全文获取类型
收费全文 | 63篇 |
免费 | 6篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 3篇 |
地球物理 | 20篇 |
地质学 | 28篇 |
海洋学 | 10篇 |
自然地理 | 6篇 |
出版年
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2017年 | 3篇 |
2016年 | 6篇 |
2015年 | 4篇 |
2014年 | 1篇 |
2013年 | 4篇 |
2012年 | 3篇 |
2011年 | 3篇 |
2010年 | 3篇 |
2009年 | 11篇 |
2008年 | 2篇 |
2007年 | 3篇 |
2006年 | 3篇 |
2005年 | 6篇 |
2004年 | 1篇 |
2003年 | 3篇 |
2002年 | 4篇 |
2001年 | 2篇 |
1999年 | 2篇 |
1997年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有70条查询结果,搜索用时 31 毫秒
21.
Bettina Knig Oliver Kohls Gerhard Holst Ronnie N. Glud Michael Kühl 《Marine Chemistry》2005,97(3-4):262-276
We describe the fabrication of organically modified sol–gel (ORMOSIL) planar optodes for mapping the two-dimensional oxygen distribution in sediments. All sensor foils were based on the use of ruthenium(II)-tris-(4,7-diphenyl-1,10-phenantrolin)-perchlorate, which is a fluorescent dye quenched dynamically by oxygen. Sensors made with different sol–gel immobilisation matrices, different concentrations of precursors and indicator dye, as well as different types of scattering particles co-immobilised in the sensor foil were investigated systematically. Optimal sensor performance was obtained with dye concentrations of 2–10 mmol/kg in an immobilisation matrix made of diphenyldiethoxy-silan and phenyltriethoxy-silan precursors with addition of organically coated TiO2 particles. The sensors exhibited a good mechanical stability and a high sensitivity from 0% to 100% oxygen, which remained constant over at least 36 days. The planar optodes were used with a fluorescent lifetime imaging system for direct mapping of the spatio-temporal variation in oxygen distribution within marine sediment inhabited by the polychaete Hediste diversicolor. The measurements demonstrated the spatio-temporal heterogeneity of the oxygen distribution in bioturbated sediments due to burrow structures and non-constant irrigation activity of the polychaete, which is difficult to resolve with microsensors or with traditional biogeochemical techniques. 相似文献
22.
Spatio‐temporal variability of zooplankton biomass and environmental control in the Northern Benguela Upwelling System: field investigations and model simulation
下载免费PDF全文
![点击此处可从《Marine Ecology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Bettina Martin Anja Eggert Rolf Koppelmann Rabea Diekmann Volker Mohrholz Martin Schmidt 《Marine Ecology》2015,36(3):637-658
Spatial and temporal distribution patterns of zooplankton are highly variable in the Northern Benguela Upwelling System. We studied the distribution of zooplankton (size class ≥ 0.33 mm) and used field data from four cruises that took place between March 2008 and February 2011, as well as simulation results of a regional ecosystem model. Remotely sensed sea surface temperatures (SST) and surface chlorophyll concentrations were analysed to investigate environmental influences on zooplankton biomass. The Intense Benguela Upwelling Index showed a distinct seasonal signal throughout the years and the highest upwelling peaks in August/September. Even though surface chlorophyll concentrations were very variable throughout the year, the highest concentrations were always detected in September, following the upwelling of nutrient‐rich water. In field catches, zooplankton biomass concentration in the upper 200 m was highest above the outer shelf and shelf‐break in December 2010 and February 2011, i.e. 6 months after the upwelling peaks. In contrast, zooplankton biomass simulated by the model in the surface water was highest in September. In March/April, biomass maxima were typically measured in the field at intermediate water depths, but the vertical distribution was also affected by extensive oxygen minimum zones. The ecosystem model reproduced this vertical pattern. Although general trends were similar, simulation data of zooplankton standing stocks overestimated the field data by a factor of 3. In upwelling systems, food webs are generally considered to be short and dominated by large cells. However, our field data indicate more small‐sized zooplankton organisms above the shelf than offshore. 相似文献
23.
On results of the surface wave analyses in poroelastic media by means of the Simple Mixture Model and the Biot model 总被引:1,自引:0,他引:1
This note is devoted to an overview of the results on the number, velocity and attenuation of surface waves in two-component saturated poroelastic media. The author's numerical results which have been obtained using the Simple Mixture Model are compared to some results of other authors who carried out either an analysis by means of the classical Biot model for poroelastic media or experiments. It is shown that the Simple Mixture Model is a simplification of the Biot model. Due to its simpler form the Simple Mixture Model is more suitable for a complex analysis which depends on several parameters. Thus, the Simple Mixture Model is the only model for which, simultaneously, either the dependence on the frequency, ω, and the dependence on the bulk permeability, π (boundary porous medium/vacuum) or the dependence on the frequency, ω, and the dependence on the surface permeability, α (boundary porous medium/fluid) has been considered. 相似文献
24.
25.
26.
In this paper we explore the motivations to migrate and the migration experiences of 22 Indian IT professionals in Germany. When studying skilled migration, Germany is an interesting case as it struggled with waves of extreme right activities whilst trying to attract IT professionals from outside the European Union at the same time. In this context, we are interested in the conflicts that the migrants may experience as a result of their desire or obligation to move, their specific cultural baggage and the way in which they encounter the different sides of German society. 相似文献
27.
