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361.
Mean latitude variations computed by Orlovs or other filters have some irregular variations in addition to secular ones. These are of the order of ±0.05 to ±0.1, they can last several years and sometimes show regional similarities. In looking for an explanation of such latitude variations several physical mechanisms have been investigated. The most probable one is the mechanism of stress propagation in the lithosphere and asthenosphere. The consequent gravitational and deformational effects could explain both the magnitude and the time dependance of the irregular latitude variations. 相似文献
362.
Electrical resistivity investigation of potential cavities underlying a proposed ash disposal area 总被引:1,自引:0,他引:1
Measurements of electrical resistivity anomalies using a Wenner electrode array in a profiling mode were conducted over a
105-acre area near Crystal River, Florida Analyzed results of collected data were used to determine the likelihood of subsurface
solution cavities beneath a proposed ash disposal area “Sounding” measurements with electrode spacing values extending up
to 100 feet and Lee electrode measurements were used to identify and locate specific anomaly maxima identified anomalies on
the order of 200 chms-feet contrasted with expected values of 300 to 400 ohms-feet and were attributed to lower resistivities
inherent in water-filled solution cavities below a shallow water table Prominent cavity complexes at 5 to 15 feet depth were
predicted in areas of low resistivity anomalies in the otherwise geoelectrically uniform, Eocene Ocala limestone Shallow test
borings confirmed the presence of a significant concentration of shallow cavities in the predicted areas This study demonstrated
the feasibility of electrical resistivity measurements as a reconnaissance tool to economically determine subsurface cavities
and to aid in developmental and environmental planning 相似文献
363.
364.
Mark Brenner David A. Hodell Barbara W. Leyden Jason H. Curtis William F. Kenney Binhe Gu Jana M. Newman 《Journal of Paleolimnology》2006,35(1):129-148
We studied the role that submersed aquatic vegetation (SAV) plays in the sedimentation of organic matter (OM) and phosphorus
(P) in Lake Panasoffkee, Florida (USA), a shallow, hard-water, macrophyte-dominated water body. Carbon/Nitrogen ratios (C/N)
and stable isotope signatures (δ13C and δ15N) in algae, higher plants, and surface sediments were measured to identify sources of OM to the lake mud. Pollen, plant macrofossils,
and geochemistry in sediment cores indicated that primary productivity and SAV abundance in Lake Panasoffkee increased in
the late 1800s, probably as a response to increased P loading from human settlement and forest clearance. SAV and associated
periphyton served as temporary sinks for soluble P, maintaining relatively clear-water, low-nutrient conditions in the lake.
P accumulation in Lake Panasoffkee sediments increased together with indicators for greater SAV presence. This suggests that
SAV and associated epiphytes promote P burial and retention in sediments. Although it might be assumed that rooted submersed
macrophytes are directly responsible for P uptake from water and transfer to sediments, C/N and stable carbon isotope results
argue for the importance of other macrophyte growth forms, and perhaps epiphytic algae, in permanent OM and P sequestration.
For instance, high rates of photosynthesis by epiphytes in hard-water systems consume CO2 and promote CaCO3 precipitation. Sloughing of accumulated carbonates from macrophyte leaves transfers epiphytes and associated P to the sediment.
Our paleolimnological findings are relevant to restoration efforts in the Florida Everglades and support the claim that constructed
SAV wetlands remove P from waters effectively. 相似文献
365.
Data preprocessing for river flow forecasting using neural networks: Wavelet transforms and data partitioning 总被引:7,自引:0,他引:7
Barbara Cannas Alessandra Fanni Linda See Giuliana Sias 《Physics and Chemistry of the Earth》2006,31(18):1164-1171
The evaluation of surface water resources is a necessary input to solving water management problems. Neural network models have been trained to predict monthly runoff for the Tirso basin, located in Sardinia (Italy) at the S. Chiara section. Monthly time series data were available for 69 years and are characterized by non-stationarity and seasonal irregularity, which is typical of a Mediterranean weather regime. This paper investigates the effects of data preprocessing on model performance using continuous and discrete wavelet transforms and data partitioning. The results showed that networks trained with pre-processed data performed better than networks trained on undecomposed, noisy raw signals. In particular, the best results were obtained using the data partitioning technique. 相似文献
366.
