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   189篇
  免费   10篇
  国内免费   6篇
测绘学   3篇
地球物理   36篇
地质学   117篇
海洋学   10篇
天文学   1篇
综合类   2篇
自然地理   36篇
  2024年   1篇
  2023年   3篇
  2022年   1篇
  2021年   3篇
  2020年   4篇
  2019年   2篇
  2018年   3篇
  2017年   6篇
  2016年   10篇
  2015年   6篇
  2014年   7篇
  2013年   23篇
  2012年   4篇
  2011年   6篇
  2010年   3篇
  2009年   7篇
  2008年   15篇
  2007年   10篇
  2006年   18篇
  2005年   13篇
  2004年   14篇
  2003年   12篇
  2002年   5篇
  2001年   2篇
  2000年   4篇
  1999年   3篇
  1998年   2篇
  1997年   2篇
  1996年   3篇
  1995年   2篇
  1994年   1篇
  1993年   1篇
  1992年   1篇
  1990年   2篇
  1988年   1篇
  1987年   2篇
  1985年   2篇
  1984年   1篇
排序方式: 共有205条查询结果,搜索用时 203 毫秒
71.
BOOK REVIEWS     
Book Reviewed in this article: Women, Work, and Ideology in the Third World . Haleh Afshar, ed. The Birth of the National Park Service. The Founding Years 1913–33 . Horace M. Albright Theatres of Accumulation: Studies in Asian and Latin American Urbanization . Warwick Armstrong and T.G. McGee. New Tools for Social Scientists, Advances and Applications in Research Methods . William D. Berry and Michael S. Lewis -Beck , eds . Uncertain Dimensions: Western Overseas Empires in the Twentieth Century . Raymond F. Betts. Geography of Sugar Cane . Helmut Blume. The Mines of Neptune: Minerals and Metals from the Sea . Elisabeth Mann Borgese. Geographical Dimensions of Energy . F.J. Calzonetti and B.D. Solomon, eds. Statistical Methods for Geographers . W. A. V. Clark and P. L. Hosking. In The Wake of Columbus, Islands and Controversy . John DeVorsey, Jr., and John Parker, eds. Housing, States and Localities . Peter Dickens, Simon Duncan, Mark Goodwin and Fred Gray. Physician Location and Specialty Choice . Richard L. Ernst and Donald E. Yett. Practical Ecology for Geography and Biology: Survey, Mapping, and Data Analysis . D.D. Gilbertson , M. Kent and F.B. Pyatt Large Scale Water Transfers: Emerging Environmental and Social Experiences . Genady N. Golubev and Asit K. Biswas, eds. The Nature of the Environment . Andrew Goudie. Planning for Population Change . W.T.S. Gould and R. Lawton. The Niger and its Neighbors: Environmental History and Hydrobiology. Human Use and Health Hazards of the Major West African Rivers . A.T. Grove, ed. Remote Sensing of Ice and Snow . Dorothy K. Hall and Jaroslav Martinec. Atlas of Antebellum Southern Agriculture . Sam Bowers Hilliard. Galilee Divided; The Israel-Lebanon Frontier, 1916-1984 . Frederic C. Hor . Plains Country Towns . John C. Hudson. Agricultural Geography: A Social and Economic Analysis . Brian W. Ilbery. Industry in the 1980s: Structural Change and Interdependence . U.N. Industrial Development Organization. Crabgrass Frontier: The Suburbanization of the United States . Kenneth T. Jackson. The Industrial Geography of Italy . Russell King. Studies in Linguistic Geography: The Dialects of English in Britain and Ireland . John M. Kirk, Stewart Sanderson, J.D.A. Widdowson, eds. Tourism: A Community Approach . Peter E. Murphy. Cities and Services: The Geography of Collective Consumption . Steven Pinch. An Historical Geography of Europe 1800–1914 . Norman J. G. Pounds. An Introduction to Human Ecology Research on Agricultural Systems in Southeast Asia . A. Terry Rambo and Percy E. Sajise, eds. Discovering Past Landscapes . Michael Reed, ed. Managing the Ocean: Resources, Research, Law . Jacques G. Richardson, ed. Carta fitosociologica de la transecta botanica de la Patagonia Austral . F.A. Roig , Juan Anchorema , Orlando Dollenz , A.M. Faggi and Eduardo Mandez Intermetropolitan Migration in Canada: Changing Determinants over Three Decades . R. Paul Shaw. Chinese Cities—The Growth of the Metropolis since 1949 . Victor F. Sit, ed. Urbanization in the World-Economy . Michael Timberlake, ed. The Al Business: Commercial Uses of Artificial Intelligence . Patrick H. Winston and Karen A. Prendergast, eds.  相似文献   
72.
