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41.
Wagner José Barreto Dilson Norio Ishikawa Ieda Spacino Scarminio João de Souza Costa Paulo dos Santos Nora Miriam de Fatima Soares Romilaine Mansano Nicolau Adriana Celeste Esteves Gonçalves Sonia Regina Giancoli Barreto 《洁净——土壤、空气、水》2008,36(4):353-359
The conservation of large water resources is essential for the preservation of human life. The quantification and, more importantly, the speciation of chemical substances that indicate the presence of anthropogenic contamination in water resources are of great importance. This paper presents the results of analysis for the determination of organic, inorganic and total phosphorus, pseudo‐sulfur, and iron and manganese, in five fractions, in water sediments collected from the Capivara Hydroelectric Power Plant, Brazil. A study on the seasonal variation of these parameters was conducted, with data having been collected in the winter and in the summer, at two sites along the dam, 5 km apart, close to the city of Primeiro de Maio. Phosphorous was found in sediments and adjacent soil in the organic form (OP), and was used as an indicator of anthropogenic influence on the reservoir banks. Speciation of potentially toxic Mn showed that it is present in the exchangeable fraction of the 0–5 cm depth layer (sediment/water interface), making its transfer to the water column possible. Results from this study showed that domestic and industrial effluent treatment measures are needed for the preservation of the quality of aquatic environments. 相似文献
42.
Michel G. Houlé Sonia Préfontaine Anthony D. Fowler Harold L. Gibson 《Bulletin of Volcanology》2009,71(8):881-901
Spinifex-textured sills (i.e., veins) characterized by komatiitic magmas that have intruded their own volcanic-piles have
long been recognized. For instance, in the early 1970s, Pyke and coworkers, in their classic work at Pyke Hill in Munro Township,
noted that not all spinifex-bearing ultramafic rocks formed as lava flows, rather some were clearly emplaced as small dikes
and sills. Several hypotheses have been proposed to explain spinifex-textured sills: intrusion into a cold host, filter pressing,
or drainage of residual liquid. However, these do not satisfactorily explain the phenomenon. Field and petrographic observations
at Pyke Hill and Serpentine Mountain demonstrate that spinifex-bearing komatiite sills and dikes were emplaced during channel
inflation processes when new magma was intruded into a cooler, semi-consolidated but permeable cumulate material. Komatiitic
liquids were intruded into the olivine cumulate rocks near the boundary between the spinifex and the cumulate zones of well-organized
to organized komatiite flows. Spinifex-textured sills are generally tabular in morphology, stacked one above another, with
curviplanar contacts sub-parallel to stratigraphy. Some sills exhibit complex digitated apophyses. Thinner sills typically
have a random olivine spinifex texture similar, though generally composed of coarser crystals, to that of komatiite lava flows.
Thicker sills exhibit more complex organization of their constituent crystals characterized by zones of random olivine spinifex,
overlying zones of organized coarse spinifex crystals similar to those found in lava flows. They have striking coarse dendritic
spinifex zones composed of very large olivine crystals, up to several centimetres long and up to 1 cm wide that are not observed
in lava flows. Typically, at the sill margins, the cumulate material of the host flow is composed of euhedral to subhedral
olivine crystals that are larger than those distal to the contact. Many of these margin-crystals have either concentric overgrowth
shells or dendritic olivine overgrowths that grew from the cumulate-sill contact toward the sill interior. The dendrites grew
on pre-existing olivine cumulate at the contact in response to a sharp temperature gradient imposed by the intrusion of hot
material, whereas the concentric overgrowths formed as new melt percolated into the unconsolidated groundmass of the host-flow
cumulate material. Spinifex-textured sills and dikes occur in well-organized to organized flows that are interpreted to have
formed by “breakouts” above and peripheral to lava pathways (channels/conduits) as a result of inflation that accompanied
voluminous komatiitic eruptions responsible for the construction and channelization of komatiitic flow fields. The spinifex-textured
dikes and sills represent komatiitic lava that was originally emplaced into the channel roof during periods of episodic inflation
that resulted in lava breakouts and was subsequently trapped in the “roof rocks” during periods of channel deflation. Accordingly,
the occurrence of spinifex-textured sills and dikes may indicate proximity to, and aid in the identification and delineation
of lava channel-ways that could potentially host Ni–Cu–(PGE) mineralization within komatiitic lava flow-fields. 相似文献
43.
Wave–current laboratory experiments have shown that the logarithmic current profile observed in pure current flows is modified due to the presence of waves. When waves propagate opposite the current, an increase in the current intensity is achieved near the mean water level, while a reduction is obtained for following waves and currents. With the aim of analyzing these nonlinear effects along the whole water column, an Eulerian wave–current model is presented. In contrast to previously presented wave–current models, the present is able to include the variation of the free surface elevation due to the wave motion and the effect of a non hydrostatic pressure field. Therefore it does not restrict its application to waves in shallow waters. Moreover, the model is able to simulate all the possible angles between waves and currents. 相似文献
44.
45.
