全文获取类型
收费全文 | 204篇 |
免费 | 11篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 15篇 |
地球物理 | 65篇 |
地质学 | 77篇 |
海洋学 | 34篇 |
天文学 | 10篇 |
综合类 | 1篇 |
自然地理 | 8篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 4篇 |
2020年 | 10篇 |
2019年 | 6篇 |
2018年 | 8篇 |
2017年 | 10篇 |
2016年 | 17篇 |
2015年 | 9篇 |
2014年 | 6篇 |
2013年 | 9篇 |
2012年 | 8篇 |
2011年 | 14篇 |
2010年 | 16篇 |
2009年 | 16篇 |
2008年 | 20篇 |
2007年 | 8篇 |
2006年 | 9篇 |
2005年 | 4篇 |
2004年 | 8篇 |
2003年 | 3篇 |
2002年 | 4篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 4篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 2篇 |
排序方式: 共有218条查询结果,搜索用时 15 毫秒
81.
82.
M. Marques I. Surez-Ruiz D. Flores A. Guedes S. Rodrigues 《International Journal of Coal Geology》2009,77(3-4):377-382
In order to identify the parameters that best characterize the chemical and structural evolution of organic matter during coalification, the relationships between optical, chemical and micro-structural parameters in high-rank coals and natural graphite were studied. The samples include anthracites from Peñarroya–Belmez–Espiel Basin (Spain), Douro Basin (Portugal), and Alto Chicama Basin (Peru); and natural graphite from Canada, Mozambique, and Austria.Correlations between the following optical parameters were assessed: vitrinite random reflectance (Rr), Reflectance Indicating Surfaces (RIS) axis (RMAX, RINT and RMIN), and RIS parameters (Ram, Rev and Rst), as well as Bw and AI anisotropy parameters. Furthermore, the chemical parameters used were chosen according to their significant variation in coals, namely volatile matter, carbon, and hydrogen contents calculated in dry ash free basis (VMdaf, Cdaf, Hdaf), as well as the H/C atomic ratio. Structural organization was characterized by micro-Raman spectroscopy and XRD. Raman parameters used were the full width at half maximum (FWHM) and position of G and D1 bands on the first-order Raman spectrum, and the ID1/IG intensity area ratio. The selected XRD parameters were interlayer spacing d002, and crystallite sizes La and Lc.Results show that: (i) RMAX RIS axis seems to correlate best with chemical and micro-structural parameters; (ii) for the majority of studied samples, Hdaf and H/C atomic ratio are the only chemical parameters with significant correlations with RMAX; (iii) the FWHM of the G band of Raman spectrum shows good linear correlation with the XRD parameter d002; and, (iv) structural organization of carbon materials, as measured by trends in their optical and crystalline parameters, is influenced by their hydrogen content (daf basis) and therefore by the H/C atomic ratio. 相似文献
83.
84.
Total dissolved gas pressure (PTDG) measurements are useful to measure accurate in situ dissolved gas concentrations in groundwater, but challenged by in-well degassing. Although in-well degassing has been widely observed, its cause(s) are not clear. We investigated the mechanism(s) by which gas-charged groundwater in a recently pumped well becomes degassed. Vertical PTDG and dissolved gas concentration profiles were monitored in the standing water column (SWC) of a groundwater well screened in a gas-charged aquifer for 7 days before and 15 days after pumping. Prior to pumping, PTDG values remained relatively constant and below calculated bubbling pressure (PBUB) at all depths. In contrast, significant increases in PTDG were observed at all depths after pumping was initiated, as fresh groundwater with elevated in situ PTDG values was pumped through the well screen. After pumping ceased, PTDG values decreased to below PBUB at all depths over the 15-day post-pumping period, indicating well degassing was active over this time frame. Vertical profiles of estimated dissolved gas concentrations before and after pumping provided insight into the mechanism(s) by which in-well degassing occurred in the SWC. During both monitoring periods, downward mixing of dominant atmospheric and/or tracer gases, and upwards mixing of dominant groundwater gases were observed in the SWC. The key mechanisms responsible for in-well degassing were (i) bubble exsolution when PTDG exceeded PBUB as gas-charged well water moves upwards in the SWC during recovery (i.e., hydraulic gradient driven convection), (ii) microadvection caused by the upward migration of bubbles under buoyancy, and (iii) long-term, thermally driven vertical convection. 相似文献
85.
da Silveira Lucas Cardoso de Oliveira Amauri Pereira Sánchez Maciel Piñero Codato Georgia Ferreira Maurício Jonas Filho Edson Pereira Marques Božnar Marija Zlata Mlakar Primož 《Boundary-Layer Meteorology》2022,185(2):197-197
Boundary-Layer Meteorology - 相似文献
86.
