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91.
Tiit Kutser Ele Vahtme Chris M. Roelfsema Liisa Metsamaa 《Estuarine, Coastal and Shelf Science》2007,75(4):559-563
The creation of seagrass biomass maps by diving/snorkelling is time-consuming and expensive. This paper presents a method for estimating seagrass dry weight using a photo-library of classes of differing seagrass biomass. Field data were collected at seagrass beds in Ngederrak Reef, Palau, in 2006. Photos of 25 × 25 cm quadrats were taken prior to the collection the above-ground biomass for determination of biomass dry weight. Fifteen classes of seagrass biomass and substrate type were identified. The dry weight for each class of seagrass was measured in laboratory. A photo-library was created for biomass classification where each in situ quadrat photo is accompanied with seagrass dry weight of the sample and a photo of the sorted sample taken in laboratory. The photo-library of quadrats was then used to estimate seagrass biomass on photos gathered along 100 m long transects at 2 m intervals. This procedure was conducted by three different observers. The seagrass dry weight estimates were consistent between interpreters even if one of the interpreters had no experience in seagrass research. This approach allows quick collection of seagrass dry weight data over large areas. The method can be used for creating seagrass biomass maps by snorkelling/diving and/or for calibrating and validating biomass maps created by remote sensing. 相似文献
92.
Osmar O. Möller Patrice Castaing Elisa Helena Leão Fernandes Pascal Lazure 《Estuaries and Coasts》2007,30(2):311-320
The Patos Lagoon is a choked, microtidal coastal laggon situated in southern Brazil between 30°S and 32°S. The response of
the lagoon to tidal oscillations is studied through data analysis and numerical modeling experiments. Two types of high frequency
oscillations are observed in the tidal frequency band: mixed tides, predominantly diurnal; and forced oscillations having
a period of 24 h occurring in the inner lagoon. In the southern portion of the lagoon, tides are selectively filtered by the
entrance channel. The main diurnal constituent O1 is linearly attenuated as it progresses landwards. In the inner parts of the lagoon, 24-h oscillations are mainly forced
by the combined effect of diurnal tides and sea breeze action. They are tied with a natural period of oscillation of 24 h.
Results also indicate that these are not inertial frequency oscillations, despite the lagoon being placed in a critical 30°S
area. The interaction between astronomical tides and meteorological effects produces a complicated picture for tidal forecasting
derived from data collected inside the lagoon. 相似文献
93.
The Bolcana ore deposit (Metaliferi Mountains, western Romania) is a porphyry ore deposit with associated epithermal veins. On the basis of different parageneses, four alteration types were distinguished: potassic, phyllic, argillic and propylitic. The mineralogical and geochemical data and estimated crystallisation temperatures of alteration minerals indicate an evolution of the system from an early period of porphyry type mineralisation (Cu+Au) to a late period of low-sulphidation epithermal mineralisation (Au+base metal). To cite this article: V. Milu et al., C. R. Geoscience 335 (2003). 相似文献
94.
Donatienne Derome Michel Cuney Michel Cathelineau Ccile Fabre Jean Dubessy Patrice Bruneton Amlie Hubert 《Journal of Geochemical Exploration》2003,80(2-3):259-275
The relative chronology and detailed chemistry of paleofluids circulating at the base of the Kombolgie Sub-basin were investigated in the East Alligator River district (Northern Territory, Australia), where world-class unconformity-type uranium deposits are located. The chemistry of fluid inclusions was determined using in-situ analysis (Raman microprobe and laser-induced breakdown spectroscopy [LIBS]) and by observing the melting sequences by microthermometry. This study revealed the occurrence of three distinct fluids: (i) a sodium-rich brine that corresponds to a diagenetic fluid percolating at the bottom of the Kombolgie sandstones at a temperature close to 150±15 °C; (ii) a calcium-rich brine, probably corresponding to a residual brine in evaporitic environment that has evolved by fluid–rock interactions with the basement lithologies; and (iii) a low salinity fluid, heated in the basement, injected into the base of the sandstone cover. H2 and O2 and/or traces of CH4 were detected in the vapor phase of some fluid inclusions, especially in the low salinity ones in quartz breccia samples taken above mineralized areas. Hydraulic brecciation of the sandstone was associated with a pressure decrease favoring fluid mixing and the subsequent cementation of breccias. According to the fluid inclusion study and other geologic constrains, the minimum thickness of the Sub-Kombolgie Basin is estimated at 4 km. Drusy quartz breccias with evidence of fluid mixing are quite common at the base of the Kombolgie Basin, but not necessarily linked to U-mineralization. However, it is proposed that the presence of gases such as H2 and O2 in fluid inclusions, which results from water radiolysis, constitutes an indicator of gas linked to significant U concentrations deeper in the basement rocks. 相似文献
95.
