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981.
Weathering rates of silicate minerals observed in the laboratory are in general up to five orders of magnitude higher than
those inferred from field studies. Simple calculations show that even if the field conditions were fully simulated in standard
laboratory experiments, it would be impossible to measure the slow rates of mineral dissolution that are observed in the field.
As it is not possible to measure the dissolution rates under typical field conditions, one should extrapolate the available
data to the field conditions. To do this, a rate law for the dissolution of plagioclase in the field was formulated by combining
the far from equilibrium dissolution rate of weathered natural oligoclase at 25°C with the effect of deviation from equilibrium
on dissolution rate of fresh albite at 80°C. In contrast to the common view that laboratory experiments predict dissolution
rates that are faster than those in the field, the simulation based on this rate law indicates that laboratory dissolution
experiments actually predict slower rates than those observed in the field. This discrepancy is explained by the effect of
precipitation of secondary minerals on the degree of saturation of the primary minerals and therefore on their dissolution
rate. Indeed, adding kaolinite precipitation to the simulation significantly enhances the dissolution rate of the plagioclase.
Moreover, a strong coupling between oligoclase dissolution and kaolinite precipitation was observed in the simulation. We
suggest that such a coupling must exist in the field as well. Therefore, any attempt to predict the dissolution rate in the
field requires knowledge of the rate of the secondary mineral precipitation. 相似文献
982.
Efficient restoration of deteriorating coastal structures requires an accurate picture of both above ground and underground
features. Although ground penetrating radar (GPR) can map underground features, it creates reflection artifacts. Here, a model
for deconvolution calibration was developed in an outdoor small-scale experiment. GPR parameters were established, then applied
at a deteriorating fishing port in northeast Taiwan. The deconvolution filter removed repetitive reflection patterns under
the lowest part of the void creating a more accurate map. A 3D-map was created from interpolated sketched void boundaries.
Due to its high lossy nature at radar frequencies and large contrasting relative dielectric permittivity (RDP) to the upper
medium, the seawater table (SWT) is easily identified. The upper boundary of reflection-free area in the deconvoluted radargram,
therefore, indicates the SWT. The methods developed here are easily modified to fit a wide range of situations. 相似文献
983.
For 5 months before the 2001 Mt. Etna eruption, a progressive gravity decrease was measured along a profile of stations on
the southern slope of the volcano. Between January and July 2001, the amplitude of the change reached 80 μGal, while the wavelength
of the anomaly was of the order of 15 km. Elevation changes observed through GPS measurements during a period encompassing
the 5-month gravity decrease, remained within 4–6 cm over the entire volcano and within 2–4 cm in the zone covered by the
microgravity profile. We review both gravity and elevation changes by a model assuming the formation of new cracks, uniformly
distributed in a rectangular prism. The inversion problem was formulated following a global optimization approach based on
the use of Genetic Algorithms. Although it is possible to explain the observed gravity changes by means of the proposed analytical
formulation, the results show that calculated elevation changes are significantly higher than those observed. Two alternative
hypotheses are proposed to account for this apparent discrepancy: (1) that the assumptions behind the analytical formulation,
used to invert the data, are fallacious at Etna, and thus, numerical models should be utilized; (2) that a second process,
enabling a considerable mass decrease to occur without deformation, acted together with the formation of new cracks in the
source volume. 相似文献
984.
地质雷达在地下水有机污染调查方面的应用研究进展 总被引:2,自引:0,他引:2
地质雷达作为一种物探方法,应用于环境地质调查已有若干年历史.但应用于地下水及土壤的有机污染调查,目前在国内还未见诸报道.叙述了地质雷达的工作原理,阐明了地质雷达在地下水有机污染调查工作中的应用条件、应用效果,并列举部分国外应用实例. 相似文献
985.
986.
Lake Algonquin, the largest glacial lake of the Great Lakes area, ended prior to 10,000 years BP by drainage to the Ottawa
Valley as the North Bay outlet was deglaciated. At that time, the outlet area was isostatically downwarped more than 100 m;
resulting low water, river-linked lakes Chippewa, Stanley, and Hough, lowstands in the basins of lakes Michigan, Huron, and
Georgian Bay respectively, were much below present lake level. While water levels were low, about half of the present lake
area was dry land. The land above the lowstands was dissected by streams and became forested. Uplift of the North Bay outlet
between 10,000 and 5,000 years BP raised lake level to above the present (the Nipissing transgression), submerging the forest
and valley system. Submerged stumps from those forests have often been encountered on the present lake floor; some stumps
have been dated.
