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281.
T. Takagi A. M. J. Mortier K. Shimasaku K. Coppin A. Pope R. J. Ivison H. Hanami S. Serjeant D. L. Clements R. S. Priddey J. S. Dunlop T. Takata I. Aretxaga S. C. Chapman S. A. Eales D. Farrah G. L. Granato M. Halpern D. H. Hughes E. van Kampen D. Scott K. Sekiguchi I. Smail M. Vaccari 《Monthly notices of the Royal Astronomical Society》2007,381(3):1154-1168
282.
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284.
Ewan O'Sullivan Duncan A. Forbes Trevor J. Ponman 《Monthly notices of the Royal Astronomical Society》2001,328(2):461-484
We present a catalogue of X-ray luminosities for 401 early-type galaxies, of which 136 are based on newly analysed ROSAT PSPC pointed observations. The remaining luminosities are taken from the literature and converted to a common energy band, spectral model and distance scale. Using this sample we fit the L X : L B relation for early-type galaxies and find a best-fit slope for the catalogue of ∼2.2. We demonstrate the influence of group-dominant galaxies on the fit and present evidence that the relation is not well modelled by a single power-law fit. We also derive estimates of the contribution to galaxy X-ray luminosities from discrete-sources and conclude that they provide . We compare this result with luminosities from our catalogue. Lastly, we examine the influence of environment on galaxy X-ray luminosity and on the form of the relation. We conclude that although environment undoubtedly affects the X-ray properties of individual galaxies, particularly those in the centres of groups and clusters, it does not change the nature of whole populations. 相似文献
285.
D. Farrah M. Rowan-Robinson S. Oliver S. Serjeant K. Borne A. Lawrence R.A. Lucas H. Bushouse L. Colina 《Monthly notices of the Royal Astronomical Society》2001,326(4):1333-1352
We present HST WFPC2 V -band imaging for 23 ultraluminous infrared galaxies (ULIRGs) taken from the QDOT redshift survey. The fraction of sources observed to be interacting is 87 per cent. Most of the merging systems show a number of compact 'knots', whose colour and brightness differ substantially from their immediate surroundings. Colour maps for nine of the objects show a non-uniform colour structure. Features include blue regions located towards the centres of merging systems which are likely to be areas of enhanced star formation, and compact red regions which are likely to be dust shrouded starbursts or active galactic nuclei. The host galaxies of the quasi-stellar objects (QSOs) in the sample were found to be either interacting systems or ellipticals. Our data show no evidence that ULIRGs are a simple transition stage between galaxy mergers and QSOs. We propose an alternative model for ULIRGs based on the morphologies in our sample and previous N -body simulations. Under this model ULIRGs as a class are much more diverse than a simple transition between galaxy merger and QSO. The evolution of IR power source and merger morphology in ULIRGs is driven solely by the local environment and the morphologies of the merger progenitors. 相似文献
286.
Solar limb scanning at 5 wavelengths from 0.35 to 2 mm on the JCMT has revealed significant limb extension which increases rapidly with wavelength, in agreement with other measurements. This appears to be related to the increasing opacity of overlapping spicules which appear to become optically thick at about 1mm. 相似文献
287.
Stephen F. Helsdon Trevor J. Ponman Ewan O'Sullivan Duncan A. Forbes 《Monthly notices of the Royal Astronomical Society》2001,325(2):693-706
We have derived the X-ray luminosities of a sample of galaxies in groups, making careful allowance for contaminating intragroup emission. The L X : L B and L X : L FIR relations of spiral galaxies in groups appear to be indistinguishable from those in other environments, however the elliptical galaxies fall into two distinct classes. The first class is central-dominant group galaxies, which are very X-ray luminous and may be the focus of group cooling flows. All other early-type galaxies in groups belong to the second class, which populates an almost constant band of L X / L B over the range 9.8< log L B <11.3 . The X-ray emission from these galaxies can be explained by a superposition of discrete galactic X-ray sources together with a contribution from hot gas lost by stars, which varies a great deal from galaxy to galaxy. In the region where the optical luminosity of the non-central group galaxies overlaps with the dominant galaxies, the dominant galaxies are over an order of magnitude more luminous in X-rays.
