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191.
192.
Vivienne Wild John A. Peacock Ofer Lahav Edward Conway Steve Maddox Ivan K. Baldry Carlton M. Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Matthew Colless Chris Collins Warrick Couch Gavin Dalton Roberto De Propris Simon P. Driver George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Carole Jackson Ian Lewis Stuart Lumsden Darren Madgwick Peder Norberg Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2005,356(1):247-269
193.
P. A. Evans Coel Hellier Gavin Ramsay 《Monthly notices of the Royal Astronomical Society》2006,369(3):1229-1234
The intermediate polar PQ Geminorum shows a complex pulsation, caused by a spinning white dwarf, which varies markedly with wavelength. We report XMM–Newton observations, including the soft and hard X-ray bands and the first ultraviolet light curves of this star. We update the ephemeris for PQ Gem allowing us to align these data with a compilation of light curves from the optical to the X-ray. Building on work by previous authors, we show how a model in which accretion flows along skewed field lines, viewed at the correct inclination, can explain the major features of the light curves in all bands. We discuss how the skew of the field lines relates to the spinning down of the white dwarf rotation. 相似文献
194.
195.
Infiltration systems are widely used as an effective urban stormwater control measure. Most design methods and models roughly approximate the complex physical flow processes in these systems using empirical equations and fixed infiltration rates to calculate emptying times from full. Sophisticated variably saturated flow models are available, but rarely applied owing to their complexity. This paper describes the development and testing of an integrated one‐dimensional model of flow through the porous storage of a typical infiltration system and surrounding soils. The model accounts for the depth in the storage, surrounding soil moisture conditions and the interaction between the storage and surrounding soil. It is a front‐tracking model that innovatively combines a soil‐moisture‐based solution of Richard's equation for unsaturated flow with piston flow through a saturated zone as well as a reservoir equation for flow through a porous storage. This allows the use of a simple non‐iterative numerical solution that can handle ponded infiltration into dry soils. The model is more rigorous than approximate stormwater infiltration system models and could therefore be valuable in everyday practice. A range of test cases commonly used to test soil water flow models for infiltration in unsaturated conditions, drainage from saturation and infiltration under ponded conditions were used to test the model along with an experiment with variable depth in a porous storage over saturated conditions. Results show that the model produces a good fit to the observed data, analytical solutions and Hydrus. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
196.
Gavin Ramsay † Mark Cropper 《Monthly notices of the Royal Astronomical Society》2007,379(3):1209-1216
We present XMM–Newton observations of the eclipsing polar V2301 Oph which cover nearly 2.5 binary orbital cycles and two eclipses. This polar is believed to have the lowest magnetic field strength (7 MG) of any known polar. We find evidence for structure in the X-ray eclipse profile which shows a 'standstill' feature lasting 26 ± 4 s. This allows us to place an upper limit on the mass of the white dwarf of ∼1.2 M⊙ . We find no evidence for quasi-periodic oscillations (QPOs) in the frequency range 0.02–10 Hz. This coupled with the absence of QPOs in RXTE data suggests that, if present, any oscillations in the shock front have a minimal effect on the resultant X-ray flux. We find no evidence for a distinct soft X-ray component in its spectrum – it therefore joins another seven systems which do not show this component. We suggest that those systems which are asynchronous, have low mass-transfer rates or have accretion occurring over a relatively large fraction of the white dwarf are more likely to show this effect. We find that the specific mass-transfer rate has to be close to 0.1 g cm−2 s−1 to predict masses which are consistent with that derived from our eclipse analysis. This may be due to the fact that the low magnetic field strength allows accretion to take place along a wide range of azimuth. 相似文献
197.
Stephen P. Todd Suzanne K. Ramsay Howat 《Monthly notices of the Royal Astronomical Society》2006,367(1):238-246
The results of B -band CCD imaging linear polarimetry obtained for stars from the Hipparcos catalogue are used to re-examine the distribution of the local interstellar medium towards the IRAS 100-μm emission void in the Lupus dark clouds. The analysis of the obtained parallax–polarization diagram assigns to the dark cloud Lupus 1 a distance between 130 and 150 pc and assures the existence of a low column density region coincident with the observed infrared void. Moreover, there are clear indications of the existence of absorbing material at distances closer than 60–100 pc, which may be associated with the interface boundary between the Local Bubble and its neighbourhood Loop I superbubble. 相似文献
198.
A detailed search has been performed at 10.7 GHz for any pulsed radio emission from four X-ray pulsators (A0535+26, X Persei, AE Aquarii and H2252-035). The results obtained indicate no radio emission-pulsed or otherwise is present at a level of ≥ 50 mJy (two standard deviations upper limit). This value is considerably more sensitive than the previous studies carried out on these sources and presents problems in the understanding of compact, magnetised stellar objects. 相似文献
199.
Observations of Uranus during the 1975, 1976, and 1978 apparitions reveal a weak absorption at the wavelength of the R5(1) line of HD with equivalent width . The ratio in Uranus' atmosphere implied by this line and other published spectra is (4.8 ± 1.5) × 10?5, and may not be significantly different from that in the atmospheres of Jupiter and Saturn. In addition, the spectra exhibit two weak absorption at which we were unable to identify. No trace of absorption is visible near these wavelengths or near the HD wavelength in a laboratory spectrum of 4.92 km-am CH4 which we obtained in an attempt to identify these absorption features and to verify that the HD feature does not arise from CH4. 相似文献
200.
We present the aim and first results of the RApid Temporal Survey (RATS) made using the Wide Field Camera on the Isaac Newton Telescope. Our initial survey covers 3 square degrees, reaches a depth of V ∼ 22.5 and is sensitive to variations on time-scales as short as 2 min: this is a new parameter space. Each field was observed for over 2 h in white light, with 12 fields being observed in total. Our initial analysis finds 45 targets which show significant variations. Around half of these systems show quasi-sinusoidal variations: we believe they are contact or short period binaries. We find four systems which show variations on a time-scale less than 1 h. The shortest period system has a period of 374 s. We find two systems which show a total eclipse. Further photometric and spectroscopic observations are required to fully identify the nature of these systems. We outline our future plans and objectives. 相似文献