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581.
Taciana K. Pinto Melanie C. V. Austen Richard M. Warwick Paul J. Somerfield André M. Esteves Francisco J. V. Castro Verônica G. Fonseca‐Genevois Paulo J. P. Santos 《Marine Ecology》2013,34(3):257-268
Mangroves are highly productive environments that play important ecological and socioeconomic roles; however, they have been impacted to different degrees in most countries worldwide. The knowledge of which organisms inhabit this environment and their ecological interactions is the first step towards its conservation. The natural variability of environmental factors in mangroves provides numerous niches available to different species. Meiofauna have patchy patterns of distribution that are related to the availability of resources. Hence, meiofauna are expected to present a high diversity of different taxa occupying the different microhabitats offered by mangroves. This work aims to test the hypothesis that the assemblage structure of Nematoda varies significantly among mangrove microhabitats and to contribute knowledge on the meiofauna diversity in mangrove environments. This work was carried out in a mangrove region at Pernambuco state, Northeastern Brazil. Qualitative samples were collected in nine microhabitats which show different characteristics mainly in terms of presence of vegetation or another organism and sediment grain size. Univariate and multivariate analysis were applied to Nematoda genera abundance data. Our results demonstrate the existence of significant differences among microhabitats regarding nematode assemblage structure corroborating the hypothesis. Different Nematoda assemblages are present in at least seven microhabitats. These assemblages are composed of nematode genera with different trophic and morphological features, demonstrating a strong relationship between morphological diversity and ecological plasticity. Furthermore, this study also demonstrates the importance of the conservation of this ecosystem and its attributes. 相似文献
582.
Emilio Santos 《Astrophysics and Space Science》2011,332(2):423-435
It is shown that quantum vacuum fluctuations give rise to a curvature of space-time equivalent to a cosmological constant,
that is a homogeneous energy density ρ and pressure p fulfilling −p=ρ>0. The fact that the fluctuations produce curvature, even if the vacuum expectation of the energy vanishes, is a consequence
of the non-linear character of the Einstein equation. A calculation is made, involving plausible hypotheses within quantized
gravity, which establishes a relation between the two-point correlation of the vacuum fluctuations and the space-time curvature.
Arguments are given which suggest that the density ρ might be of order the “dark energy” density currently assumed to explain the observed accelerated expansion of the universe. 相似文献
583.
Heavy metal mobility assessment in sediments from the Odiel River (Iberian Pyritic Belt) using sequential extraction 总被引:1,自引:1,他引:0
Rafael Beltrán J. D. de la Rosa J. C. Santos M. Beltrán J. L. Gómez-Ariza 《Environmental Earth Sciences》2010,61(7):1493-1503
The Tessier sequential extraction scheme (SES) was applied to sediments from the Odiel river catchment (Iberian Pyritic Belt,
SW of Spain), one of the most acid rivers on Earth, to assess the chemical association (exchangeable, carbonatic, bound to
manganese and iron oxides, bound to organic matter and residual mineral) of heavy metals (Zn, Cd, Pb, Cu, Cr, Mn, Ni, Fe,
and Hg). Sediments are very heterogeneous in their textural characteristics, showing different grain size. Twenty-seven samples
were studied from from areas along the Odiel River, from the source to the mouth, with special interest in the Odiel Marshes
Natural Park due to its ecological significance. Samples were classified as sandy (especially at the river mouth with low
iron oxide and organic matter content) and clay-silty (in the middle of the river catchment with high iron oxide content).
The numerous sandy samples with low pH values explain the low levels of metals upstream, although potential metals contributions
arise from mining and ore. However, the presence of sulfate in the mining area and carbonate at the mouth may explain the
high presence of lead and iron in these sandy zones. Some percentage of mobile Ni, Cu, and Zn were detected in the mining
area, but the elevated relative percentage of exchangeable Cd in the estuary is even more remarkable. The percentage of Zn
bound to carbonate is considerable in the catchment but especially in the estuary. However, Cu is only detected in the carbonate
phase downstream, in spite of the low concentration of carbonate, which represents a drawback in the application of the Tessier
SES to these types of samples. Finally, relatively high percentages of residual, non-mobile, Hg and Pb were observed, in the
estuarine and mining areas, respectively. Sand, lime, and clay fractions of representative samples from Areas I, II, and III
were used in a metal speciation study. Mainly, the elements analyzed had accumulated in the non-residual fractions. In the
mining area of the Pyrite Belt, the elements analyzed are mainly bound to Fe–Mn oxides (Fe + Mn + Cu + Cr + Pb + Mn ± Zn)
and the organic matter/sulfide fraction (Ni + Zn + Hg ± Cd), independent of sediment grain size. In conclusion, we show that
the results of the study of chemical speciation in sediments from acid rivers are independent of the sediment grain size considered. 相似文献
584.
