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21.
22.
Christopher J. Daughney Uwe Morgenstern Rob van der Raaij Robert R. Reeves 《Hydrogeology Journal》2010,18(2):417-428
Concentrations of tritium, chlorofluorocarbons and sulfur hexafluoride have been measured at over 100 groundwater monitoring sites across New Zealand, followed by interpretation of groundwater age distribution using the exponential-piston flow model. Interpreted mean residence times ranged from less than 1 year to more than 100 years, with the 25th, 50th (median) and 75th percentiles being approximately 10, 40 and 100 years, respectively. Classification functions derived from discriminant analysis and based on nine input variables (well depth, electrical conductivity and the concentrations of the ions Na, K, Ca, Mg, HCO3, Cl and SO4) allowed assignment of 71% of the sites to the correct of four age categories (mean residence time 10 years or less, 11–40 years, 41–100 years, or more than 100 years). The discriminant analysis classification functions were more effective than regression methods for estimating groundwater age from hydrochemistry and well depth, and can thus be used to predict the groundwater age category for any monitoring site in New Zealand. 相似文献
23.
Sewage sludges are potential targets for economic extraction of Au because of the documented Au content of sewage sludges worldwide, which are of the order of some ore deposits currently mined for Au. The sewage of Melbourne, Australia, was stockpiled in large, closed, lagoonal tanks from 1898 until 1980. Reeves, Plimer and Foster, 1999, have conducted, and published, an extensive and exhaustive study of the Werribee sewage reserves utilising RNAA, INAA, GFAAS, ICPMS, and FLAAS to determine 31 elements, including Au, Ag, Sb, As, Cd, Hg, Zn, Cu, and Pb. The study was initiated to determine Au, Ag and other metal variations in both space and time and to investigate the economics of chemical extraction of the precious metals. A total of 149 samples from over 50 hand-auger drillholes to a depth up to 4m were analysed from the stockpiles, with Au assays yielding remarkably consistent results. Average grades of 0.77 g/t Au and 18.8 g/t Ag have been documented for a measured resource of 770,000 m3. Laboratory-based extractive metallurgy of the Werribee sludges has demonstrated that Au, Ag, and Zn can be removed with relative ease by heap-leaching using modified conventional technology, albeit with prohibitive reagent consumption. The extraction of the precious metals also results in the variable removal of contaminant metals such as Cd, As, Sb, Hg and Cr which may render the sludges fit for sale as agricultural fertiliser, provided organic pollutants and pathogenic organisms are below governmental environmental protection limits. 相似文献
24.
J. P. Morelli R. J. Bunting S. W. H. Cowley C. J. Farrugia M. P. Freeman E. Friis-Christensen G. O. L. Jones M. Lester R. V. Lewis H. Lühr D. Orr M. Pinnock G. D. Reeves P. J. S. Williams T. K. Yeoman 《Annales Geophysicae》1995,13(11):1144-1163
We present an analysis of ground magnetic field, ionospheric flow, geosynchronous particle, and interplanetary data during a multiple-onset substorm on 12 April 1988. Our principal results concern the modulations of the ionospheric flow which occur during the impulsive electrojet activations associated with each onset. During the first hour of the disturbance these take place every \sim12.5 min and involve the formation of a new intense westward current filament in the premidnight sector, just poleward of the preexisting extended current system driven by the large-scale flow. These filaments are \sim1 h MLT wide (\sim600 km), and initially expand poleward to a width of \sim300 km before contracting equatorward and coalescing with the preexisting current, generally leaving the latter enhanced in magnitude and/or expanded in latitude. Within the impulsive electrojets the flow is found to be suppressed to values 50–100 m s−1 or less during the first few minutes, before surging equatorward at 0.5-1.0 km s−1 during the phase of rapid coalescence. The implication is that the precipitation-induced Hall conductivity within the impulsive electrojet initially rises to exceed \sim100 mho, before decaying over a few minutes. This value compares with Hall conductivities of \sim20 mho in the quasi-steady current regions, and a few mho or less in the regions poleward of the electrojets and in the preonset ionosphere. Preliminary evidence has also been found that the flow surges propagate from midnight to the morning sector where they are associated with arrested equatorward motion or poleward contractions of the current system. These observations are discussed in terms of present theoretical paradigms of the global behaviour of fields and flows which occur during substorms. 相似文献
25.