We also compared these group galaxies with a sample of isolated early-type galaxies, and used previously published work to derive LX : L B relations as a function of environment. The non-dominant group galaxies have mean L X / L B ratios very similar to those of isolated galaxies, and we see no significant correlation between L X / L B and environment. We suggest that previous findings of a steep L X : L B relation for early-type galaxies result largely from the inclusion of group-dominant galaxies in samples. 相似文献
We also compared these group galaxies with a sample of isolated early-type galaxies, and used previously published work to derive L
288.
J. Duncan Keppie Fernando Ortega-Gutiérrez 《Journal of South American Earth Sciences》2010,29(1):21-27
Rocks with ages of ca. 1 Ga occur in central and southern Mexico as inliers surrounded by ubiquitous Mesozoic and Cenozoic rocks. They appear to share a common history consisting of: (i) ca. 1300–1200 Ma arc magmatism and deposition of sediments including evaporites; (ii) ca.1160–1100 Ma intrusion of syenite, granite and anorthosite, the later part of which is synchronous with migmatization; (iii) intrusion of a ca. 1035–1010 Ma anorthosite–gabbro–charnockite–granite (AMCG) suite; (iv) a 1000–980 Ma granulite facies tectonothermal event with a stretching axis parallel to the long axis of Oaxaquia; (v) gradual exhumation at 750 and/or 545 Ma; and (vi) 517 Ma intrusion of an isolated calcalkaline granitoid pluton. The common Precambrian geological record of these outcrops suggests that they belonged to a single terrane (Oaxaquia) and formed a juvenile arc/backarc bordering a continent that underwent collision with, and overthrusting of, the Avalonian arc at 1000–980 Ma. This buried Oaxaquia to 25–30 km and was followed by further supra-subduction zone magmatism at ca. 917 Ma. These Precambrian rocks are unconformably overlain by uppermost Cambrian and Silurian platform rocks containing Gondwanan fauna and ca. 1 detrital zircons of Oaxacan provenance. The neighbouring Mixteca terrane includes lower Paleozoic, rift-passive margin sedimentary rocks that also contain 900–750 Ma detrital zircons probably derived from the Goiás arc in eastern Amazonia. The arc-backarc tectonic setting inferred for the 1300–900 Ma rocks also suggests that Oaxaquia lay on an active periphery of Amazonia until ca. 900 Ma, well after the amalgamation of Rodinia. This precludes a location for Oaxaquia off southern and western Amazonia that are inferred to have been juxtaposed against eastern Laurentia; contiguity with eastern Amazonia is also unlikely given the absence of the 900–750 Ma convergent tectonics in the Goiás arc. This leaves northern Amazonia as the most likely position, a location that requires the least relative displacement between Oaxaquia and Amazonia. The inferred 750 and 545 Ma exhumation episodes of Oaxaquia correspond to two proposed breakup stages of Rodinia. 相似文献
289.
The recent discovery of a fossilized assemblage of juvenile Ediacaran rangeomorph macro‐organisms, fern‐like impressions from the Drook Formation of Newfoundland, suggests that the morphological diversity present within the earliest known communities of the Ediacaran biota was relatively high. The fledgling population of these Proterozoic organisms was smothered by volcanic material from a nearby eruption, preserving the standing community on the seafloor. As many as six different genera are identified, present less than three million years after the end of the Gaskiers glacial event. This hints at a hidden evolutionary history for these organisms that is yet to be discovered. Co‐occurring filamentous impressions, and other fossils interpreted to represent the remains of decayed and ‘effaced’ organisms, suggest that the bedding plane exhibits unusual ecological completeness, with the assemblage as a whole documenting an early example of secondary community succession. Discoveries such as this reveal the potential for high‐quality preservation of soft‐bodied Ediacaran organisms in siliciclastic successions, and provide valuable insights into rangeomorph development and palaeoecology. 相似文献
290.
A. Hernán-Caballero I. Pérez-Fournon E. Hatziminaoglou A. Afonso-Luis M. Rowan-Robinson D. Rigopoulou D. Farrah C. J. Lonsdale T. Babbedge D. Clements S. Serjeant F. Pozzi M. Vaccari F. M. Montenegro-Montes I. Valtchanov E. González-Solares S. Oliver D. Shupe C. Gruppioni B. Vila-Vilaró C. Lari F. La Franca 《Monthly notices of the Royal Astronomical Society》2009,395(3):1695-1722