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361.
We performed spectral analyses on the ages of 89 well-dated major geological events of the last 260 Myr from the recent geologic literature.These events include times of marine and non-marine extinctions,major ocean-anoxic events,continental flood-basalt eruptions,sea-level fluctuations,global pulses of intraplate magmatism,and times of changes in seafloor-spreading rates and plate reorganizations.The aggregate of all 89 events shows ten clusters in the last 260 Myr,spaced at an average interval of~26.9 Myr,and Fourier analysis of the data yields a spectral peak at 27.5 Myr at the≥96%confidence level.A shorter period of~8.9 Myr may also be significant in modulating the timing of geologic events.Our results suggest that global geologic events are generally correlated,and seem to come in pulses with an underlying~27.5-Myr cycle.These cyclic pulses of tectonics and climate change may be the result of geophysical processes related to the dynamics of plate tectonics and mantle plumes,or might alterna-tively be paced by astronomical cycles associated with the Earth's motions in the Solar System and the Galaxy. 相似文献
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Glibert PM Azanza R Burford M Furuya K Abal E Al-Azri A Al-Yamani F Andersen P Anderson DM Beardall J Berg GM Brand L Bronk D Brookes J Burkholder JM Cembella A Cochlan WP Collier JL Collos Y Diaz R Doblin M Drennen T Dyhrman S Fukuyo Y Furnas M Galloway J Granéli E Ha DV Hallegraeff G Harrison J Harrison PJ Heil CA Heimann K Howarth R Jauzein C Kana AA Kana TM Kim H Kudela R Legrand C Mallin M Mulholland M Murray S O'Neil J Pitcher G Qi Y Rabalais N Raine R Seitzinger S Salomon PS Solomon C 《Marine pollution bulletin》2008,56(6):1049-1056
The proposed plan for enrichment of the Sulu Sea, Philippines, a region of rich marine biodiversity, with thousands of tonnes of urea in order to stimulate algal blooms and sequester carbon is flawed for multiple reasons. Urea is preferentially used as a nitrogen source by some cyanobacteria and dinoflagellates, many of which are neutrally or positively buoyant. Biological pumps to the deep sea are classically leaky, and the inefficient burial of new biomass makes the estimation of a net loss of carbon from the atmosphere questionable at best. The potential for growth of toxic dinoflagellates is also high, as many grow well on urea and some even increase their toxicity when grown on urea. Many toxic dinoflagellates form cysts which can settle to the sediment and germinate in subsequent years, forming new blooms even without further fertilization. If large-scale blooms do occur, it is likely that they will contribute to hypoxia in the bottom waters upon decomposition. Lastly, urea production requires fossil fuel usage, further limiting the potential for net carbon sequestration. The environmental and economic impacts are potentially great and need to be rigorously assessed. 相似文献
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Abstract: The basalt JB–1a was reacted with 2M NaCl solutions, and the leaching behavior of the cations Na, K, Ca, Mg, Fe, Mn, Zn and Co was monitored. The experiments were carried out using standard cold-seal pressure vessels in the temperature range from 300 to 800C under the constant pressure of 1000 bars and also in the pressure range from 500 to 1000 bars at 600°C.
The concentrations of Fe, Mn, Zn and Co in the hydrothermal solutions increased significantly with increasing temperature and with decreasing pressure. The thermodynamic analysis of the experimental results suggests that this is due to the formation of trichloro-complexes and also partly due to the temperature dependence of ion exchange between augite and aqueous chloride solution. The Na concentration in the aqueous solution decreases with increasing temperature and with decreasing pressure. On the other hand, the behavior of K, Ca and Mg is complex and their concentrations seem to be controlled by the coexisting minerals.
Judging from the experimental results, it is concluded that the transition elements are effectively leached from the basalt under higher temperatures and lower pressures. This means that higher temperature and lower pressure conditions are preferable for the production of ore-forming hydrothermal solutions. 相似文献
The concentrations of Fe, Mn, Zn and Co in the hydrothermal solutions increased significantly with increasing temperature and with decreasing pressure. The thermodynamic analysis of the experimental results suggests that this is due to the formation of trichloro-complexes and also partly due to the temperature dependence of ion exchange between augite and aqueous chloride solution. The Na concentration in the aqueous solution decreases with increasing temperature and with decreasing pressure. On the other hand, the behavior of K, Ca and Mg is complex and their concentrations seem to be controlled by the coexisting minerals.
Judging from the experimental results, it is concluded that the transition elements are effectively leached from the basalt under higher temperatures and lower pressures. This means that higher temperature and lower pressure conditions are preferable for the production of ore-forming hydrothermal solutions. 相似文献
368.
A tectono-geomorphic model of the hydrogeology of deeply weathered crystalline rock: Evidence from Uganda 总被引:7,自引:4,他引:3
Deeply weathered crystalline rock forms important aquifers for public water supply throughout low-latitude regions of Africa,
South America, and Asia, but these aquifers have considerable heterogeneity and produce low well yields. Aquifers occur in
the bedrock and overlying weathered mantle and are the products of geomorphic activity of meteoric water, principally deep
weathering and stripping. The fundamental relationship between the hydrogeology and geomorphology of these terrains has, however,
remained unresolved. This study demonstrates the ability of a recently developed tectono-geomorphic model of landscape evolution
in Uganda to explain the hydrogeological characteristics of two basins, as determined using a combination of textural analysis,
slug tests, packer tests, and pumping tests. The geopetal imprint of long-term deep weathering and erosional unloading is
identified in the vertical heterogeneity of the fractured-bedrock and weathered-mantle aquifers; horizontal heterogeneity
is lithologically controlled. The two units form an integrated aquifer system in which the more transmissive (5–20 m2/d) and porous weathered mantle provides storage to underlying bedrock fractures (transmissivity, T, ≈1 m2/d). The thickness and extent of the more productive weathered-mantle aquifer are functions of contemporary geomorphic processes.
The utility of the tectono-geomorphic model, applicable to deeply weathered environments, is that it coherently describes
the basin-scale hydrogeological characteristics of these complex terrains.
Received, June 1999/Revised, January 2000/Accepted, January 2000 相似文献
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In the arid to semi-arid district of Chengcheng, Weinan City, in central Shaanxi Province, diminishing groundwater reserves in the shallow Quaternary (QLB) aquifer and elevated fluoride in the similarly shallow Permo-Triassic (PTF) aquifer, have promoted interest in the development of groundwater resources in the deep but poorly understood Cambrian-Ordovician carbonate aquifer system (COC). To investigate the origin of the COC groundwaters and the relationship between the deep and shallower systems, a hydrochemical study was undertaken involving 179 major and minor ion analyses, 39 stable isotope analyses (δD and δ18O), and 14 carbon isotope analyses (14C and δ13C). PHREEQC 3.0 was used to investigate mixing. Hydrochemical data support the presence of a well-connected regional flow system extending southwards from the more mountainous north. Stable isotope data indicate that the COC groundwaters originate as soil zone infiltration, under a much cooler regime than is found locally today. This is confirmed by 14C, which indicates the groundwater to be palaeowater recharged during the late Pleistocene (∼10–12 ka B.P.). The presence of nitrate in the COC groundwaters suggests leakage from overlying shallow aquifers currently provides an additional source of COC recharge, with major faults possibly providing the primary pathways for downward vertical flow. 相似文献