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581.
Rainer?ThomasEmail author Hans-Jürgen?F?rster Karen?Rickers James?D.?Webster 《Contributions to Mineralogy and Petrology》2005,148(5):582-601
Quartz crystals from topaz–zinnwaldite–albite granites from Zinnwald (Erzgebirge, Germany) contain, in addition to primary and secondary fluid inclusions (FIs), abundant crystalline silicate-melt inclusions (MIs) with diameters up to 200 m. These MIs represent various stages of evolution of a highly evolved melt system that finally gave rise to granite-related Sn–W mineralization. The combination of special experimental techniques with confocal laser Raman-microprobe spectroscopy and EMPA permits precise measurement of elevated contents of H2O, F, and B in re-homogenized MIs. The contents of H2O and F were observed to increase from 3 to 30 and 1.9 to 6.4 wt%, respectively, during magma differentiation. However, there is a second MI group, very rich in H2O, with values up to 55 wt% H2O and an F concentration of approximately 3 wt%. Ongoing enrichment of volatiles H2O, F, B, and Cl and of Cs and Rb can be explained in terms of magma differentiation triggered by fractional crystallization and thus, is suggested to reflect elemental abundances in natural magmas, and not boundary-layer melts. Partitioning between melt and cogenetic fluids has further modified the magmatic concentrations of some elements, particularly Sn. The coexistence of two types of MIs with primary FIs indicates fluid saturation early in the history of magma crystallization, connected with a continuous sequestration of Sn, F, and B. The results of this study provide additional evidence for the extraordinary importance of the interplay of H2O, F, and B in the enrichment of Sn during magma differentiation by decreasing the viscosity of and increasing the diffusivity in the melts as well as by the formation of various stable fluoride complexes in the melt and coexisting fluid.
相似文献
Rainer ThomasEmail: Phone: +49-331-2881474 |
582.
583.
584.
Variability of dense water formation in the Ross Sea 总被引:1,自引:0,他引:1
This paper presents results from a model study of the interannual variability of high salinity shelf water (HSSW) properties
in the Ross Sea. Salinity and potential temperature of HSSW formed in the western Ross Sea show oscillatory behaviour at periods
of 5–6 and 9 years superimposed on long-term fluctuations. While the shorter oscillations are induced by wind variability,
variability on the scale of decades appears to be related to air temperature fluctuations. At least part of the strong decrease
of HSSW salinities deduced from observations for the period 1963–2000 is shown to be an aliasing artefact due to an undersampling
of the periodic signal. While sea ice formation is responsible for the yearly salinity increase that triggers the formation
of HSSW, interannual variability of net freezing rates hardly affects changes in the properties of the resulting water mass.
Instead, results from model experiments indicate that the interannual variability of dense water characteristics is predominantly
controlled by variations in the shelf inflow through a sub-surface salinity and a deep temperature signal. The origin of the
variability of inflow characteristics to the Ross Sea continental shelf can be traced into the Amundsen and Bellingshausen
Seas. The temperature anomalies are induced at the continental shelf break in the western Bellingshausen Sea by fluctuations
of the meridional transport of circumpolar deep water with the eastern cell of the Ross Gyre. In the Amundsen Sea, upwelling
due to a persistently cyclonic wind field carries the signal into the surface mixed layer, leading to fluctuations of the
vertical heat flux, anomalies of brine release near the sea ice edge, and consequently to a sub-surface salinity anomaly.
With the westward flowing coastal current, both the sub-surface salinity and deep temperature signals are advected onto the
Ross Sea continental shelf. Convection carries the signal of salinity variability into the deep ocean, where it interacts
with modified circumpolar deep water upwelled onto the continental shelf as the second source water mass of HSSW. Sea ice
formation on the Ross Sea continental shelf thus drives the vertical propagation of the signal rather than determining the
signal itself. 相似文献
585.
