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991.
992.
Since 1991, the Caernarvon Freshwater Diversion has been reintroducing Mississippi River water into a previously hydrologically isolated estuary in an effort to restore wetlands. To determine the effect of freshwater inflow on estuarine nekton community structure, a Before?CAfter?CControl?CImpact study design was applied. As a result of the opening, salinities in the impact area decreased, and the nekton community structure in the estuary changed significantly. Species of economical or ecological importance either increased in biomass or exhibited no response to the opening of the diversion. Higher abundances of small fish were observed in the area receiving freshwater flow, which is an indication that the area serves as a refuge from large marine predators. Because a salinity gradient was established, as opposed to a uniform but lower salinity regime, aquatic habitat was available to nekton species from a wide spectrum of salinity tolerances. 相似文献
993.
The scopes of this work are to study the mechanisms of load transfer and the deformations of the ground during slurry trenching and concreting in dry sand and to evaluate their effects on service structural loads, wall deflections and ground displacements behind the wall caused by subsequent excavation. A series of three-dimensional finite element analyses was carried out modelling the installation of diaphragm walls consisting of panels of different length. The soil was modelled as either linearly elastic-perfectly plastic or incrementally non-linear (hypoplastic) with elastic strain range. Plane strain analyses of diaphragm walls of identical cross section were also carried out in which wall installation was either modelled or the wall was wished in place (WIP). The analyses predict ground movements consistent with the experimental observations both in magnitude and trend. The results also show that the maximum horizontal wall deflections and structural loads reduce with increasing panel aspect ratio towards a minimum which is about twice the value computed for WIP analyses. Panel aspect ratios should be larger than about three to take advantage of the three-dimensional effects. The pattern and magnitude of surface vertical displacements obtained from linearly elastic-perfectly plastic analyses, no matter whether three- or two-dimensional, are unrealistic. 相似文献
994.
Jens-Olaf?DelfsEmail author Frank?Blumensaat Wenqing?Wang Peter?Krebs Olaf?Kolditz 《Environmental Earth Sciences》2012,65(5):1439-1457
This paper presents the hydrological coupling of the software framework OpenGeoSys (OGS) with the EPA Storm Water Management
Model (SWMM). Conceptual models include the Saint Venant equation for river flow, the 2D Darcy equations for confined and
unconfined groundwater flow, a two-way hydrological coupling flux in a compartment coupling approach (conductance concept),
and Lagrangian particles for solute transport in the river course. A SWMM river–OGS aquifer inter-compartment coupling flux
is examined for discharging groundwater in a systematic parameter sensitivity analysis. The parameter study involves a small
perturbation (first-order) sensitivity analysis and is performed for a synthetic test example base-by-base through a comprehensive
range of aquifer parametrizations. Through parametrization, the test cases enables to determine the leakance parameter for
simulating streambed clogging and non-ocillatory river-aquifer water exchange rates with the sequential (partitioned) coupling
scheme. The implementation is further tested with a hypothetical but realistic 1D river–2D aquifer model of the Poltva catchment,
where discharging groundwater in the upland area affects the river–aquifer coupling fluxes downstream in the river course
(propagating feedbacks). Groundwater contribution in the moving river water is numerically determined with Lagrangian particles.
A numerical experiment demonstrates that the integrated river–aquifer model is a serviceable and realistic constituent in
a complete compartment model of the Poltva catchment. 相似文献
995.
996.
Frank?DethlefsenEmail author Christoph?Haase Markus?Ebert Andreas?Dahmke 《Environmental Earth Sciences》2012,65(4):1105-1117
One of the uncertainties in the field of carbon dioxide capture and storage (CCS) is caused by the parameterization of geochemical
models. The application of geochemical models contributes significantly to calculate the fate of the CO2 after its injection. The choice of the thermodynamic database used, the selection of the secondary mineral assemblage as
well as the option to calculate pressure dependent equilibrium constants influence the CO2 trapping potential and trapping mechanism. Scenario analyses were conducted applying a geochemical batch equilibrium model
for a virtual CO2 injection into a saline Keuper aquifer. The amount of CO2 which could be trapped in the formation water and in the form of carbonates was calculated using the model code PHREEQC.
Thereby, four thermodynamic datasets were used to calculate the thermodynamic equilibria. Furthermore, the equilibrium constants
were re-calculated with the code SUPCRT92, which also applied a pressure correction to the equilibrium constants. Varying
the thermodynamic database caused a range of 61% in the amount of trapped CO2 calculated. Simultaneously, the assemblage of secondary minerals was varied, and the potential secondary minerals dawsonite
and K-mica were included in several scenarios. The selection of the secondary mineral assemblage caused a range of 74% in
the calculated amount of trapped CO2. Correcting the equilibrium constants with respect to a pressure of 125 bars had an influence of 11% on the amount of trapped
CO2. This illustrates the need for incorporating sensitivity analyses into reaction pathway modeling. 相似文献
997.
