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91.
Giorgio Riccardi 《Ocean Dynamics》2018,68(2):273-293
A new mathematical approach to kinematics and dynamics of planar uniform vortices in an incompressible inviscid fluid is presented. It is based on an integral relation between Schwarz function of the vortex boundary and induced velocity. This relation is firstly used for investigating the kinematics of a vortex having its Schwarz function with two simple poles in a transformed plane. The vortex boundary is the image of the unit circle through the conformal map obtained by conjugating its Schwarz function. The resulting analysis is based on geometric and algebraic properties of that map. Moreover, it is shown that the steady configurations of a uniform vortex, possibly in presence of point vortices, can be also investigated by means of the integral relation. The vortex equilibria are divided in two classes, depending on the behavior of the velocity on the boundary, measured in a reference system rotating with this curve. If it vanishes, the analysis is rather simple. However, vortices having nonvanishing relative velocity are also investigated, in presence of a polygonal symmetry. In order to study the vortex dynamics, the definition of Schwarz function is then extended to a Lagrangian framework. This Lagrangian Schwarz function solves a nonlinear integrodifferential Cauchy problem, that is transformed in a singular integral equation. Its analytical solution is here approached in terms of successive approximations. The self-induced dynamics, as well as the interactions with a point vortex, or between two uniform vortices are analyzed. 相似文献
92.
Giorgio Spada 《Surveys in Geophysics》2017,38(1):153-185
Glacial isostatic adjustment (GIA) encompasses a suite of geophysical phenomena accompanying the waxing and waning of continental-scale ice sheets. These involve the solid Earth, the oceans and the cryosphere both on short (decade to century) and on long (millennia) timescales. In the framework of contemporary sea-level change, the role of GIA is particular. In fact, among the processes significantly contributing to contemporary sea-level change, GIA is the only one for which deformational, gravitational and rotational effects are simultaneously operating, and for which the rheology of the solid Earth is essential. Here, I review the basic elements of the GIA theory, emphasizing the connections with current sea-level changes observed by tide gauges and altimetry. This purpose is met discussing the nature of the “sea-level equation” (SLE), which represents the basis for modeling the sea-level variations of glacial isostatic origin, also giving access to a full set of geodetic variations associated with GIA. Here, the SLE is employed to characterize the remarkable geographical variability of the GIA-induced sea-level variations, which are often expressed in terms of “fingerprints”. Using harmonic analysis, the spatial variability of the GIA fingerprints is compared to that of other components of contemporary sea-level change. In closing, some attention is devoted to the importance of the “GIA corrections” in the context of modern sea-level observations, based on tide gauges or satellite altimeters. 相似文献
93.
Armando Bazzani Stefano Marmi Giorgio Turchetti 《Celestial Mechanics and Dynamical Astronomy》1989,47(4):333-359
We prove that non resonant isochronous symplectic maps in a neighborhood of an elliptic fixed point are stable for exponentially long times with the inverse of the distance from the fixed point. In the proof we make use of the majorant series method together with an idea for optimizing remainder estimates first applied to Hamiltonian problems by Nekhoroshev. 相似文献
94.
The influence of streambed sediment clogging on macroinvertebrate communities was investigated in the Lemme creek (NW Italy). To assess how fine sediment accumulation can influence the colonisation process and community composition of macroinvertebrates, we placed 48 traps in the riverbed. The traps consisted of boxes built with metal net (mesh 1 cm, height 15 cm, sides 5 cm) covered with nylon net except for the apex, allowing access exclusively from the top. We created four trap types filled with 100% gravel, 30% sand and 70% gravel, 70% sand and 30% gravel and 100% sand. After 20 and 40 days, we removed 6 traps/type. Macroinvertebrates rapidly colonised the traps, as we found no significant community differences between the two removal dates. Among the four trap types, we found significant differences in taxa number and abundance, which both decreased with increasing clogging. Thus, our study supports the hypothesis that clogging and the accumulation of fine substratum elements strongly affects benthic stream communities. 相似文献
95.