Barbara Radwanek-Bąk 《Environmental Geology》2007,52(1):137-145
The author deals with a complex, multi-criteria system of protection of mineral resources, based on the evaluation of their
deposits, both with identified and inferred reserves, and perspective areas, i.e., the areas where mineral deposits may occur.
The purpose of valorization is to compare different deposits using the same, uniform criteria, and then assign them to particular
groups with the intention of protecting the most valuable deposits and highly perspective areas more efficiently. The criteria
represent three separate groups: geological and mining assets, the level of certainty (the degree of our knowledge on the
mineral raw material and its deposit), as well as environmental and spatial planning constraints. Inclusion of the prognostic
areas (the D1 category of resources in Poland) to the procedure of deposit valorization forms the basis for their legal protection, especially
when they have not been protected until now. 相似文献
367.
Sonia Maria Barros de Oliveira Paulo Sergio Cardoso da Silva Barbara Paci Mazzilli Deborah Ines Teixeira Favaro Catia Heloisa Saueia 《Applied Geochemistry》2007
In the Cubatão region, southern Brazil, sediments are transported by several rivers from the Serra do Mar Ridge into the Santos estuary. Fertilizer plants have been operating along the margins of one of these rivers (Mogi River) producing a large volume of phosphogypsum, which is stockpiled in nearby areas. Surface sediments of the Mogi River were sampled upstream and downstream in relation to the point where the effluents of the phosphogypsum piles flow into the drainage system. In the vicinity of this point one sediment core was collected. Results show that REE, Ba, Zr and Th concentrations in the non-contaminated sediments are of the same order as those present in the upper continental crust. The contaminated samples present a composition affected by that of the phosphogypsum, marked by a higher concentration of these elements and a stronger degree of REE fractionation. These phosphogypsum characteristics are inherited from the Catalão igneous phosphate ore and were moderately modified by the industrial process of phosphoric acid production. The phosphogypsum signal decreases rapidly downstream, pointing to a limited area of influence of the stacks. The deepest sediments of the core are also free of contamination, representing a time interval prior to the deposition of phosphogypsum wastes on the banks of the estuary. 相似文献
368.
The authors determine the composition of a river that is impacted by acid-mine drainage, evaluate dominant physical and geochemical processes controlling the composition, and assess dissolved metal speciation and toxicity using a combination of laboratory, field and modeling studies. Values of pH increase from 3.3 to 7.6 and the sum of dissolved base metal (Cd + Co + Cu + Ni + Pb + Zn) concentrations decreases from 6270 to 100 μg/L in the dynamic mixing and reaction zone that is downstream of the river’s confluence with acid-mine drainage. Mixing diagrams and PHREEQC calculations indicate that mixing and dilution affect the concentrations of all dissolved elements in the reach, and are the dominant processes controlling dissolved Ca, K, Li, Mn and SO4 concentrations. Additionally, dissolved Al and Fe concentrations decrease due to mineral precipitation (gibbsite, schwertmannite and ferrihydrite), whereas dissolved concentrations of Cd, Co, Cu, Ni, Pb and Zn decrease due to adsorption onto newly formed Fe precipitates. 相似文献
369.
Zhixiong Shen Barbara Mauz Andreas Lang Jan Bloemendal John Dearing 《Quaternary Geochronology》2007,2(1-4):150-154
Optically stimulated luminescence of fine silt quartz was investigated to establish chronologies for lake sediments from the British Isles. Feldspar contamination and its potential effects on equivalent dose (De) determination were examined. A new feldspar contamination test based on the thermal quenching of quartz OSL and thermal assistance of feldspar OSL identified feldspar contamination in samples being treated for 20 min in 20% hydrofluoric acid. Feldspar component monitoring based on the post-IR OSL/OSL ratio was not sufficiently sensitive to monitor a feldspar component, but is a good indicator whether a standard SAR procedure can be applied successfully, despite the presence of feldspar. Based on these results we used a modified SAR protocol including a 100 s IRSL stimulation at 50 °C before OSL readout. This protocol could overcome any malign effects of feldspar even for a feldspar bearing polymineral sub-sample. 相似文献
370.
Benthic diatoms of an Alpine stream/lake network in Switzerland 总被引:1,自引:0,他引:1