William C. Johnson Karen L. Willey Joseph A. Mason David W. May 《Quaternary Research》2007,67(3):474-486
The middle Wisconsinan Gilman Canyon Formation at the Buzzard's Roost type locality in southwestern Nebraska was investigated to document the stratigraphy and to reconstruct the environmental and climate record. The Gilman Canyon Formation was subdivided into three loess units and three soils, with radiocarbon ages constraining it between about 40 ka and 25 ka. Stable carbon isotope ratios, magnetic susceptibility, and carbon content were used to define and characterize soils within both the Gilman Canyon Formation and underlying Illinoian Loveland Loess. At the height of soil development within the Gilman Canyon Formation, climate was supporting C4-dominated grassland, with July temperatures equal to or exceeding those of today. Soil-forming intervals within the Loveland Loess, including the Sangamon Soil, also exhibited relative increases in C4 biomass. Climate, as recorded in the Gilman Canyon Formation, is corroborated by regional proxy data. The formation accumulated during MIS 3, and concurrent soil formation coincided with a summer insolation maximum. 相似文献
586.
User Assessment as Input for Useful Geospatial Representations within Mobile Location-Based Services
Karen Wealands Peter Benda Suzette Miller William E Cartwright 《Transactions in GIS》2007,11(2):283-309
Mobile Location‐Based Services (mLBS) are an increasingly consumer‐based concept borne from, and continually driven by, technology‐centred development; as opposed to the needs of end users. Where users have been made a focus, the research generally concerns issues of overall system appearance, functionality, information content and interaction methods, with little emphasis on the component geospatial representations. This paper describes the initial stages of a research project aimed at filling this void through the application of a qualitative User‐Centred Design (UCD) methodology for optimising geospatial representations within mLBS applications, in order to support a selected user group: Australian ‘leisure‐based travellers’. Presented in this paper is an account of two UCD activities adopted for the research. The first, user profiling, served to define the target user population in terms of their technological, geospatial and travel experiences, using an online questionnaire. The second, user task analysis, involved in‐depth interviews with a subset of users in order to obtain a deeper understanding of the geospatial goals, tasks, needs and preferences within the population, as well as the range of user differences and variability in tasks present. An overall user assessment, through combined analysis of the two result sets, highlighted considerations for the ongoing research, including a set of specific implications for the design of alternative models for geospatial services, representations and interactions. The themes described in this paper represent an initial and necessary component of UCD, which has been largely overlooked in research relating to mLBS. Whilst the focus here is on a specific user group and context of use, it is envisaged that many of the concepts tested and ratified by the resulting models will be relevant to mLBS applications in general. 相似文献
587.
Variability of dissolved Fe2+ and ∑H2S concentrations in porewaters were studied, using cathodic stripping voltammetry (CSV) microelectrodes, in sediments overlain
by hypoxic waters in the summer from the southeastern region of Corpus Christi Bay, Texas (CCB) and the Mississippi River
Bight (MRB), Louisiana. These measurements were complimented by sediment microcosm studies where oxygen concentrations in
the overlying water were manipulated. Sulfate reduction rates, benthic oxygen demand, total reduced sulfide, porewater sulfate,
and total organic carbon were also determined. Fe2+ and ∑H2S were the major dissolved redox-reactive dissolved species in these sediments. During hypoxic conditions, an upward migration
of porewater Fe2+ and ∑H2S occurred, with Fe2+ reaching much higher maximum concentrations than ∑H2S. Statistically significant (p < 0.05) differences in both Fe2+ and ∑H2S occurred between sediments at the CCB and MRB study sites. Although both sites were Fe-dominated, reactive and dissolved
iron were higher while ∑H2S was lower at the MRB site. However, there were no statistically significant (p > 0.05) difference in regard to ∑H2S between microcosm and field monitoring studies. Results indicated that, for Fe2+ and ∑H2S, relatively large and rapid changes occurred in both the concentrations and distributions of these important porewater constituents
in response to relatively short-term changes in overlying water oxygen content. Model calculations indicated that conditions
in the sediments can be responsible for the induction of hypoxic conditions in the formation of hypoxic overlying waters in
<6 days at CCB and ~20 days at MRB. 相似文献
588.
