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101.
Sílvia Pedro Vera Canastreiro Isabel Caçador Eduarda Pereira Armando C. Duarte Pedro Raposo de Almeida 《Estuarine, Coastal and Shelf Science》2008
The stomach contents of thin-lipped grey mullets Liza ramado were analysed in terms of granulometric composition and compared to the sediment of potential feeding areas in the Tagus estuary. Total organic matter (TOM) content and heavy metal content were determined in the surface sediment of three areas and eight trace elements were quantified: Cd, Co, Cr, Cu, Hg, Ni, Pb and Zn. The three sampled areas did not differ in TOM; and the heavy metal content was below Effects Range-Low level for most elements. The mean observed concentrations were present in the following sequence: Zn > Pb > Cr > Cu ≈ Ni > Co > Cd > Hg. Stomach contents granulometric composition provided information about the feeding selectivity of the mullets. Sediment fractions with particle size between 20 and 50 μm are preferred, independently of the fishes' length. Smaller standard length (SL) fishes have a higher positive selection of fine grained sediments than those with a larger SL. Finer fractions usually have higher concentration of heavy metals, which makes younger specimens of the thin-lipped grey mullet potentially more exposed to heavy metal load in the estuary. Metal concentration was not independent from the sampling point, presenting higher values near the margins and the estuary tidal drainage system. This means that during the first period of each tidal cycle, the mullets will feed first on the most contaminated areas, as a consequence of their movement following the rising tide to feed on previously exposed areas. 相似文献
102.
Large-eddy simulations of an evolving cloud field are used to investigate the contribution of microphysical processes to the evolution of the variance of total water and liquid water potential temperature in the boundary layer. While the first hours of such simulations show a transient behaviour and have to be analyzed with caution, the final portion of the simulation provides a quasi-equilibrium situation. This allows investigation of the budgets of the variances of total water and liquid water potential temperature and quantification of the contribution of several source and sink terms. Accretion is found to act as a strong sink for the variances, while the contributions from the processes of evaporation and autoconversion are small. A simple parametrization for the sink term connected to accretion is suggested and tested with a different set of simulations. 相似文献
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Svetlana A. Suleymanova Vera A. Izvekova Joanna M. Rankin N. Rathnasree 《Journal of Astrophysics and Astronomy》1998,19(1-2):1-18
The characteristics of the “burst” (B) mode and “quiescent” (Q) mode pulse sequences–long known from studies at or below 103
MHz–are identified at 430 MHz for the first time. An 18-minute, Polarimetrie observation begins with a long Bmode sequence,
which has a higher average intensity, regular drifting subpulses, and a preponderance of primary polarisationmode radiation.
An abrupt transition to a Q-mode sequence is then marked by a) weaker average intensity, but occasional very bright individual
subpulses, b) a complete cessation of drifting subpulses, with disorganized subpulses now being emitted over a much wider
longitude interval, and c) near parity between the primary and secondary polarisation modes, resulting in pronounced depolarisation,
both of individual pulses and the average profile.
Careful study, however, of profile changes before and after this mode change reveals slower variations which both anticipate
the abrupt transition and respond to it. A slow attenuation of the intensity level of the dominant component is observed throughout
the duration of the B-mode sequence, which then accelerates with the onset of the Q-mode sequence. This slow variation appears
to represent a “preswitching transition” process; and the combination of effects on slow and abrupt time scales are finally
responsible for the formation of the characteristic B and Q-mode average profiles. 相似文献
106.
Valery?IsidorovEmail author Vera?Vinogorova Krzysztof?Rafa?owski 《Journal of Atmospheric Chemistry》2005,50(3):263-278
A combination of solid-phase microextraction (SPME) and gas chromatography can be successfully used both for establishing the qualitative composition of volatile organic compounds (VOC) emitted by leaf litter and for determining their emission rates. Taking as an example European larch litter, it is shown that dead plant material contains considerable amounts of volatile components as well as non-volatile compounds that can be VOC precursors formed as a result of enzymatic reactions. It is proposed to include the determination of extractable compounds into the methodology of studying litter as a source of atmospheric VOC. Some data on litter mass are reported and it is concluded that this data may be included into special models for emission evaluation. In this work the distribution coefficients of monoterpene hydrocarbons between the gas phase and polydimethylsiloxane fiber coating necessary for quantitative determinations in SPME were estimated. 相似文献
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Silvia N. Césari Carlos O. Limarino Magdalena Llorens Mauro G. Passalia Valeria Pérez Loinaze Ezequiel I. Vera 《Journal of South American Earth Sciences》2011,31(4):426-431
The Baqueró Group holds a rich fossil flora including macrofloristic and palynological remains that characterize the Early Cretaceous vegetation of Argentina. The age of the upper part of the Group, known as Punta del Barco Formation, has been a topic of several discussions in the past. The type locality of this stratigraphic unit exposes fossiliferous tuffs together with muddy tuffs and tuffaceous sandstones beds. However, there have been no reliable age constraints for the fossil assemblages. 206Pb/238U analyses of zircon crystals yielded an age of 114.67 ± 0.18 Ma. This age control makes possible an improved analysis and comparison of the floras in the southern region. 相似文献
110.
The need for improved product quality in the aggregates industry is driving the search for greater automation in rock type
identification. In practice, reflectance spectra in visible and near-infrared light may reliably be used for the classification
of rock classes and their variants. Previous studies introduced statistical classification of six rock variants by means of
infrared spectra. The present investigation extends these studies to cover twelve rock types and variants of worldwide economic
importance. These were measured by visible and near-infrared light. Statistical classification of these spectra is highly
challenging due to the high number of groups and the high dimensionality of the data. In functional data analysis, spectra
are regarded as curves instead of vectors of characteristics. To obtain a compact form that is more susceptible to further
analysis, the spectra are represented by a B-spline basis. Two functional versions of linear support vector machines and penalized
functional discriminant analysis are considered for classification. The multiclass problem is addressed by margin trees and
by considering all one-against-one classifications combined with a voting strategy for testing. Since classification error
estimated by 5-fold cross-validation is very low, in particular for penalized discriminant analysis, we conclude that the
rock types can be classified reliably. 相似文献