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61.
Pieter Hoekstra Raye Lahti Jim Hild C. Richard Bates David Phillips 《Ground Water Monitoring & Remediation》1992,12(4):110-117
Time domain electromagnetic (TDEM) soundings were utilized in site assessment studies for the purpose of accomplishing two objectives: (1) measuring the migration of brines from oil and gas field evaporation pits, and (2) mapping the continuity of clay strata. Both case histories are representative of common objectives in site assessment. The data for both examples were analyzed by one-dimensional ridge regression inversions.
Both case histories illustrate that TDEM is an effective method for determining the lateral and vertical resistivity distribution (geoelectric section) of the subsurface in the depth range from about 5 m to 100 m, and it is known from other investigations that depths of investigations up to 2500 m can be achieved with TDEM.
Frequently, the lateral extent of contaminant plumes emanating from localized sources are of limited areal extent. The case history involving the use of TDEM to map a brine plume shows that a TDEM measurement has a relatively small zone of influence, so that meaningful information about the lateral and vertical extent of the plume can be obtained. Both case histories demonstrate the ability of TDEM to determine geoelectric sections below layers of low resistivity. 相似文献
Both case histories illustrate that TDEM is an effective method for determining the lateral and vertical resistivity distribution (geoelectric section) of the subsurface in the depth range from about 5 m to 100 m, and it is known from other investigations that depths of investigations up to 2500 m can be achieved with TDEM.
Frequently, the lateral extent of contaminant plumes emanating from localized sources are of limited areal extent. The case history involving the use of TDEM to map a brine plume shows that a TDEM measurement has a relatively small zone of influence, so that meaningful information about the lateral and vertical extent of the plume can be obtained. Both case histories demonstrate the ability of TDEM to determine geoelectric sections below layers of low resistivity. 相似文献
62.
Adolf Best 《Pure and Applied Geophysics》1968,69(1):193-204
Summary Geomagnetic storms of middle intensity—the so-called moderate storms—are characterized in middle latitudes by fluctuations of pulsation and bay type in all three componentsD, H andZ, the periods of which are within the range of 20 to 120 minutes. They are appearing in all three storm phases (initial, main and recovery phase), generally showing a maximum in the main phase. By the aid of statistic frequency analysis as well as of the calculation of the autocorrelation function and power spectra the fluctuations of this period ranges were analysed for 22 geomagnetic storms of middle intensity during the period of 1952 to 1962, recorded at the Niemegk observatory. In order to get an impression about the dependence on latitude 7 parallel records from a station in higher latitude (Dombas, Norway) were analysed in the same way. Power spectra show that there are favoured some periodicities within the period range of 20 to 120 minutes, especially near 50 to 60 and 90 to 120 minutes. This applies to the investigatedX(H)- andY(D)-components as well in middle as in northern latitudes.
Mitt. aus dem Geomagnetischen Inst. Potsdam Nr. 263. 相似文献
Mitt. aus dem Geomagnetischen Inst. Potsdam Nr. 263. 相似文献
63.
Attention to detail is essential for the reduction of pollution. By detective work, a river purification board has been able to track down an important single source of PCB contamination of its sewage sludge and institute remedial action. 相似文献
64.
There is widespread acceptance of the phosphorus retention capability of wetlands even though research findings are often inconclusive and contradictory. The results of a one year phosphorus budget study indicate that internal wetland processes may transform sediment bound phosphorus to plant available orthophosphorus. While total phosphorus imports were nearly double the total phosphorus exports for the study wetland, orthophosphorus exports were 22 per cent greater than imports. This study supports the recent finding that wetlands have limited capability to retain orthophosphorus and indicates that wetlands may even increase the export of orthophosphorus. The generally accepted nutrient retention function of wetlands and their possible role in eutrophication is thus questionable. 相似文献
65.
66.
Heat and bromide were compared as tracers for examining stream/ground water exchanges along the middle reaches of the Santa Clara River, California, during a 10-hour surface water sodium bromide injection test. Three cross sections that comprise six shallow (<1 m) piezometers were installed at the upper, middle, and lower sections of a 17 km long study reach, to monitor temperatures and bromide concentrations in the shallow ground water beneath the stream. A heat and ground water transport simulation model and a closely related solute and ground water transport simulation model were matched up for comparison of simulated and observed temperatures and bromide concentrations in the streambed. Vertical, one-dimensional simulations of sediment temperature were fitted to observed temperature results, to yield apparent streambed hydraulic conductivities in each cross section. The temperature-based hydraulic conductivities were assigned to a solute and ground water transport model to predict sediment bromide concentrations, during the sodium bromide injection test. Vertical, one-dimensional simulations of bromide concentrations in the sediments yielded a good match to the observed bromide concentrations, without adjustment of any model parameters except solute dispersivities. This indicates that, for the spatial and temporal scales examined on the Santa Clara River, the use of heat and bromide as tracers provide comparable information with respect to apparent hydraulic conductivities and fluxes for sediments near streams. In other settings, caution should be used due to differences in the nature of conservative (bromide) versus nonconservative (heat) tracers, particularly when preferential flowpaths are present. 相似文献
67.