The main goals of experimental simulation in the laboratory of a planetary atmosphere are to feed the theoretical models,
and to help the treatment of observations. This type of simulation permits the direct study of objects that space missions
can't study or have not studied yet, through the production of laboratory analogues of gaseous or solid phases. But the representativity
of these laboratory analogues is of crucial importance.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
96.
Mathematical models applied to urban and regional planning have been widely developed during the sixties. Since that time
the scientific and technologic developments have deeply transformed the field of spatial modelling. There has been a reaction
against the idea that reality could be reduced to deterministic models. The paradigms of complexity, chaos, self-organisation,
fractal geometry have made obvious the unpredictability of complex socio-economic systems. At the same time the progress of
computation has led to the substitution of simulation methods to analytic solutions of mathematical models. In such a context,
models are loosing in generality and reproducibility what they earn in adaptation to empirical situations. An important challenge
is also to confirm the pertinence and specificity of the geographical approach. In that respect the spatial analysis programs
must prove the evidence of a common methodology dealing either with physical or human and economic domain. We are working,
for instance, on cellular automata programs applied to the historical evolution of an urban space and also to the run-off
process in an elementary basin. The spatial structure of the models may be slightly different: rectangular or hexagonal tessellations
in the “Human Geography” program, TIN structure, closer to the physical reality, in the other. The relations between the cells
may also differ: they are often defined by a distance matrix for the socio-economic models, but a contiguity matrix is of
course needed for the streaming process. But, beyond these technical differences, it appears that the geographical programs
are developed on a macro-level, that is on aggregate statistical units. The elementary particle is always (or should be for
a geographer...) a material, spatial unit, unlike the drop of water of the hydrologists, or the individual “agents” of the
sociologists' multi-agents systems. The difference between the micro and macro level is not a question of scale, but a difference
of logic. The simulation approach has a requisite, which is a need of systematic validation by a permanent comparison with
the actual situation, but the objective is not prediction. The scientific concern is, before all, a precise understanding
of the past and recent evolutions, more than a forecasting, which escapes to the specific field of scientific research. What
is scientific is what can be measured. The possible prediction may rely on the scientific research, but belongs strictly to
the domain of intellectual and personal thinking.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
97.
A Compilation of Silicon and Thirty One Trace Elements Measured in the Natural River Water Reference Material SLRS-4 (NRC-CNRC) 总被引:1,自引:0,他引:1
Delphine Yeghicheyan Jean Carignan Michel Valladon Martine Bouhnik Le Coz Florence Le Cornec Maryse Castrec-Rouelle Michel Robert Luc Aquilina Emmanuel Aubry Carine Churlaud Aline Dia Samuel Deberdt Bernard Dupré Rémi Freydier Gérard Gruau Odile Hénin Anne-Marie de Kersabiec Joël Macé Luc Marin Nicole Morin Patrice Petitjean Elodie Serrat 《Geostandards and Geoanalytical Research》2001,25(2-3):465-474
The natural river water certified reference material SLRS-4 (NRC-CNRC, National Research Council-Conseil National de Recherches Canada) has been routinely analysed for major and trace elements by six French laboratories. Most measurements were made using inductively coupled plasma-mass spectrometry. For silicon and thirty one trace elements (rare earth elements, Ag, B, Br, Cs, Ga, Ge, Li, P, Pd, Rb, Se, Th, Ti, Tl, W, Y and Zr), no certified values are assigned by NRC-CNRC. We propose some compilation values and related uncertainties according to the results obtained by the different laboratories. 相似文献
98.
