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551.
Thomas Wilson Carol Stewart Jim Cole David Johnston Shane Cronin 《Environmental Earth Sciences》2010,61(4):675-688
Agriculture is critically dependent on continuity of water quality and quantity. It is well-established that even small quantities
of volcanic ash can disrupt municipal water supplies, with known impacts to quality including: acidification, increases in
turbidity and ionic concentrations. In addition, delivery systems may be blocked or damaged by hard and abrasive suspended
ash and related ash-cleanup operations place extra stress on water reserves. The aim of this study was to characterise the
key areas of vulnerability of farm water supplies to volcanic ashfall, and to identify management recommendations to reduce
these. From literature review and case studies of farms impacted by the 1991 Pinatubo (Philippines) and 1991 Hudson (Chile)
eruptions, key issues were: sedimentation of irrigation ditches and drinking water ponds, turbidity induced abrasion of sprinkler
nozzles and water pumps, and damage to electric pumps (by ash on air-intakes). Building on this, we characterised the water-use
regimes and water supply system vulnerability of eight case-study farms from across the North Island, New Zealand. From this,
we propose an index system to evaluate the vulnerability of farm water supply systems. The key contributors to the vulnerability
index include: water source, storage capacity, reliance on electricity, independence/interconnectedness of system elements,
volume of water use and other load factors. These allow identification of key strategies for mitigating water supply vulnerability
during prevention, preparation, response and recovery phases of a volcanic eruption. 相似文献
552.
Y.K. Kharaka D.R. Cole J.J. Thordsen E. Kakouros H.S. Nance 《Journal of Geochemical Exploration》2006,89(1-3):183
To investigate the potential for the geologic storage of CO2 in saline sedimentary aquifers, 1600 ton of CO2 were injected at 1500 m depth into a 24-m sandstone section of the Frio Formation — a regional reservoir in the US Gulf Coast. Fluid samples obtained from the injection and observation wells before, during and after CO2 injection show a Na–Ca–Cl type brine with 93,000 mg/L TDS and near saturation of CH4 at reservoir conditions. As injected CO2 gas reached the observation well, results showed sharp drops in pH (6.5 to 5.7), pronounced increases in alkalinity (100 to 3000 mg/L as HCO3) and Fe (30 to 1100 mg/L), and significant shifts in the isotopic compositions of H2O and DIC. Geochemical modeling indicates that brine pH would have dropped lower, but for buffering by dissolution of calcite and Fe oxyhydroxides. Post-injection results show the brine gradually returning to its pre-injection composition. 相似文献
553.
Capture of high-speed (hypervelocity) particles in aerogel at ambient temperatures of 175-763 K is reported. This extends previous work which has mostly focussed on conducting experiments at ambient laboratory temperatures, even though aerogels are intended for use in cosmic dust capture cells in space environments which may experience a range of temperatures (e.g., the NASA Stardust mission which collected dust at 1.81 AU and putative Mars atmospheric sampling missions). No significant change in track length (normalised to impactor size) was found over the range 175-600 K, although at 763 K a significant reduction (30%) was found. By contrast, entrance hole diameter remained constant only up to 400 K, above this sudden changes of up to 50% were observed. Experiments were also carried out at normal laboratory temperature using a wide range of aerogel densities and particle sizes. It was found that track length normalised to particle size varies inversely with aerogel density. This is a power law dependence and not linear as previously reported, with longer tracks at lower densities. Glass projectiles (up to 100 μm size) were found to undergo a variety of degrees of damage during capture. In addition to the well known acquisition of a coating (partial or complete) of molten aerogel the mechanical damage includes pitting and meridian fractures. Larger (500 μm diameter) stainless steel spheres also showed damage during capture. In this case melting and ablation occurs, suggesting surficial temperatures during impact in excess of 1400 °C. The response of the aerogel itself to passage of particles through it is reported. The presence of fan-like fractures around the tracks is attributed to cone cracking similar to that in glasses of normal density, with the difference that here it is a repetitive process as the particles pass through the aerogel. 相似文献
554.
