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81.
Robert H. Gilkeson Paul C. Heigold Douglas E. Laymon 《Ground Water Monitoring & Remediation》1986,6(1):54-61
Wastes were to be exhumed and removed from a hazardous and chemical waste disposal site. The major disposal practice was shallow burial of wastes in metal drums in parallel trenches. The actual boundaries of the trenches beneath the landscaped cover were not accurately known.
Theoretical two-dimensional models were used to evaluate the application of magnetic methods to define trench boundaries on the disposal site. The models predicted that both the total field and the vertical component anomalies were diagnostic; however, the vertical component anomaly was more focused on the trench boundaries.
A survey with a vertical component fluxgate magnetometer was successful in defining trench boundaries. Observations made along traverses that trended perpendicular to the long axis of the parallel trenches indicated vertical magnetic intensity values with a cyclical pattern of large positive values over trenches and large negative values over intertrench corridors. Vertical magnetic intensity values determined with theoretical two-dimensional models compared favorably to the observed vertical magnetic values. The models were used to constrain the interpretation of the field observations to define trench boundaries; the magnetic survey defined trench boundaries with an accuracy within ± 2 feet. 相似文献
Theoretical two-dimensional models were used to evaluate the application of magnetic methods to define trench boundaries on the disposal site. The models predicted that both the total field and the vertical component anomalies were diagnostic; however, the vertical component anomaly was more focused on the trench boundaries.
A survey with a vertical component fluxgate magnetometer was successful in defining trench boundaries. Observations made along traverses that trended perpendicular to the long axis of the parallel trenches indicated vertical magnetic intensity values with a cyclical pattern of large positive values over trenches and large negative values over intertrench corridors. Vertical magnetic intensity values determined with theoretical two-dimensional models compared favorably to the observed vertical magnetic values. The models were used to constrain the interpretation of the field observations to define trench boundaries; the magnetic survey defined trench boundaries with an accuracy within ± 2 feet. 相似文献
82.
Ian Douglas 《地球表面变化过程与地形》1987,12(5):481-495
The variety of active, exhumed, and buried limestone landforms of northern England, North Wales, and the Isle of Man arises in part from the way in which Dinantian (Lower Carboniferous) sedimentation was affected by a tilt-block basement structure evolved during the closure of the Iapetus Ocean suture to the north, and partly to subsequent plate tectonic movements associated with the closure of the proto-Tethys ocean, the opening of the Atlantic Ocean and the Alpine orogeny. Landforms created during the Dinantian now form important exhumed and buried landscape features. The Permian half-graben structures of the eastern Irish Sea-Cheshire-Worcester Basins account for many of the contrasts between the upland karsts of the Pennines and the lowland karsts of coastal areas. 相似文献
83.
David W. Graham Michael L. Bender Douglas F. Williams Lloyd D. Keigwin 《Geochimica et cosmochimica acta》1982,46(7):1281-1292
The ratio and other parameters have been measured in fossil planktonic foraminifera from the Atlantic and Pacific Ocean basins in order to evaluate the ratio of seawater during the last 75 million years. Results on well-preserved samples indicate that the ratio has increased to its present value by 10–15% during the Cenozoic, and that minima occurred between 55-45 Ma and 10-5 Ma, when the ratio was 15–25% less than at present. The long-term increase may reflect either decreasing deposition of aragonite with a high ratio in shallow seas, or decreasing seafloor spreading rates and consequently decreasing hydrothermal supply of Ca during the Cenozoic. Other geologic evidence suggests that the Eocene minimum (near 50 Ma) may have resulted from increased aragonite sedimentation, while the Late Miocene minimum (between 10-5 Ma) may have been caused by an increased rate of seawater-basalt exchange when seafloor spreading rates increased on the East Pacific Rise near 10 Ma. 相似文献
84.
Douglas G. Brookins 《Environmental Geology》1982,4(3-4):201-208
The Oklo natural reactor, Gabon, permits study of fission-produced elemental behavior in a natural geologic environment. The
uranium ore that sustained fission reactions formed about 2 billion years before present (BYBP), and the reactor was operative
for about 5 × 105 yrs between about 1.95 to 2 BYBP. The many tons of fission products can, for the most part, be studied for their abundance
and distribution today. Since reactor shutdown, many fissiogenic elements have not migrated from host pitchblende, and several
others have migrated only a few tens of meters from the reactor ore. Only Xe and Kr have apparently been largely removed from
the reactor zones. An element by element assessment of the Oklo rocks' ability to retain the fission products, and actinides
and radiogenic Pb and Bi as well, leads to the conclusion that no widespread migration of the elements occurred. This suggests
that rocks with more favorable geologic characteristics are indeed well suited for consideration for the storage of radioactive
waste. 相似文献
85.