Ben Yang Yun Qian Larry K. Berg Po-Lun Ma Sonia Wharton Vera Bulaevskaya Huiping Yan Zhangshuan Hou William J. Shaw 《Boundary-Layer Meteorology》2017,162(1):117-142
We evaluate the sensitivity of simulated turbine-height wind speeds to 26 parameters within the Mellor–Yamada–Nakanishi–Niino (MYNN) planetary boundary-layer scheme and MM5 surface-layer scheme of the Weather Research and Forecasting model over an area of complex terrain. An efficient sampling algorithm and generalized linear model are used to explore the multiple-dimensional parameter space and quantify the parametric sensitivity of simulated turbine-height wind speeds. The results indicate that most of the variability in the ensemble simulations is due to parameters related to the dissipation of turbulent kinetic energy (TKE), Prandtl number, turbulent length scales, surface roughness, and the von Kármán constant. The parameter associated with the TKE dissipation rate is found to be most important, and a larger dissipation rate produces larger hub-height wind speeds. A larger Prandtl number results in smaller nighttime wind speeds. Increasing surface roughness reduces the frequencies of both extremely weak and strong airflows, implying a reduction in the variability of wind speed. All of the above parameters significantly affect the vertical profiles of wind speed and the magnitude of wind shear. The relative contributions of individual parameters are found to be dependent on both the terrain slope and atmospheric stability. 相似文献
46.
Sonia E. Ruiz 《地震工程与结构动力学》1991,20(1):1-9
Asymmetrically yielding single-degree-of-freedom elastoplastic systems are subjected to simulated accelerograms based on El Centro-NS, 1940 ground motion (wide frequency band) to calculate the corresponding ductility demands. Results are compared with those corresponding to simulated accelerograms of the SCT-EW, 1985 Mexico earthquake (narrow frequency band) obtained in a previous work. Results obtained reveal that the characteristics of the excitation influence the response of asymmetrically yielding structures and that the differences found on responses corresponding to both earthquakes are due to frequency content, duration and/or intensity of motion. The effect of the latter concepts is studied using modulating sinusoidal excitations as well as accelerograms recorded on soft and hard soils of Mexico City. Two alternate expressions are proposed to evaluate the increase in ductility demands of structures with asymmetric force-displacement curves with respect to symmetric ones. Those expressions take into account motion intensity and duration, as well as seismic design coefficient. 相似文献
47.
48.
Observations of Comet 9P/Tempel 1 around the Deep Impact event by the OSIRIS cameras onboard Rosetta
Horst Uwe Keller Sonia Fornasier Stubbe F. Hviid Jörg Knollenberg Miriam Rengel Gabriele Cremonese Detlef Koschny Ekkehard Kührt Holger Sierks Cesare Barbieri Hans Rickman Michael F. A'Hearn Maria-Antonella Barucci Vania da Deppo Björn J.R. Davidsson Stefano Debei Fritz Gliem José J. Lopez Moreno Giampiero Naletto Angel Sanz Andrés 《Icarus》2007,187(1):87-103
The OSIRIS cameras on the Rosetta spacecraft observed Comet 9P/Tempel 1 from 5 days before to 10 days after it was hit by the Deep Impact projectile. The Narrow Angle Camera (NAC) monitored the cometary dust in 5 different filters. The Wide Angle Camera (WAC) observed through filters sensitive to emissions from OH, CN, Na, and OI together with the associated continuum. Before and after the impact the comet showed regular variations in intensity. The period of the brightness changes is consistent with the rotation period of Tempel 1. The overall brightness of Tempel 1 decreased by about 10% during the OSIRIS observations. The analysis of the impact ejecta shows that no new permanent coma structures were created by the impact. Most of the material moved with . Much of it left the comet in the form of icy grains which sublimated and fragmented within the first hour after the impact. The light curve of the comet after the impact and the amount of material leaving the comet ( of water ice and a presumably larger amount of dust) suggest that the impact ejecta were quickly accelerated by collisions with gas molecules. Therefore, the motion of the bulk of the ejecta cannot be described by ballistic trajectories, and the validity of determinations of the density and tensile strength of the nucleus of Tempel 1 with models using ballistic ejection of particles is uncertain. 相似文献
49.
Gwendolynne Young Humberto Zavala Johanna Wandel Barry Smit Sonia Salas Elizabeth Jimenez Melitta Fiebig Roxana Espinoza Harry Diaz Jorge Cepeda 《Climatic change》2010,98(1-2):245-276
Livelihoods in drylands are already challenged by the demands of climate variability, and climate change is expected to have further implications for water resource availability in these regions. This paper characterizes the vulnerability of an irrigation-dependent agricultural community located in the Elqui River Basin of Northern Chile to water and climate-related conditions in light of climate change. The paper documents the exposures and sensitivities faced by the community in light of current water shortages, and identifies their ability to manage these exposures under a changing climate. The IPCC identifies potentially increased aridity in this region with climate change; furthermore, the Elqui River is fed by snowmelt and glaciers, and its flows will be affected by a warming climate. Community vulnerability occurs within a broader physical, economic, political and social context, and vulnerability in the community varies amongst occupations, resource uses and accessibility to water resources, making some more susceptible to changing conditions in the future. This case study highlights the need for adaptation to current land and water management practices to maintain livelihoods in the face of changes many people are not expecting. 相似文献
50.
Several reinforced concrete frames with different dissipator distributions, and a conventional moment-resisting frame, are compared in order to select the best dissipator distribution from the point of view of seismic response and structural design. The structures with dissipators are designed according to a criterion proposed in the present paper. Each frame is excited with a set of eleven simulated accelerograms. The choice of the best dissipation distribution is based mainly on the differences between the mean of the maximum overturning moments developed at the base of the frames and between the weights of steel reinforcement and concrete resulting from the structural design of each frame. A comparison of initial construction costs of a building with dissipators and a conventional building shows that the former is 3·5 per cent more expensive. 相似文献