Caroline van Breukelen Chris Simpson Steve Rawlings Masayuki Akiyama David Bonfield Lee Clewley Matt J. Jarvis Tom Mauch Tony Readhead Ann-Marie Stobbart Mark Swinbank Mike Watson 《Monthly notices of the Royal Astronomical Society》2009,395(1):11-27
We discuss the optical properties, X-ray detections and active galactic nucleus (AGN) populations of four clusters at z ∼ 1 in the Subaru–XMM Deep Field (SXDF). The velocity distribution and plausible extended X-ray detections are examined, as well as the number of X-ray point sources and radio sources associated with the clusters. We find that the two clusters that appear virialized and have an extended X-ray detection contain few, if any, AGN, whereas the two pre-virialized clusters have a large AGN population. This constitutes evidence that the AGN fraction in clusters is linked to the clusters' evolutionary stage. The number of X-ray AGN in the pre-virialized clusters is consistent with an overdensity of a factor of ∼200; the radio AGN appear to be clustered with a factor of 3 to 6 higher. The median K -band luminosities of LK = 1.7 ± 0.7 L * for the X-ray sources and LK = 2.3 ± 0.1 L * for the radio sources support the theory that these AGN are triggered by galaxy interaction and merging events in sub-groups with low internal velocity distributions, which make up the cluster environment in a pre-virialization evolutionary stage. 相似文献
555.
A spatial relationship between high capacity municipal production wells (>5,000 m3/day), completed in a deep bedrock aquifer, and a buried bedrock valley was recognized in the city of Guelph, southwestern Ontario, Canada. Most production wells are completed in a discrete zone, ~60 m below ground surface, within flat-lying dolostones of the Silurian Amabel Formation. Thick overburden and limited subsurface data make characterization of the karstic aquifer difficult. This study integrates hydrogeologic data with models of karst formation, deriving a conceptual model of porosity development as it relates to valley incision. Bedrock valley incision likely occurred prior to the early Wisconsinan age (>60–75 ka). Incision created steep hydraulic gradients within the flat-lying bedrock, and provided the driving force required to integrate regional groundwater flow into karst conduits that drained at the base of the valley. Dissolution in production zone dolostones was favoured over dissolution in shallower bedrock due to abundant bedding plane partings and fossiliferous facies with high intercrystalline porosity. Burial of the valley during subsequent ice advances reduced the valley’s hydraulic influence and the efficacy of the flow system to cause dissolution. The high capacity municipal wells near the buried bedrock valley tap into the now dormant karst aquifer system. 相似文献
556.
A 30 ka paleo-climate record of the Boise area, Idaho, USA has been delineated using groundwater stable isotopic compositions. Groundwater ages are modern (cold batholith), 5-15 ka (thermal batholith) , 10-20 ka (frontal fault) , and 20-30 ka (Snake River plain thermal). The stable isotopic composition of groundwaters have been used as a surrogate for the stable isotopic composition of precipitation. Using δ2H and δ18O compositions, local groundwater lines (LGWL's) were defined for each system. Each LGWL has been evaluated with defined slopes of 6.94 and 8, respectively, and resulting deuterium excess values (d) were found for each groundwater system for each slope. Time dependent changes in moisture source humidity and temperature, and Boise area recharge temperatures, calculated from stable isotopic data and the deuterium excess factors, agree with previous paleo-climate studies. Results indicate that from the last glacial maximum to the present time the humidity over the ocean moisture source increased by 9%, sea surface temperature at the moisture source increased 6-7°C, and local Boise temperature increased by 4-5°C. A greater increase of temperature at the moisture source as compared to the Boise area may impart be due to a shift in the moisture source area. 相似文献
557.
Claudia I. Mora Lee R. Riciputi David R. Cole Karen D. Walker 《Contributions to Mineralogy and Petrology》2009,157(6):781-795
The Boehls Butte anorthosite consists predominantly of an unusual bimodal assemblage of andesine and bytownite–anorthite.
Oxygen isotope compositions of the anorthosite were profoundly altered by high temperature, retrograde interaction with meteoric-hydrothermal
fluids that varied in composition from isotopically evolved to nearly pristine meteoric water. Oxygen isotope ratios of bulk
plagioclase separates are in the range +7.0 to −6.2‰ V-SMOW, however, secondary ion mass spectrometry indicates spot-sized
isotope values as low as −16‰. Typical inter- and intra-plagioclase grain variability is 3–6‰, and extreme heterogeneity of
up to 20‰ is noted in a few samples. High-temperature hydrothermal alteration of intermediate plagioclase is proposed to explain
the origin of bytownite–anorthite in the anorthosite and creation of its unusual bimodal plagioclase assemblage. The anorthite-forming
reaction created retrograde reaction-enhanced permeability which, together with rapid decompression, extension, and unroofing
of the anorthosite complex, helped to accommodated influx of significant volumes of meteoric-hydrothermal fluids into the
anorthosite. 相似文献
558.