An incentive mechanism for reducing emissions from conversion of intact and non-intact forests 总被引:1,自引:0,他引:1
Danilo Mollicone Frédéric Achard Sandro Federici Hugh D. Eva Giacomo Grassi Alan Belward Frank Raes Günther Seufert Hans-Jürgen Stibig Giorgio Matteucci Ernst-Detlef Schulze 《Climatic change》2007,83(4):477-493
This paper presents a new accounting mechanism in the context of the UNFCCC issue on reducing emissions from deforestation
in developing countries, including technical options for determining baselines of forest conversions. This proposal builds
on the recent scientific achievements related to the estimation of tropical deforestation rates and to the assessment of ‘intact’
forest areas. The distinction between ‘intact’ and ‘non intact’ forests used here arises from experience with satellite-based
deforestation measurements and allows accounting for carbon losses from forest degradation. The proposed accounting system
would use forest area conversion rates as input data. An optimal technical solution to set baselines would be to use historical
average figures during the time period from 1990 to 2005. The system introduces two different schemes to account for preserved
carbon: one for countries with high forest conversion rates where the desired outcome would be a reduction in their rates,
and another for countries with low rates. A ‘global’ baseline rate would be used to discriminate between these two country
categories (high and low rates). For the hypothetical accounting period 2013–2017 and considering 72% of the total tropical
forest domain for which data are available, the scenario of a 10% reduction of the high rates and of the preservation of low
rates would result in approximately 1.6 billion tCO2 of avoided emissions. The resulting benefits of this reduction would be shared between those high-rate countries which reduced
deforestation and those low-rate countries which did not increase their deforestation over an agreed threshold (e.g., half
of “global” baseline rate). 相似文献
96.
Giorgio E. O. Giacaglia 《Celestial Mechanics and Dynamical Astronomy》1975,12(4):519-520
Using Sylvester's theorem on matrices, an elegant expression is obtained for the solutions of the restricted problem of three bodies in the neighborhood of the equilibrium points. 相似文献
97.
A comparison between the single ring pressure infiltrometer and simplified falling head techniques
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Testing the relative performances of the single ring pressure infiltrometer (PI) and simplified falling head (SFH) techniques to determine the field saturated soil hydraulic conductivity, Kfs, at the near point scale may help to better establish the usability of these techniques for interpreting and simulating hydrological processes. A sampling of 10 Sicilian sites showed that the measured Kfs was generally higher with the SFH technique than the PI one, with statistically significant differences by a factor varying from 3 to 192, depending on the site. A short experiment with the SFH technique yielded higher Kfs values because a longer experiment with the PI probably promoted short‐term swelling phenomena reducing macroporosity. Moreover, the PI device likely altered the infiltration surface at the beginning of the run, particularly in the less stable soils, where soil particle arrangement may be expected to vary upon wetting. This interpretation was supported by a soil structure stability index, SSI, and also by the hydraulic conductivity data obtained with the tension infiltrometer, i.e. with a practically negligible disturbance of the sampled soil surface. In particular, a statistically significant, increasing relationship with SSI and an unsaturated conductivity greater than the saturated one were only detected for the Kfs data obtained with the PI. The SFH and PI techniques should be expected to yield more similar results in relatively rigid porous media (low percentages of fine particles and structurally stable soils) than in soils that modify appreciably their particle arrangement upon wetting. The simultaneous use of the two techniques may allow to improve Kfs determination in soils that change their hydrodynamic behaviour during a runoff producing rainfall event. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
98.