Field observations of an evolving rip current on a meso-macrotidal well-developed inner bar and rip morphology 总被引:1,自引:0,他引:1
Nicolas Bruneau Bruno Castelle Philippe Bonneton Rodrigo Pedreros Rafael Almar Natalie Bonneton Patrice Bretel Jean-Paul Parisot Nadia Snchal 《Continental Shelf Research》2009,29(14):1650-1662
The Aquitanian Coast (France) is a high-energy meso-macrotidal environment exhibiting a highly variable double sandbar system. The inner and the outer bar generally exhibit a bar and rip morphology and persistent crescentic patterns, respectively. In June 2007, an intense five-day field experiment was carried out at Biscarrosse Beach. A large array of sensors was deployed on a well-developed southward-oriented bar and rip morphology. Daily topographic surveys were carried out together with video imaging to investigate beach morphodynamic evolution. During the experiment, offshore significant wave height ranged from 0.5 to 3 m, with a persistent shore-normal angle. This paper identifies two types of behavior of an observed rip current: (1) for low-energy waves, the rip current is active only between low and mid tide with maximum mean rip current velocity reaching 0.8 m/s for an offshore significant wave height (Hs) lower than 1 m; (2) for high-energy waves (Hs≈ 2.5–3 m), the rip current was active over the whole tide cycle with the presence of persistent intense offshore-directed flows between mid and high tide. For both low and high-energy waves, very low-frequency pulsations (15–30 min) of the mean currents are observed on both feeder and rip channels.A persistent slow shoreward migration of the sandbar was observed during the experiment while no significant alongshore migration of the system was measured. Onshore migration during the high-energy waves can be explained by different sediment transport processes such as flow velocity skewness, wave asymmetry or bed ventilation. High-frequency local measurements of the bed evolution show the presence of significant (in the order of 10 cm) fluctuations (in the order of 1 h). These fluctuations, observed for both low- and high-energy waves, are thought to be ripples and megaripples, respectively and may play an important but still poorly understood role in the larger scale morphodynamics. The present dataset improves the knowledge of rip dynamics as well as the morphological response of strongly alongshore non-uniform meso-macrotidal beaches. 相似文献
99.
Evidence of the presence of a group of sei whales (Balaenoptera borealis) detected around drifting fish aggregating devices (FADs) was provided by omnidirectional multi‐beam sonar during a survey off the Seychelles (Indian Ocean). The short visit by the sei whales produced a significant change in the behaviour of the fish assemblage associated with the FAD. There was first a significant increase in fish density when the whales approached the FAD, then a marked decrease after the whales had moved away from the FAD. Furthermore, the fish density was still low, 3 h after the whales had left the FAD. We assume that the presence and behaviour of the sei whales led some of the fish initially associated with the FAD to move away from it. There has been a considerable increase in the use of drifting artificial FADs in the Indian Ocean in recent decades. The frequency of cetacean visits to drifting FADs in the Indian Ocean is unknown, but they may have a major impact on assemblages of pelagic fish species around FADs. The effect of marine mammals on FAD‐associated fish could be relevant to the ecological trap theory (FAD acting as a trap for their associated fish) because of their impact on the dynamics of fish aggregation processes, through commensalism and/or predator–prey interactions. 相似文献
100.
Dominique Schwartz Michel Thinon Stéphanie Goepp Christian Schmitt Julien Casner Thierry Rosique Patrice Wuscher Anne Alexandre Étienne Dambrine Charly Martin Bernard Guillet 《Comptes Rendus Geoscience》2005,337(14):1250-1256
The age of the upland grasslands of the Vosges Mountains is still not well known. On the basis of the study of historical archives, it was assumed that the forest clearings, which led to grasslands establishment, were done by the monks who colonized the Vosges valleys between the 7th and the 8th centuries. Our pedo-anthracological study raises questions about this hypothesis, based on the discovery of Juniperus communis charcoal in soils from the 2nd or 1st century BC. This plant specie is characteristic of grasslands developing into fallows. The occurrence of Juniperus communis charcoals indicates that upland grasslands did exist at least 800 years earlier than it was expected before our study, i.e. at least since the late Iron Age. To cite this article: D. Schwartz et al., C. R. Geoscience 337 (2005). 相似文献