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201.
Fire regime changes in the Western Mediterranean Basin: from fuel-limited to drought-driven fire regime 总被引:2,自引:0,他引:2
Wildfires are an integral part of Mediterranean ecosystems; humans impact on landscapes imply changes in fuel amount and continuity, and thus in fire regime. We tested the hypothesis that fire regime changed in western Mediterranean Basin during the last century using time series techniques. We first compiled a 130-year fire history for the Valencia province (Spain, Eastern Iberian Peninsula, Western Mediterranean Basin) from contemporary statistics plus old forest administration dossiers and newspapers. We also compiled census on rural population and climatic data for the same period in order to evaluate the role of climate and human-driven fuel changes on the fire regime change. The result suggested that there was a major fire regime shift around the early 1970s in such a way that fires increased in annual frequency (doubled) and area burned (by about an order of magnitude). The main driver of this shift was the increase in fuel amount and continuity due to rural depopulation (vegetation and fuel build-up after farm abandonment) suggesting that fires were fuel-limited during the pre-1970s period. Climatic conditions were poorly related to pre-1970s fires and strongly related to post-1970s fires, suggesting that fire are currently less fuel limited and more drought-driven than before the 1970s. Thus, the fire regime shift implies also a shift in the main driver for fire activity, and this has consequences in the global change agenda. 相似文献
202.
M. J. Matias J. M. Marques P. Figueiredo M. J. Basto M. M. Abreu P. M. Carreira C. Ribeiro A. Flambó J. Feliciano E. M. Vicente 《Environmental Geology》2009,56(6):1227-1235
Santa Margarida Military Camp (S.M.M.C.) is the only one Portuguese military training area, including firing ranges for tactical
military manoeuvres of mechanised divisions. For this reason, various negative effects on the environment were expected due
to the military activities, as the Military Camp’s area is classified as a high vulnerability area to pollution of its multilayer
porous aquifers. The aim of this study was to identify and characterise local/regional geochemical impacts caused by the continuing
military training activities performed at S.M.M.C. in the course of 52 years. An overview of the geochemical research issues
as a basis for risk assessment is presented. A special attention has been put on the quality of local and regional surface
waters, shallow groundwaters and groundwaters. Local soils and sediments as well as fragments of shells and bullets were sampled
and analysed. The results so far obtained, indicated that none pollution effects were a consequence of the military training
activities. Till now, the geochemical signatures such as, high levels of K, Cl and NO3 in waters, detected in particular sites, should be faced as tracers of diffuse pollution ascribed to urban waste disposal
and cattle breading. 相似文献
203.
The present-day topography of the Iberian peninsula can be considered as the result of the Mesozoic–Cenozoic tectonic evolution of the Iberian plate (including rifting and basin formation during the Mesozoic and compression and mountain building processes at the borders and inner part of the plate, during the Tertiary, followed by Neogene rifting on the Mediterranean side) and surface processes acting during the Quaternary. The northern-central part of Iberia (corresponding to the geological units of the Duero Basin, the Iberian Chain, and the Central System) shows a mean elevation close to one thousand meters above sea level in average, some hundreds of meters higher than the southern half of the Iberian plate. This elevated area corresponds to (i) the top of sedimentation in Tertiary terrestrial endorheic sedimentary basins (Paleogene and Neogene) and (ii) planation surfaces developed on Paleozoic and Mesozoic rocks of the mountain chains surrounding the Tertiary sedimentary basins. Both types of surfaces can be found in continuity along the margins of some of the Tertiary basins. The Bouguer anomaly map of the Iberian peninsula indicates negative anomalies related to thickening of the continental crust. Correlations of elevation to crustal thickness and elevation to Bouguer anomalies indicate that the different landscape units within the Iberian plate can be ascribed to different patterns: (1) The negative Bouguer anomaly in the Iberian plate shows a rough correlation with elevation, the most important gravity anomalies being linked to the Iberian Chain. (2) Most part of the so-called Iberian Meseta is linked to intermediate-elevation areas with crustal thickening; this pattern can be applied to the two main intraplate mountain chains (Iberian Chain and Central System) (3) The main mountain chains (Pyrenees and Betics) show a direct correlation between crustal thickness and elevation, with higher elevation/crustal thickness ratio for the Central System vs. the Betics and the Pyrenees. Other features of the Iberian topography, namely the longitudinal profile of the main rivers in the Iberian peninsula and the distribution of present-day endorheic areas, are consistent with the Tertiary tectonic evolution and the change from an endorheic to an exorheic regime during the Late Neogene and the Quaternary. Some of the problems involving the timing and development of the Iberian Meseta can be analysed considering the youngest reference level, constituted by the shallow marine Upper Cretaceous limestones, that indicates strong differences induced by (i) the overall Tertiary and recent compression in the Iberian plate, responsible for differences in elevation of the reference level of more than 6 km between the mountain chains and the endorheic basins and (ii) the effect of Neogene extension in the Mediterranean margin, responsible for lowering several thousands of meters toward the East and uplift of rift shoulders. A part of the recent uplift within the Iberian plate can be attributed of isostatic uplift in zones of crustal thickening. 相似文献
204.
