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   380篇
  免费   16篇
  国内免费   1篇
测绘学   13篇
大气科学   65篇
地球物理   87篇
地质学   122篇
海洋学   18篇
天文学   58篇
综合类   2篇
自然地理   32篇
  2023年   5篇
  2021年   10篇
  2020年   8篇
  2019年   9篇
  2018年   13篇
  2017年   13篇
  2016年   23篇
  2015年   7篇
  2014年   20篇
  2013年   32篇
  2012年   16篇
  2011年   16篇
  2010年   17篇
  2009年   24篇
  2008年   14篇
  2007年   16篇
  2006年   12篇
  2005年   19篇
  2004年   14篇
  2003年   5篇
  2002年   3篇
  2001年   11篇
  2000年   9篇
  1999年   4篇
  1998年   3篇
  1997年   2篇
  1996年   3篇
  1995年   3篇
  1994年   3篇
  1993年   5篇
  1992年   8篇
  1991年   5篇
  1990年   3篇
  1988年   1篇
  1987年   1篇
  1985年   3篇
  1984年   5篇
  1983年   3篇
  1982年   3篇
  1981年   2篇
  1980年   3篇
  1979年   1篇
  1978年   4篇
  1977年   4篇
  1975年   3篇
  1974年   2篇
  1973年   2篇
  1970年   1篇
  1969年   1篇
  1962年   1篇
排序方式: 共有397条查询结果,搜索用时 15 毫秒
301.
Clearly understanding the connections among land use, demographics, and sensitivity and engagement with natural areas can provide insight into landowner decision making. Pertinent findings from our mailed survey of landowners in Brown County, Indiana, include that (1) individuals already engaged in land conservation or environmental activities are most likely to consider a conservation easement (CE), (2) hunters and anglers are less likely to have interest in CEs, and (3) few differences exist between seasonal and permanent residents. Among other things, this research highlights the significance for landowner willingness to grant a CE of involving landowners in conservation activities and environmental organizations.  相似文献   
302.
Magnetic sector mass spectrometers dominate the field of 40Ar/39Ar geochronology. Recent advances in quadrupole mass spectrometer technology, especially improvements in resolution, have increased the performance of these instruments to the extent that they can be used for isotopic determinations. We describe a triple filter quadrupole mass spectrometer (Hiden HAL 3F Series Pulse Ion Counting Triple Filter QMS) linked to an automated furnace extraction and cleaning system dedicated to 40Ar/39Ar incremental heating experiments.The instrument produces peaks with broad flat tops and a width of 0.9 amu at 10 cps height and 0.84 amu at 500,000 cps height on a 1 million cps high peak (peak width at 0.01‰ and 50% peak height respectively). This allows measurement of ratios of the main Ar peaks in the 1‰ range. Measurements of 1.6 × 10?12 mole of air reference gas over two years yields 40Ar/36Ar = 257.9 ± 1.3 (1σ, n = 34). The ability of the instrument to produce 40Ar/39Ar ages from rocks/minerals of a wide age range, reaching into the late Quaternary, are demonstrated by a series of tests and comparison with geochronological data from other studies and an in-house MAP 215-50 magnetic sector mass spectrometer. We demonstrate that high-end quadrupole systems can be used for routine 40Ar/39Ar dating purposes.  相似文献   
303.
Chemical characterization of cryptotephra is critical for temporally linking archaeological sites. Here, we describe cryptotephra investigations of two Middle–Upper Paleolithic sites from north-west Italy, Arma Veirana and Riparo Bombrini. Cryptotephra are present as small (<100 µm) rhyolitic glass shards at both sites, with geochemical signatures rare for volcanoes in the Mediterranean region. Two chemically distinct shard populations are present at Arma Veirana (P1 and P2). P1 is a high silica rhyolite (>75 wt.%) with low FeO (<1 wt.%) and a K2O/Na2O > 1 and P2 is also a high silica rhyolite (>75 wt.%) but with higher FeO (2.33–2.65 wt.%). Shards at Riparo Bombrini (P3) are of the same composition as P1 shards at Arma Veirana, providing a distinct link between deposits at both sites. Geochemical characteristics suggest three possible sources for P1 and P3: eruptions from Lipari Island (56–37.7 ka) in Italy, the Acigöl volcanic field (200–20 ka) in Turkey and the Miocene Kirka-Phrigian caldera (18 Ma) in Turkey. Eruptions from Lipari Island are the most likely source for P1,3 cryptotephra. This study highlights how cryptotephra can benefit archaeology, by providing a direct link between Arma Veirana and Riparo Bombrini as well as other deposits throughout the Mediterranean.  相似文献   
304.