Warren HP Bookbinder JA Forbes TG Golub L Hudson HS Reeves K Warshall A 《The Astrophysical journal》1999,527(2):L121-L124
The ability of the Transition Region and Coronal Explorer (TRACE) to image solar plasma over a wide range of temperatures (Te approximately 104-107 K) at high spatial resolution (0&farcs;5 pixels) makes it a unique instrument for observing solar flares. We present TRACE and Yohkoh observations of an M2.4 two-ribbon flare that began on 1999 July 25 at about 13:08 UT. We observe impulsive footpoint brightenings that are followed by the formation of high-temperature plasma (Te greater, similar10 MK) in the corona. After an interval of about 1300 s, cooler loops (Te<2 MK) form below the hot plasma. Thus, the evolution of the event supports the qualitative aspects of the standard reconnection model of solar flares. The TRACE and Yohkoh data show that the bulk of the flare emission is at or below 10 MK. The TRACE data are also consistent with the Yohkoh observations of hotter plasma (Te approximately 15-20 MK) existing at the top of the arcade. The cooling time inferred from these observations is consistent with a hybrid cooling time based on thermal conduction and radiative cooling. 相似文献
26.
MODFLOW 2000 head uncertainty,a first-order second moment method 总被引:1,自引:0,他引:1
A computationally efficient method to estimate the variance and covariance in piezometric head results computed through MODFLOW 2000 using a first-order second moment (FOSM) approach is presented. This methodology employs a first-order Taylor series expansion to combine model sensitivity with uncertainty in geologic data. MODFLOW 2000 is used to calculate both the ground water head and the sensitivity of head to changes in input data. From a limited number of samples, geologic data are extrapolated and their associated uncertainties are computed through a conditional probability calculation. Combining the spatially related sensitivity and input uncertainty produces the variance-covariance matrix, the diagonal of which is used to yield the standard deviation in MODFLOW 2000 head. The variance in piezometric head can be used for calibrating the model, estimating confidence intervals, directing exploration, and evaluating the reliability of a design. A case study illustrates the approach, where aquifer transmissivity is the spatially related uncertain geologic input data. The FOSM methodology is shown to be applicable for calculating output uncertainty for (1) spatially related input and output data, and (2) multiple input parameters (transmissivity and recharge). 相似文献
27.
The peridotite xenoliths from Wangqing display a downward-concave PGE pattern with Pt at maximum due to Pt-Pd fractionation,
which is different from the flat or negatively sloped patterns commonly observed for worldwide peridotite xenoliths and massifs.
Taking into account the difference in partition coefficients of Pt and Pd between alloy and sulfide melt, it is suggested
that some of the Wangqing peridotites must have been equilibrated with a melt in which alloy and sulfide coexisted. Segregation
of Pt-rich alloy from Pd-sulfide melts due to density contrast and extraction of residual melts without sulfide saturation
resulted in the fractionation of Pt from Pd.
Project supported by the Ministry of Human Affairs and a part of an international collaboration program between the Chinese
Academy of Sciences and Centre National de Recherche Scientifique (CNRS, France), and Australian Institute of Nuclear Sciences
and Engineering (AINSE) grant to SJR. 相似文献
28.
Geologie en Mijnbouw - The more one considers the earth sciences these days, the more one realises that any view that falls short of global runs the risk of being short-sighted. This article... 相似文献
29.
The interpretation of new and pre-existing aeromagnetic survey data for Kenya, in conjunction with published gravity data, indicates the existence of a palaeo-triple junction of Jurassic age in eastern Kenya. Two arms, represented by the Mombasa coast and the Somali coast respectively, developed into a part of the Indian Ocean. The third arm, which is now concealed by a cover of Quaternary sediments and volcanic rocks, remains as a rifted, sediment-filled trough extending at least as far northwest as the presently active East Africa Rift in Lake Turkana. It has a remarkable similarity, both in scale and geometry, with the Benue Trough of the Niger Delta. As with the Niger Delta, the present Kenyan coastline is not indicative of the true continental margin, as extensive sedimentation has occurred beyond the continental edge in the region of the triple junction since dispersal. Delineation of the true continental margin from aeromagnetic evidence allows pre-drift Madagascar to be re-assembled in closer proximity to the coast than indicated in many reconstructions though the geological evidence supporting this pre-drift position is still controversial. 相似文献
30.
William J. Brennan Mark J. Hamilton Richard K. Kilbury Richard L. Reeves Laura J. Covert 《Earth and Planetary Science Letters》1984,70(2):363-372
A secular variation record of the geomagnetic declination has been obtained from glaciolacustrine varved clays and postglacial sediments, sampled both from outcrop and from piston cores from Lake Ontario. It appears to be uninterrupted and covers the interval 14,000 years B.P. (14C) to the present. The record for the interval 14,000–12,300 years B.P. consists of true declination and was obtained from samples collected from outcrop. The record for the interval 12,500 + years B.P. to the present consists of relative declination and was obtained from piston cores. The secular variation record is internally consistent and is compatible with the chronology of events known to have occurred during and following the deglaciation of western New York. Use of the record for magnetic correlation within the study area is demonstrated. 相似文献