During the deglaciation stages of the last glacial period a rock avalanche took place on the glacier that occupied the upper sector of the Cuerpo de Hombre Valley (Sierra de Béjar). The material displaced during the avalanche fell onto the ice, was transported by the glacier and later deposited as supraglacial ablation till. The cause of the avalanche was the decompression of the valley slopes after they were freed from the glacier ice (stress relaxation). Reconstruction of the ice masses has been carried out to quantify the stress relaxation that produced the collapse. The rock avalanche took place on a lithologically homogeneous slope with a dense fracture network. The avalanche left a 0.4 ha scar on the slope with a volume of displaced material of 623 ± 15 × 103 m3. The deposit is an accumulation of large, angular, heterometric boulders (1–100 m3 in volume) with a coarse pebble‐size matrix. The avalanche can be explained as a relaxation process. This implies rock decompression once the glacier retreat left the wall ice free (debuttressing). Calculations show that the avalanche took place where the decompression stresses were highest (130–170 kPa). In the Spanish Central System paleoglaciers the largest accumulation of morainic deposits occurred after the glacial maximum and the earliest stages of the ice retreat. The process described here is used as an example to formulate a hypothesis that the largest accumulations of tills were formed in relation to enhanced slope dynamics once some glacier retreat had occurred.  相似文献   
73.
Abstract

A review of data on the Lys-Caillaouas massif leads to a re-interpretation of its Variscan structural evolution. During a first phase of N-S shortening upright folds with steep axial plane foliations were formed. Subsequent regional metamorphism was followed by porphyroblast rotation and formation of gently dipping crenulation cleavages. During this event a N-closing recumbent fold at the scale of the massif developed, with relatively undeformed first phase foliations in the upper limb (suprastrucfure) and highly deformed and transposed foliations in the lower limb (infrastructure). This recumbent fold is argued to result from temperature induced gravity collapse of a crustal block previously having subvertical planes of anisotropy.  相似文献   
74.
《Geodinamica Acta》2013,26(4):187-202
A sackung scarp has been investigated by trenching in the central Spanish Pyrenees. This feature is located 18 km to the SW of the North Maladeta Fault, which is the most probable source of the Mw 5.3 Vielha earthquake of 1923. Three displacement events have been inferred for the trenched sackung based on colluvial wedge stratigraphy and fault truncation. The increasing amount of deformation in each successive faulting event may be related to the progressive weakening of the slope through time. A minimum vertical slip rate of 0.19 mm/yr has been calculated for the sackung scarp. Several arguments suggest that the episodic displacement of the analysed sackung is controlled by strong seismic shaking: (a) Spatial association of the sackung features with the North Maladeta Fault; (b) Episodic displacement with a millennial recurrence (5.6 kyr) consistent with the expectable earthquake recurrence interval for a low slip rate fault, like the neighbouring North Maladeta Fault. Demonstrating in future investigations that the sackung features in the area constitute archives of large paleoearthquakes would be of great interest for seismic hazard assessments. They might help to improve the catalogue of paleoearthquakes and might provide information on earthquake recurrence intervals and the age of the most recent event (MRE).  相似文献   
75.
This paper analyses the effect of environmental changes observed in the 20th century on hydrology and water management in the southern Pyrenees, in terms of land use and climate. Moreover, a projected water-resource scenario for the 21st century is presented and discussed. Our results demonstrate that changes in precipitation, temperature, and snow accumulation, together with an increase in vegetation density in headwater regions, have led to a marked reduction in water availability in the region. Water resource managers have introduced major changes to dam operations to meet increasing water demand for irrigation purposes in lowland areas. Climatic and land-cover scenarios for the next century indicate that the sustainability of the equilibrium between available resources and water demand will be seriously threatened. These changes predicted for the Pyrenees may be representative of the changes that will occur within many other Mediterranean mountain sectors with similar climatic and socio-economic conditions.  相似文献   
76.
ABSTRACT. The Pyrenees are becoming an environmental reservoir. The acute human depopulation experienced during the twentieth century and the progressive appropriation of large parts of the mountainous territory by the state in order to implement conservation policies have resulted in the return, via reintroduction or natural regeneration, of bears, wolves, beavers, river otters, marmots, mouflon, feral goats, and deer, among other species. This development, however, has not occurred without social and scientific controversy and leads to questions about territorialization and governmentality. Herders perceive wild animals as unregulated public property subsidized by the work of the local populace. Agriculturalists see their fields trespassed on a daily basis by animals they cannot kill because of their protected status. Ranchers, under extremely strict sanitation regulations, see their animals coming into contact with these unchecked wild populations. The work and living space of the mountain communities has fallen under the jurisdiction of external institutions and constituencies that value conservation and ecotourism above local subsistence.  相似文献   
77.
The hydrological and geomorphological effects of an exceptional rainstorm event that occurred in the central Spanish Pyrenees during 19–21 October 2012 were studied in five experimental catchments under various land covers: (i) subhumid badlands; (ii) dense forest; (iii) an abandoned farmland area recolonized by shrubs and forest patches; and (iv) subalpine grasslands. Hydrographs and sedigraphs demonstrated that vegetation cover is a major factor affecting the control of floods even during exceptional rainstorms, at least at the spatial scale at which the phenomenon was studied (catchment sizes: 0.3–2.8 km2) and under dry catchment conditions. The combined precipitation over the two days (c. 250 mm) was the greatest for any two‐day event recorded since 1950 in the central‐western Pyrenees for all but one of the stations in the study. Five pulses of most intense rainfall were recorded. The forested catchment did not react to the two most intense rainfall pulses, because of the very low antecedent level of the water table. The main peak flow occurred only when at least a part of the catchment was saturated. The abandoned farmland catchment had two small peak discharges at the beginning of the event, which were produced by infiltration excess overland flow from eroded areas close to the main stream. During the third most intense rainfall period a large part of this catchment contributed to runoff and a relatively high peak discharge was produced. The badland catchment reacted immediately from the beginning of the rainstorm, yielding very high discharges accompanied by high suspended sediment concentrations. The subalpine catchment showed a hydrograph mirroring the hyetograph, with brief but intense hydrological responses to increased precipitation, because of the marked gradients and the presence of bare rock in the headwaters. A high volume of bedload was carried during the peak discharge. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
78.
