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251.
Annette T. Hollingshead Steven Businger Roland Draxler John Porter Duane Stevens 《Boundary-Layer Meteorology》2003,109(1):107-107
Corrigendum
Corrigendum 相似文献252.
Bonnie A. Stevens Andrzej J. Maciejewski 《Celestial Mechanics and Dynamical Astronomy》2002,82(2):111-112
Preface
Preface 相似文献253.
Esmé?M.?SpicerEmail author Gary?Stevens Ian?S.?Buick 《Contributions to Mineralogy and Petrology》2004,148(2):160-179
This study has examined the ~300 MPa partial melting behaviour of four metapelites collected from the highest grade rocks occurring below the anatectic zone of the Mt. Stafford area, Arunta Inlier, central Australia. In this area, metasediments are interpreted to have undergone partial melting within the andalusite stability field; possibly as a result of a lowering of the metapelite solidus by the presence of boron in the rocks. Two of the samples were two mica metapelites (MTS70 and MTS71). These both contained significant quantities of tourmaline and were thus boron enriched. The other two samples are biotite metapelites. One of these rocks contains only a trace of tourmaline (MTS8) and the other is tourmaline free (MTS7). Despite expectations that muscovite in the two mica samples would break down via a subsolidus reaction, muscovite was stable to above 750°C due to the incorporation of Ti, phengitic and possibly F components into its structure. Between 750 and 800°C, muscovite melted out completely via a coupled muscovite + biotite fluid-absent incongruent reaction. Tourmaline was partially consumed in this reaction, with the elbaitic component being preferentially consumed. In the most mica-rich sample this reaction produced ~60% melt at 800°C. In the biotite metapelites, biotite melting began at a temperature below 800°C and was accompanied by very modest melt production at this low temperature. In contrast to the two mica metapelites, the main pulse of melt production in these samples occurred at a temperature between 850 and 950°C. In both these samples biotite + melt coexisted over a temperature range in excess of 150°C, and in MTS8, biotite was still in the run products at 950°C. The very refractory nature of these evolved biotite compositions is most likely a consequence of both the presence of a Ti buffering phase in the assemblage (ilmenite) and the essentially plagioclase-free nature of the starting compositions. Under the fluid-absent conditions of this study, tourmaline is clearly a reactant in the partial melting process, but does not appear to shift the fluid-absent incongruent melting reactions markedly. In the tourmaline-rich two mica metapelites, tourmaline only disappears from the run products at a temperature above 850°C, where it coexisted with a substantial melt proportion. This appears to coincide with the point of maximum boron concentration in the melts.
相似文献
Esmé M. SpicerEmail: |
254.
E.I. Robson J.A. Stevens T. Jenness 《Monthly notices of the Royal Astronomical Society》2001,327(3):751-770
Calibrated data for 65 flat-spectrum extragalactic radio sources are presented at a wavelength of 850 μm, covering a three-year period from 1997 April. The data, obtained from the James Clerk Maxwell Telescope using the SCUBA camera in pointing mode, were analysed using an automated pipeline process based on the Observatory Reduction and Acquisition Control–Data Reduction ( orac–dr ) system. This paper describes the techniques used to analyse and calibrate the data, and presents the data base of results along with a representative sample of the better-sampled light curves. 相似文献
255.
256.
