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   119篇
  免费   8篇
  国内免费   2篇
测绘学   6篇
大气科学   12篇
地球物理   39篇
地质学   39篇
海洋学   10篇
天文学   17篇
自然地理   6篇
  2021年   5篇
  2020年   6篇
  2019年   3篇
  2018年   8篇
  2017年   7篇
  2016年   5篇
  2015年   6篇
  2014年   5篇
  2013年   10篇
  2012年   3篇
  2011年   4篇
  2010年   2篇
  2009年   5篇
  2008年   8篇
  2007年   9篇
  2006年   7篇
  2004年   8篇
  2003年   2篇
  2002年   1篇
  2001年   4篇
  2000年   1篇
  1997年   2篇
  1996年   1篇
  1995年   1篇
  1994年   2篇
  1993年   2篇
  1991年   1篇
  1990年   1篇
  1989年   1篇
  1988年   1篇
  1984年   1篇
  1983年   1篇
  1977年   2篇
  1975年   2篇
  1941年   1篇
  1940年   1篇
排序方式: 共有129条查询结果,搜索用时 46 毫秒
91.
Fatal landslides in Europe   总被引:4,自引:3,他引:1  
Landslides are a major hazard causing human and large economic losses worldwide. However, the quantification of fatalities and casualties is highly underestimated and incomplete, thus, the estimation of landslide risk is rather ambitious. Hence, a spatio-temporal distribution of deadly landslides is presented for 27 European countries over the last 20  years (1995–2014). Catastrophic landslides are widely distributed throughout Europe, however, with a great concentration in mountainous areas. In the studied period, a total of 1370 deaths and 784 injuries were reported resulting from 476 landslides. Turkey showed the highest fatalities with 335. An increasing trend of fatal landslides is observed, with a pronounced number of fatalities in the latest period from 2008 to 2014. The latter are mostly triggered by natural extreme events such as storms (i.e., heavy rainfall), earthquakes, and floods and only minor by human activities, such as mining and excavation works. Average economic loss per year in Europe is approximately 4.7 billion Euros. This study serves as baseline information for further risk mapping by integrating deadly landslide locations, local land use data, and will therefore help countries to protect human lives and property.  相似文献   
92.
With one-factor experiments, the drift of larvae ofEcdyonurus venosus has been analysed in a stream model. The distances travelled by drifting animals as a function of water velocity have been determined, as well as some drift rhythms. Drift-inducing factors are principally scarecity of food (lack of periphyton) and movement of substrate. Induction of drift by small water velocities can be caused by insufficient oxygen supply. The typical drift minimum during the final larval instar is said to be caused by a pseudo-pupal stage. After temperature shocks of ±5°C respectively, the animals acclimate within 2 days. An increase in temperature induces a decrease in drift reates and vice versa. Sex, predation and competition do not influence drift. The mean flight range of the imagoes (flight-mill) is 2,794 m, the maximum upstream movement of the larvae 140 m/24 h.  相似文献   
93.
Two very similar species of freshwater snails,Lymnaea auricularia andL. peregra coexist in Lake Zürich. We examined their diets to determine possible differences. Microscopic analysis of stomach and hind gut contents revealed no marked differences between the diets of the two snail species collected from the same substrate. However, in both species we found significant differences between the composition of the substrate and that of the stomach contents, using discriminant analysis. We conclude that both species of snails feed preferentially on patches of favourable food supply and that their diets overlap almost totally. The coexistence of the two species under these conditions suggests that food does not limit their density in the area studied.  相似文献   
94.
A complete Bouguer-anomaly map of the Betic Cordillera and surrounding areas has been compiled from 2995 land-gravity observations. The measurements used to construct the map come from previous surveys as well as from a survey carried out specially for this project.A large negative anomaly reaching −145 mGal is centered on the intra-mountain basins of Loja-Granada and Baza-Guadix, and systematically displaced from the region of greatest topographic relief. This gravity low is interpreted as produced by the thickeming of the earth's crust at a principal contact between two domains of continental crust having different origins and geological evolution.Three gravity profiles selected to investigate the deep structure of the crust in the Betic Cordillera are presented and discussed.  相似文献   
95.