Vicente G. Ruiz de Argandoa Lope Calleja ngel Rodríguez-Rey Luis Miguel Surez del Río Carmen Celorio 《Engineering Geology》2009,103(3-4):69-75
X-ray Computed Tomography (X-ray CT) has been used to study the petrophysical characteristics of a Jurassic sandstone from Asturias (Northern Spain) used as building stone in several monuments in the region. CT monitoring of water capillarity tests has made it possible to visualize the movement of water inside the samples, to relate this movement with texture characteristics, and to measure the height reached in successive images, thereby determining the capillary penetration coefficient; based on this coefficient, the effective capillary pore radius has also been estimated. An advantage of the use of CT is that, as the information comes from the sample interior, border effects that can be generated in the external faces can be avoided.The CT was also used to visualize how a commercial organosilicon consolidant penetrates inside the rock by means of capillarity, a usual way of consolidant application in stone restoration processes. The coefficient of capillary penetration of the product, determined on the basis of the measurements made on the tomographic images, is 53% less than that of water. The influence of rock texture characteristics on the capillarity both of the consolidant and the water was also observed.The samples underwent CT water capillarity studies before and after the consolidant application, proving that the treatment improves the rock's hydric properties. The coefficient of capillary penetration decreased by 24% following the application of the consolidant, whereas the effective pore radius decreased by more than 40%. 相似文献
205.
Juan Carlos Afonso Giorgio Ranalli Manel Fernàndez William L. Griffin Suzanne Y. O'Reilly Ulrich Faul 《Earth and Planetary Science Letters》2010,289(3-4):606-618
We use thermodynamically self-consistent and hybrid methods to analyze the correlation of important physical parameters (e.g. bulk density, elastic moduli) with bulk Mg# and modal composition in mantle peridotites at upper mantle conditions. Temperature (anharmonic and anelastic), pressure and compositional derivatives for all these parameters are evaluated. The results show that the widely used correlations between Vp/Vs and Mg# in peridotites are strictly valid only for garnet-bearing assemblages at temperatures < 900 °C. The correlation breaks down when: i) spinel is the stable Al-rich phase in the assemblage and ii) when anelastic attenuation of seismic velocities becomes important (T ? 900 °C). This implies that the range of applicability of published Vp/Vs–Mg# correlations for the upper mantle is limited to a depth interval between the spinel–garnet phase transition and the 900 °C isotherm. We use numerical simulations to show that this depth interval is virtually nonexistent in lithospheres thinner than ~ 140 km and can comprise up to ~ 50% of the lithospheric mantle in thick (> 220 km) lithospheric domains. In addition, we show that for most of the upper mantle the expected Δ(Vp/Vs) values associated with compositional variations are smaller than the resolution limit of current seismological methods. All these considerations suggest that the Vp/Vs ratio is not a reliable measure of compositional variations and that for large parts of the upper mantle compositional anomalies cannot be separated from thermal anomalies on the basis of seismological studies only. We further confirm that the only reliable indicator of compositional anomalies in a peridotitic mantle is the ratio of density to shear wave velocities (ρ/Vs). Our results demonstrate that geophysical–petrological models (forward or inverse) that model these two fields (i.e. density and Vs) self-consistently within a robust thermodynamic framework are necessary for characterizing the small-scale thermal and compositional structure of the lithosphere and sublithospheric upper mantle. 相似文献
206.
