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71.
The Chirripó hydrological research site (CHRS) is located within the Chirripó National Park, Costa Rica (between 3100 and 3820 m asl) whereby ~100 km2 are covered by Páramo, a high-elevation tropical grassland ecosystem. A lake district with approximately 30 lakes of glacial origin is also protected in this area. The CHRS has been monitored since April 2015 with the aim of establishing the first water isotope baseline for the Central American Páramo. At a regional scale, the water isotope ratios (δ2H and δ18O) in precipitation and surface water at CHRS are useful for describing the governing moisture transport from the Caribbean Sea and Pacific Ocean and the complex rainfall producing systems across the N–S mountain range of Central America. These data are also providing unique information about the evaporation and water balance conditions of tropical glacial lakes and the formation of orographic and convective precipitation in high-elevation tropical ecosystems. Current data sets from CHRS include continuous lake water temperature and meteorological conditions (i.e., precipitation amount, air temperature and relative humidity), as well as water stable isotopes in precipitation, stream water, and lake water (daily to biweekly sampling frequency). Stream water is collected at several locations across the topographic gradient whereas lake water is sampled in the three main lake systems of CHRS. CHRS serves as a reference site for conducting pilot isotopic research in high-elevation ecosystems to advance the atmospheric, hydrogeological and ecohydrological studies in these understudied biomes. All data from April 2015 to November 2020 are publicly available. 相似文献
72.
Luca Olmi Pietro Bolli Luca Cresci Francesco D’Agostino Massimo Migliozzi Daniela Mugnai Enzo Natale Renzo Nesti Dario Panella Lorenzo Stefani 《Experimental Astronomy》2017,43(3):285-309
The concept of super-resolution refers to various methods for improving the angular resolution of an optical imaging system beyond the classical diffraction limit. Although several techniques to narrow the central lobe of the illumination Point Spread Function have been developed in optical microscopy, most of these methods cannot be implemented on astronomical telescopes. A possible exception is represented by the variable transmittance filters, also known as “Toraldo Pupils” (TPs) since they were introduced for the first time by G. Toraldo di Francia in 1952 (Toraldo di Francia, Il Nuovo Cimento (Suppl.) 9, 426, 1952). In the microwave range, the first successful laboratory test of TPs was performed in 2003 (Mugnai et al. Phys. Lett. A 311, 77–81, 2003). These first results suggested that TPs could represent a viable approach to achieve super-resolution in Radio Astronomy. We have therefore started a project devoted to a more exhaustive analysis of TPs, in order to assess their potential usefulness to achieve super-resolution on a radio telescope, as well as to determine their drawbacks. In the present work we report on the results of extensive microwave measurements, using TPs with different geometrical shapes, which confirm the correctness of the first experiments in 2003. We have also extended the original investigation to carry out full-wave electromagnetic numerical simulations and also to perform planar scanning of the near-field and transform the results into the far-field. 相似文献
73.
Rosalba Napoli Gilda Currenti Ciro Del Negro Agnese Di Stefano Filippo Greco Enzo Boschi 《Bulletin of Volcanology》2011,73(9):1311-1322
Significant changes in the local magnetic field marked the resumption of eruptive activity at Stromboli volcano on February
27, 2007. After differential magnetic fields were obtained by filtering out external noise using adaptive filters and seasonal
thermal noise using temperature data, we identified step-like changes of 1–4 nT coincident with the opening of eruptive fissures
in the upper part of the Sciara del Fuoco. The magnetic variations detected at two stations are closely related to the propagation
of a shallow NE–SW magmatic intrusion extending beyond the summit craters area. These observations are consistent with those
calculated using piezomagnetic models in which stress-induced changes in rock magnetization are produced by the magmatic intrusion.
No significant magnetic changes were observed when the first fractures opened along the NE crater rim. Indeed, the stress-induced
magnetization caused by this magmatic activity is expected to be too low because of the structural weakness and/or thermal
state of the summit area. The continuous long-term decay characterizing the post-eruptive magnetic pattern can be related
to a time-dependent relaxation process. A Maxwell rheology was assumed and the temporal evolution of the piezomagnetic field
was evaluated. This allowed us to estimate the rheological properties of the medium; in particular, an average viscosity ranging
between 1016 and 1017 Pa⋅s was a relaxation time τ of about 38 days. 相似文献
74.
Paul Eccleston Bruce Swinyard Marcel Tessenyi Giovanna Tinetti Ingo Waldmann Marc Ferlet Ranah Irshad Tanya Lim Kevin Middleton Tom Bradshaw Martin Crook Tom Hunt Berend Winter Ian Bryson Naidu Bezawada William Taylor Neil Bowles Enzo Pascale Gianluca Morgante Emanuele Pace Alberto Adriani Jean-Michel Reess Marc Ollivier Roland Ottensamer Mirek Rataj Gonzalo Ramos Zapata Jan-Rutger Schrader Avri Selig Kate Isaak Martin Linder Ludovic Puig 《Experimental Astronomy》2015,40(2-3):427-447
75.
