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991.
Abstract The measurement of radiation fluxes suffers from inaccuracies at low solar elevations and this poses a problem for determining the snow albedo at high latitudes. From the data of Resolute, NWT, three situations were observed: (1) an often‐reported situation when albedo decreases with increasing solar elevation, (2) an inverse situation when albedo increases with increasing solar elevation and (3) no obvious relationship. There were also cases when albedo exceeded 100%. The possible causes for such anomalous conditions or for erroneous albedos include instrument response deviating from the cosine law, instrument tilt, sensing of the sun by the inverted pyranometer and change in the spectral quality of incoming radiation with changing solar height. However, omission of the radiation values measured during the period of low solar elevation will not seriously affect the prediction of snowmelt. In this note, we have identified the anomalies and suggested possible causes; but further investigations are required to verify the causative mechanisms. 相似文献
992.
Abstract Evaluating horizontal gradients in three‐dimensional shallow water models that use bottom‐following sigma coordinates can lead to large errors near steep bathymetry. A technique that has been proposed to minimize this problem involves computing horizontal gradients in cartesian coordinates, while treating all other terms in a sigma coordinate framework. We study this technique through both truncation error analysis and numerical experimentation, and compare it to the direct application of sigma coordinates. While the Cartesian coordinate method has better convergence properties and generally smaller truncation errors when horizontal gradients are zero, the sigma coordinate method can be more accurate in other physically relevant situations. Also, the Cartesian coordinate method introduces significant numerical diffusion of variable sign near the bottom (where physical diffusion is particularly small), thus potentially leading to instabilities. Overall, we consider the sigma coordinates to be the best approach. 相似文献
993.
Andrews José de Lucena Otto Corrêa Rotunno Filho José Ricardo de Almeida França Leonardo de Faria Peres Luciano Nóbrega Rodrigues Xavier 《Theoretical and Applied Climatology》2013,111(3-4):497-511
This paper aims to map the thermal field in the metropolitan region of Rio de Janeiro (MARJ) considering the atmospheric characteristics and the land use that contribute to understanding the urban heat island. Three thermal maps are defined through the use of Landsat5-TM satellite images for three winter events chosen for the decades of 1980, 1990, and 2000, respectively. The results reveal a concentration of warmer cores in urban central areas as well as some local warmer areas in suburban region. Sites with lower temperatures correspond to vegetated areas which are away from the central part of the MARJ, including points of suburban areas. This work emphasizes the importance of the combined analysis of surface temperature with land use and atmospheric conditions, depicting a distinct pattern of heat islands for tropical climate. 相似文献
994.
René Laprise Leticia Hernández-Díaz Kossivi Tete Laxmi Sushama Leo Šeparović Andrey Martynov Katja Winger Michel Valin 《Climate Dynamics》2013,41(11-12):3219-3246
Following the CORDEX experimental protocol, climate simulations and climate-change projections for Africa were made with the new fifth-generation Canadian Regional Climate Model (CRCM5). The model was driven by two Global Climate Models (GCMs), one developed by the Max-Planck-Institut für Meteorologie and the other by the Canadian Centre for Climate Modelling and Analysis, for the period 1950–2100 under the RCP4.5 emission scenario. The performance of the CRCM5 simulations for current climate is discussed first and compared also with a reanalysis-driven CRCM5 simulation. It is shown that errors in lateral boundary conditions and sea-surface temperature from the GCMs have deleterious consequences on the skill of the CRCM5 at reproducing specific regional climate features such as the West African Monsoon and the annual cycle of precipitation. For other aspects of the African climate however the regional model is able to add value compared to the simulations of the driving GCMs. Climate-change projections for periods until the end of this century are also analysed. All models project a warming throughout the twenty-first century, although the details of the climate changes differ notably between model projections, especially for precipitation changes. It is shown that the climate changes projected by CRCM5 often differ noticeably from those of the driving GCMs. 相似文献
995.