Rapid estimation of ground-shaking maps for seismic emergency management in the Campania Region of southern Italy 总被引:1,自引:1,他引:0
Vincenzo Convertito Raffaella De Matteis Luciana Cantore Aldo Zollo Giovanni Iannaccone Mauro Caccavale 《Natural Hazards》2010,52(1):97-115
Strong ground-shaking mapping soon after a moderate-to-large earthquake is crucial to recognize the areas that have suffered
the largest damage and losses. These maps have a fundamental role for emergency services, loss estimation and planning of
emergency actions by the Civil Protection Authorities. This is particularly important for areas with high seismic risk levels,
such as the Campania-Lucania Region in southern Italy. Taking advantage of the Irpinia Seismic Network (ISNet), a recently
installed dense and wide dynamic seismic network, we have developed a procedure for rapid estimation of ground-shaking maps
after moderate-to-large earthquakes (GRSmap). This uses an optimal data gridding scheme designed to account for bi-dimensional
features of strong ground-motion fields, such as directivity, radiation patterns and focal mechanisms, to which most damage
can be correlated. The basis of the mapping technique is a triangulation procedure to locally correct predicted data at the
triangle barycentres where their vertices correspond to seismic stations. The method has been tested off-line using a simulated
M 6.6 earthquake located at the centre of ISNet and applied to data of the 23 November 1980 Irpina M 6.9 earthquake recorded by a sparse network. This has highlighted its ability to predict peak ground-motion parameters of
large magnitude earthquakes with respect to the attenuation relationships. 相似文献
585.
D. P. Renouard F. J. Seabra Santos A. M. Temperville 《Dynamics of Atmospheres and Oceans》1985,9(4):341-358
In a (36 m × 0.55 m × 1.30 m) channel we did numerous experiments to study the generation, propagation, damping and reflexion along a wall of a solitary wave. The data are compared with the available analytical or numerical results. From a given paddle movement, the Inverse Scattering Method is proved to provide with great accuracy the number and amplitude of the generated solitary waves. Then, studying the damping of the wave due to dispersion and viscosity, we find that the formula proposed by Keulegan describes the phenomenon well. This last result enables us to modify the KdV equation with the second term used by Kakutani and Matsuuchi, to compute the solitary wave and tail generated by a given intumescence or a given paddle movement. We notice that the computations fit well with the experimental measurements. Finally, we study the reflexion of a solitary wave from a plane vertical wall. To obtain good experimental data requires great care, but the results agree with the analytical prediction. The reflexion appears to be a rather complex phenomenon and needs further theoretical developments. We present here some experimetal data which confirm recent numerical observations (Mirie and Su, Fenton and Rienecker). 相似文献
586.
Geraldo Magela Santos Sampaio Jacinta Enzweiler 《Geostandards and Geoanalytical Research》2015,39(1):105-119
Iron formations (IFs) typically contain low mass fractions of most trace elements, including the rare earth elements (REE), and few publications describe analytical methods dedicated to this matrix. In this study, we used bomb and table‐top acid dissolution procedures and ICP‐MS to determine the mass fractions of trace elements in IF reference materials FER‐1, FER‐2, FER‐3, FER‐4 and IF‐G. The full digestion of the IF samples with the bomb procedure required the addition of a small amount of water together with the acids. The results obtained by this method mostly agreed statistically with published values. The most remarkable exception was the higher values obtained for the heavy REE in FER‐3. The recoveries of the REE obtained with the table‐top procedure were slightly higher than those of the bomb digestion, except for the values of the heavy REE in FER‐3 and FER‐4, which were up to 30% lower than published values. Sintering of the samples with sodium peroxide was performed to determine the REE, but the results tended to be lower than those derived following acid digestion. On the whole, the recoveries showed dependence on the conditions of digestion, but subtle differences in trace mineral composition between samples also exerted influence on the analytical results for trace elements. 相似文献
587.
Wagner da Silva Billa Leonardo Bacelar Lima Santos Rogério Galante Negri 《Transactions in GIS》2023,27(8):2159-2174
Rainfall is one of the primary triggers for many geological and hydrological natural disasters. While the geological events are related to mass movements in land collapse due to waterlogging, the hydrological ones are usually assigned to runoff or flooding. Studies in the literature propose predicting mass movement events as a function of accumulated rainfall levels recorded at distinct periods. According to these approaches, a two-dimensional rainfall levels feature space is segmented into the occurrence and non-occurrence decision regions by an empirical critical curve (CC). Although this scheme may easily be extended to other purposes and applications, studies in the literature need to discuss its use for flooding prediction. In light of this motivation, the present study is unfolded in (1) verifying that defining CCs in the rainfall levels feature space is a practical approach for flooding prediction and (2) analyzing how geospatial components interact with rainfall levels and flooding prediction. A database containing the rainfall levels recorded for flooding and non-flooding events in São Paulo city, Brazil, regarding the period 2015–2016, was considered in this study. The results indicate good accuracy for flooding prediction using only partial rain, which can be improved by adding physical characteristics of the flooding locations, demonstrating a direct correlation with spatial interactions, and rainfall levels. 相似文献