全文获取类型
收费全文 | 189篇 |
免费 | 9篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 21篇 |
地球物理 | 62篇 |
地质学 | 56篇 |
海洋学 | 21篇 |
天文学 | 27篇 |
综合类 | 3篇 |
自然地理 | 6篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 1篇 |
2018年 | 11篇 |
2017年 | 6篇 |
2016年 | 6篇 |
2015年 | 12篇 |
2014年 | 10篇 |
2013年 | 8篇 |
2012年 | 11篇 |
2011年 | 14篇 |
2010年 | 13篇 |
2009年 | 11篇 |
2008年 | 18篇 |
2007年 | 10篇 |
2006年 | 13篇 |
2005年 | 12篇 |
2004年 | 5篇 |
2003年 | 4篇 |
2002年 | 1篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1998年 | 5篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1988年 | 1篇 |
排序方式: 共有198条查询结果,搜索用时 506 毫秒
81.
Ayrton F. Martins Lucas E. W. de Jesus Nádia Vendruscolo Tibiriçá G. Vasconcelos Marcelo L. Wilde 《洁净——土壤、空气、水》2008,36(1):66-69
In this study, a semi‐micro procedure for the COD (Chemical Oxygen Demand) was undertaken to allow the measurement of effluent samples with a high chloride content. It was found that the COD values for standard and effluent samples, corresponded closely to those obtained using the standard method of Burns and Marshall. When the method was applied to samples of industrial wastewater, with a very high chloride content, the recommended procedure proved to be accurate and precise, with RSDs of 6% and 4.3% for the standard and effluent solutions, respectively. The required amount of hazardous reagents was similar to that found in the standard closed reflux method. It was also possible to determine the total amount of oxidized halides. The use of this low‐cost, laboratory‐made system made it unnecessary to acquire an expensive, imported analytical system, while maintaining a high level of accuracy in the determinations. 相似文献
82.
Liliane Janikian Renato Paes de Almeida Antonio Romalino Santos Fragoso-Cesar Veridiana Teixeira de Souza Martins Elton Luiz Dantas Eric Tohver Ian McReath Manoel Souza D'Agrella-Filho 《Gondwana Research》2012,21(2-3):466-482
During the Ediacaran, southern Brazil was the site of multiple episodes of volcanism and sedimentation, which are best preserved in the 3000 km2 Camaquã Basin. The interlayered sedimentary and volcanic rocks record tectonic events and paleoenvironmental changes in a more than 10 km-thick succession. In this contribution, we report new U–Pb and Sm–Nd geochronological constraints for the 605 to 580 Ma Bom Jardim Group, the 570 Ma Acampamento Velho Formation, and a newly-recognized 544 Ma volcanism. Depositional patterns of these units reveal the transition from a restricted, fault-bounded basin into a wide, shallow basin. The expansion of the basin and diminished subsidence rates are demonstrated by increasing areal distribution and compressed isopachs and increasing onlap of sediments onto the basement to the west. The Sm–Nd isotopic composition of the volcanic rocks indicates mixed sources, including crustal rocks from the adjacent basement. Both Neoproterozoic and Paleoproterozoic sources are indicated for the western part of the basin, whereas only the older Paleoproterozoic signature can be discerned in the eastern part of the basin. 相似文献
83.