A centrographic method for analysing mineral deposit clusters is illustrated using the komatiite-hosted Kambalda nickel sulphide deposit cluster, Yilgarn craton, Western Australia. In this method, the standard distance circle divides the cluster into a more endowed inner part and a less endowed peripheral part. The standard deviational ellipse, another centrographic object, depicts the preferred northwest–southeast trend of nickel orebodies at Kambalda. Weighted centrography shows that nickel endowment is greater in the eastern than western part of the cluster. The spatio-geometric interaction of the circle and ellipse splits the cluster into several partitions. The relative concentration of nickel orebodies or endowment within a partition in relation to their concentration within the entire cluster is termed ‘capture efficiency’. Komatiite areal trace exhibits higher nickel orebody capture efficiency than spatio-geometric partitions; however, some spatio-geometric partitions exhibit nickel endowment capture efficiencies comparable to that of komatiite. Furthermore, nickel orebody and endowment capture efficiencies of komatiite are elevated only within the standard distance circle. These results suggest that at Kambalda, (i) the standard distance circle is a prime window for understanding the komatiite-hosted nickel system, and (ii) spatio-geometric partitions are plausible locales for spatial analysis of nickel orebodies and endowment. The proposed centrographic method is potentially useful in mineral resource estimations and mineral exploration targeting. 相似文献
559.
Key findings from the Indian Ocean Climate Initiative and their impact on policy development in Australia 总被引:1,自引:0,他引:1
Bryson C. Bates Pandora Hope Brian Ryan Ian Smith Steve Charles 《Climatic change》2008,89(3-4):339-354
Since the mid-1970s the climatic changes that have taken place in southwest Western Australia have generated a variety of impacts, the most prominent of which is a reduction in dam inflows of at least 50 percent. These impacts were the catalyst for the formation of the Indian Ocean Climate Initiative in 1998, a research partnership between two national research organizations and several state government departments and agencies. This paper describes the key scientific findings of the Initiative with respect to the nature of the climatic changes that have taken place within the region, explores the factors that might have caused these changes, and describes the most recent climate projections for the region. We reflect on the factors leading to the rapid acceptance of the research outcomes from the Initiative, the impact of the Initiative on policy development across Australia and its likely evolution post-2006. 相似文献
560.
Whole-rock geochemical and radiogenic data are combined with in situ trace and isotopic analyses of amphibole grains to characterize
the source and the emplacement mechanisms of the magmas of the Sunda arc in the Batu Hijau district, Sumbawa, Indonesia. The
low-K calc-alkaline magmatic suite in the area is characterized by a distinctively juvenile signature (143Nd/144Nd ~0.5130). Whole-rock trace element and Pb isotopic data (207Pb/204Pb ~15.603) suggest the involvement of a minimal (<0.1%) sediment component in arc petrogenesis. During the petrogenesis of
the calc-alkaline plutons, the involvement of fluids that were not entirely derived from the dehydration of a subducting slab
is reflected in the mineral chemistry of the primary hydrous magmatic amphiboles, which contain very low B and Li concentrations.
We argue that the B- and Li-poor fluids implicated in the petrogenesis of the calc-alkaline melts were at least partially
derived from dehydration of uprising asthenospheric mantle. The δD values of selected hydrous magmatic amphibole grains range
between ca. −70‰ and 0‰, consistent with an original mantle-derived signature, which was subsequently modified due to a de-hydrogenation
process. We put forward the hypothesis that in the Batu Hijau district an arc-transverse fault system facilitated the rise
of asthenosphere-derived melts above a kink, or tear, in the subducting Indian Ocean Plate that underlies the Sunda arc. The
melts ascended to upper-crustal levels and underwent fractionation while interacting with the arc crust or metasomatized lithospheric
mantle wedge. As a result of this study, we emphasize the significance of crustal-scale faults as conduits that connect the
mantle to upper-crustal levels in arc settings. The de-hydrogenation process that the tonalite plutons underwent in the Batu
Hijau district may have been crucial to the genesis of associated Cu–Au porphyry mineralization and the development of the
Pliocene Batu Hijau deposit. Consequently, we argue that deep structures may facilitate the efficient release of mineralizing
fluids at high crustal-levels. 相似文献