全文获取类型
收费全文 | 53篇 |
免费 | 2篇 |
专业分类
测绘学 | 12篇 |
大气科学 | 2篇 |
地球物理 | 11篇 |
地质学 | 9篇 |
海洋学 | 12篇 |
天文学 | 3篇 |
自然地理 | 6篇 |
出版年
2021年 | 1篇 |
2018年 | 3篇 |
2013年 | 1篇 |
2011年 | 4篇 |
2010年 | 3篇 |
2009年 | 6篇 |
2008年 | 2篇 |
2007年 | 6篇 |
2006年 | 5篇 |
2005年 | 4篇 |
2004年 | 1篇 |
2003年 | 1篇 |
1998年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有55条查询结果,搜索用时 15 毫秒
1.
Page DS Boehm PD Brown JS Neff JM Burns WA Bence AE 《Marine environmental research》2005,60(4):422-436
Polycyclic aromatic hydrocarbons (PAH) were measured in mussels (Mytilus trossulus) collected between 1990 and 2002 from 11 sites on the shores of Prince William Sound (PWS), Alaska, that were heavily oiled by the 1989 Exxon Valdez oil spill (EVOS). This study, utilizing the methods of the NOAA Status and Trends Mussel Watch Program, found that concentrations of PAH released from spill remnants have decreased dramatically with time and by 2002 were at or near the range of total PAH (TPAH) of 3-355 ng/g dry weight obtained for mussels from unoiled reference sites in PWS. Time-series TPAH data indicate a mean TPAH half-life in mussel tissues of 2.4 years with a range from 1.4 to 5.3, yielding an annual mean loss of bioaccumulated TPAH of 25%. The petroleum-derived TPAH fraction in mussel tissues has decreased with time, reflecting the decreasing release of EVOS residues in shoreline sediments. These results show that PAH from EVOS residues that remain buried in shoreline sediments after the early 1990s are in a form and at locations that have a low accessibility to mussels living in the intertidal zone. 相似文献
2.
A 3-year program, to determine spatial and temporal trends in sediment concentrations of hydrocarbons and metals from oil and gas exploration and development activities, was conducted in the US Beaufort Sea. Concentrations of saturated and aromatic hydrocarbons in sediments from the Beaufort Sea were elevated in comparison to non-polluted shelf-sediments from other regions of the US coast. Potential natural sources for hydrocarbons that were examined included riverine sediments and coastal peat. Significant quantities of fossil hydrocarbons characterize the surface sediments from the entire region. Sediment inputs from river discharges appear to account for this observation. The use of source-diagnostic ratios has allowed the differentiation of various sources in an area with high naturally-occurring hydrocarbon concentrations where effects due to oil and gas exploration and development activities may be obscured. 相似文献
3.
Modeling path delays in the neutral atmosphere for the analysis of Very Long Baseline Interferometry (VLBI) observations has
been improved significantly in recent years by the use of elevation-dependent mapping functions based on data from numerical
weather models. In this paper, we present a fast way of extracting both, hydrostatic and wet, linear horizontal gradients
for the troposphere from data of the European Centre for Medium-range Weather Forecasts (ECMWF) model, as it is realized at
the Vienna University of Technology on a routine basis for all stations of the International GNSS (Global Navigation Satellite
Systems) Service (IGS) and International VLBI Service for Geodesy and Astrometry (IVS) stations. This approach only uses information
about the refractivity gradients at the site vertical, but no information from the line-of-sight. VLBI analysis of the CONT02
and CONT05 campaigns, as well as all IVS-R1 and IVS-R4 sessions in the first half of 2006, shows that fixing these a priori
gradients improves the repeatability for 74% (40 out of 54) of the VLBI baseline lengths compared to fixing zero or constant
a priori gradients, and improves the repeatability for the majority of baselines compared to estimating 24-h offsets for the
gradients. Only if 6-h offsets are estimated, the baseline length repeatabilities significantly improve, no matter which a
priori gradients are used. 相似文献
4.
Temperature variations at very long baseline interferometry (VLBI) sites cause thermal deformations of the VLBI antennas and
corresponding displacements of the VLBI reference points. The thermal deformation effects typically contain seasonal and daily
signatures. The amplitudes of the annual vertical motion of the antenna reference point can reach several millimeters, depending
on the design of the antenna structure, on the material, and on the environmental effects such as global station position,
station height and climatology effects. Simple methods to correct this effect use the difference of the environmental temperature
with respect to a defined reference temperature, the antenna dimensions, the elevation of the antenna, the material of antenna
structure. Applying these simple models for thermal deformation in the VLBI data analysis improves the baseline length repeatability
by 3.5%. A comparison of these simple models with local thermal deformation measurements at the antennas in Onsala and Wettzell
show that the local measurements and the modeled corrections agree well when the temperature of the antenna structure is used,
but agree less good when the surrounding air temperatures are used. To overcome this problem we present a method to model
temperature penetration into the antenna structures, that allows to model thermal deformation effects that agree with the
observed vertical deformation of the Onsala and Wettzell radio telescopes with a root mean square deviation of 0.07 and 0.13 mm,
respectively. Possible implementations in the VLBI analysis are presented, and the definition of an adequate reference temperature
is discussed. 相似文献
5.