Four sites in Ontario (Parkhill, Owen Sound, St. Joseph Island, Meaford) provide on-land evidence of pre-Nipissing drainage
and valley formation. Radiocarbon ages of valley fill organic materials range from 7,310 to 5,410 years BP. At three sites,
present drainage is known to be displaced from the pre-Nipissing drainage. Geophysical methods (EM, GPR, resistivity) have
been used to refine valley location and morphology at Parkhill and Meaford. There is the potential of tracing the valleys
down slope to the low-water shorelines with shipboard geophysics, with implications for archaeology, hydrology and hydrogeology,
paleogeography, and Great Lakes history.
This is the eighth in a series of ten papers published in this special issue of Journal of Paleolimnology. These papers were
presented at the 47th Annual Meeting of the International Association for Great Lakes Research (2004), held at the University
of Waterloo, Waterloo, Ontario, Canada. P.F. Karrow and C.F.M. Lewis were guest editors of this special issue. 相似文献
987.
S. Feyza Cinicioglu Ilknur Bozbey Sadik Oztoprak M. Kubilay Kelesoglu 《Engineering Geology》2007,94(3-4):145-165
This paper presents an integrated, earthquake-damage assessment that standardizes and quantifies methods of analysis. The proposed methodology evaluates all damage-causing phenomena, both individually and in combination. This approach inherently relates to soil-structure interactions by quantifying site-specific geotechnical and structural properties. Specifically considered is ground shaking, the primary damage-causing phenomenon. Also evaluated are the collateral effects of liquefaction, degradation of seismic-bearing capacity and slope failure (landslides). The methodology incorporates a literature-derived probabilistic assessment of damage-causation, and is interpreted and presented as single numbers deemed “Damage Grades.” These damage grades integrate the initial probabilistic evaluation with professional experience and judgment in order to determine potential damage to a particular structure at a particular location. This methodology was applied, with success, to two different locations in Istanbul, Turkey. It should be tested by engineering geologists and geotechnical engineers, for it may be applicable to earthquake-prone areas elsewhere. 相似文献
988.
Since landfill operations ceased in the early 1980s at the Woodlawn landfill Superfund site in northeastern Maryland, USA,
the carcinogen vinyl chloride monomer (VCM) has persisted in the site ground water at concentrations in places greater than
100 ppb. Investigations of VCM concentrations from monitoring well data from 1981 through 1991, which were published in 2001,
concluded that concentrations were cyclic and were not dissipating. Data from 1991 to 2000 confirm VCM persistence, showing
concentration peaks as late as 1997 in the eastern part of the site. These values are significantly above both drinking water
standards (>MCL of 2 ppb) and lifetime excess cancer risk (E-6 risk level) from exposure since birth (>0.024 ppb). Sources
for VCM are landfill wastes (PVC-sludge) and effluent from an on-site transfer station. In addition to direct release of VCM
from wastes, other chlorinated hydrocarbons, trichloroethene and perchloroethene (TCE and PCE) are also present in the ground
water, and these compounds can degrade into VCM. Persistence of VCM concentrations is the result of leachate generation, mostly
from multi-source wastes in the vadose zone, with subsequent infiltration into the regional aquifer. Increases in VCM concentrations
(new leachate generation) alternated with decreases in VCM concentrations (infiltration without leachate) in a cyclic fashion,
during this 20-year period. 相似文献
989.
Juliet F. Bird Julian J. Bommer Helen Crowley Rui Pinho 《Soil Dynamics and Earthquake Engineering》2006,26(1):15-30
The assessment of building damage caused by liquefaction-induced ground deformations requires the definition of building capacity and vulnerability as a function of the demand, as well as damage scales to describe the state of the damaged building. This paper presents a framework for resolving these issues within the context of earthquake loss estimations, where large variations in building stock and ground conditions must be considered. The principal modes of building response to both uniform and differential ground movements are discussed and the uncertainties in their evaluation are highlighted. A unified damage scale is proposed for use in both reconnaissance and assessment of all modes of building damage, including ‘rigid body’ response of structures on stiff foundations to uniform or differential ground movements. The interaction of ground shaking and liquefaction in the context of induced structural damage is also briefly considered. The paper raises important aspects of earthquake loss estimations in regions of liquefaction potential, which remain relatively poorly defined at present. 相似文献
990.
An aquifer containing a skin zone is considered as a two-zone system. A mathematical model describing the head distribution is presented for a slug test performed in a two-zone confined aquifer system. A closed-form solution for the model is derived by Laplace transforms and Bromwich integral. This new solution is used to investigate the effects of skin type, skin thickness, and the contrast of skin transmissivity to formation transmissivity on the distributions of dimensionless hydraulic head. The results indicate that the effect of skin type is marked if the slug-test data is obtained from a radial two-zone aquifer system. The dimensionless well water level increases with the dimensionless positive skin thickness and decreases as the dimensionless negative skin thickness increases. In addition, the distribution of dimensionless well water level due to the slug test depends on the hydraulic properties of both the wellbore skin and formation zones. 相似文献