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171.
We studied the problematic of uncertainties in the diffuse gamma radiation apparent in stacking analysis of EGRET data at low Galactic latitudes. Subsequently, we co-added maps of counts, exposure and diffuse background, and residuals, in varying numbers for different sub-categories of putatively and known source populations (like PSRs). Finally we tested for gamma-ray excess emission in those maps and attempt to quantify the systematic biases in such approach. Such kind of an analysis will help the classification processes of sources and source populations in the GLAST era. 相似文献
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Denuncio P Bastida R Dassis M Giardino G Gerpe M Rodríguez D 《Marine pollution bulletin》2011,62(8):1836-1841
Plastic debris (PD) ingestion was examined in 106 Franciscana dolphins (Pontoporia blainvillei) incidentally captured in artisanal fisheries of the northern coast of Argentina. Twenty-eight percent of the dolphins presented PD in their stomach, but no ulcerations or obstructions were recorded in the digestive tracts. PD ingestion was more frequent in estuarine (34.6%) than in marine (19.2%) environments, but the type of debris was similar. Packaging debris (cellophane, bags, and bands) was found in 64.3% of the dolphins, with a lesser proportion (35.7%) ingesting fishery gear fragments (monofilament lines, ropes, and nets) or of unknown sources (25.0%). PD ingestion correlated with ontogenetic changes in feeding regimes, reaching maximum values in recently weaned dolphins. Because a simultaneous increase in gillnet entanglement and the bioaccumulation of heavy metals take place at this stage, the first months after trophic independence should be considered as a key phase for the conservation of Franciscana dolphin stocks in northern Argentina. 相似文献
177.
Cristina P. De Campos Diego Perugini Werner Ertel-Ingrisch Donald B. Dingwell Giampiero Poli 《Contributions to Mineralogy and Petrology》2011,161(6):863-881
Magma mixing is common in the Earth. Understanding the dynamics of the mixing process is necessary for dealing with the likely
consequences of mixing events in the petrogenesis of igneous rocks and the physics of volcanic eruptive triggers. Here, a
new apparatus has been developed in order to perform chaotic mixing experiments in systems of melts with high viscosity contrast.
The apparatus consists of an outer and an inner cylinder, which can be independently rotated at finite strains to generate
chaotic streamlines. The two cylinder axes are offset. Experiments have been performed for ca. 2 h, at 1,400°C under laminar
fluid dynamic conditions (Re ~ 10−7). Two end-member silicate melt compositions were synthesized: (1) a peralkaline haplogranite and (2) a haplobasalt. The viscosity
ratio between these two melts was of the order of 103. Optical analysis of post-experimental samples reveals a complex pattern of mingled filaments forming a scale-invariant (i.e.
fractal) distribution down to the μm-scale, as commonly observed in natural samples. This is due to the development in space
and time of stretching and folding of the two melts. Chemical analysis shows strong non-linear correlations in inter-elemental
plots. The original end-member compositions have nearly entirely disappeared from the filaments. The generation of thin layers
of widely compositionally contrasting interfaces strongly enhances chemical diffusion producing a remarkable modulation of
compositional fields over a short-length scale. Notably, diffusive fractionation generates highly heterogeneous pockets of
melt, in which depletion or enrichment of chemical elements occur, depending on their potential to spread via chemical diffusion
within the magma mixing system. Results presented in this work offer new insights into the complexity of processes expected
to be operating during magma mixing and may have important petrological implications. In particular: (1) it is shown that,
in contrast with current thinking, rheologically contrasting magmas can mix (i.e. with large proportions of felsic magmas
and high viscosity ratios), thus extending significantly the spectrum of geological conditions under which magma mixing processes
can occur efficiently; (2) the mixing process cannot be modeled using the classical linear two-end-member mixing model; and
(3) the chemical compositions on short-length scales represent snapshots within the process of mixing and therefore may not
reflect the final composition of the magmatic system. This study implies that microanalysis on short-length scales may provide
misleading information on the parental composition of magmas. 相似文献
178.
Geoarchaeological analysis of the Middle and Upper Palaeolithic record preserved in cave, rock-shelter and open-air sites in the northern sector of the Meso-Cenozoic of the Western Iberian Peninsula margin (Portugal) reveals several disconformities (erosive unconformities), hiatuses and surface stabilization phases. A recurrent disconformity, dated to ca. 29,500-32,000 cal yr BP, in the time range of Heinrich event 3, must correspond to a main erosive event related to the impacts of climate change on the landscape, including a reduction in vegetation cover and altered precipitation patterns, with the consequent accelerated down-cutting by stream systems, slope reactivation and endokarstic reorganisation, causing the erosion of sediments and soils accumulated in cave, rock-shelter and open-air sites. These processes create a preservation bias that may explain why Early Upper Palaeolithic finds in primary deposition context remains exceptional in the carbonate areas of central-western Portugal, and possibly elsewhere in the other places of Iberia. The impact of such site formation processes must therefore be duly considered in interpretations of the current patchy and scarce archaeological record of the Middle-Upper Palaeolithic transition in south-western Iberia. 相似文献
179.