305.
This paper describes glaciological features observed on the surface of the large outlet glacier Kuannersuit Glacier on Disko Island, West Greenland, during its initial quiescent phase after a major surge event occurred in 1995–98 in order to classify the glaciomorphological surge system. Focus is on surge features either associated with active surging such as a propagating surge front and serac formation or formed as a consequence of surging such as looped medial moraines and potholes; and on hydrological features related to the evolution of the glacier drainage system such as the supraglacial routing, moulin types and chasms. A chronological glaciomorphological model of the initial quiescent phase of Kuannersuit Glacier, which can be regarded as representative for large outlet surge‐type glaciers with terrestrial terminal regime and long quiescent phase, is proposed.  相似文献   
306.
307.
Morphological instabilities in periodic patterns occurring both in precipitation and crystallization processes (Liesegang rings and crystal zoning) are investigated and compared with similar patterns in geological samples (zebra rocks and mud bands in snow sediments). In classical Liesegang systems, undisturbed parallel or concentric precipitation bands are emanated from even or concentric diffusion sources in homogeneous diffusion matrices of gelatine or other gels. In the case of superposing diffusion sources, sources with undulatory curvatures or local diffusion barriers there may occur several types of instabilities within the sequence of regular patterns: (a) gaps within the bands forming radial alleys free of precipitate, (b) transition from broken bands to speckled patterns and (c) apparent branching of bands linked together by so-called anastomoses. Calculations with a competitive particle growth (CPG) model show that lateral instabilities in Liesegang bands (gaps and radial alleys of gaps) are the result of Ostwald ripening effects taking place after precipitation. Apparent branching of bands or formation of anastomoses can be simulated with a prenucleation model according to Ostwald's supersaturation theory. Similar irregularities can be observed in zebra rocks (e.g. banded siderite) whose bandings are commonly explained by sequential sedimentation processes. A very different mechanism is assumed to be responsible for the origin of mud bands in snow sediments. An initially homogeneous distribution of intrinsic mud in snow sediments can be arranged into parallel bands according to a crystal zoning mechanism which is based on repeated thawing and freezing of the snow sediment due to the daily alternation of sun and darkness.  相似文献   
308.
GeoJournal - Schools are unique places that greatly influence the daily lives of learners. Examining any factors that may be contributing to school absenteeism and dropout rates is vital as gaining...  相似文献   
309.
310.
Simulations of the Indonesian rainfall variability using the Max Planck Institute regional climate model REMO have been performed using three different lateral boundary forcings: Reanalyses from the European Centre for Medium-Range Weather Forecasts (ERA15), the National Centers for Environmental Prediction and National Center for Atmospheric Research (NRA) as well as from ECHAM4 climate model simulation. The result of those simulations are compared to station data. REMO simulations were performed at 0.5° horizontal resolution for the whole archipelago and at 1/6° for Sulawesi Island. In general the REMO model, reproduces the spatial pattern of monthly and seasonal rainfall well over land, but overestimates the rainfall over sea. Superiority of REMO performance over land is due to a high-resolution orography, while over sea, REMO suffers from erroneously low surface fluxes. REMO reproduces variability during El Niño-Southern Oscillations years well but fails to show a good (wet and dry) monsoon contrast. Despite strong influences of the lateral boundary fields, REMO shows a realistic improvement of a local phenomenon over Molucca. Significant improvement for the step from the relatively high global 1.125° to 0.5° resolution is noticeable, but not from 0.5° into 1/6°. The REMO simulation driven by ERA15 has the best quality, followed by NRA and ECHAM4 driven simulations. The quality of ERA15 is the main factor determining the quality of REMO simulations. A predictability study shows small internal variability among ensemble members. However, there are systematic intrinsic climatological errors as shown in the predictability analysis. These intrinsic errors have monthly, seasonal and regional dependencies and the one over Java is significantly large. The intrinsic error study suggests the presence of the spring predictability barrier and a high level of predictability in summer.  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