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21.
The impact of tar aggregates deriving from the Haven oil spill that occurred in 1991 on the soft-bottom macrobenthos off Arenzano (Ligurian Sea, NW Mediterranean; Italy) was investigated in this study. Core samples were collected to evaluate the composition, abundance and stratification of macrobenthos in three contaminated and three control sites. The distribution of tar aggregates (often settled by hydroids, bryozoans and serpulids) in the impacted area did not show distinct patterns related to sediment depth. The macrobenthos was numerically dominated by polychaetes, followed by crustaceans (amphipods, isopods and tanaids) and sipunculids, whereas bivalve molluscs were less represented. Ophiuroids and nemerteans were only occasionally found. Stratification was the main factor explaining the distribution of benthic invertebrates, highest abundances being observed in the upper 5 cm of sediment, while densities of individuals declined sharply in deeper sediment layers. No significant differences were observed in the abundance of both the whole benthic assemblage and of the main benthic taxonomic groups between contaminated and control sites. The higher abundance of sipunculids at the contaminated sites, instead, was attributed to the availability of empty tubes of polychaetes in which they take refuge. The polychaetes/amphipods ratios did not show strong differences between impacted and control sites. Multivariate analysis (MDS) showed a wide scattering among deep bottom samples and a comparatively high similarity among intermediate and superficial layers, regardless of the contamination level. In conclusion, the results reported here suggest that tar aggregates do not determine appreciable detrimental effects on the soft-bottom macrobenthos, which appeared to have recovered towards natural pristine conditions. 相似文献
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M.Satyanarayanan D.V.Subba Rao M.L.Renjith S.P.Singh E.V.S.S.K.Babu M.M.Korakoppa 《地学前缘(英文版)》2018,9(2):531-547
Petrographic, mineral chemical and whole-rock geochemical characteristics of two newly discovered lamproitic dykes(Dyke 1 and Dyke 2) from the Sidhi Gneissic Complex(SGC), Central India are presented here. Both these dykes have almost similar sequence of mineral-textural patterns indicative of:(1) an early cumulate forming event in a deeper magma chamber where megacrystic/large size phenocrysts of phlogopites have crystallized along with subordinate amount of olivine and clinopyroxene;(2) crystallization at shallow crustal levels promoted fine-grained phlogopite, K-feldspar, calcite and Fe-Ti oxides in the groundmass;(3) dyke emplacement related quench texture(plumose K-feldspar, acicular phlogopites) and finally(4) post emplacement autometasomatism by hydrothermal fluids which percolated as micro-veins and altered the mafic phases. Phlogopite phenocrysts often display resorption textures together with growth zoning indicating that during their crystallization equilibrium at the crystal-melt interface fluctuated multiple times probably due to incremental addition or chaotic dynamic self mixing of the lamproitic magma. Carbonate aggregates as late stage melt segregation are common in both these dykes, however their micro-xenolithic forms suggest that assimilation with a plutonic carbonatite body also played a key role in enhancing the carbonatitic nature of these dykes. Geochemically both dykes are ultrapotassic(K_2 O/Na_2 O: 3.0-9.4) with low CaO, Al_2 O_3 and Na_2 O content and high SiO_2(53.3-55.6 wt.%)and K_2 O/Al_2 O_3 ratio(0.51-0.89) characterizing them as high-silica lamproites. Inspite of these similarities, many other features indicate that both these dykes have evolved independently from two distinct magmas. In dyke 1, phlogopite composition has evolved towards the minette trend(Al-enrichment) from a differentiated parental magma having low MgO, Ni and Cr content; whereas in dyke 2, phlogopite composition shows an evolutionary affinity towards the lamproite trend(Al-depletion) and crystallized from a more primitive magma having high MgO, Ni and Cr content. Whole-rock trace-elements signatures like enriched LREE, LILE, negative Nb-Ta and positive Pb anomalies; high Rb/Sr, Th/La, Ba/Nb, and low Ba/Rb, Sm/La, Nb/U ratios in both dykes indicate that their pareintal magmas were sourced from a subduction modified garnet facies mantle containing phlogopite. From various evidences it is proposed that the petrogenesis of studied lamproitic dykes stand out to be an example for the lamproite magma which attained a carbonatitic character and undergone diverse chemical evolution in response to parental melt composition, storage at deep crustal level and autometasomatism. 相似文献
24.
Banded iron formations have been studied for decades, particularly regarding their potential as archives of the Precambrian environment. In spite of this effort, the mechanism of their deposition and, specifically, the role that microbes played in the precipitation of banded iron formation minerals, remains unresolved. Evidence of an anoxic Earth with only localized oxic areas until the Great Oxidation Event ca 2·45 to 2·32 Ga makes the investigation of O2‐independent mechanisms for banded iron formation deposition relevant. Recent studies have explored the long‐standing proposition that Archean banded iron formations may have been formed, and diagenetically modified, by anaerobic microbial metabolisms. These efforts encompass a wide array of approaches including isotope, ecophysiological and phylogeny studies, molecular and mineral marker analysis, and sedimentological reconstructions. Herein, the current theories of microbial processes in banded iron formation mineral deposition with particular regard to the mechanisms of chemical sedimentation and post‐depositional alteration are described. The main findings of recent years are summarized and compared here, and suggestions are made regarding cross‐disciplinary information still required to constrain the role of the biosphere in banded iron formation deposition. 相似文献
25.