M. Babinski A.C. Pedrosa-Soares R.I.F. Trindade M. Martins C.M. Noce D. Liu 《Gondwana Research》2012,21(2-3):451-465
Glacigenic diamictite successions of the Macaúbas Group are widespread in the western domain of the Araçuaí orogen, east of the São Francisco craton (Brazil). Diamictites also occur on this craton and in the African counterpart of the Araçuaí orogen, the West Congo belt. Detrital zircon grains from the matrix of diamictites and sandstones from the Macaúbas Group were dated by the U–Pb SHRIMP technique. The geochronological study sets the maximum depositional age of the glacial diamictites at 900 Ma, and indicates multiple sources for the Macaúbas basin with ages ranging from 900 to 2800 Ma. Sm–Nd TDM model ages, determined on whole rock samples, range from 1.8 Ga to 2.5 Ga and get older up-section. Comparison of our data with those from the cratonic area suggest that these glacial deposits can be correlated to the Jequitaí and Carrancas diamictites in the São Francisco craton, and to the Lower Mixtite Formation of the West Congolian Group, exposed in Africa. The 900–1000 Ma source is most probably represented by the Zadinian–Mayumbian volcanic rocks and related granites from the West Congo belt. However, one of the most voluminous sources, with ages in the 1.1–1.3 Ga interval, has not been detected in the São Francisco-Congo craton. Possible sources for these grains could occur elsewhere in Africa, or possibly from within the Brasília Belt in western central Brazil. 相似文献
84.
António A. Martins Pedro P. Cunha Luiz Osterbeek Stefano Grimaldi Jan-Pieter Buylaert João Matos 《Proceedings of the Geologists' Association. Geologists' Association》2010,121(2):128-140
This paper aims to provide insight into human occupation and landscape change during the Pleistocene in a central area of the Lower Tejo basin (Portugal). Detailed geomorphological mapping, coupled with lithostratigraphy, sedimentology and luminescence dating, supports the identification of a complete terrace staircase sequence. It consists of six gravely terraces located below the culminant (Pliocene) basin unit. A chronological framework for the sedimentary sequences and associated human industries is proposed and correlated with marine oxygen isotope stages (MIS): T1 terrace, not dated; T2, not dated; T3, >300 ka; T4, ∼300-160 ka (MIS8, MIS7 and MIS6); T5, ∼136-75 ka (MIS5); T6, ∼62-30 ka (MIS3); colluvium and aeolian sands, ∼30-14 ka (MIS2); valley fill deposits, ∼14 ka to present (MIS1). The oldest artefacts were found at the base of the T4 terrace, with the local stratigraphic level dated to ≥175 ± 6 ka (Middle Pleistocene). The lithic assemblages collected from distinct stratigraphic levels (T4, T5 top, T6 terraces and colluvium) are characterized by the predominance of opportunistic technological choices, a feature that can be attributed partly to the preferential exploitation of the available raw material, dominated by local-sourced quartzites and quartz pebbles. The adaptation to local raw material (texture and volume), together with subsistence patterns and behaviours, could explain the rarity of Acheulian types (handaxes and cleavers) and picks in the T4 terraces of the Tejo tributaries; this is in contrast to the same terrace of the Tejo valley, in which these types are found. Interpretation of the environmental conditions (controlled by climate and glacio-eustatic sea-level changes) affecting the hunter-gatherer human groups is also presented. 相似文献
85.
86.
Roberto Wagner Lourenço Paulo M. Barbosa Landim André Henrique Rosa José Arnaldo F. Roveda Antonio César Germano Martins Leonardo Fernandes Fraceto 《Environmental Earth Sciences》2010,60(3):495-504
Spatial analysis and fuzzy classification techniques were used to estimate the spatial distributions of heavy metals in soil.
The work was applied to soils in a coastal region that is characterized by intense urban occupation and large numbers of different
industries. Concentrations of heavy metals were determined using geostatistical techniques and classes of risk were defined
using fuzzy classification. The resulting prediction mappings identify the locations of high concentrations of Pb, Zn, Ni,
and Cu in topsoils of the study area. The maps show that areas of high pollution of Ni and Cu are located at the northeast,
where there is a predominance of industrial and agricultural activities; Pb and Zn also occur in high concentrations in the
northeast, but the maps also show significant concentrations of Pb and Zn in other areas, mainly in the central and southeastern
parts, where there are urban leisure activities and trade centers. Maps were also prepared showing levels of pollution risk.