6.
7.
We propose linear response functions to separately estimate the sea-level contributions of thermal expansion and solid ice discharge from Greenland and Antarctica. The response function formalism introduces a time-dependence which allows for future rates of sea-level rise to be influenced by past climate variations. We find that this time-dependence is of the same functional type, R(t) ~ t α, for each of the three subsystems considered here. The validity of the approach is assessed by comparing the sea-level estimates obtained via the response functions to projections from comprehensive models. The pure vertical diffusion case in one dimension, corresponding to α = ?0.5, is a valid approximation for thermal expansion within the ocean up to the middle of the twenty first century for all Representative Concentration Pathways. The approximation is significantly improved for α = ? 0.7. For the solid ice discharge from Greenland we find an optimal value of α = ?0.7. Different from earlier studies we conclude that solid ice discharge from Greenland due to dynamic thinning is bounded by 0.42 m sea-level equivalent. Ice discharge induced by surface warming on Antarctica is best captured by a positive value of α = 0.1 which reflects the fact that ice loss increases with the cumulative amount of heat available for softening the ice in our model. 相似文献
8.
9.
Moritz Nykamp Fabian Becker Ricarda Braun Nadja Pöllath Daniel Knitter Joris Peters Brigitta Schütt 《地球表面变化过程与地形》2021,46(2):430-442
This study presents a meta-analysis of radiocarbon ages for the environs of Göbekli Tepe – one of the oldest monumental structures worldwide – using cumulative probability functions to diachronically assess phases of geomorphodynamic activity as controlled by natural or anthropogenic drivers. We employ sediment cascades as a heuristic framework to study the complex responses of the geomorphological system to various triggers at local to supra-regional scales. Possible triggers include climatic variability as documented by supra-regional hydroclimatic proxy data, regional demographic trends, and local to regional socioeconomic developments such as the emergence of sedentism or the introduction and dispersal of livestock herding. Our results show that phases of intensified geomorphodynamic activity occurred between ca. 7.4–7.0 and 5.8–3.3 ka BP. These phases roughly coincide with phases of population growth in southern Turkey and climatic variations in Turkey and the Levant. The phase between ca. 5.8–3.3 ka BP also corresponds to the time when organized agriculture and the seeder plough were introduced. Also, the identified phases are in agreement with the general trend of varying geomorphodynamic activity in the Eastern Mediterranean as driven by human impact and climatic change. However, neither the Younger Dryas–Holocene transition nor the development of herding during the Pre-Pottery Neolithic left a clear signature. We demonstrate how the different depositional environments in the studied landscape compartments vary with respect to their spatiotemporal coverage and discuss challenges when trying to understand processes that once shaped landscapes of past societies. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd 相似文献
10.
Jennifer Coston‐Guarini Jean‐Marc Guarini Frederike Ricarda Boehm Thomas R. H. Kerkhove Frances C. Rivera Karim Erzini François Charles Tim Deprez Laurent Chauvaud 《Marine Ecology》2018,39(3)
A new probabilistic approach is proposed to assess muricid species population abundances at scales relevant to both Ancient and Modern coastal fisheries. Motivated by the long‐term goal of reconstructing the dynamics of exploited murex populations during Antiquity, the objective was to estimate the population density of the banded dye‐murex, Hexaplex trunculus (Linnaeus, 1758) from successive captures with baited traps, using a method similar to the technique employed in the Mediterranean purple dye industry. The stochastic model developed simulates cumulative captures while accounting for high variability. It was calibrated with data acquired during a field trapping experiment (Crete Island, Greece). Traps’ catchability and Effective Area of Attraction (EAA) were estimated using the individual speed and behavioural response towards bait from laboratory experiments. Average density of H. trunculus was estimated as 2.2 ± 1.4 SE individuals per square metre, with no significant differences between seagrass and rocky habitats. The clearing time of successive capture experiments averaged 84 ± 6 SE hr. Clearing ca. 0.4 ha of subtidal area would be necessary to produce ca. 1.0 g of pure Tyrian purple pigment. The method described is generalizable to making population abundance estimates for similar groups, such as whelks, in modern fisheries. 相似文献