全文获取类型
收费全文 | 411篇 |
免费 | 11篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 17篇 |
大气科学 | 19篇 |
地球物理 | 65篇 |
地质学 | 141篇 |
海洋学 | 69篇 |
天文学 | 82篇 |
综合类 | 1篇 |
自然地理 | 30篇 |
出版年
2021年 | 3篇 |
2020年 | 2篇 |
2019年 | 6篇 |
2018年 | 8篇 |
2017年 | 10篇 |
2016年 | 10篇 |
2015年 | 4篇 |
2014年 | 4篇 |
2013年 | 22篇 |
2012年 | 27篇 |
2011年 | 18篇 |
2010年 | 21篇 |
2009年 | 24篇 |
2008年 | 26篇 |
2007年 | 23篇 |
2006年 | 28篇 |
2005年 | 12篇 |
2004年 | 14篇 |
2003年 | 5篇 |
2002年 | 20篇 |
2001年 | 9篇 |
2000年 | 11篇 |
1999年 | 11篇 |
1998年 | 7篇 |
1997年 | 9篇 |
1996年 | 10篇 |
1995年 | 5篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1956年 | 1篇 |
1935年 | 1篇 |
排序方式: 共有424条查询结果,搜索用时 15 毫秒
311.
Geostatistics provides a suite of methods, summarized as kriging, to analyze a finite data set to describe a continuous property of the Earth. Kriging methods consist of moving window optimum estimation techniques, which are based on a least-squares principle and use a spatial structure function, usually the variogram. Applications of kriging techniques have become increasingly wide-spread, with ordinary kriging and universal kriging being the most popular ones. The dependence of the final map or model on the input, however, is not generally understood. Herein we demonstrate how changes in the kriging parameters and the neighborhood search affect the cartographic result. Principles are illustrated through a glaciological study. The objective is to map ice thickness and subglacial topography of Storglaciären, Kebnekaise Massif, northern Sweden, from several sets of radio-echo soundings and hot water drillings. New maps are presented. 相似文献
312.
Small‐scale experiments have demonstrated that forest clearance leads to an increase in water yield, but it is unclear if this result holds for larger river basins (>1000 km2). No widespread changes in rainfall totals and patterns were found in the 12 100 km2 Nam Pong catchment in northeast Thailand between 1957 and 1995, despite a reduction in the area classified as forest from 80% to 27% in the last three decades. Neither were any detectable changes found in any other water balance terms nor in the dynamics of the recession at the end of the rainy season. When a hydrological model calibrated against data from the period before the deforestation was applied for the last years of the study period (1987–1995), runoff generation was however underestimated by approximately 15%, indicating increased runoff generation after the deforestation. However, this was mainly due to the hydrological response during one single year in the first period, when the Q/P ratio was very low. When excluding this year, neither analysis based on the hydrological model could reveal any significant change of the water balance due to the deforestation. More detailed land‐use analysis revealed that shade trees were left on agricultural plots as well as a number of abandoned areas where secondary growth can be expected, which is believed to account for the results. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
313.
Frequent sampling during an annual cycle of dissolved(<0.45 m) and suspended (>0.45 m) elementshas been conducted in the Kafue River at Raglan'sFarm, upstream from the mining activities within theCopperbelt Province, Zambia. Additional sampling ofsediment and interstitial pore water was conductedduring low water discharge. The presence of carbonateswithin the drainage basin naturally gives rise to highelement concentrations in the dissolved phase(Ca = 626, Mg = 494, Na = 360 and K = 24 mmol l-1).During the rainy season the relative composition ofthe dissolved elements indicated a wash out ofaccumulated weathering products and mineralisedorganic material from the unsaturated zone of the soilprofile. High concentrations of dissolved Al, Fe andMn were measured during high water discharge. At lowwater discharge the sediment was a major source of Fe,Mn and associated Co and Cu to the water column.Enhanced concentrations of dissolved and suspended S,Co and Cu during the rainy season indicated thatatmospheric deposited particles from the mining areawere washed out into the river. Autochthonousformation of particles rich in Si indicated diatomproduction during low water discharge. 相似文献
314.