Colony morphology is important for Microcystis to sustain a competitive advantage in eutrophic lakes. The mechanism of colony formation in Microcystis is currently unclear. Extracellular polysaccharide (EPS) has been reported to play an important role in cell aggregate formation of some phytoplankton. Microcystis aeruginosa was cultivated under varied abiotic conditions, including different nutrient, light, and temperature conditions, to investigate their effects on EPS production and morphological change. The results show that nutrient concentration and light intensity have great effects on EPS production in M. aeruginosa. There was a considerable increase in EPS production after M. aeruginosa was cultivated in adjusted culture conditions similar to those present in the field (28.9mg C/L, 1.98mg N/L, 0.65mg P/L, light intensity:100 μmol/(m2s)). These results indicate that abiotic factors might be one of the triggers for colony formation in Microcystis. 相似文献
26.
Does the invisible hand have a green thumb? Incentives, linkages, and the creation of wealth out of industrial waste in Victorian England 总被引:1,自引:0,他引:1
PIERRE DESROCHERS 《The Geographical journal》2009,175(1):3-16
'Loop closing', that is, the creation of waste recycling linkages between different industries, has been hailed as a means of simultaneously achieving improved economic and environmental performance. As a result of the widespread assumption that traditional market incentives and institutions are not conducive to such an outcome, however, there remains a fair amount of scepticism as to what the capacity of business self-interest to promote this behaviour actually is. This article challenges the dominant negative perspective by discussing by-product development in one of the most market-oriented societies in human history, Victorian England. Building on nineteenth and early twentieth century writings on the topic, as well as a more detailed analysis of the development of valuable by-products from highly problematic iron and coal gas production residuals, a case is made that the search for increased profitability within the context of private property rights often simultaneously promoted economic and environmental progress in the long run, as well as on different geographical scales. 相似文献
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In this research, the possibility of replacing different portions of the normally used aggregate by acidic rocks was investigated.
These rock types outcrop at the northern part of Eastern Desert, southwest Ras Gharib area where large quantities of good
quality acidic rocks are available their. Portland cement concrete is a composite material made up of the hydrated cement
matrix, fine aggregate and coarse aggregate. The scanning electron microscope equipped with an energy dispersive X-ray analysis
system (EDX) has been applied to investigate several aspects of Portland cement concrete microstructure. The topics investigated
so far include the influence of aggregate composition on the development of the cement paste-aggregate interface and the formation
of calcium silicate hydrate CSH/calcium silicate aluminate CSA formation. The silicate gel coated the aggregates in the concrete
paste and crystallized into well defined needle like shape, cotton shape as well as euhedral to subhedral crystals of silicate/alumiante
and ettringite minerals with free lime librated from the hydrolysis process. The free lime can react again with the aggregates
leading to the formation of cementing materials which increase strength and durability of the concrete paste by increasing
the interfacial bonds between the used aggregates. 相似文献
29.
Christopher R.S. Barrio Froján Siân E. BoydKeith M. Cooper Jacqueline D. EggletonSuzanne Ware 《Estuarine, Coastal and Shelf Science》2008
The temporal variability of benthic assemblages inhabiting offshore gravel deposits in the North Sea is poorly known, as purpose-collected long-term data sets have until recently been non-existent. It has therefore proved difficult to understand the stability and resilience of these benthic ecosystems after disturbance caused by the extraction of aggregates on an industrial scale. The present investigation examines an 8-year time series of data collected in and around an active commercial aggregate extraction site off the east coast of the United Kingdom. Both physical and biological data sets suggest a distinct yet localised effect after sustained gravel extraction, with impacted sediments generally appearing more physically homogeneous and faunistically impoverished than undisturbed sediments. Although inter-annual variability of selected assemblage metrics was reduced in disturbed sediments, differences in some assemblage metrics became significant between years. Despite such observations, significant impacts to the benthos in any given year were not sustained for long. However, the magnitude of impact in almost every year would be enough to merit remedial intervention based on an existing model of measuring acceptable levels of disturbance as a result of organic enrichment. Caution must be exercised in making any such recommendations, especially as there are presently no models specifically designed to assess the degree of acceptable disturbance from aggregate extraction. This study not only highlights the importance of and need for long-term data sets in order to better understand the difference between natural and human-induced variability in benthic assemblages, but also emphasises the need to develop more relevant monitoring tools to better manage the activities of the marine aggregate extraction industry. 相似文献
30.