S. Paul Hansard William M. Landing Chris I. Measures Bettina M. Voelker 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(7):1117-1129
The redox speciation of dissolved iron in seawater was evaluated at 121 locations in the Pacific Ocean at depths of 15-1000 m, using the method of luminol chemiluminescence. The results indicate that reduced iron, Fe(II), is ubiquitous in surface seawater with a relatively consistent pattern of occurrence. Surface maxima were present in most profiles, with median concentrations of 25-30 pM representing 12-14% of the total dissolved iron. Concentrations decreased monotonically with depth to<12 pM within the upper euphotic zone. This pattern was observed during both day and nighttime sampling events, which suggests that non-photochemical production mechanisms can produce photochemical-like signatures. Further, if theoretical rates of Fe(II) oxidation are applicable to the open ocean, then the employed sampling methods precluded assessment of photochemically-produced Fe(II), regardless of ambient light conditions. For this and other reasons, the concentrations reported here for the upper water column likely represent lower limits of labile iron concentration, and suggest that dissolved iron may be more available for uptake than previously believed. Deeper in the water column, Fe(II) was also frequently detected, though it constituted a small fraction of the total dissolved iron. Possible source mechanisms at these depths include thermal (dark) reduction of Fe(III) organic complexes or remineralization of sinking biogenic particles containing Fe(II). In the northern Philippine Sea between the Japanese coast and the Izu-Bonin volcanic arc system, Fe(II) concentrations were found to be atypically high, possibly because of high atmospheric dust deposition near the surface and transport of sediment-derived iron at depth. 相似文献
28.
Permeability and degassing of dome lavas undergoing rapid decompression: An experimental determination 总被引:1,自引:1,他引:0
Sebastian Mueller Oleg Melnik Oliver Spieler Bettina Scheu Donald B. Dingwell 《Bulletin of Volcanology》2005,67(6):526-538
The gas permeability of volcanic rocks may influence various eruptive processes. The transition from a quiescent degassing dome to rock failure (fragmentation) may, for example, be controlled by the rocks permeability, in as much as it affects the speed by which a gas overpressure in vesicles is reduced in response to decompression. Using a modified shock-tube-based fragmentation bomb (Alidibirov and Dingwell 1996a,b; Spieler et al. 2003a), we have measured unsteady-state permeability at a high initial pressure differential. Following sudden decompression above the rock cylinder, pressurized gas flows through the sample. Two pressure transducers record the pressure signals above and below the sample. A transient 1D filtration code has been developed to calculate permeability using the experimental decay curve of the lower pressure transducer. Additionally an analytical steady-state method to achieve permeability is presented as an alternative to swiftly predict the sample permeability in a sufficiently precise manner. Over 100 permeability measurements have been performed on samples covering a wide range of porosity. The results show a general positive relationship between porosity and permeability with a high data scatter. Our preferred interpretation of the results is a combination of two different, but overlapping effects. We propose that at low porosities, gas escape occurs predominantly through microcracks or elongated micropores and therefore could be described by simplified forms of Kozeny–Carman relations (Carman 1956) and fracture flow models. At higher porosities, the influence of vesicles becomes progressively stronger as they form an increasingly connected network. Therefore, a model based on the percolation theory of fully penetrable spheres is used, as a first approximation, to describe the permeability-porosity trend. In the data acquired to date it is evident, that in addition to the porosity control, the samples bubble size, shape and distribution strongly influence the permeability. This leads to a range of permeability values up to 2.5 orders of magnitude at a given porosity. 相似文献
29.
30.
Jordan G. Hamilton Jay Grosskleg David Hilger Kris Bradshaw Trevor Carlson Steven D. Siciliano Derek Peak 《Geochemical transactions》2018,19(1):1
Adsorption and precipitation reactions often dictate the availability of phosphorus in soil environments. Tripolyphosphate (TPP) is considered a form of slow release P fertilizer in P limited soils, however, investigations of the chemical fate of TPP in soils are limited. It has been proposed that TPP rapidly hydrolyzes in the soil solution before adsorbing or precipitating with soil surfaces, but in model systems, TPP also adsorbs rapidly onto mineral surfaces. To study the adsorption behavior of TPP in calcareous soils, a short-term (48 h) TPP spike was performed under laboratory conditions. To determine the fate of TPP under field conditions, two different liquid TPP amendments were applied to a P limited subsurface field site via an in-ground injection system. Phosphorus speciation was assessed using X-ray absorption spectroscopy, total and labile extractable P, and X-ray diffraction. Adsorption of TPP to soil mineral surfaces was rapid (< 48 h) and persisted without fully hydrolyzing to ortho-P. Linear combination fitting of XAS data indicated that the distribution of adsorbed P was highest (~ 30–40%) throughout the site after the first TPP amendment application (high water volume and low TPP concentrations). In contrast, lower water volumes with more concentrated TPP resulted in lower relative fractions of adsorbed P (15–25%), but a significant increase in total P concentrations (~ 3000 mg P kg soil) and adsorbed P (60%) directly adjacent to the injection system. This demonstrates that TPP application increases the adsorbed P fraction of calcareous soils through rapid adsorption reactions with soil mineral surfaces. 相似文献