An SO2 flux of 1170±400 (1) tonnes per day was measured with a correlation spectrometer (COSPEC) in October and November 1986 from the continuous, nonfountaining, basaltic East Rift Zone eruption (episode 48A) of Kilauea volcano. This flux is 5–27 times less than those of highfountaining episodes, 3–5 times greater than those of contemporaneous summit emissions or interphase Pu'u O'o emissions, and 1.3–2 times the emissions from Pu'u O'o alone during 48A. Calculations based on the SO2 emission rate resulted in a magma supply rate of 0.44 million m3 per day and a 0.042 wt% sulfur loss from the magma upon eruption. Both of these calculated parameters agree with determinations made previously by other methods.  相似文献   
96.
Detailed understanding of global carbon cycling requires estimates of CO 2 emissions on temporal and spatial scales finer than annual and country. This is the first attempt to derive such estimates for a large, developing, Southern Hemisphere country. Though data on energy use are not complete in terms of time and geography, there are enough data available on the sale or consumption of fuels in Brazil to reasonably approximate the temporal and spatial patterns of fuel use and CO 2 emissions. Given the available data, a strong annual cycle in emissions from Brazil is not apparent. CO 2 emissions are unevenly distributed within Brazil as the population density and level of development both vary widely.  相似文献   
97.
The Angélica copper deposit is situated at the southernmost sector of the Jurassic Tocopilla plutonic complex in the North Chilean Coastal Cordillera. This deposit occurs in monzonitic to monzodioritic rocks, and has platelike orebodies with no appreciable hydrothermal alteration nor sulfide mineralization. The mineralized zones are located in the western side of the two main normal faults with NE and NW orientations, and are characterized principally by impregnation of supergene copper products of atacamite and minor amounts of chrysocolla, lavendulan and “black copper”. Generally, chrysocolla is more abundant at a distal NE sector of the deposit. The black copper is Cu‐Fe‐Mn‐Si‐Cl‐rich multimineral aggregates composed of atacamite with minor amounts of quartz, pseudomalachite, dioptase, neotocite, gypsum, paratacamite and melanothallite, and its surface exhibits nanometer‐sized cylindrical morphologies. All these characteristics suggest an exotic origin for the Angélica copper deposit. A few vein‐type copper deposits situated at the southwestern sector along the NE‐oriented fault are inferred as the possible source of the Angélica copper deposit.  相似文献   
98.
The passive margin Texas Gulf of Mexico Coastal Plain consists of coalescing late Pleistocene to Holocene alluvial–deltaic plains constructed by a series of medium to large fluvial systems. Alluvial–deltaic plains consist of the Pleistocene Beaumont Formation, and post-Beaumont coastal plain incised valleys. A variety of mapping, outcrop, core, and geochronological data from the extrabasinal Colorado River and the basin-fringe Trinity River show that Beaumont and post-Beaumont strata consist of a series of coastal plain incised valley fills that represent 100 kyr climatic and glacio-eustatic cycles.

Valley fills contain a complex alluvial architecture. Falling stage to lowstand systems tracts consist of multiple laterally amalgamated sandy channelbelts that reflect deposition within a valley that was incised below highstand alluvial plains, and extended across a subaerially-exposed shelf. The lower boundary to falling stage and lowstand units comprises a composite valley fill unconformity that is time-transgressive in both cross- and down-valley directions. Coastal plain incised valleys began to fill with transgression and highstand, and landward translation of the shoreline: paleosols that define the top of falling stage and lowstand channelbelts were progressively onlapped and buried by heterolithic sandy channelbelt, sandy and silty crevasse channel and splay, and muddy floodbasin strata. Transgressive to highstand facies-scale architecture reflects changes through time in dominant styles of avulsion, and follows a predictable succession through different stages of valley filling. Complete valley filling promoted avulsion and the large-scale relocation of valley axes before the next sea-level fall, such that successive 100 kyr valley fills show a distributary pattern.