José C. Aponte Jason P. Dworkin Jamie E. Elsila 《Meteoritics & planetary science》2015,50(10):1733-1749
The CI1 Orgueil meteorite is a highly aqueously altered carbonaceous chondrite. It has been extensively studied, and despite its extensive degree of aqueous alteration and some documented instances of contamination, several indigenous organic compounds including amino acids, carboxylic acids, and nucleobases have been detected in its carbon‐rich matrix. We recently developed a novel gas chromatographic method for the enantiomeric and compound‐specific isotopic analyses of meteoritic aliphatic monoamines in extracts and have now applied this method to investigate the monoamine content in Orgueil. We detected 12 amines in Orgueil, with concentrations ranging from 1.1 to 332 nmol g?1 of meteorite and compared this amine content in Orgueil with that of the CM2 Murchison meteorite, which experienced less parent‐body aqueous alteration. Methylamine is four times more abundant in Orgueil than in Murchison. As with other species, the amine content in Orgueil extracts shows less structural diversity than that in Murchison extracts. We measured the compound‐specific stable carbon isotopic ratios (δ13C) for 5 of the 12 monoamines detected in Orgueil and found a range of δ13C values from –20 to +59‰. These δ13C values fall into the range of other meteoritic organic compounds, although they are 13C‐depleted relative to their counterparts extracted from the Murchison meteorite. In addition, we measured the enantiomeric composition for the chiral monoamines (R)‐ and (S)‐sec‐butylamine in Orgueil, and found it was racemic within experimental error, in contrast with the l ‐enantiomeric excess found for its amino acid structural analog isovaline. The racemic nature of sec‐butylamine in Orgueil was comparable to that previously observed in Murchison, and to other CM2 and CR2 carbonaceous chondrites measured in this work (ALH 83100 [CM1/2], LON 94101 [CM2], LEW 90500 [CM2], LAP 02342 [CR2], and GRA 95229 [CR2]). These results allow us to place some constraints on the effects of aqueous alteration observed over the monoamine concentrations in Orgueil and Murchison, and to evaluate the primordial synthetic relationships between meteoritic monoamines and amino acids. 相似文献
996.
Sediment production and accumulation on shallow carbonate platforms are controlled by allogenic, externally controlled processes
(such as sea level, climate, and/or platform-wide subsidence patterns) as well as by autogenic factors that are inherent to
the sedimentary system (such as lateral migration of sediment bodies). The challenge is to determine how and in which proportion
these processes interacted to create the observed sedimentary record. Here, a case study of Middle Berriasian, shallow-marine
carbonates of the Swiss and French Jura Mountains is presented. Based on vertical facies evolution and bedding surfaces, different
orders of depositional sequences (elementary, small-scale, medium-scale) have been identified in the studied sections. The
hierarchical stacking pattern of these sequences and the time span represented by the investigated interval imply that eustatic
sea-level fluctuations in the Milankovitch frequency band were an important controlling factor. The small-scale and medium-scale
sequences relate to the 100 and 400-kyr orbital eccentricity cycles, respectively. The elementary sequences are attributed
to the 20-kyr precession cycle. Differential subsidence additionally produced accommodation changes. The present study focuses
on one specific small-scale sequence situated at the base of the transgressive systems tract of large-scale sequence Be4,
which is identified also in other European basins. This small-scale sequence has been logged in detail at eight different
outcrops in the Jura Mountains. Detailed facies analysis reveals that different depositional environments (tidal flats, internal
lagoons, open lagoons, carbonate sand shoals) were juxtaposed and evolved through time, often shifting position on the platform.
The boundaries of the small-scale (100-kyr) sequence can be followed over the entire study area and thus must have formed
through predominantly allogenic processes (eustatic sea-level fall, the effect of which was locally modified by differential
subsidence). In two sections, five well-developed elementary sequences constitute the small-scale sequence. In the other sections,
the identification of elementary sequences often is difficult because sedimentation was dominated by autogenic processes that
overruled the influence of sea-level fluctuations. In low-energy, tidal-flat and internal-lagoonal settings, orbitally induced
sea-level changes were recorded more faithfully, while high-energy shoals were mainly submitted to autogenic processes and
the allogenic signal is masked. Consequently, the studied Jura platform experienced a combination of auto- and allogenic processes,
which created a complex facies mosaic and a complex stacking of depositional sequences. Nevertheless, the 100-kyr orbital
signal was strong enough to create correlatable sequence boundaries. Within a 100-kyr sequence, however, the unambiguous definition
of sequences related to the 20-kyr orbital cycle is often difficult and the prediction of their lateral or vertical facies
evolution impossible. 相似文献
997.
