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91.
E. Hawkins S. J. Maddox M. R. Merrifield 《Monthly notices of the Royal Astronomical Society》2002,336(1):L13-L16
I suggest that there are two classes of ultraluminous X-ray sources (ULXs), corresponding to super-Eddington mass inflow in two situations: (a) thermal-time-scale mass transfer in high-mass X-ray binaries, and (b) long-lasting transient outbursts in low-mass X-ray binaries. These two classes are exemplified by SS433 and microquasars like GRS 1915+105 respectively. The observed ULX population is a varying mixture of the two, depending on the star formation history of the host galaxy. ULXs in galaxies with vigorous star formation (such as the Antennae) are generally SS433-like, while ULXs in elliptical galaxies must be of the microquasar type. The latter probably have significantly anisotropic radiation patterns. They should also be variable, but demonstrating this may require observations over decades. The close analogy between models of X-ray binaries and active galactic nuclei (AGN) suggests that there should exist an apparently super-Eddington class of the latter, which may be the ultrasoft AGN, and a set of X-ray binaries with Doppler-boosted X-ray emission. These are presumably a subset of the ULXs, but remain as yet unidentified. 相似文献
92.
Darren S. Madgwick Ed Hawkins Ofer Lahav Steve Maddox Peder Norberg John A. Peacock 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 Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2003,344(3):847-856
93.
Marine reserves are places where wildlife and habitats are protected from extractive and depositional uses of the sea. Although considered to be the pinnacle in marine conservation, many permit non-consumptive activities with little or no regulation. This paper examines the potential impacts of 16 non-consumptive activities including scuba diving, sailing, scientific research and motor boating, and how they might compromise the conservation objectives of marine reserves. Examination of 91 marine reserves from 36 countries found little agreement or consistency in what non-consumptive activities are permitted in marine reserves and how they are regulated. The two most common activities allowed without regulation were swimming (mentioned in 80% of marine reserves and allowed in 63% of these) and kayaking (mentioned in 85%, allowed in 53%). Scuba diving was mentioned in 91% and allowed without regulation in 41%. A risk score for the likely level of threat to wildlife and/or habitats that each activity could produce was then assigned based on effects reported in the literature. The risk analysis suggests that motor boating and activities which include or require it have a high potential to negatively impact wildlife and habitats if inadequately managed. Hence protection against extractive or depositional activities alone is insufficient to secure the high standard of protection usually assumed in marine reserves. For this to be achieved activities typically considered as benign must receive appropriate management, especially with increasing recreational use. 相似文献
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Metamorphic rocks of the Yap arc-trench system 总被引:1,自引:0,他引:1
99.
A. C. Warn-Varnas S. A. Chin-Bing D. B. King Z. Hallock J. A. Hawkins 《Surveys in Geophysics》2003,24(1):39-79
Shallow water internal solitary waves have become a major topic ofinterest to oceanographers and acousticians. In this paper we reviewthe cross-disciplinary status of joint ocean-acoustic solitary wavestudies and predictions. We consider the process of acoustical modecoupling in the presence of solitary waves and the correspondingacoustical intensity loss due to increased coupling with the bottom. Astudy of the interaction of an acoustical field with a train ofsolitary waves is undertaken at a range of frequencies. At a resonantfrequency the acoustic field can interact with the solitary wavepacket which results in mode conversions (acoustic energy isredistributed among the modes, often from lower-order to higher-ordermodes). Higher signal losses can occur in the higher order modesthrough increased bottom attenuation and result in an anomalousacoustical intensity loss at the resonant frequency.We present some new results of joint ocean-acoustic research, from adedicated study in the Strait of Messina, where solitary waves aregenerated by semidiurnal tidal flow over topographic variations. TheUniversity of Hamburg weakly nonhydrostatic two layer model is used forsimulating the generation and propagation of solitary waves. In particular, the physicalstates encountered during an October 1995 cruise in the Strait of Messina (betweenItaly and Sicily) are simulated. Various parameter space sensitivity studies, about theexisting cruise conditions, are performed. The modelled solitary wave trains arecompared against conductivity-temperature-depth (CTD) chain measurements interms of amplitudes, wavelengths, phase speeds and correlations with data. Predictedand observed sound speeds are used in acoustical intensity calculations thatare conducted with a parabolic equation (PE) model. The differences in theresultant acoustical intensity fields provide a guide for the tuning of theoceanographic model parameters. The tuned oceanographic model showsagreement with data for the first and second solitary waves in terms ofamplitude, wavelength and phase speed. The calculated available potentialenergy from the simulation results is in the range of the data analogue. 相似文献
100.
Bioavailable copper and manganese in soils from Iceland and their relationship with scrapie occurrence in sheep 总被引:1,自引:0,他引:1
The bioavailability of trace metals can be directly linked with many common animal and human diseases. It is easier to correlate regional geochemical trends with disease distribution in the developing world because local populations and animals live from the land. In the western world, humans tend to live from the global food market whereas animals graze on the land. Recent biochemical studies have shown that the prion protein needs copper to keep its structure. If copper is not available, the prion protein can take up manganese and unfold. Preliminary results for trace metals in soil samples from scrapie-affected areas in Iceland show that bioavailable manganese manganese (easily reducible and exchangeable Mn) is very high whereas soluble copper and free copper are very low. 相似文献