Potential evidence for slab detachment from the flexural backstripping of a foredeep: Insight on the evolution of the Pescara basin (Italy)
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Paolo Mancinelli Cristina Pauselli Giorgio Minelli Massimiliano R. Barchi Guy Simpson 《地学学报》2018,30(3):222-232
The discrepancy between the size of the Apenninic chain and the depth of the Adriatic foredeep is investigated using 2D flexural backstripping on well‐constrained depth‐converted cross‐sections in the Pescara basin (Central Italy). The procedure consisted of removal, uplift, unfolding and unfaulting of the Pliocene–Pleistocene foreland deposits to produce a palaeogeographic map of the basin at the end of the Messinian and to constrain sedimentary rates since the Miocene. Results are found to support the contribution of an external load to the foreland evolution together with the Apenninic chain load. The interplay of the two types of loads resulted in spatial and temporal variations of the foredeep evolution that are quantified by palaeogeographic maps and sedimentation rates obtained through backstripping. Results are interpreted as representing the effects of a southward‐migrating wave linked to slab detachment beneath the Adriatic foredeep. This procedure can be useful to investigate similar problems on other chains worldwide. 相似文献
99.
Paula M. Carreira José M. Marques M. Rosário Carvalho Giorgio Capasso Fausto Grassa 《Journal of Volcanology and Geothermal Research》2010,189(1-2):49-56
Na–HCO3–CO2-rich thermomineral waters issue in the N of Portugal, within the Galicia-Trás-os-Montes region, linked to a major NNE-trending fault, the so-called Penacova-Régua-Verin megalineament. Along this tectonic structure different occurrences of CO2-rich thermomineral waters are found: Chaves hot waters (67 °C) and also several cold (16.1 °C) CO2-rich waters. The δ2H and δ18O values of the thermomineral waters are similar to those of the local meteoric waters. The chemical composition of both hot and cold mineral waters suggests that water–rock reactions are mainly controlled by the amount of dissolved CO2 (g) rather than by the water temperature. Stable carbon isotope data indicate an external CO2 inorganic origin for the gas. δ13CCO2 values ranging between ? 7.2‰ and ? 5.1‰ are consistent with a two-component mixture between crustal and mantle-derived CO2. Such an assumption is supported by the 3He/4He ratios measured in the gas phase, are between 0.89 and 2.68 times the atmospheric ratio (Ra). These ratios which are higher than that those expected for a pure crustal origin (≈ 0.02 Ra), indicating that 10 to 30% of the He has originated from the upper mantle. Release of deep-seated fluids having a mantle-derived component in a region without recent volcanic activity indicates that extensive neo-tectonic structures originating during the Alpine Orogeny are still active (i.e., the Chaves Depression). 相似文献
100.
Marco Bertolino Barbara Calcinai Riccardo Cattaneo‐Vietti Carlo Cerrano Anna Lafratta Maurizio Pansini Daniela Pica Giorgio Bavestrello 《Marine Ecology》2014,35(2):149-158
The Mediterranean coralligenous substratum is a hard bottom of biogenic origin, mainly composed of calcareous algae, growing in dim light conditions. Sponges are among of the most representative taxa of the coralligenous assemblages, with more than 300 recorded species of different habits: massive, erect, boring and insinuating. When sponges die, their siliceous spicules remain trapped in the biogenic concretion, offering the opportunity to describe the coralligenous spongofauna over a very long span of time, virtually dating back to a large part of the Holocene period. The data reported here were obtained from core samples collected from four coralligenous concretions. Each block was collected in a different locality of the Ligurian Sea: Santo Stefano Shoals, Bogliasco, Punta del Faro (Portofino Promontory) and Punta Manara. Radiocarbon age determinations indicate for these conglomerates a maximal age between 1600 and 3100 years. The spicules trapped in the cores show deep dissolution marks in the form of circular holes on their surface or present an enlargement of the axial canal. However, their original shape, generally intact, suggests the absence of mechanical injuries and allows a tentative identification at the species level. The analysis of these old spicules reveals an ancient sponge assemblage composed of 30 recognisable species. This indicates that almost one half of the sponge community today settled on coralligenous substrata has been present in the conglomerates for their entire existence. 相似文献