Sediment resuspension in two adjacent shallow coastal lakes: controlling factors and consequences on phosphate dynamics 总被引:1,自引:0,他引:1
Inmaculada de Vicente Luis Cruz-Pizarro Francisco J. Rueda 《Aquatic Sciences - Research Across Boundaries》2010,72(1):21-31
A combination of field measurements, modelling and laboratory experiments was used to evaluate the potential impact of sediment
resuspension on phosphorus (P) dynamics. The study was carried out in two adjacent shallow coastal lakes (Lake Honda and Lake
Nueva) which, due to their geographic proximity (only 200 m apart), are subject to equal meteorological forcing and represent
ideal systems to study how morphometry and sediment properties relate to wind events. The focusing factors (a measure of the
fluxes of sediment into the water column through resuspension) estimated by comparing settling fluxes measured in surface
sediment traps with those measured in bottom traps, were significantly larger (approximately 34% larger) in Lake Honda (LH;
1.18) than in Lake Nueva (LN; 0.88). Our model estimates of resuspension fluxes (E) were also ca. 40% larger in LH than in LN, in agreement with the observed focusing factors. The larger resuspension fluxes
encountered in LH, in comparison with LN, can mainly be explained by differences in lake morphometry. Still, they could arise
from differences in grain size distribution or in benthic algae concentration encountered in the lake sediments. By means
of adsorption experiments in the laboratory, we show that resuspension events will have different effects on P-dynamics in
LH and LN. While the resuspended material from LH tends to adsorb phosphate (PO4
3−), removing it from the water column, in LN the resuspended sediments tend to increase the availability of PO4
3− in solution. These differences arise from (1) higher concentrations of PO4
3− in water in LH compared to LN; and (2) larger PO4
3−adsorption capacity of the LH sediments as a result of the more abundant iron oxyhydroxides and clay. 相似文献
207.
Stéphane Homke Jaume Vergés Peter Van Der Beek Manel Fernàndez Eduard Saura Luis Barbero Balazs Badics Erika Labrin 《Basin Research》2010,22(5):659-680
We present the first fission‐track (FT) thermochronology results for the NW Zagros Belt (SW Iran) in order to identify denudation episodes that occurred during the protracted Zagros orogeny. Samples were collected from the two main detrital successions of the NW Zagros foreland basin: the Palaeocene–early Eocene Amiran–Kashkan succession and the Miocene Agha Jari and Bakhtyari Formations. In situ bedrock samples were furthermore collected in the Sanandaj‐Sirjan Zone. Only apatite fission‐track (AFT) data have been successfully obtained, including 26 ages and 11 track‐length distributions. Five families of AFT ages have been documented from analyses of in situ bedrock and detrital samples: pre‐middle Jurassic at ~171 and ~225 Ma, early–late Cretaceous at ~91 Ma, Maastrichtian at ~66 Ma, middle–late Eocene at ~38 Ma and Oligocene–early Miocene at ~22 Ma. The most widespread middle–late Eocene cooling phase, around ~38 Ma, is documented by a predominant grain‐age population in Agha Jari sediments and by cooling ages of a granitic boulder sample. AFT ages document at least three cooling/denudation periods linked to major geodynamic events related to the Zagros orogeny, during the late Cretaceous oceanic obduction event, during the middle and late Eocene and during the early Miocene. Both late Cretaceous and early Miocene orogenic processes produced bending of the Arabian plate and concomitant foreland deposition. Between the two major flexural foreland episodes, the middle–late Eocene phase mostly produced a long‐lasting slow‐ or nondepositional episode in the inner part of the foreland basin, whereas deposition and tectonics migrated to the NE along the Sanandaj‐Sirjan domain and its Gaveh Rud fore‐arc basin. As evidenced in this study, the Zagros orogeny was long‐lived and multi‐episodic, implying that the timing of accretion of the different tectonic domains that form the Zagros Mountains requires cautious interpretation. 相似文献
208.