Thomas Stevens Yunus Baykal 《Proceedings of the Geologists' Association. Geologists' Association》2021,132(2):240-248
The sources of the Paleocene London Basin marine to fluviodeltaic sandstones are currently unclear. High analysis number detrital zircon U-Pb age investigation of an early-mid Thanetian marine sand from East Kent, reveals a large spread of zircon age peaks indicative of a range of primary sources. In particular, a strong Ediacaran age peak is associated with the Cadomian Orogeny, while secondary peaks represent the Caledonian and various Mesoproterozoic to Archean orogenies. The near absence of grains indicative of the Variscan orogeny refutes a southerly or southwesterly source from Cornubia or Armorica, while the strong Cadomian peak points to Avalonian origin for a major component of the material. Furthermore, the relatively well expressed Mesoproterozoic to Archean age components most likely require significant additional Laurentian input. Comparison to published data shows that both Devonian Old Red Sandstone and northwesterly (Avalonia-Laurentia) derived Namurian-Westphalian Pennine Basin sandstones show strong similarities to the Thanetian sand. This pattern is consistent with derivation of Thanetian material via a SE draining proto-Thames River system that was initiated in the Paleocene due to uplift of western and northwestern Britain. This river system would have incised and eroded cover sandstones and potentially also Avalonian basement of mid to north Wales and England. However, the possibility of a contribution of Laurentian grains directly from the north via longshore drift cannot be excluded by the data, and the extent to which the sediment source signatures of Paleogene sands of the London Basin are variable both geographically and over time remains unclear. 相似文献
257.
The S-type Peninsula Pluton (South Africa) exhibits substantial compositional variability and hosts a large variety of mafic and felsic magmatic enclaves with contrasting textures and compositions. Moreover, the pluton is characterized by mechanical concentrations of K-feldspar megacrysts, cordierite and biotite, generating a complex array of magmatic structures including schlieren, pipes, and spectacular sheeted structures. Chemical evidence indicates that the pluton is constructed incrementally by rapid emplacement of numerous magma pulses. Field, and textural data suggest that magmatic structures form by local flow at the emplacement level of highly viscous crystal-rich magmas (i.e. crystallinity up to 50?vol.%) through magma mushes assembled from older batches. At the time of arrival of relatively late magma batches, some areas within the pluton had achieved crystal fractions that allowed the material to act as a solid, whilst maintaining enough melt to prevent formation of sharp intrusional contacts. Magmatic structures represent “snapshots” of processes that operate in multiphase crystal-rich mushes and their genesis is due to mechanical and thermal instabilities in the crystal-rich magma chamber that are triggered by the emplacement of pulses of new magma derived from the melting of a compositionally variable metasedimentary source. 相似文献
258.
A.?VillarosEmail author I.?S.?Buick G.?Stevens 《Contributions to Mineralogy and Petrology》2012,163(2):243-257
Inherited zircons from S-type granites provide exceptionally good insight into the isotopic heterogeneity of their sources.
Zircons from four samples (one granite, two granodiorites, one granodioritic enclave) of Pan-African S-type granite of the
Cape Granite Suite (c. 540 Ma) have been the subject of a laser LA-ICP-MS zircon U/Pb study to determine emplacement ages
and inheritance. Zircons from three of these samples (2 granodiorites and 1 granodioritic enclave) were also analysed for
Hf isotopes by LA-MC-ICP-MS. Ages of inherited cores range from 1,200 to 570 Ma and show Hafnium isotope values (εHf,t
) for the crystallisation age (t) of the different cores that range from −14.1 to +9.1. Magmatic zircons and magmatic overgrowth with concordant spot ages
between ca. 525 and ca. 555 Ma show a similar range of εHf,t
, between −8.6 and +1.5, whilst εHf values calculated at 540 Ma (εHf,540) for inherited cores range from −15.2 to +1.7. Thus, our results show that the time evolved εHf arrays of the inherited cores overlap closely with the εHf range displayed by the magmatic rims at the time of crystallisation of the pluton. These similarities imply a genetic relationship
between magmatic and inherited zircons. Within the inherited cores, four main peak ages can be identified. This, coupled with
their large Hf isotopic range, emphasises that the source of the granite is highly heterogeneous. The combination of the U/Pb
zircon ages ranges and Hf isotope data implies that: (1) The source of S-type granite consists of crustal material recording
