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   361篇
  免费   31篇
  国内免费   4篇
测绘学   14篇
大气科学   27篇
地球物理   82篇
地质学   157篇
海洋学   37篇
天文学   56篇
综合类   2篇
自然地理   21篇
  2022年   6篇
  2021年   10篇
  2020年   11篇
  2019年   4篇
  2018年   14篇
  2017年   25篇
  2016年   22篇
  2015年   18篇
  2014年   35篇
  2013年   40篇
  2012年   26篇
  2011年   26篇
  2010年   30篇
  2009年   31篇
  2008年   14篇
  2007年   2篇
  2006年   10篇
  2005年   9篇
  2004年   8篇
  2003年   4篇
  2002年   2篇
  2001年   2篇
  2000年   4篇
  1999年   1篇
  1998年   6篇
  1997年   6篇
  1995年   2篇
  1994年   7篇
  1993年   2篇
  1992年   2篇
  1990年   4篇
  1989年   1篇
  1985年   1篇
  1984年   1篇
  1982年   4篇
  1980年   1篇
  1978年   1篇
  1968年   1篇
  1962年   1篇
  1960年   1篇
  1958年   1篇
排序方式: 共有396条查询结果,搜索用时 46 毫秒
51.
In Spain, the birth of interest in the nation's industrial heritage dates from the 1980s and occurred alongside the process of deindustrialization. Policies concerning derelict industrial sites have shifted gradually from destruction to preservation, rehabilitation, and enhancement, and industrial heritage enhancement projects are now widespread in the country. However, a clear mismatching has arisen between institutional and academic initiatives and local communities, which exhibit widespread disinterest in or even rejection of industrial remains. This problematic situation can be related to the utilization of industrial heritage as an economic resource without paying much attention to its connections with memory and identity. Also, the mismatching is due to a positivist approach to industrial heritage whereby the monument and the museum are prioritized. We argue that projects which consider industrial remains as part of cultural landscapes might shorten the gap between the institutional and economic side of industrial heritage and its identity‐building and popular facets.  相似文献   
52.
Landscape changes are driven by a combination of physical, ecological and socio-cultural factors. Hence, a large amount of information is necessary to monitor these changes and to develop effective strategies for management and conservation. For this, novel strategies for combining social and environmental data need to be developed. The purpose of this study is to demonstrate the value of an innovative interdisciplinary approach to help in explaining landscape change. We integrated three main sources of information: biophysical landscape attributes, land-use/cover change analysis and social perceptions of land-use change, institutional and policy factors and environmental services. Multivariate statistical analysis was used to develop a weight for each variable described or quantified. Finally we identified proximate causes and underlying driving forces of land transformation in the study area. The study was undertaken in a typical community in Mexico.  相似文献   
53.
The presence of pingos on Mars has been hypothesized since the period of the Viking mission. In fact, a diverse range of pingo-like features has been found at various martian sites including Elysium, Chryse and Utopia Planitiae in the northern lowlands. Due to the morphology and the geological setting, some of those features were interpreted in different ways, creating some controversies, as happened in Athabasca Valles. This reflects the complexity of interpreting these features by remote sensing and multiple plausible interpretations of the same feature. With the objective of identifying new possible pingos or rootless cones on Mars, we selected a study area in Utopia Planitia (10-55° N, 210-260° W) where the presence of both features is possible due to its geological history (volcanic and hydrological). We analyzed more than 2100 Mars Orbiter Camera (MOC)-narrow angle images in addition to Viking, Thermal Emission Imaging System (THEMIS), and High Resolution Stereo Camera (HRSC) images, together with Mars Orbiter Laser Altimeter (MOLA)-derived Digital Elevation Models (DEMs) with a Geographic Information System (GIS). We found in 94 MOC-narrow angle images dome, cone, and ring-shaped features. We analyzed them from morphological and morphometrical points of view in order to compare them with relevant features on Mars and Earth. We tested different possible origins for those features following the approach of multiple working hypotheses. We conclude that the dome, cone, and ring-shaped features could be pingos, which is in agreement with their geological settings. Regarding the driving heat source for the formation of the purported pingos, we propose the existence of a heat source, possibly a magma chamber, underneath the surface of the Utopia basin. Together with possible climatic shifts, the past activities of the heat source may have caused melting of ground ice. The pingo growth due to freezing of the water would have occurred during the following cold climatic conditions.  相似文献   
54.
This article presents the study conducted and the actions taken to stabilise the foundations of 25 low-rise (two/three-storey) buildings in Alcázar de San Juan (Ciudad Real, central Spain). Owing to the immediate attention required, it was decided that the study would focus on procuring a synthetic model that would be able to provide a satisfactory explanation for the tendency of the movements, overlooking the detailed model of each building. This analysis pointed out that the mobilisation was probably due to both the shrinkage caused by the existing trees during the dry-growing seasons, and to the loss of lateral confinement caused by the excavation of a service trench adjacent to the footings of the buildings. In keeping with this mechanism, stabilization was carried out by transplanting the trees growing near the damaged buildings and installing a line of piles to provide lateral support to the footings. The evolution of the damage was therefore stopped.  相似文献   
55.