Michel Michaelovitch de Mahiques Ilana Klein Coaracy Wainer Leticia Burone Renata Nagai Silvia Helena de Mello e Sousa Rubens Cesar Lopes Figueira Ilson Carlos Almeida da Silveira Mrcia Caruso Bícego Daniel Pavani Vicente Alves
yvind Hammer 《Quaternary International》2009,206(1-2):52
A high-resolution, multi-proxy record has been used to determine the environmental changes during the Holocene on the southern Brazilian shelf. Present oceanographic conditions reveal wind and freshwater input as the determinants of short-term productivity changes in the study area. Magnetic susceptibility and grain-size variations, together with proxies of productivity (organic carbon, carbon accumulation rate, Ba, Sr, and Ca content, Ba/Al, Ba/Ti, and Al/Ti ratios) were analyzed and compared with proxies of redox condition (V/Ti ratio), terrigenous input (Fe/Ca and Ti/Ca ratios), as well as other Element/Ti ratios, to evaluate the paleoceanographic and paleoclimatic changes over the period.The core covers a time interval of about 7650 years, with sedimentation rates varying from 0.025 to 0.250 cm a−1, which represent time intervals of between 8 and 80 a per sample. There is a clear change in the sedimentation rate at about 2800 B.P.All grain-size and elemental results indicate the occurrence of conspicuous changes between 5200 and 5000 cal. B.P., as well as between 3000 and 2800 cal. B.P. A comparison of the results with the palynological information available from the adjacent continental areas suggests that the sedimentary changes in this last interval may be correlated with the onset of modern climatic conditions in South America, and especially, with the onset of the Plata Plume Water, a water mass that carries cold, less saline waters towards the north. However, minor changes are observed at ca. 1500 B.P. and are correlated with an increase in the atmospheric humidity. Furthermore, a time-series analysis undertaken using several proxies indicated the occurrence of Sub-Milankovitch cycles, which may be compared with those reported worldwide. 相似文献
209.
José R. Martínez Catalán Ricardo Arenas Jacobo Abati Sonia Sánchez Martínez Florentino Díaz García Javier Fernández Suárez Pablo González Cuadra Pedro Castiñeiras Juan Gómez Barreiro Alejandro Díez Montes Emilio González Clavijo Francisco J. Rubio Pascual Pilar Andonaegui Teresa E. Jeffries James E. Alcock Rubén Díez Fernández Alicia López Carmona 《Comptes Rendus Geoscience》2009,341(2-3):114-126
Ophiolites of different Paleozoic ages occur in North-West (NW) Iberia in a rootless suture representing the remnants of the Rheic Ocean. Associated allochthonous terranes in the hanging- and foot-walls of the suture derive from the former margins, whereas the relative autochthon corresponds to the Paleozoic passive margin of northern Gondwana. The Paleozoic tectonic evolution of this part of the circum-Atlantic region is deduced from the stratigraphical, petrological, structural and metamorphic evolution of the different units and their ages. The tectonic reconstruction covers from Cambro-Ordovician continental rifting and the opening of the Rheic Ocean to its Middle to Upper Devonian closure. Then, the Variscan Laurussia–Gondwana convergence and collision is briefly described, from its onset to the late stages of collapse associated with the demise of the orogenic roots. 相似文献
210.
Antonio Algaba Fernando Fernández-Sánchez Manuel Merino Alejandro J. Rodríguez-Luis 《Theoretical and Applied Climatology》2016,126(3-4):797-799
The paper, “Study on the reliable computation time of the numerical model using the sliding temporal correlation method,” was published in Theoretical and Applied Climatology. In that work, the sliding temporal correlation analysis is employed to investigate the predictable time of two typical chaotic numerical models, namely the Lorenz system and the Chen chaotic system. However, it has been recently shown by us when using a linear scaling in time and state variables that generically, the Chen system is only a particular case of the Lorenz system, with time reversion if the parameter c is positive. Consequently, to study the Chen chaotic system is simply to consider the Lorenz system integrated backwards. 相似文献