Soil erosion is one of the most severe land degradation processes in the Mediterranean region. Although badlands occupy a relatively small fraction of the Mediterranean area, their erosion rates are very high. Many studies have investigated to what extent vegetation controls soil erosion rates. This study, however, deals with the impact of erosion on vegetation establishment. In semi‐arid badlands of the Mediterranean, soil water availability constitutes the main limiting factor for vegetation development. As a consequence, south‐facing slopes are typically less vegetated due to a very large water stress. However, these findings do not necessarily apply to humid badlands. The main objective of this paper is to determine the topographic thresholds for plant colonization in relation to slope aspect and to assess the spatial patterns of vegetation cover and species richness. We surveyed 179 plots on highly eroded badland slopes in the Central Pyrenees. We defined four aspect classes subdivided into slope angle classes. Colonization success was expressed in terms of vegetation cover and species richness. Slope angle thresholds for plant colonization were identified for each slope aspect class by means of binary logistic regressions. The results show that a critical slope angle exists below which plants colonize the badland slopes. Below this critical slope angle, plant cover and species richness increase with a decreasing slope angle. The largest critical slope angles in humid badlands are observed on south‐facing slopes, which contrasts with the results obtained in semi‐arid badlands. North‐facing slopes however are characterized by a reduced overall vegetation cover and species richness, and lower topographic threshold values. The possible underlying processes responsible for this slope‐aspect discrepancy in vegetation characteristics are discussed in terms of environmental variables that control regolith development, weathering and erosion processes. Moreover, possible restoration strategies through the use of vegetation in highly degraded environments are highlighted. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
79.
Several processes can contribute to the formation of hemipelagic limestone–marl alternations as a consequence of astronomically driven climate change. The aim of this study was to decipher which environmental factors governed the formation of three Eocene hemipelagic successions of the Basque–Cantabrian Basin using a comprehensive set of physical and bulk carbonate geochemical data (bed thickness, mineralogy, %CaCO3, δ13C and δ18O). The results show that the significance of several environmental processes varied depending on the palaeogeographic setting and eccentricity‐modulated precessional seasonality. In the Sopelana starved deep‐sea basin, limestones were formed as a consequence of high pelagic carbonate productivity during periods of warm seawater and sluggish circulation, which corresponded with periods of low seasonality (summers at aphelion); conversely, marls accumulated when pelagic carbonate productivity decreased during periods with cooler waters and more vigorous circulation, which occurred when seasonality was higher (summers at perihelion). In the Gorrondatxe submarine fan fringe, marls accumulated when high seasonality produced significant continental rainfall and run‐off, causing the dilution of pelagic carbonate sedimentation with terrigenous supplies. In the Oyambre upper slope, marls also accumulated when seasonality was high, as pelagic carbonate productivity decreased due to both the expansion of low‐salinity waters on the ocean surface and the increase in continentally derived nutrients, which caused detrimental seawater conditions for calcareous plankton. Both in Gorrondatxe and Oyambre, limestones accumulated when boreal summer at aphelion caused low seasonality, which allowed relatively stable conditions to prevail. At minimum eccentricity, when precession‐driven seasonality contrast diminished, changes in pelagic carbonate productivity were significant in the three sections. On the contrary, at maximum eccentricity, when seasonality peaked due to summers occurring at perihelion, the effects of other environmental processes, such as continental and oceanic currents, became influential. However, the influence of these processes minimized when summertime coincided with aphelion at maximum eccentricity and seasonality was weakest.  相似文献   
80.
The External Sierras of the southern Pyrenees represent the frontal thrust complex of a south Pyrenean thrust sheet which was active from the late Eocene to early Miocene. Triassic, Cretaceous and Eocene limestones, sandstones and mudstones involved in this thrusting can be divided into eight mappable units. Mapping and the construction of serial sections across the Western External Sierras show that the amount of southward translation of the thrust sheet increases eastwards from the thrust tip. There is an increased slip of at least 5km along 30km of the External Sierras. Structures show a progressive development from a “primitive” form in the west to a more complex thrust and fold geometry in the east. The general pattern is one of thrust and fold development in response to compression from the north. Backthrusting has occurred on the forward side of the frontal thrust complex. These backthrusts cut up section towards the north and form triangle zones where they intersect thrusts which cut up sections towards the south. The latest thrust movements deformed early Miocene fanglomerates and were out-of-sequence reactivations of earlier thrusts.  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