (2) differences in diatom assemblages in billabongs on different river reaches;
and (3) differences in assemblages in billabongs with different hydrology. Of all water quality variables tested, total phosphorus
(TP), total nitrogen (TN) and pH exerted the strongest independent influence on diatom distribution; however, only TP remained
an important variable when species variation due to river reach, hydrology, and aquatic plant cover was taken into account.
The weak influence of water quality on diatom distribution is interpreted as reflecting the dichotomy between plankton and
non-plankton-dominated billabongs, the influence of hydrology and biogeography, the lack of strong spatial water quality gradients
and the high degree of temporal variability in water quality. The findings show that diatom records from billabong sediments
can provide evidence of long-term changes in the abundance of aquatic macrophytes and hydrology. They also suggest that merging
calibration data sets across regions for the purpose of improving diatom transfer functions for water quality reconstruction
is of limited value for floodplain lakes, and that performance is more likely to be gained by boosting site numbers within
regions. 相似文献
109.
浅析江河源区生态系统脆弱性研究的科学问题 总被引：2，自引：0，他引：2
长江、黄河源区位于青藏高原腹地,是我国气候变化的敏感区和脆弱区,面对全球气候变化以及我国冰冻圈萎缩的压力,明晰基于冰冻圈变化条件下江河源区生态系统脆弱性的科学问题,是长江、黄河流域生态安全保障及社会经济持续发展的客观要求。在分析江河源区范围、江河源区和我国冰冻圈的关系、目前生态系统脆弱性研究的基本特点的基础上,在全球气候变化和冰冻圈变化的复杂背景下,提出并阐述了江河源区生态系统脆弱性研究的5个重要科学问题：（1）脆弱性概念的延伸和拓展;（2）气候系统的非线性作用;（3）脆弱性评价的时空尺度;（4）脆弱性评价的临界阈值;（5）脆弱性评价的界面链接等。 相似文献
110.
长江黄河源区积雪空间分布与年代际变化 总被引：1，自引：0，他引：1
应用长江黄河源区及其周边地区16个气象站逐日积雪资料,分析了长江黄河源区积雪的空间分布和年代际变化特征.结果表明:以巴颜喀拉山主峰为中心的黄河源头和长江源东南部地区是年积雪深度高值中心,黄河源头以西和五道梁以东的长江源东北部和黄河源西北部广大地区是低值中心.冬春累积积雪深度占年累积积雪深度的比例>71.0%,夏半年(6~9月)对其的贡献小,但夏半年的积雪日数占年积雪日数的1/3.曲麻莱达日一线以南地区积雪主要发生在1月份,以北地区一年有两个高值期:前冬10~11月和春季3~5月.长江源和黄河源头地区积雪建立早,积雪季节长,结束晚,消退过程缓慢;而黄河源东部地区,积雪建立稍晚,积雪发展比较缓慢,消退过程迅速.近40 a来长江黄河源区积雪呈确定的增长态势,长江源区冬春积雪增长了62.11%,黄河源区增长了60.18%.但二者积雪变化位相基本相反,变化幅度长江源大起大落,而黄河源比较平缓,多雪年份出现也不一致.整个源区20世纪60年代至70年代初为积雪偏少期,70年代中期至90年代是积雪偏多期.从20世纪70年代中至80年代末,积雪明显增加,90年代积雪增加速度有所放慢,近40 a江河源区平均冬春累积积雪深度增加了60.95%.长江源区对整个源区积雪变化起主导作用,源区平均冬春累积积雪深度变化主要表现长江源的特征. 相似文献