Klaus Wemmer André Steenken Stefan Müller Mónica G. López de Luchi Siegfried Siegesmund 《International Journal of Earth Sciences》2011,100(2-3):659-669
The Sierra de San Luis forms the southern tip of the Eastern Sierras Pampeanas in central Argentina. Two narrow belts of low-grade phyllites and quartz arenites, i.e. the San Luis Formation, have accommodated part of the strain-related differential exhumation of the medium- to high-grade metamorphic domains that constitute to the basement complex of the sierra. Eleven phyllite samples were subjected to the K/Ar fine-fraction dating technique. Results are interpreted in relation to the Kübler index of the illites, which indicate epimetamorphic conditions for the majority of the samples. Obtained ages between 330 and 290 Ma cover a period of compressional tectonics in the late Mississippian (Visean/Serpukhovian boundary) followed by the subsidence during the formation of the Paganzo Basin in the provinces of La Rioja and San Luis. These tectonic movements are coincident with the Toco orogeny in northern Chile and southern Bolivia. This suggests that the older K/Ar ages document the compressional stage and that younger ages record the cooling of the basement during the subsequent extensional uplift of the basement. 相似文献
998.
Laurent Charlet Guillaume Morin Jérôme Rose Yuheng Wang Mélanie Auffan André Burnol Alejandro Fernandez-Martinez 《Comptes Rendus Geoscience》2011,343(2-3):123-139
Massive deleterious impacts to human health are resulting from the use of arsenic-bearing groundwaters in South-East Asia deltas and elsewhere in the world for drinking, cooking and/or irrigation. In Bangladesh alone, a fifth of all deaths are linked to arsenicosis. In the natural and engineered subsurface environment, the fate of arsenic is, to a large extent, controlled by redox potential, pH, as well as total iron, sulfur and carbonate content, via sorption and coprecipitation on a variety of natural and engineered (nano)particles. In the present article, we address: (1) new insights in the sorption mechanisms of As on Fe(II) and Fe(III) nanophases recognized to play an important role in the microbial cycling of As and Fe; (2) artifacts often encountered in field and laboratory studies of As speciation due to the extreme redox sensitivity of the Fe-As-O-H phases; and (3) as a conclusion, the implications for water treatment. Indeed the specific reactivity of nanoparticles accounts not only for the As bioavailability within soils and aquifers, but also opens new avenues in water treatment. 相似文献
999.
Here we report the first observations of loggerhead turtles Caretta caretta preying on a conspicuous molluscan invader, the rapa whelk Rapana venosa. An average number of 136 opercula were found in stomach contents of five turtles, the curved carapace length ranging in from 51 to 112 cm. No other alimentary items were found in the turtles analyzed. We suggest that the rapa whelk may constitute up to 100% of the diet for immature and mature loggerheads in the Río de la Plata estuary (Uruguay), highlighting the plastic nature of the foraging behavior of loggerheads. 相似文献
1000.
Joel E. Saylor Brian K. Horton Junsheng Nie Jaime Corredor Andrés Mora 《Basin Research》2011,23(4):377-402
This paper addresses foreland basin fragmentation through integrated detrital zircon U–Pb geochronology, sandstone petrography, facies analysis and palaeocurrent measurements from a Mesozoic–Cenozoic clastic succession preserved in the northern Andean retroarc fold‐thrust belt. Situated along the axis of the Eastern Cordillera of Colombia, the Floresta basin first received sediment from the eastern craton (Guyana shield) in the Cretaceous–early Palaeocene and then from the western magmatic arc (Central Cordillera) starting in the mid‐Palaeocene. The upper‐crustal magmatic arc was replaced by a metamorphic basement source in the middle Eocene. This, in turn, was replaced by an upper‐crustal fold‐thrust belt source in the late Eocene which persisted until Oligocene truncation of the Cenozoic section by the eastward advancing thrust front. Sedimentary facies analysis indicates minimal changes in depositional environments from shallow marine to low‐gradient fluvial and estuarine deposits. These same environments are recorded in coeval strata across the Eastern Cordillera. Throughout the Palaeogene, palaeocurrent and sediment provenance data point to a uniform western or southwestern sediment source. These data show that the Floresta basin existed as part of a laterally extensive, unbroken foreland basin connected with the proximal western (Magdalena Valley) basin from mid‐Paleocene to late Eocene time when it was isolated by uplift of the western flank of the Eastern Cordillera. The Floresta basin was also connected with the distal eastern (Llanos) basin from the Cretaceous until its late Oligocene truncation by the advancing thrust front. 相似文献