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101.
Frank Früngel 《Theoretical and Applied Climatology》1960,10(2):252-263
Zusammenfassung Das impulsoptische Signalübertragungsprinzip mit Funkenlicht als Sender und einem photoelektrischen Impulsempfänger wurde als Transmissometer ausgeführt. Mittels unterkritischem Betrieb der Funkenstrecke unterliegt der Sender keinen störenden Intensitätsschwankungen. Der Meßbereich der Extinktion beträgt 1105, entsprechend etwa 40 m bis Normsichtweite. Das Gerät ist klimafest für Flugplatzbelange ausgebildet und benötigt zum Schreiber hin nur Telephonkabel.
Mit 6 Textabbildungen 相似文献
Summary A transmission-measuring apparatus was constructed on the principle of transmitting impulse-optic signals by means of spark light as transmitter and a photo-electric cell as impulse receiver. The transmitter shows no disturbing variations of intensity if the spark gap is operated under the critical value. The measuring range of extinction amounts to 1105 corresponding to a normal range of visibility from about 40 m to infinite. The apparatus is designed for airports. A simple telephon cable serves as conection with the recording system.
Résumé Le procédé à impulsions lumineuses reçues par une cellule photoélectrique a été developpé sous forme d'appareil à transmission. L'emeteur fonctionnant sous longueur sous-critique des étincelles n'éprouve pas de variations gênantes d'intensité. Le domaine de mesure de l'extinction est de 1105, correspondant à une portée comprise entre 40 m. et l'infini. L'appareil, à l'abri des intempéries, se prête à l'emploi sur les aérodromes; la liaison avec l'enregistreur se fait à l'aide d'un simple câble téléphonique.
Mit 6 Textabbildungen 相似文献
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Jacques Mathieu Fabrice Jeannerod Frédéric Hervant Thomas C. Kane 《Aquatic Sciences - Research Across Boundaries》1997,59(1):39-47
Electrophoretic variation in proteins encoded by seven presumptive gene loci was analyzed in four populations of the stygobiont amphipodNiphargus rhenorhodanensis. The four populations occur in different habitats, including one in drainage canals, another from sediments of the Ain River, a tributary of the Rhône River, and the remaining two occur in a karstic massif (Dorvan, Ain, France) in the epikarstic and at the base level of the massif, respectively. Six of the seven loci were polymorphic within or among populations, with as many as three electromorphs segregating at the most variable loci. Significant deficiencies in the frequency of heterozygotes were common. Genetic divergence between the two populations of the Dorvan Massif and between the two of the Ain River (forest and sediment habitats) was large. This was highly unexpected, particularly in the case of the two hydrologically connected populations of the Dorvan Massif. It is suggested that either low migration rates or the presence of ecological barriers to gene flow may result in strong genetic differention among local populations ofNiphargus. 相似文献
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Laurent J. Michot Frédéric Villiéras Michèle François Isabelle Bihannic Manuel Pelletier Jean-Maurice Cases 《Comptes Rendus Geoscience》2002,334(9):611-631
The aim of this review is to examine the present knowledge about water structure close to an interface or confined in porous spaces. First, the structure of liquid water is briefly described. Though its understanding remains incomplete, it appears that it is largely dominated by the hydrogen bond network and its dynamical evolution. The presence of any ‘foreign’ substance in water perturbs such a structure by changing at least locally the hydrogen bond network. For this reason, the presence of a solid interface significantly modifies the structure of the first adsorbed layers. Whatever the support, it is now clearly evidenced that structural perturbations are limited to distances lower than 10–15 Å from the interface. The nature, energetic heterogeneity and hydrophilicility/hydrophobicity of the solid surface influence the arrangement of water molecules. This surface organisation must definitely be considered when studying adsorption phenomena at the solid–aqueous solution interface. The relevance of such problems to geosciences is illustrated by a few situations in which water structure plays a prominent role. To cite this article: L.J. Michot et al., C. R. Geoscience 334 (2002) 611–631. 相似文献
108.