G. Diego Gatta Paolo Lotti Fabrizio Nestola Marco Merlini Daria Pasqual Andrea Lausi 《Physics and Chemistry of Minerals》2013,40(5):401-409
The thermo-elastic behaviour of Be2BO3(OH)0.96F0.04 (i.e. natural hambergite, Z = 8, a = 9.7564(1), b = 12.1980(2), c = 4.4300(1) Å, V = 527.21(1) Å3, space group Pbca) has been investigated up to 7 GPa (at 298 K) and up to 1,100 K (at 0.0001 GPa) by means of in situ single-crystal X-ray diffraction and synchrotron powder diffraction, respectively. No phase transition or anomalous elastic behaviour has been observed within the pressure range investigated. P?V data fitted to a third-order Birch–Murnaghan equation of state give: V 0 = 528.89(4) Å3, K T0 = 67.0(4) GPa and K′ = 5.4(1). The evolution of the lattice parameters with pressure is significantly anisotropic, being: K T0(a):K T0(b):K T0(c) = 1:1.13:3.67. The high-temperature experiment shows evidence of structure breakdown at T > 973 K, with a significant increase in the full-width-at-half-maximum of all the Bragg peaks and an anomalous increase in the background of the diffraction pattern. The diffraction pattern was indexable up to 1,098 K. No new crystalline phase was observed up to 1,270 K. The diffraction data collected at room-T after the high-temperature experiment showed that the crystallinity was irreversibly compromised. The evolution of axial and volume thermal expansion coefficient, α, with T was described by the polynomial function: α(T) = α 0 + α 1 T ?1/2. The refined parameters for Be2BO3(OH)0.96F0.04 are: α 0 = 7.1(1) × 10?5 K?1 and α 1 = ?8.9(2) × 10?4 K ?1/2 for the unit-cell volume, α 0(a) = 1.52(9) × 10?5 K?1 and α 1(a) = ?1.4(2) × 10?4 K ?1/2 for the a-axis, α 0(b) = 4.4(1) × 10?5 K?1 and α 1(b) = ?5.9(3) × 10?4 K ?1/2 for the b-axis, α 0(c) = 1.07(8) × 10?5 K?1 and α 1(c) = ?1.5(2) × 10?4 K ?1/2 for the c-axis. The thermo-elastic anisotropy can be described, at a first approximation, by α 0(a):α 0(b):α 0(c) = 1.42:4.11:1. The main deformation mechanisms in response to the applied temperature, based on Rietveld structure refinement, are discussed. 相似文献
180.
On the crystal structure and compressional behavior of talc: a mineral of interest in petrology and material science 总被引:1,自引:1,他引:0
G. Diego Gatta Marco Merlini Giovanni Valdrè Hanns-Peter Liermann Gwilherm Nénert André Rothkirch Volker Kahlenberg Alessandro Pavese 《Physics and Chemistry of Minerals》2013,40(2):145-156
The crystal structure of a natural triclinic talc (1Tc polytype) [with composition: (Mg2.93Fe0.06)Σ2.99(Al0.02Si3.97)Σ3.99O10(OH)2.10] has been investigated by single-crystal X-ray diffraction at 223 and 170 K and by single-crystal neutron diffraction at 20 K. Both the anisotropic X-ray refinements (i.e. at 223 and 170 K) show that the two independent tetrahedra are only slightly distorted. For the two independent Mg-octahedra, the bond distances between cation-hydroxyl groups are significantly shorter than the others. The ditrigonal rotation angle of the six-membered ring of tetrahedra is modest (α ~ 4°). The neutron structure refinement shows that the hydrogen-bonding scheme in talc consists of one donor site and three acceptors (i.e. trifurcated configuration), all the bonds having O···O ≤ 3.38 Å, H···O ~ 2.8 Å, and O–H···O ~ 111–116°. The three acceptors belong to the six-membered ring of tetrahedra juxtaposed to the octahedral sheet. The vibrational regime of the proton site appears being only slightly anisotropic. The elastic behavior of talc was investigated by means of in situ synchrotron single-crystal diffraction up to 16 GPa (at room temperature) using a diamond anvil cell. No evidence of phase transition has been observed within the pressure range investigated. P–V data fit, with an isothermal third-order Birch-Murnaghan equation of state, results as follows: V 0 = 454.7(10) Å3, K T0 = 56(3) GPa, and K′ = 5.4(7). The “Eulerian finite strain” versus “normalized stress” plot yields: Fe(0) = 56(2) GPa and K′ = 5.3(5). The compressional behavior of talc is strongly anisotropic, as reflected by the axial compressibilities (i.e. β(a):β(b):β(c) = 1.03:1:3.15) as well as by the magnitude and orientation of the unit-strain ellipsoid (with ε 1:ε 2:ε 3 = 1:1.37:3.21). A comparison between the elastic parameters of talc obtained in this study with those previously reported is carried out. 相似文献