Seth Stein Joseph F. Engeln Douglas A. Wiens Robert C. Speed Kazuya Fujita 《Tectonophysics》1983,99(2-4)
The Lesser Antilles subduction zone is an extreme case of the subduction of old (~ 90 m.y.) lithosphere at a slow (~ 2 cm/y) convergence rate. Focal mechanisms of the largest earthquakes in the area have been obtained using body and surface wave data. During the time period (1950–1978) studied the subduction seismicity appears to represent primarily intraplate rather than interplate deformation. All three large (magnitude seven) earthquakes were from intraplate normal faults; no large thrust faulting earthquakes and few small ones occurred. These observations suggest that the plate boundary is largely decoupled, that subduction is at least partially aseismic, and that the downgoing slab is in a state of extension. 相似文献
86.
W. Douglas Thompson Daniel Wartenberg 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(5):635-646
Much research in environmental epidemiology relies on aggregate-level information on exposure to potentially toxic substances
and on relevant covariates. We compare the use of additive (linear) and multiplicative (log-linear) regression models for
the analysis of such data. We illustrate how both additive and multiplicative models can be fit to aggregate-level data sets
in which disease incidence is the dependent variable, and contrast these results with similar models fitted to individual-level
data. We find (1) that for aggregate-level data, multiplicative models are more likely than additive models to introduce bias
into the estimation of rates, an effect not found with individual-level data; and (2) that under many circumstances multiplicative
models reduce the precision of the estimates, an effect also not found in individual-level models. For both additive and multiplicative
models of aggregate-level data, we find that, in the presence of covariates, narrow confidence interval are obtained only
when two or more antecedent factors are strongly related to the measured covariate and/or the exposure of primary substantive
interest. We conclude that the equivalency of fitting additive versus multiplicative models in studies with individual-level
binary data does not carry over to studies that analyze aggregate-level information. For aggregate data, we strongly recommend
use of additive models.
Supported by Grant #1 U19 EH000102 from the National Center for Environmental Health, Centers for Disease Control and Prevention,
Atlanta, GA. 相似文献
87.
John Douglas 《Bulletin of Earthquake Engineering》2007,5(3):363-376
Accurate estimates of the ground motions that occurred during damaging earthquakes are a vital part of many aspects of earthquake
engineering, such as the study of the size and cause of the uncertainties within earthquake risk assessments. This article
compares a number of methods to estimate the ground shaking that occurred on Guadeloupe (French Antilles) during the 21st
November 2004 (M
w
6.3) Les Saintes earthquake, with the aim of providing more accurate shaking estimates for the investigation of the sources
of uncertainties within loss evaluations, based on damage data from this event. The various techniques make differing use
of the available ground-motion recordings of this earthquake and by consequence the estimates obtained by the different approaches
are associated with differing uncertainties. Ground motions on the French Antilles are affected by strong local site effects,
which have been extensively investigated in previous studies. In this article, use is made of these studies in order to improve
the shaking estimates. It is shown that the simple methods neglecting the spatial correlation of earthquake shaking lead to
uncertainties similar to those predicted by empirical ground-motion models and that these are uniform across the whole of
Guadeloupe. In contrast, methods (such as the ShakeMap approach) that take account of the spatial correlation in motions demonstrate
that shaking within roughly 10 km of a recording station (covering a significant portion of the investigated area) can be
defined with reasonable accuracy but that motions at more distant points are not well constrained. 相似文献
88.
89.
Douglas D. Walker Björn Gylling Anders Ström Jan-Olof Selroos 《Hydrogeology Journal》2001,9(5):419-431
Safety Report 1997 (SR 97) of the Swedish Nuclear Fuel and Waste Management Company is a comprehensive performance assessment
of three hypothetical radioactive waste repositories in Sweden. It includes hydrogeologic studies (data compilation, parameter
synthesis, and groundwater flow modeling) to determine groundwater flow and the associated uncertainties for the three sites.
This report reviews and compares the hydrogeologic characterization programs, the site characteristics, and the groundwater
flow models used in the SR 97 performance assessment. Although differences in site-characterization programs tend to mask
differences in site characteristics, the sites do have notable differences that affect the results of the performance assessment.
The effects of model uncertainties evaluated by the variant cases appear to be smaller than the variability of results for
the base case (best estimate of site conditions) of each site.
Electronic Publication 相似文献
90.
Changshou Sun Douglas W. Later Gang Chen 《Fragblast: International Journal for Blasting and Fragmentation》2001,5(4):235-246
In this paper, studies were conducted on the effect of borehole size on explosive energy loss in rock blasting. Since most industrial explosives are nonideal ones, the charge size and the confinement condition have significant impact on the detonation performance of these explosives. Analyses indicated that smaller boreholes will cause more loss of explosive energy than larger ones. This is especially true for most industrial explosives. The paper presents the analyses of energy loss for a number of different explosives with various borehole sizes. Based on these analyses recommendations and guidelines were given for borehole size determination in rock blasting operations. 相似文献