Frédéric Fluteau 《Comptes Rendus Geoscience》2003,335(1):157-174
The evolution of the Earth's climate over geological time is now relatively well known. Conversely, the causes and feedback mechanisms involved in these climatic changes are still not well determined. At geological timescales, two factors play a prevailing role: plate tectonics and the chemical composition of the atmosphere. Their climatic effects will be examined using palaeoclimatic indicators as well as results of climate models. I focus primarily on the influence of continental drift on warm and cold climatic episodes. The consequences of peculiar land sea distributions (amalgamation/dispersal of continental blocks) are discussed. Plate tectonics also drive sea level changes as well as mountain uplift. Marine transgressions during the Mid-Cretaceous favoured warmth within the interiors of continents, although their effect could be very different according to the season. Mountain uplift is also an important factor, which is able to alter climate at large spatial scales. Experiments relative to climatic sensitivity to the elevation of the Appalachians during the Late Permian are discussed. To affect the whole Earth, the chemical composition of the atmosphere appears to be a more efficient forcing factor. The carbon dioxide driven by the long-term carbon cycle has influenced the global climate. Geochemical modelling simulates more or less accurately the long-term evolution of pCO2, which corresponds roughly to the icehouse/greenhouse climatic oscillations. However, the uncertainties on pCO2 are still important because different parameters involved in the long-term carbon cycle (degassing rate, chemical weathering of silicates, burial of organic matter) are not well constrained throughout the past. The chemical composition of the atmosphere is also altered by the emissions of modern volcanic eruptions leading to weak global cooling. The influence of large flood basalt provinces on climate is not yet known well enough; this volcanism may have released huge amounts of SO2 as well as CO2. At last, the chemical composition of the atmosphere may have been altered by the release of methane in response to the dissociation of gas hydrates. This scenario has been proposed to explain the abrupt warming during the Late Palaeocene. 相似文献
109.
Anne-Lise Mariet Fabrice Monna Frédéric Gimbert Carole Bégeot Christophe Cloquet Simon Belle Laurent Millet Damien Rius Anne-Véronique Walter-Simonnet 《Journal of Paleolimnology》2018,60(3):399-412
A 157-cm-long sediment core from Longemer Lake in the Vosges Mountains of France spans the past two millennia and was analyzed for trace metal content and lead isotope composition. Trace metal accumulation rates highlight three main input phases: Roman Times (cal. 100 BC–AD 400), the Middle Ages (cal. AD 1000–1500), and the twentieth century. Atmospheric contamination displays a pattern that is similar to that seen in peat bogs from the region, at least until the eighteenth century. Thereafter, the lake sediment record is more precise than peat records. Some regional mining activity, such as that in archaeologically identified eighteenth-century mining districts, was detected from the lead isotope composition of sediment samples. Compositional data analysis, using six trace metals (silver, arsenic, cadmium, copper, lead and zinc), enabled us to distinguish between background conditions, periods of mining, and of other anthropogenic trace metal emissions, such as the recent use of leaded gasoline. 相似文献
110.
Marie Lothon Fleur Couvreux Sylvie Donier Françoise Guichard Pierre Lacarrère Donald H. Lenschow Joël Noilhan Frédérique Saïd 《Boundary-Layer Meteorology》2007,124(3):425-447
During the Hydrological-Atmospheric Pilot Experiment (HAPEX)-Sahel, which took place in Niger in the transitional period between
the wet and dry seasons, two French aircraft probed the Sahelian boundary layer to measure sensible and latent heat fluxes.
The measurements over the Niamey area often revealed organised structures of a few km scale that were associated with both
thermals and dry intrusions. We study the impact of these coherent structures using a single day’s aircraft-measured fluxes
and a numerical simulation of that day with a mesoscale model. The numerical simulation at high horizontal resolution (250 m)
contains structures that evolve from streaks in the early morning to cells by noon. This simulation shows distribution, variance
and skewness similar to the observations. In particular, the numerical simulation shows dry intrusions that can penetrate
deeply into the atmospheric boundary layer (ABL), and even reach the surface in some cases, which is in accordance with the
observed highly negatively skewed water vapour fluctuations. Dry intrusions and thermals organised at a few km scale give
skewed flux statistics and can introduce large errors in measured fluxes. We use the numerical simulation to: (i) evaluate
the contribution of the organised structures to the total flux, and (ii) estimate the impact of the organised structures on
the systematic and random errors resulting from the 1D sampling of the aircraft as opposed to the 2D numerical simulation
estimate. We find a significant contribution by the organised structures to the total resolved fluxes. When rolls occur, and
for a leg length of about 30 times the ABL depth, the 1D sampled flux is shown to be sometimes 20% lower than the corresponding
2D flux when the 1D sampling direction is the same as the main axis of the rolls, whereas the systematic error is much lower
when the direction of the leg is transverse to the rolls. In the case of cells, an underestimate of around 10% can still be
observed with the 1D approach independent of direction, due to poor sampling of the energy-containing scales. 相似文献