Temporal variations of colloidal carrier phases and associated trace elements in a boreal river 总被引:1,自引:0,他引:1
Ralf Dahlqvist Karen Andersson Johan Ingri Björn Stolpe 《Geochimica et cosmochimica acta》2007,71(22):5339-5354
Elemental size distributions, from truly dissolved through colloidal to particulate, have been studied in a subarctic boreal river. The measurements, carried out during 2002, ranged from winter to summer conditions, including an intense spring flood event. Results are reported for a total of 42 elements. Size distributions were characterised using a combination of cross-flow (ultra)filtration (CFF), flow field-flow fractionation (FlFFF), and diffusive gradients in thin-films (DGT). The three techniques showed similar trends, but quantitative comparisons reveal some important differences that warrant further investigation.Previous work has identified two colloidal carrier phases in fresh waters, dominated by iron and carbon, respectively. The majority of the elements studied are associated with one or both of these colloidal carrier phases. The exceptions are the alkali metals and several anions that are only very weakly associated with colloidal material, and which therefore occur mainly as truly dissolved material (<1 kDa in molecular weight). We discuss the likely origin for the two colloidal carrier phases and consider how associated trace elements fit into the geochemical framework. The relative affinities of the elements for iron and carbon colloidal carrier phases are related to their chemistries, and are compared with earlier data from the Delsjö Creek in southern Sweden.Elemental colloidal concentrations show strong seasonal variations related to changes in the colloidal carrier phase(s) with which they associate. In particular, many elements show a strong spring maximum in colloidal concentrations associated with the strong maximum in colloidal carbon concentration during the spring flood. 相似文献
315.
Ingrid Anell Valentin Zuchuat Anna Daniela Rhnert Aleksandra Smyrak‐Sikora Simon Buckley Gareth Lord Harmon Maher Ivar Midtkandal Kei Ogata Snorre Olaussen Per T. Osmundsen Alvar Braathen 《Basin Research》2021,33(1):478-512
The study describes the depositional development and sediment partitioning in a prograding paralic Triassic succession. The deposits are associated with the advance of large prism‐scale clinoforms across a shallower platform area. Approaching the platform, the limited accommodation and associated relative higher rates of deposition generated straighter clinoforms with lower foreset angles. The vertical restriction across the platform is interpreted to have amplified the tidal signature. Sediment was redistributed from the coast into increasingly sandy delta‐front deposits, compared to offshore equivalents. The deposits comprise extensive compound dune fields of amalgamated and increasingly clean sandbodies up‐section. Rapid deposition of significant amounts of sand led to differential subsidence and growth‐faulting in the delta front, with downthrown fault blocks further amplifying the tidal energy through funnelling. A mixed‐energy environment created along‐strike variability along the delta front with sedimentation governing process‐regime. Areas of lower sedimentation were reworked by wave and storm‐action, whereas high sedimentation rates preserved fluvially dominated mouth bars. A major transgression, however, favoured tidally dominated deposits also in these areas, attributed to increasing rugosity of the coastline. Formation of an extensive subaqueous platform between the coast and delta front dampened incoming wave energy, and tidally dominated deposits dominate the near‐shore successions. Meanwhile formation of wave‐built sand‐bars atop the platform attest to continued wave influence. The strong tidal regime led to the development of a heterolithic near‐shore tidally dominated channel system, and sandier fluvial channels up‐river. The highly meandering tidal channels incising the subaqueous platform form kilometre wide successions of inclined heterolithic stratification. The fluvially dominated channels which govern deposition on the delta plain are narrower and slightly less deep, straighter, generally symmetric and filled with cleaner sands. This study provides important insight into tidal amplification and sand redistribution during shallowing on a wide shelf, along with along‐strike process‐regime variability resulting from variations in sediment influx. 相似文献
316.
ABSTRACTThe “subsumption of nature” framework focuses on productivity increases and extractive innovations in nature-based industries. In this article, we argue that it can also be employed beyond that context in order to capture the convoluted dynamics of market environmentalism. To substantiate our argument, we draw on recent fieldwork on “Trees for Global Benefits,” a forestry-based offsetting project in western Uganda. Like industrial tree plantations, this project relies on the subsumption of carbon sequestration to market imperatives in order to guarantee the quality of its carbon credits. The ecological and socioeconomic difficulties this process engenders give rise to unintended consequences and set in motion the disciplining of the carbon offset producers themselves. The application of the subsumption framework to nonindustrial sectors in this way calls attention to the interlinked socioecological dynamics involved in the subsumption of nature, and highlights potential synergies with previous work on the subsumption of labor. 相似文献
317.
1 Introduction
It has been elucidated that high levels of neurotoxic mercury (Hg) in the Arctic is related to a rapid, near-compete depletion of Hg0 (MDE) in the atmospheric boundary-layer occurring episodically during the Polar spring[1]. 相似文献
318.
The eclipsing binary system Epsilon Aurigae, containing an unseen component, is discussed on the basis of its orbital elements. The masses of the components can be approximately 4M
and 1M
, respectively. It is shown that there is no reason to reject a low-mass model. An opaque elongated eclipsing body is briefly discussed as one of the components which is an accretion disc surrounding a central Main-Sequence star. 相似文献
319.
320.