This paper presents a method for transforming the information of an engineering geological map into useful information for
non-specialists involved in land-use planning. The method consists of classifying the engineering geological units in terms
of land use capability and identifying the legal and the geologic restrictions that apply in the study area. Both informations
are then superimposed over the land use and a conflict areas map is created. The analysis of these data leads to the identification
of existing and forthcoming land use conflicts and enables the proposal of planning measures on a regional and local scale.
The map for the regional planning was compiled at a 1:50,000 scale and encompasses the whole municipal land area where uses
are mainly rural. The map for the local planning was compiled at a 1:10,000 scale and encompasses the urban area. Most of
the classification and operations on maps used spatial analyst tools available in the Geographical Information System. The
regional studies showed that the greater part of Analandia’s territory presents appropriate land uses. The local-scale studies
indicate that the majority of the densely occupied urban areas are in suitable land. Although the situation is in general
positive, municipal policies should address the identified and expected land use conflicts, so that it can be further improved. 相似文献
998.
P. C. S. Carvalho A. M. R. Neiva M. M. V. G. Silva 《Environmental Earth Sciences》2012,65(4):1215-1230
The main purpose of this study is to assess arsenic and antimony availability in soils, as well as Co, Cr, Cu, Fe, Mn, Ni,
Pb and Zn availability in soils derived from the schist–metagraywacke complex close to old Sb–Au mines and in soils developed
from Ordovician slates and close to an old As–Au mine in Portugal. The availability was determined using a European certified
sequential extraction procedure (BCR). The results demonstrated that metalloids are not readily bioavailable, because they
are mainly associated with the residual fraction. Arsenic and antimony proportions in exchangeable fractions are up to 3 and
1%, respectively. However, arsenic is up to 24% in oxy-hydroxide fractions, while antimony is up to 4% in them, demonstrating
the highest bioavailability of arsenic compared to that of antimony, as metalloids are weakly bound to the soils in that fraction.
Therefore, arsenic tends to be more toxic than antimony in all soils studied. However, the pseudo-total contents show that
both metalloids are above the Italian and Dutch guidelines. Therefore, if physico-chemical changes occur arsenic and antimony
will show higher potential environmental risk than evidenced by Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn. 相似文献
999.
The morphosedimentary evolution of a sector of the southern Espinhaco range (northern Minas Gerais State, Brazil) and its
regional neotectonic setting are presented herein. The studied site is a stream at base level flowing along the western border
of the range. Its identification was accomplished by using remote sensing techniques including the analysis of 3D slope models
generated with shuttle radar topography mission images. The main geomorphological features of the identified site were surveyed
in a 1:500 scale. In addition, seven stratigraphic logs are described. A regional geologic compilation and facies diagrams
were used as a basis for the integration of the geomorphological and stratigraphic data, which produced some conclusions about
the recent tectonic reactivations at the eastern border of Sao Francisco Craton. The results point to a local eastward tilting
of the Espinhaco range. This fact is in accordance with previous findings in neighboring areas and results in the asymmetric
evolution of the fluvial valley, as well as the regional relief. 相似文献
1000.
Analysis of aquifer vulnerability and water quality using SINTACS and geographic weighted regression
Jose A. Ramos Leal Felipe O. Tapia Silva Ismael Sandoval Montes 《Environmental Earth Sciences》2012,66(8):2257-2271
Aquifer vulnerability and water quality were assessed in the Central Valleys of Oaxaca (Mexico) using the SINTACS method, based on a geographic information system. SINTACS layers were prepared using data such as climate (rainfall and temperature), water table, hydraulic conductivity, geology, soil type and topographic model. Maps for water quality index (WQI), contamination index and pollution sources index (PSI) were also obtained by this work. Groundwater quality in the Central Valleys may be affected by two factors, those with an anthropogenic origin and those with natural origin. High vulnerability values are located in the valleys of the basin, where granular sediments are exposed. Low vulnerability values are distributed in the basin??s ranges, where metamorphic rocks are found. Given that many of the zones with the highest groundwater vulnerability values correspond to zones with the greatest PSI values, there is great risk of groundwater contamination for the area of study because external (indicated by PSI) and internal (indicated by SINTACS) factors that cause pollution can be frequently observed in the same place. Geographic weighted regression (GWR) is used to test the dependency between WQI as dependent variable and SINTACS, PSI, Urban localities, Agriculture, Pastures and Rivers as predictors. The results indicate the non-stationary behavior of the dependent variable with respect to the predictors. While the obtained GWR models used to model WQI cannot be used in practical situations to predict the behavior of said variable, they can be used to estimate the degree to which the predictors influence the variable of interest. 相似文献