Fernando O. Marques Fernando M. S. F. Marques António Mateus Jorge Figueiras Fernando M. Santos Rogério Mota Helena Amaral 《Environmental Geology》2005,47(8):1128-1137
A sodium bentonite is being used in the basal-isolation of landfills installed on strongly fractured granitic rocks of N Portugal (NW Iberia). To evaluate the performance of this clay as the ultimate impermeable basal barrier, a detailed study was carried out of the granite fracture network; the Na-bentonite was tested to characterize its mechanical and geotechnical behavior; geophysical surveys were made to search for landfill leakage and the waters found around the landfill were geochemically characterized. Fractures in the granite are usually open and devoid of mineral infillings or clay materials and, thus, permeability of the granite is very high. Dispersal of contaminants can be further enhanced by the position of the landfill on a high steep-sided ridge. Geophysical and geochemical data show evidence for seepage and dispersion of pollutants, which means that the clay failed as an ultimate isolation barrier against seepage. This investigation shows that this can be due to fracturing of the clay under load and/or to its non-homogeneous saturation and extreme shrinking character upon drying, which are accompanied by the formation of extensive cracking. Observations and experimental results suggest that the use of synthetic clays in the safe building of landfill bottom liners needs further research, and extreme care should be taken in preventing that clay water content suffers large variations after saturation, as this process considerably degrades the mechanical behavior and sealing properties of the studied Na-bentonite. 相似文献
87.
T. Múrias J. A. Cabral J. C. Marques J. D. Goss-Custard 《Estuarine, Coastal and Shelf Science》1996,43(6):677-688
The possible effects of intertidal macroalgal blooms on the feeding distribution and behaviour of the waders in the Mondego Estuary (West Portugal) are discussed in the present paper. The presence of algae over the sediments did not deter the waders absolutely from feeding in a place, but most species did show some tendency to avoid highly eutrophic areas. However, there were no clear signs that the species redistributed themselves within the Estuary as the amount of algae changed, nor did the alternative feeding habitats (the salt pans) seem to be used more when algae were particularly abundant on the mud flats. In one species, bird numbers, rather than the amount of algae present, explained the numbers of birds using the salt pans when the two factors were considered together in a multiple regression analysis. There were no striking differences between algae-free and algae-weeded areas in some aspects of the foraging of two representative species, the scolopacid DunlinCalidris alpinaand the charadriid Grey PloverPluvialis squatarola. The results suggest either: (1) that the presence of algae did not strongly influence the distribution of the feeding waders, at least in the conditions prevailing during the study; or (2) that most waders were able to adapt to feeding on weeded areas; perhaps through subtle and undetected alterations in their feeding behaviour. 相似文献
88.
S.M. Ferreira M.A. Pardal A.I. Lilleb P.G. Cardoso J.C. Marques 《Estuarine, Coastal and Shelf Science》2004,61(4):669-677
From January 1993 to September 1995, Cyathura carinata was a target species of a monitoring programme carried in the Mondego Estuary (Portugal). Being one of the key species of the intertidal mud flats, this isopod was found to be most abundant in a eutrophic area, where seasonal macroalgal blooms usually occur. Its density decreased towards downstream areas, where some Zostera noltii beds exist. At the Mondego Estuary, the present work stated that C. carinata: (a) had a 2-year life span, even though, 80–90% of the individuals died when 1 year old, revealing a strong post-reproduction mortality; (b) produced a single cohort per year; (c) showed continuous growth (with lower rates during winter); (d) evidenced protogynous hermaphroditism and (e) presented a high growth production and a low turnover ratio. A latitudinal gradient reflected in the life features of C. carinata was described. Except for the life span and the frequency of reproduction, which are generally valid for all populations, C. carinata from the Mondego Estuary fitted the characteristics of other populations from the south of Europe.The effects of macroalgal blooms were assessed. Cyathura carinata seemed to temporarily benefit from the presence of macroalgae, due to higher energy resources and more efficient protection against predators. In a long term, algal blooms had negative consequences. It was particularly evident on the recruitment success, which had repercussions in population abundance, and on the secondary production. Therefore, repeated events of algal blooms embracing the distribution areas of C. carinata represent a threat to this species in eutrophic estuaries. 相似文献
89.
90.