Abstract– We used a combination of different analytical techniques to study particle W7190‐D12 using microinfrared spectroscopy, micro‐Raman spectroscopy, and field emission scanning electron microscopy (FESEM) energy dispersive X‐ray spectroscopy (EDS). The particle consists mainly of hematite (α‐Fe2O3) with considerable variations in structural disorder. It further contains amorphous (Na,K)‐bearing Ca,Al‐silicate and organic carbon. Iron‐bearing spherules (<150 nm in diameter) cover the surface of this particle. At local sites of structural disorder at the hematite surface, the hematite spheres were reduced to FeO in the presence of organic carbons forming FeO‐spheres. However, metallic Fe spheres cannot be excluded based on the available data. To the best of our knowledge, this particle is the first detection of such spherules at the surface of a stratospheric dust particle. Although there is no definitive evidence for an extraterrestrial origin of particle W7190‐D12, we suggest that it could be an IDP that had moved away from the asteroid‐forming region of the early solar system into the outer solar system of the accreting Kuiper Belt objects. After it was released from a Jupiter family comet, this particle became part of the zodiacal cloud. Atmospheric entry flash‐heating caused (1) the formation of microenvironments of reduced iron oxide when indigenous carbon materials reacted with hematite covering its surface resulting in the formation of FeO‐spheres and (2) Na‐loss from Na,Al‐plagioclase. The particle of this study, and other similar particles on this collector, may represent a potentially new type of nonchondritic IDPs associated with Jupiter family comets, although an origin in the asteroid belt cannot be ignored.  相似文献   
56.
57.
An increase in walking or hiking activities in natural areas requires improvements in information and advice about trails, including their difficulty, available services and estimated travel time. Comparative studies show remarkable differences between measured and calculated travel times obtained by available predictive procedures (Naismith’s rule, Tobler’s hiking function or MIDE). A new procedure has been designed by combining pre-existing methods (Tobler’s and MIDE), and travel times have been calculated for 21 trails located in different protected natural areas of Spain. Times obtained are compared with travel times measured by individual users and uploaded into specialized walking-hiking websites (Wikiloc). Results show that the new procedure (Modified Tobler) reduces differences between calculated and measured travel times, which makes it suitable not only for trail managers to estimate travel times but also as a key part of pedestrian transport analysis in trail networks.  相似文献   
58.
The paper deals with a selection of the climatological baseline, GCM validity and construction of the climate change scenarios for an impact assessment in the Czech territory. The period of 1961–1990 has been selected as the climatological baseline. The corresponding database includes more than 50 monthly mean temperature and precipitation series, and 16 time series of daily meteorological data that contain also the solar radiation data. The 1× CO2 outputs produced by four GCMs, provided by the CSMT (GISS, GFD30, GFD01, and CCCM), were compared with observed temperature and precipitation conditions in western and central Europe with a particular attention devoted to the Czech territory. The GCM ability to simulate annual cycles of temperature, precipitation and radiation was thoroughly examined. The GISS and CCCM were selected as a basis for constructing climate change scenarios as they simulated reasonably the observed patterns. According to the GISS variant, 2× CO2 climate assumes a higher winter and lower summer warming, and an increase in annual precipitation amounts. A dangerous combination of the summer temperature increase and declining precipitation amounts is a specific feature of the CCCM scenario. An incremental scenario for temperature and precipitation is based on the combination of prescribed changes in both annual means and annual courses.  相似文献   
59.
The Yucatán Peninsula, Mexico, has typically been considered a tectonically stable region with little significant seismic activity. The region though, is one that is regularly affected by hurricanes. A detailed survey of ca 100 km of the eastern Yucatán and Cozumel coast identified the presence of ridges containing individual boulders measuring >1 m in length. The boulder ridges reach 5 m in height and their origin is associated with extreme wave event activity. Previously modelled tsunami waves from known seismically active zones in the region (Muertos Thrust Belt and South Caribbean Deformed Belt) are not of sufficient scale in the area of the Yucatán Peninsula to have produced the boulder ridges recorded in this study. The occurrence of hurricanes in this region is more common, but two of the most destructive (Hurricane Gilbert 1988 and Hurricane Wilma 2005) produced coastal waves too small to have created the ridges recorded here. In this paper, a new tsunami model with a source area located on the Motagua/Swan Island Fault System has been generated that indicates a tsunami event may have caused the extreme wave events that resulted in the deposition of the boulder ridges.  相似文献   
60.
Image network geometry, including the number and orientation of images, impacts the error, coverage, and processing time of 3D terrain mapping performed using structure-from-motion and multiview-stereo (SfM-MVS). Few studies have quantified trade-offs in error and processing time or ways to optimize image acquisition in diverse topographic conditions. Here, we determine suitable camera locations for image acquisition by minimizing the occlusion produced by topography. Viewshed analysis is used to select the suitable images, which requires a preliminary digital elevation model (DEM), potential camera locations, and sensor parameters. One aerial and two ground-based image collections were used to analyse differences between SfM-MVS models produced using: (1) all available images (ALL); (2) images selected using conventional methods (CON); and (3) images selected using the viewshed analysis (VIEW). The resulting models were compared with benchmark point clouds acquired by a terrestrial laser scanner (TLS) and TLS-derived DEMs. The VIEW datasets produced denser point clouds (28–32% more points) and DEMs with up to 66% reduction in error compared with CON datasets due to reduction of gaps in the DEM. VIEW datasets reduced processing time by 37–76% compared with ALL, with no reduction in coverage or increase in error. DEMs produced with ALL and VIEW datasets had similar slope and roughness, while slight differences that may be locally important were observed for the CON dataset. The new method helps optimize SfM-MVS image collection strategies that significantly reduce the number of images required with minimal loss in coverage or accuracy over complex surfaces. © 2020 John Wiley & Sons, Ltd.  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