Basic elements within coastal plain valleys can be correlated with the record offshore, where cross-shelf valleys have been described from seismic data. Falling stage to lowstand channelbelts within coastal plain valleys were feeder systems for shelf-phase and shelf-margin deltas, respectively, and demonstrate that falling stage fluvial deposits are important valley fill components. Signatures of both upstream climate change vs. downstream sea-level controls are therefore interpreted to be present within incised valley fills. Signatures of climate change consist of the downstream continuity of major stratigraphic units and component facies, which extends from the mixed bedrock–alluvial valley of the eroding continental interior to the distal reaches, wherever that may be at the time. This continuity suggests the development of stratigraphic units and facies is strongly coupled to upstream controls on sediment supply and climate conditions within hinterland source regions. Signatures of sea-level change are critical as well: sea-level fall below the elevation of highstand depositional shoreline breaks results in channel incision and extension across the newly emergent shelf, which in turn results in partitioning of the 100 kyr coastal plain valleys. Moreover, deposits and key surfaces can be traced from continental interiors to the coastal plain, but there are downstream changes in geometric relations that correspond to the transition between the mixed bedrock–alluvial valley and the coastal plain incised valley. Channel incision and extension during sea-level fall and lowstand, with channel shortening and delta backstepping during transgression, controls the architecture of coastal plain and cross-shelf incised valley fills.  相似文献   

99.
We studied the feeding ecology of the Andean hog-nosed skunk (Conepatus chinga) in three areas with different land use in Patagonia. Two areas were heavily grazed by sheep or horses and wild exotic herbivores and the third area was lightly grazed by cattle. In each area, we assessed skunk diet, prey abundance and carrion availability. Skunks were generalist feeders, with invertebrates composing the bulk of their diet, but also consumed small vertebrates and carrion. Differences in diet composition were found among areas, mainly because skunks consumed more beetle larvae in the sheep area and more cricetines and spiders in the exotic-herbivore area. All prey but rodents were significantly more abundant in spring and summer than in fall and winter, but skunk diets were similar among seasons. In the sheep area, where the soil was most disturbed, we found reduced abundances of invertebrate prey and rodents. High consumption of beetles during autumn and winter when these were least abundant and in the sheep area indicates that skunks had a preference for beetles and their larvae. We conclude that Andean hog-nosed skunks in Patagonia might be negatively affected by reductions of their main prey due to soil and plant alterations by livestock.  相似文献   
100.
This paper discusses the preliminary results of a study on the vegetation pattern and its relationship with meteorological parameters in and around Istanbul. The study covers an area of over 6800 km2 consisting of urban and suburban centers, and uses the visible and near-infrared bands of Landsat. The spatial variation of the Normalized Difference Vegetation Index (NDVI) and meteorological parameters such as sensible heat flux, momentum flux, relative humidity, moist static energy, rainfall rate and temperature have been investigated based on observations in ten stations in the European (Thracian) and Anatolian parts of Istanbul. NDVI values have been evaluated from the Landsat data for a single day, viz. 24 October 1986, using ERDAS in ten different classes. The simultaneous spatial variations of sensible heat and momentum fluxes have been computed from the wind and temperature profiles using the Monin-Obukhov similarity theory. The static energy variations are based on the surface meteorological observations. There is very good correlation between NDVI and rainfall rate. Good correlation also exists between: NDVI and relative humidity; NDVI, sensible heat flux and relative humidity; NDVI, momentum flux and emissivity; and NDVI, sensible heat flux and emissivity. The study suggests that the momentum flux has only marginal impact on NDVI. Due to rapid urbanization, the coastal belt is characterized by reduced NDVI compared to the interior areas, suggesting that thermodynamic discontinuities considerably influence the vegetation pattern. This study is useful for the investigation of small-scale circulation models, especially in urban and suburban areas where differential heating leads to the formation of heat islands. In the long run, such studies on a global scale are vital to gain accurate, timely information on the distribution of vegetation on the earth’s surface. This may lead to an understanding of how changes in land cover affect phenomena as diverse as the atmospheric CO2 concentrations, the hydrological cycle and the energy balance at the surface-atmosphere interface.  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