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111.
112.
Distinguishing Carbonate Reservoir Pore Facies with Nuclear Magnetic Resonance Measurements 总被引:1,自引:0,他引:1
Characterization of carbonate rocks may involve identifying the important pore types which are present. In the past, this
task has required detailed petrographic analysis of many core samples. Here, we describe a method which uses nuclear magnetic
resonance (NMR) measurements to reduce the amount of petrographic analysis needed for porosity typing of carbonate reservoir
rocks.
For a rock sample which has been measured with NMR, our method decomposes the log(T2) spectrum into at most three Gaussian-shaped components and gives a set of nine parameters. Two characteristic quantities
having geological significance are extracted from the nine parameters. Values of the two quantities are compared with a reference
set, established from samples having both NMR and petrographic evaluations of porosity types. We use a Bayesian approach to
the classification of the dominant porosity type.
Tests of our method on 103 samples show a correct prediction in 60 to 90 percent of the samples. The lower success rate was
obtained for samples with five porosity types from three fields; the higher success rate obtained with samples with three
porosity types from one well. The use of geologically significant quantities extracted from the decomposition gives comparable
success rate to those obtained using a standard, non-geological approach such as canonical variates. 相似文献
113.
The past decade has brought substantial transition to South Africa. The introduction of democracy in 1994 has yielded important political and socioeconomic transformations affecting millions of people. Here, we explore the impact of institutional and structural changes on the availability and management of fuelwood, a key natural resource in rural South Africa. As in other developing regions, many households depend on natural resources for both sustenance and energy needs. Drawing on qualitative data from 32 interviews, our objective is to describe, from the perspective of the respondents, (1) resource scarcity, (2) the underlying causes of resource scarcity, (3) the role of traditional authority in managing resources, and (4) strategies used by community members in the face of resource scarcity. The results have important implications for the well-being of both social and natural systems in many transitional, rural developing societies. 相似文献
114.
A review of water column processes influencing hypoxia in the northern Gulf of Mexico 总被引:1,自引:0,他引:1
Michael J. Dagg James W. Ammerman Rainer M. W. Amon Wayne S. Gardner Rebecca E. Green Steven E. Lohrenz 《Estuaries and Coasts》2007,30(5):735-752
In this review, we use data from field measurements of biogeochemical processes and cycles in the Mississippi River plume
and in other shelf regions of the northern Gulf of Mexico to determine plume contributions to coastal hypoxia. We briefly
review pertinent findings from these process studies, review recent mechanistic models that synthesize these processes to
address hypoxia-related issues, and reinterpret current understanding in the context of these mechanistic models. Some of
our conclusions are that both nitrogen and phosphorus are sometimes limiting to phytoplankton growth; respiration is the main
fate of fixed carbon in the plume, implying that recycling is the main fate of nitrogen; decreasing the river nitrate loading
results in less than a 1:1 decrease in organic matter sinking from the plume; and sedimenting organic matter from the Mississippi
River plume can only fuel about 23% of observed coastal hypoxia, suggesting significant contributions from the Atchafalaya
River and, possibly, coastal wetlands. We also identify gaps in our knowledge about controls on hypoxia, and indicate that
some reinterpretation of our basic assumptions about this system is required. There are clear needs for improved information
on the sources, rates, and locations of organic matter sedimentation; for further investigation of internal biogeochemical
processes and cycling; for improved understanding of the rates of oxygen diffusion across the pycnocline; for identification
and quantification of other sources of organic matter fueling hypoxia or other mechanisms by which Mississippi River derived
organic matter fuels hypoxia; and for the development of a fully coupled physical-biogeochemical model. 相似文献
115.
The Effect of Tidal Fluctuation on a Coastal Aquifer in the UK 总被引:10,自引:0,他引:10
A. D. Erskine 《Ground water》1991,29(4):556-562
116.
