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排序方式: 共有199条查询结果,搜索用时 31 毫秒
101.
Sabine Rijnsburger Carola M. van der Hout Onno van Tongeren Gerben J. de Boer Bram C. van Prooijen Wil G. Borst Julie D. Pietrzak 《Ocean Dynamics》2016,66(5):719-736
This study identifies and unravels the processes that lead to stratification and destratification in the far field of a Region of Freshwater Influence (ROFI). We present measurements that are novel for two reasons: (1) measurements were carried out with two vessels that sailed simultaneously over two cross-shore transects; (2) the measurements were carried out in the far field of the Rhine ROFI, 80 km downstream from the river mouth. This unique four dimensional dataset allows the application of the 3D potential energy anomaly equation for one of the first times on field data. With this equation, the relative importance of the depth mean advection, straining and nonlinear processes over one tidal cycle is assessed. The data shows that the Rhine ROFI extends 80 km downstream and periodic stratification is observed. The analysis not only shows the important role of cross-shore tidal straining but also the significance of along-shore straining and depth mean advection. In addition, the nonlinear terms seem to be small. The presence of all the terms influences the timing of maximum stratification. The analysis also shows that the importance of each term varies in the cross-shore direction. One of the most interesting findings is that the data are not inline with several hypotheses on the functioning of straining and advection in ROFIs. This highlights the dynamic behaviour of the Rhine ROFI, which is valuable for understanding the distribution of fine sediments, contaminants and the protection of coasts. 相似文献
102.
Chicgoua Noubactep Sabine Caré Brice Donald Btatkeu K. Charles Péguy Nanseu‐Njiki 《洁净——土壤、空气、水》2012,40(1):100-109
Filtration systems containing metallic iron as reactive medium (Fe0 beds) have been intensively used for water treatment during the last two decades. The sustainability of Fe0 beds is severely confined by two major factors: (i) reactivity loss as result of the formation of an oxide scale on Fe0 and (ii) permeability loss due to pore filling by generated iron corrosion products. Both factors are inherent to iron corrosion at pH > 4.5 and are common during the lifespan of a Fe0 bed. It is of great practical significance to improve the performance of Fe0 beds by properly addressing these key factors. Recent studies have shown that both reactivity loss and permeability loss could be addressed by mixing Fe0 and inert materials. For a non‐porous additive like quartz, the threshold value for the Fe0 volumetric proportion is 51%. Using the Fe0/quartz system as reference, this study theoretically discusses the possibility of (i) replacing Fe0 by bimetallic systems (e.g., Fe0/Cu0), or (ii) partially replacing quartz by a reactive metal oxide (MnO2 or TiO2) to improve the efficiency of Fe0 beds. Results confirmed the suitability of both tools for sustaining Fe0 bed performance. It is shown that using a Fe0:MnO2 system with the volumetric proportion 51:49 will yield a filter with 40% residual porosity at Fe0 depletion (MnO2 porosity 62%). This study improves Fe0 bed design and can be considered as a basis for further refinement and detailed research for efficient Fe0 filters. 相似文献
103.
In this article we review the occurrence and consequences of long-term memory in geophysical records like climate and seismic
records, and describe similarities with financial data sets. We review several methods to detect linear and nonlinear long-term
correlations, also in the presence of external trends, and show how external trends can be detected in data with long-term
memory. We show as well that long-term correlations lead to a natural clustering of extreme events and discuss the implications
for several geophysical data sets. 相似文献
104.