These maps show that (1) Cu presents a large pollution risk in the north–northwest, midwest, and southeast sectors, (2) Pb
represents a moderate risk in most areas, (3) Zn generally exhibits low risk, and (4) Ni represents either low risk or no
risk in the studied area. This study shows that combining geostatistics with fuzzy theory can provide results that offer insight
into risk assessment for environmental pollution. 相似文献
87.
The amino acid and hydrocarbon contents of the Paris meteorite: Insights into the most primitive CM chondrite
下载免费PDF全文
![点击此处可从《Meteoritics & planetary science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Zita Martins Paola Modica Brigitte Zanda Louis Le Sergeant d'Hendecourt 《Meteoritics & planetary science》2015,50(5):926-943
The Paris meteorite is one of the most primitive carbonaceous chondrites. It is reported to be the least aqueously altered CM chondrite, and to have experienced only weak thermal metamorphism. We have analyzed for the first time the amino acid and hydrocarbon contents of this pristine meteorite by gas chromatography–mass spectrometry (GC–MS). When plotting the relative amino acids abundances of several CM chondrites according to the increasing hydrothermal scale (petrologic subtypes), from the CM2.7/2.8 Paris to the CM2.0 MET 01070, Paris has the lowest relative abundance of β‐alanine/glycine (0.15), which fits with the relative abundances of β‐alanine/glycine increasing with increasing aqueous alteration for CM chondrites. These results confirm the influence of aqueous alteration on the amino acid abundances and distribution. The amino acid analysis shows that the isovaline detected in this meteorite is racemic (d /l = 0.99 ± 0.08; l ‐enantiomer excess = 0.35 ± 0.5%; corrected d /l = 1.03; corrected l ‐enantiomer excess = ?1.4 ± 2.6%). The identified hydrocarbons show that Paris has n‐alkanes ranging from C16 to C25 and 3‐ to 5‐ring nonalkylated polycyclic aromatic hydrocarbons (PAHs). The lack of alkylated PAHs in Paris seems to be also related to this low degree of aqueous alteration on its parent body. The extraterrestrial hydrocarbon content, suggested by the absence of any biomarker, may well have a presolar origin. The chemistry of the Paris meteorite may thus be closely related to the early stages of the solar nebula with a contribution from interstellar (molecular cloud) precursors. 相似文献
88.
89.
R. M. González Delgado M. Cerviño L. P. Martins C. Leitherer P. H. Hauschildt 《Monthly notices of the Royal Astronomical Society》2005,357(3):945-960
We present the single stellar population (SSP) synthesis results of our new synthetic stellar atmosphere models library with a spectral sampling of 0.3 Å, covering the wavelength range from 3000 to 7000 Å for a wide range of metallicities (twice solar, solar, half solar and 1/10 solar). The stellar library is composed of 1650 spectra computed with the latest improvements in stellar atmospheres. In particular, it incorporates non-local thermodynamic equilibrium (LTE) line-blanketed models for hot ( T eff ≥ 27 500 K) , and LTE line-blanketed models (Phoenix) for cool (3000 ≤ T eff ≤ 4500 K) stars. Because of the high spectral resolution of this library, evolutionary synthesis models can be used to predict the strength of numerous weak absorption lines and the evolution of the profiles of the strongest lines over a wide range of ages. The SSP results have been calculated for ages from 1 Myr to 17 Gyr using the stellar evolutionary tracks provided by the Geneva and Padova groups. For young stellar populations, our results have a very detailed coverage of high-temperature stars with similar results for the Padova and Geneva isochrones. For intermediate and old stellar populations, our results, once degraded to a lower resolution, are similar to the ones obtained by other groups (limitations imposed by the stellar evolutionary physics notwidthstanding). The limitations and advantages of our models for the analysis of integrated populations are described. The full set of the stellar library and the evolutionary models are available for retrieval at the websites http://www.iaa.csic.es/~rosa and http://www.iaa.csic.es/~mcs/sed@ , or on request from the first two authors. 相似文献
90.