several regional events between 1,200 and 600 Ma. This material records the recycling of a much older crust derived from depleted
mantle between 1.14 and 2.02 Ga. (2) The homogenisation of Hf isotopic variation in the magma acquired through dissolution
of the entrained zircon, via mechanical mixing and/or diffusion between within the granite was particularly inefficient. (3)
This evidence argues for the assembly of the pluton through many relatively small magma batches that undergo rapid cooling
from their intrusion temperature (ca. 850°C) to background magma chamber temperature that is low enough to ensure that much
of the magmatic zircon crystallised rapidly (>80% by 700°C). (4) There is no evidence for the addition of mantle-derived material
in the genesis of S-type Cape Granite Suite, where the most mafic granodiorites are strongly peraluminous, relatively low
in CaO and K2O rich. Interpreted more widely, these findings imply that S-type granites inherit their isotopic characteristic from the
source. Source heterogeneity transfers to the granite magma via the genesis of discrete magma batches. The information documented
from the S-type CGS zircons has been recorded because the individual batches of magma crystallised the bulk of their magmatic
zircon prior to mechanical or diffusional magma homogenisation. This is favoured by zirconium saturation in the magma shortly
after emplacement, by partial dissolution of the entrained zircon fraction, as well as by the intrusion of volumetrically
subordinate magma batches into a relatively cool pluton. Consequently, evidence recorded within inherited cores will most
likely be best preserved in S-type granite plutons intruded at shallow depths. Other studies that have documented similar
εHf arrays in magmatic zircons have interpreted these to reflect mixing between crustal- and mantle-derived magmas. This study
indicates that such arrays may be wholly source inherited, reflecting mixing of a range of crustal materials of different
ages and original isotopic signatures. 相似文献
259.
Channel constrictions within an estuary can influence overall estuary-sea exchange of salt or suspended/dissolved material. The exchange is modulated by turbulent mixing through its effect on density stratification. Here we quantify turbulent mixing in Hikapu Reach, an estuarine channel in the Marlborough Sounds, New Zealand. The focus is on a period of relatively low freshwater input but where density stratification still persists throughout the tidal cycle, although the strength of stratification and its vertical structure vary substantially. The density stratification increases through the ebb tide, and decreases through the flood tide. During the spring tides observed here, ebb tidal flow speeds reached 0.7?m?s?1 and the buoyancy frequency squared was in the range 10?5 to 10?3?s?2. Turbulence parameters were estimated using both shear microstructure and velocimeter-derived inertial dissipation which compared favourably. The rate of dissipation of turbulent kinetic energy reached 1?×?10?6?m2?s?3 late in the ebb tide, and estimates of the gradient Richardson number (the ratio of stability to shear) fell as low as 0.1 (i.e. unstable) although the results show that bottom-boundary driven turbulence can dominate for periods. The implication, based on scaling, is that the mixing within the channel does not homogenise the water column within a tidal cycle. Scaling, developed to characterise the tidal advection relative to the channel length, shows how riverine-driven buoyancy fluxes can pass through the tidal channel section and the stratification can remain partially intact. 相似文献
260.
Jií Svoboda Zbigniew M. Bochenski Vra ulíkov Alena Dohnalov Srka Hladilov Martin Hloek Ivan Hor
ek Martin Ivanov Miroslav Krlík Martin Novk Alexander J.E. Pryor Sandra Szelov Rhiannon E. Stevens Jarosaw Wilczynski Piotr Wojtal 《Geoarchaeology》2011,26(6):838-866
The Dolní Věstonice–Pavlov–Milovice area (Czech Republic) on the slopes of the Pavlov Hills provides an opportunity for correlating the geomorphology of the Dyje River valley with Gravettian settlement patterns. Although the sites vary in size and complexity, they create a regular chain of strategic locations at elevations between 200 m and 240 m asl. In 2009, a road collapsed into deserted cellars inside the village of Milovice and revealed a complex of archaeological layers deep within loess, at an elevation of only 175 m asl. This paper presents an analysis of this atypical archaeological site location and compares the results with the other sites. We argue that this location allowed direct contact with mammoth herds concentrated on the floodplain, while the aquatic environment offered possibilities for gathering plants and fishing. This site represents a new aspect of organized settlement, hunting strategies, and short‐distance human movements during the Gravettian within this area. © 2011 Wiley Periodicals, Inc. 相似文献