Sarah L. Moll Richard de Grijs Sabine Mengel Linda J. Smith Paul A. Crowther 《Astrophysics and Space Science》2009,324(2-4):177-182
We present virial mass estimates of young massive clusters (YMCs) in the starburst galaxies NGC1140 and M83, determined from high spectral resolution VLT echelle spectroscopy and high spatial resolution Hubble Space Telescope imaging. The survivability of such clusters is important in testing the scenario that YMCs are potentially proto-globular clusters. As young clusters, they lie in the domain in which dynamical masses appear to overestimate true cluster masses, most likely due to the clusters not being virialised. We find that the dynamical mass of NGC1140-1 is approximately ten times greater than its photometric mass. We propose that the most likely explanation for this disparity is the crowded environment of NGC1140-1, rather than this being solely due to a lack of virial equilibrium. 相似文献
105.
It is commonly suggested that older non-Western migrants have a higher risk of experiencing multiple forms of disadvantage than native older adults. However, few researchers have studied the life situation and urban conditions of older migrants in relation to each other and in comparison to native older adults with a similar socioeconomic status. This paper investigates whether different groups of older non-Western migrants (of Surinamese, Moroccan and Turkish origin) in deprived neighbourhoods in Amsterdam experience similar or different levels of multiple disadvantage compared to socioeconomically similar native Dutch older residents living in the same neighbourhoods, and explores how multiple disadvantage can be explained in relation to life and residential histories and neighbourhood changes. Analysis of 85 in-depth interviews indicates that all categories of low-income older adults experienced certain levels of disadvantage, although they evaluated their circumstances using different frames of reference. Regarding health, both native-born and migrant older people experienced chronic illness. However, the results of this study suggest that those in the latter group (especially Moroccans and Turks) experienced health problems and related functional limitations at a younger age. Native Dutch older adults were somewhat better off with respect to the availability of household resources, but compared to older non-Western migrants were more likely to experience the negative effects of neighbourhood deprivation. In summary, this study refines common assertions that older migrants are more disadvantaged than native older adults. Differences in experiences of advantage and disadvantage have their origin in differences in life and residential histories and neighbourhood change. 相似文献
106.
Sabine Méhay Pierre Adam Isabelle Kowalewski Pierre Albrecht 《Organic Geochemistry》2009,40(4):531-545
The sulfur isotopic composition (δ34S) of petroleum is believed to be affected mainly by sulfur incorporation reactions into the sedimentary organic matter during the early diagenesis. However, secondary processes could affect the original δ34S of oil under the effect of thermal maturity or of the microbial activity of biodegraded reservoirs. In this study, the different processes that may affect the δ34S of in-reservoir oils were assessed based on the sulfur content and isotopes of a series of oil and core samples coming from various reservoirs of the Lower Cretaceous Mannville Group, Western Canada Sedimentary Basin (WCSB). Based on the molecular study, these samples appear to have reached various levels of maturity and biodegradation, ranging from 0 to 6.5 on the biodegradation scale of Peters and Moldowan. In addition, mixing of organic matter coming from different source rocks was identified based on the comparison with extensive correlation studies performed in the WCSB.Investigation of the δ34S shows a trend that seems a priori correlated to the level of biodegradation. However, a careful interpretation of molecular and sulfur isotope data leads to the conclusion that the observed δ34S variations have rather to be ascribed to contributions of oils generated by various source rocks. Alternatively, variations of δ34S could neither be related to maturity differences nor to kinetic effects during organic sulfur compounds biodegradation. In the case of some specific core samples showing a common origin based on biomarker study, δ34S variations might not be related to different sources but to secondary sulfur incorporation/exchange processes occurring within the reservoir. These processes would involve reduced sulfur species from bacterial sulfate reduction formed in situ or migrated into Mannville reservoirs. This hypothesis is supported by laboratory experiments showing sulfur exchange/incorporation under plausible conditions for shallow reservoirs. 相似文献
107.
108.