Issues in sediment toxicity and ecological risk assessment 总被引:8,自引:0,他引:8
This paper is based on a facilitated Workshop and Roundtable Discussion of key issues in sediment toxicology and ecological risk assessment (ERA) as applied to sediments that was held at the Conference on Dredged Material Management: Options and Environmental Considerations. The issues addressed included how toxicity is defined and perceived, how it is measured, and how it should be used within the context of ERA to support management decisions. The following conclusions were reached regarding scientific considerations of these issues. Toxicity is a measure of hazard and not a risk per se. Thus, toxicity testing is a means but not the end to understand risks of sediments. Toxicity testing cannot presently be replaced by chemical analyses to define hazard. Toxicity test organisms need to be appropriate to the problem being addressed, and the results put into context relative to both reference and baseline comparisons to understand hazard. Use of toxicity tests in sediment ERAs requires appropriate endpoints and risk hypotheses, considering ecological not just statistical significance, and recognizing that hazard does not equate to risk. Toxicity should be linked to population and community response to support decision-making, assessing possible genotypic adaptations that can influence risk estimates, and addressing uncertainty. Additionally, several key scientific issues were identified to improve future sediment ERAs, including the need to improve basic understanding of ecological mechanisms and processes, recognition of variability in the assessment process, and an improved focus and ability to assess risks to populations and communities. 相似文献
117.
118.
Denis Lacelle Alfonso F. Davila Wayne H. Pollard Dale Andersen Jennifer Heldmann Margarita Marinova Christopher P. McKay 《Earth and Planetary Science Letters》2011,301(1-2):403-411
To date, studies of the stability of subsurface ice in the McMurdo Dry Valleys of Antarctica have been mainly based on climate-based vapor diffusion models. In University Valley (1800 m), a small glacier is found at the base of the head of the valley, and adjacent to the glacier, a buried body of massive ice was uncovered beneath 20–40 cm of loose cryotic sediments and sandstone boulders. This study assesses the origin and stability of the buried body of massive ice by measuring the geochemistry and stable O–H isotope composition of the ice and applies a sublimation and molecular diffusion model that accounts for the observed trends. The results indicate that the buried massive ice body represents an extension of the adjacent glacier that was buried by a rock avalanche during a cold climate period. The contrasting δ18O profiles and regression slope values between the uppermost 6 cm of the buried massive ice (upward convex δ18O profile and SD-18O = 5.1) and that below it (progressive increase in δ18O and SD-18O = 6.4) suggest independent post-depositional processes affected the isotope composition of the ice. The upward convex δ18O profile in the uppermost 6 cm is consistent with the ice undergoing sublimation. Using a sublimation and molecular diffusion model, and assuming that diffusion occurred through solid ice, the sublimation rate needed to fit the measured δ18O profile is 0.2 ? 10? 3 mm yr? 1, a value that is more similar to net ice removal rates derived from 3He data from cobbles in Beacon Valley till (7.0 ? 10? 3 mm yr? 1) than sublimation rates computed based on current climate (0.1–0.2 mm yr?1). We suggest that the climate-based sublimation rates are offset due to potential ice recharge mechanisms or to missing parameters, particularly the nature and thermo-physical properties of the overlying sediments (i.e., temperature, humidity, pore structure and ice content, grain size). 相似文献
119.
While much work has been done in investigating determinants of oil spillage attributed to vessel accidents, little research has been conducted on the effectiveness of ship hull design in reducing marine pollution. This paper addresses whether the double-hull requirement reduces vessel-accident oil spillage. The volume of oil spillage due to oil-cargo vessel accidents was investigated using tobit regressions and an empirical data set of individual vessel accident pollution incidents investigated by the US Coast Guard from 2001 to 2008. The results indicate that the double hull design on average reduces the size of oil spills by 20% and 62% in tank barge and tanker ship accidents, respectively. 相似文献
120.
Abstract Three sites were instrumented to measure all components of the energy balance. The sites were located in the Churchill, Manitoba region and comprised a Sea Site on a sand spit 1 km seaward from the mainland, a Nearcoast Site 2 km inland from the coast and an Inland Site 65 km inland. Measurements were made continuously over a 90‐day period from 19 May to 16 August 1984. This period encompassed the bulk of the growing season. The measurements were stratified into onshore and offshore wind directions and were compared for 10‐day periods. The comparisons show very significant differences attributable to the cold summer conditions promoted by the sea ice in Hudson Bay. The ground heat flux and latent heat flux were much greater during offshore winds but the sensible heat flux was greatest for onshore winds. Air temperatures averaged 7°C warmer for offshore than for onshore winds. The reasons for these differences are detailed and the climatic modifications that would probably result from earlier sea‐ice melt are discussed. Some implications of climatic modification are also noted. 相似文献