Mads Solgaard Thomsen Karen J. McGlathery Anna Christina Tyler 《Estuaries and Coasts》2006,29(3):465-473
We determined the distribution of macroalgae in Hog Island Bay, a shallow coastal lagoon in Virginia, USA, seasonally at 12
sites from 1998 to 2000 and at 3 representative sites from 2000 to 2002. We analyzed macroalgal biomass, taxonomic richness,
and abundance of two non-native species, the cryptic invaderGracilaria vermiculophylla and the conspicuousCodium fragile, with respect to season, location (mainland, mid lagoon, barrier island sites), and elevation (intertidal, subtidal). Taxonomic
richness, total algal biomass, and nonnative biomass peaked in the summer months when temperature and light availability were
highest. A few stress tolerant and ephemeral algae dominated the algal assemblage.G. vermiculophylla constituted 74% of the entire algal biomass, was the most abundant alga in all seasons, locations, and elevation levels,
and was positively correlated with taxonomic richness and abundance of filamentous species.Ulva curvata, Bryopsis plumosa, andC. fragile accounted for an additional 16% of the algal biomass. There are distinct habitats in Hog Island Bay that can be classified
into low diversity-low biomass regions near the mainland and barrier islands and high diversity-high biomass regions in the
open mid lagoon, where abundant shells for attachment and intermediate levels of water column nutrients and turbidity likely
create better growth conditions. Taxonomic richness and biomass were higher in subtidal than intertidal zones, presumably
due to lower desiccation stress. This study provides an example of how a single invasive species can dominate an entire assemblage,
both in terms of biomass (being most abundant in all seasons, locations, and tidal levels) and species richness (correlating
positively with epiphytic filamentous taxa). By adding hard-substratum structural complexity to a relatively homogenous soft-substratum
system,G. vermiculophylla increases substratum availability for attachment and entanglement of other algal species and enhances local diversity. Without
widespread and abundantG. vermiculophylla, taxa likePolysiphonia, Ceramium, Bryopsis, Ectocarpus, andChampia would likely be much less common. This study also highlights the importance of using DNA analysis of voucher specimens in
monitoring programs to accurately identify cryptic invaders. 相似文献
589.
Lead- and Pb-As-jarosites are minerals common to acidic, sulphate-rich environments, including weathering zones of sulphide ore deposits and acid rock or acid mine drainage (ARD/AMD) sites, and often form on or near galena. The structures of these jarosites are based on linear tetrahedral-octahedral-tetrahedral (T-O-T) sheets, comprised of slightly distorted FeO6 octahedra and SO42− (-AsO43− in Pb-As-jarosites) tetrahedra. To better understand the dissolution mechanisms and products of the break down of Pb- and Pb-As-jarosite, preliminary batch dissolution experiments were conducted on synthetic Pb- and Pb-As-jarosite at pH 2 and 20 °C, to mimic environments affected by ARD/AMD, and at pH 8 and 20 °C, to simulate ARD/AMD environments recently remediated with slaked lime (Ca(OH)2). All four dissolutions are incongruent. Dissolution of Pb-jarosite at pH 2 yields aqueous Pb, Fe and SO42−. The pH 8 Pb-jarosite dissolution yields aqueous Pb, SO42− and poorly crystalline Fe(OH)3, which does not appear to resorb Pb or SO42−, possibly due to the low solution pH (3.44-3.54) at the end of the experiment. The pH 2 and 8 dissolutions of Pb-As-jarosite result in the formation of secondary compounds (poorly crystalline PbSO4 for pH 2 dissolution; poorly crystalline PbSO4 and Fe(OH)3 for pH 8 dissolution), which may act as dissolution inhibitors after 250 to 300 h of dissolution. In the pH 2 dissolution, aqueous Fe, SO42− and AsO43− also form, and in the pH 8 dissolution, Fe(OH)3 precipitates then subsequently resorbs aqueous AsO43−. The dissolutions probably proceed by preferred dissolution of the A- and T-sites, which contain Pb, and SO42− and AsO43−, respectively, rather than Fe, which is sterically remote, within the T-O-T Pb- and Pb-As-jarosite structures. These data provide the foundation necessary for further, more detailed investigations into the dissolution of Pb- and Pb-As-jarosites. 相似文献
590.
Tim McCreanor Liane Penney Victoria Jensen Karen Witten Robin Kearns Helen Moewaka Barnes 《New Zealand geographer》2006,62(3):196-207
Abstract: This paper examines the culturally specific experiences of belonging within Oruāmo/Beachhaven, a suburb in North Shore City. In-depth interviews with 32 caregivers of young children expose the fact that the ethnic groups represented – Māori, Samoan and Pākehā– vary in their uses and understandings of, as well as feelings for, residential neighbourhood. Examination of the themes of natural environment, social relations, continuity of residence, facilities, organisations and place transformation reveal that, while representatives of all groups had views on these matters, there was a variable degree of engagement with and priority afforded to these concerns. 相似文献