Jim Wild recounts the rationale and success of AuroraWatch, a service that alerts you when you might be able to see aurorae. 相似文献
68.
M. J. Best 《Theoretical and Applied Climatology》2006,84(1-3):47-55
Summary The current resolution of operational weather forecast model is not sufficient in general to explicitly resolve even the major
cities of the World. As a consequence, urban areas have traditionally been neglected in such models. The introduction of tiled
land surface models has enabled sub-gridscale landuse to be modelled, and hence has provided the opportunity to model cities
within weather forecast models. However, to date there has been little effort made within the operational weather forecast
community.
At present there is only one operational centre that explicitly resolves urban areas. This centre includes a simple urban
scheme within its mesoscale and global models, which has been shown to have a positive impact on the forecast. However, with
the recent developments within urban meteorology there are now a variety of urban schemes, which vary in their complexity
and parameter requirements, that would be suitable for operational weather forecast models. So it is likely that more operational
models, and in particular mesoscale models, will include urban areas in the near future.
With the majority of the World‘s population living in cities, the resilience of these cities to the impacts of climate change
is also becoming of increasing interest. This means that urban areas will have to be included within climate change simulations,
as well as weather forecast simulations, in the future. At present, only one climate change model has included a parametrisation
for urban areas. However, this is likely to increase if work in this area grows rapidly. 相似文献
69.
M. J. Best C. S. B. Grimmond Maria Gabriella Villani 《Boundary-Layer Meteorology》2006,118(3):503-525
The UK Met Office has introduced a new scheme for its urban tile in MOSES 2.2 (Met Office Surface Exchange Scheme version 2.2), which is currently implemented within the operational Met Office weather forecasting model. Here, the performance of the urban tile is evaluated in two urban areas: the historic core of downtown Mexico City and a light industrial site in Vancouver, Canada. The sites differ in terms of building structures and mean building heights. In both cases vegetation cover is less than 5%. The evaluation is based on surface energy balance flux measurements conducted at approximately the blending height, which is the location where the surface scheme passes flux data into the atmospheric model. At both sites, MOSES 2.2 correctly simulates the net radiation, but there are discrepancies in the partitioning of turbulent and storage heat fluxes between predicted and observed values. Of the turbulent fluxes, latent heat fluxes were underpredicted by about one order of magnitude. Multiple model runs revealed MOSES 2.2 to be sensitive to changes in the canopy heat storage and in the ratio between the aerodynamic roughness length and that for heat transfer (temperature). Model performance was optimum with heat capacity values smaller than those generally considered for these sites. The results suggest that the current scheme is probably too simple, and that improvements may be obtained by increasing the complexity of the model. 相似文献
70.
Roberto Stanley Molina–Garza Jim Pindell Diego Villagómez 《International Geology Review》2020,62(4):415-420
ABSTRACTWe discuss the 2018 publication that reports petrographic, heavy mineral data, mineral chemistry, and zircon geochronology for Oligocene sandstones in the Cerro Pelón area in southern Mexico Sureste basin. As the title of their paper says, the goal of their study is to establish the source (s) of the voluminous Cenozoic section in this region, reaching several kilometres in thickness and important as a petroleum system. These authors conclude that Oligocene sandstones of La Laja Formation were mostly sourced from eclogite- to greenschist-facies metasedimentary, metaigneous, and ultramafic rocks of the Guatemala suture complex. Minor contributions from the Chiapas Massif Complex, exposed directly to the south ~60 km of the Cerro Pelón area, were also suggested by the authors. They thus conclude that the Palaeogene stratigraphic record in southeastern Mexico was mostly controlled by the development of the Caribbean–North America plate boundary rather than by orogenic processes at the Pacific margin of North America. Presently, we do not agree with the conclusions of Ortega Flores and colleagues who studied the Cerro Pelón section, thus some discussion is required. Serpentinite bearing Nanchital Conglomerate is well exposed in the Cerro Pelón area, and high- to low-grade metamorphic rocks experienced an uplift in the vicinity of the Cerro Pelón area at the time of deposition of the La Laja Formation. We believe the data are better explained by multiple local sources in southern and eastern Oaxaca as well as sources to the south and southwest, which include the Cenozoic coastal batholith, the Grenvillean/Guichicovi basement complexes, the Chiapas Massif, the Mazatlán schist and other units in the Cuicateco Belt, as well as the Mesozoic cover of these areas (Todos Santos Formation, Cretaceous carbonate rocks, and Paleogene strata such as the Soyaló and Bosque Formations). 相似文献