We have used a new thermodynamic model of barium and calcium sulfate solubilities in multicomponent electrolyte solutions (Monnin, 1999) to investigate the stabilities of barite and anhydrite in seawater or in marine sediment porewaters at high temperature and pressure. As a further test supplementing those previously carried out during model development, we have calculated the temperature at which standard seawater becomes saturated with respect to anhydrite. The model predicts that, upon heating at 500 bars, standard seawater becomes saturated with respect to anhydrite at 147 ± 5°C, which compares well with the literature value of 150°C (Bishoff and Seyfried, 1978). At 20 bars the calculated saturation temperature is 117 ± 3°C. This points to a non negligible pressure effect even at moderate pressures.We have calculated the barite and anhydrite saturation indices for the in situ temperatures and pressures, from the composition of porewaters collected at ODP Sites 855, 856, 857, 858, 1035 and 1036 during ODP Legs 139 and 169 (Juan de Fuca and Gorda ridges, NE Pacific). Calculated saturation indices for porewater samples collected at depths corresponding to temperatures between 70° and 110-120°C at an in situ pressure of about 260 bars yield equilibrium values for anhydrite and barite. Saturation indices of samples collected at depths where the temperature exceeds 110-120°C, however, yield values indicating supersaturation with respect to anhydrite and undersaturation with respect to barite. This result is consistent with the redissolution of anhydrite during cooling, leading to the well documented sampling artifact affecting porewater compositions in high temperature marine sediments: anhydrite dissolution increases the porewater sulfate content, which in turn induces a loss of barium from solution through barite precipitation (the common ion effect). We postulate that this redissolution occurs in sediment samples for which the in situ temperature exceeds 110-120°C: below this limit anhydrite remains at equilibrium or does not have time to significantly dissolve before porewaters are sampled. 相似文献
109.
Sabine Thiemann Helmut Schiller 《International Journal of Applied Earth Observation and Geoinformation》2003,4(4):339-349
The spatial and temporal variability of the bulk temperature gives important insights into biological and hydrodynamic processes. However, standard algorithms for satellite data only provide information of the surface temperature. The comparison of current and new split-window coefficients applied on NOAA-14/AVHRR brightness temperatures of Lake Constance showed that a regional adaption was most promising. To derive the bulk temperature information, a priori progression from a weather station was included into the AVHRR analysis. Among the weather is data, the mean temperature of the three preceding days and the day of the year were the most relevant additional information. By a multiple regression approach the bulk temperature in the upper 4 m of Lake Constance could be determined with an accuracy of ±1.20 °C. The training of a neural network improved the determination of the bulk temperature to ±1.04 °C.An extended field campaign demonstrated that the algorithm is also applicable to other sensors with the same spectral band settings (in this case NOAA-16/AVHRR) with an acceptable error and that it is equally accurate over the entire lake. 相似文献
110.
3D Geographic Reconstruction and Visualization Techniques Applied to Land Resource Management 总被引:1,自引:0,他引:1
Optimized land resource management depends on reliable and detailed information describing the spatial distribution of soils, geology, topography, and land use. Soil–landscapes are three–dimensional (3D) systems commonly represented using 2D maps utilizing geographic information systems. Addressing 3D soil–landscape reality is crucial for land resource management in terms of crop growth and transport processes (e.g. nitrate leaching) that are driving soil and water quality. Our objective was to investigate the usefulness of 3D geographic information technology (GIT) applied to land resource management. Our approach is based on 2D and 3D ordinary kriging interpolating surface and subsurface attributes to reconstruct soil–landscapes. We used Virtual Reality Modeling Language, which is a web–based 3D graphics language, to visualize objects (e.g. voxels, polyhedrons) representing soil and landscape attributes. We produced a 3D block model showing the spatial distribution of bulk densities and relief for a site in southern Wisconsin and a 3D stratigraphic model showing the spatial distribution of soil horizons and relief for a site in northern Florida. Emerging GIT was used to develop 3D soil–landscape models describing continuous changes of soil and landscape attributes. Combining multimedia elements (e.g. WWW, 3D visualization, and interactivity) can produce insight that would not arise from use of the elements alone. Three–dimensional scientific visualization is a powerful tool to help us see what is invisible from above the ground. 相似文献