Saleem Zaroubi Enzo Branchini 《Monthly notices of the Royal Astronomical Society》2005,357(2):527-534
We introduce a simple linear equation relating the line-of-sight peculiar-velocity and density contrast correlation functions. The relation, which we call the Gaussian cell two-point 'energy-like' equation , is valid at the distant-observer limit and requires Gaussian smoothed fields. In the variance case, i.e. at zero lag, the equation is similar in its mathematical form to the Irvine–Layzer cosmic energy equation. β estimation with this equation from the Point Source Catalogue Redshift (PSC) survey and the SEcat catalogue of peculiar velocities is carried out, returning a value of β= 0.44 ± 0.08 . The applicability of the method for the 6dF galaxy redshift and peculiar motions survey is demonstrated with mock data where it is shown that β could be determined with ≈10 per cent accuracy. The prospects for constraining the dark energy equation of state with this method from the kinematic and thermal Sunyaev–Zel'dovich cluster surveys are discussed. The equation is also used to construct a non-parametric mass-density power-spectrum estimator from peculiar-velocity data. 相似文献
76.
77.
Adi Nusser Luiz N. da Costa Enzo Branchini Mariangela Bernardi M.V. Alonso Gary Wegner C. N. A. Willmer P. S. Pellegrini 《Monthly notices of the Royal Astronomical Society》2001,320(3):L21-L24
We present a comparison between the peculiar velocity field measured from the ENEAR all-sky D n – σ catalogue and that derived from the galaxy distribution of the IRAS Point Source Catalog Redshift Survey (PSC z ). The analysis is based on a modal expansion of these data in redshift space by means of spherical harmonics and Bessel functions. The effective smoothing scale of the expansion is almost linear with redshift reaching 1500 km s−1 at 3000 km s−1 . The general flow patterns in the filtered ENEAR and PSC z velocity fields agree well within 6000 km s−1 , assuming a linear biasing relation between the mass and the PSC z galaxies. The comparison allows us to determine the parameter where Ω is the cosmological density parameter and b is the linear biasing factor. A likelihood analysis of the ENEAR and PSC z modes yields in good agreement with values obtained from Tully–Fisher surveys. 相似文献
78.
79.
In the present study, the dissolution and mobilization of Ce introduced in a simulated nuclear waste glass (MW) as a surrogate of Pu was investigated after leaching in pure water over 12 a at 90 °C and pH ∼ 9.6. The microscopic distribution and oxidation state of Ce in the altered glass were studied using micro-X-ray fluorescence (micro-XRF) mapping techniques and micro-X-ray near-edge absorption spectroscopy (micro-XANES). Distribution maps of CeIII and CeIV were obtained by recording the Lα fluorescence emission at two different incident X-ray energies, coinciding with the maximum contrast between CeIII and CeIV fluorescence intensities. The micro-XRF maps revealed that Ce was dominantly present as oxidized species (CeIV) in the original glass. After dissolution from the glass matrix, CeIV was partly reduced and re-immobilized as CeIII at grain boundaries or in the interstitial spaces between the glass particles. The concentration of CeIII was found to correlate with the spatial distribution of secondary Mg-clay formed during the aqueous corrosion as the main glass alteration product. Micro-XANES spectra collected at locations representative of both altered and non-altered glass domains confirmed the findings obtained by the redox mapping. Because redox-sensitive elements in the pristine MW glass (Fe, Cr, Se) occur almost exclusively as oxidized species, reduction of CeIV was probably mediated by an external source of reductants, such as Fe(0) from the steel reaction vessel. 相似文献
80.
Lapo Boschi 《Geophysical Journal International》2006,167(1):238-252
I invert a large set of teleseismic phase-anomaly observations, to derive tomographic maps of fundamental-mode surface wave phase velocity, first via ray theory, then accounting for finite-frequency effects through scattering theory, in the far-field approximation and neglecting mode coupling. I make use of a multiple-resolution pixel parametrization which, in the assumption of sufficient data coverage, should be adequate to represent strongly oscillatory Fréchet kernels. The parametrization is finer over North America, a region particularly well covered by the data. For each surface-wave mode where phase-anomaly observations are available, I derive a wide spectrum of plausible, differently damped solutions; I then conduct a trade-off analysis, and select as optimal solution model the one associated with the point of maximum curvature on the trade-off curve. I repeat this exercise in both theoretical frameworks, to find that selected scattering and ray theoretical phase-velocity maps are coincident in pattern, and differ only slightly in amplitude. 相似文献