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191.
Thomas K. Greathouse John H. Lacy Bruno Bézard Matthew J. Richter Claudia Knez 《Icarus》2006,181(1):266-271
We report the first detection of propane, C3H8, in Saturn's stratosphere. Observations taken on September 8, 2002 UT at NASA's IRTF using TEXES, show multiple emission lines due to the 748 cm−1ν21 band of C3H8. Using a line-by-line radiative transfer code, we are able to fit the data by scaling the propane vertical mixing ratio profile from the photochemical model of Moses et al. [2000. Icarus 143, 244-298]. Multiplicative factors of 0.7 and 0.65 are required to fit the −20° and −80° planetocentric latitude spectra. The resultant profiles are characterized by a 5 mbar mixing ratio of 2.7±0.8×10−8 at −20° and at −80° latitude. These results suggest that the time scale for meridional circulation lies between the net photochemical lifetimes of C2H2 and C3H8, ≈30-600 years. 相似文献
192.
Devon M. Burr Barbara C. Bruno Peter D. Lanagan Lori S. Glaze Windy L. Jaeger Richard J. Soare Jean-Michel Wan Bun Tseung James A. Skinner Stephen M. Baloga 《Planetary and Space Science》2009,57(5-6):579-596
Fields of mesoscale raised rim depressions (MRRDs) of various origins are found on Earth and Mars. Examples include rootless cones, mud volcanoes, collapsed pingos, rimmed kettle holes, and basaltic ring structures. Correct identification of MRRDs on Mars is valuable because different MRRD types have different geologic and/or climatic implications and are often associated with volcanism and/or water, which may provide locales for biotic or prebiotic activity. In order to facilitate correct identification of fields of MRRDs on Mars and their implications, this work provides a review of common terrestrial MRRD types that occur in fields. In this review, MRRDs by formation mechanism, including hydrovolcanic (phreatomagmatic cones, basaltic ring structures), sedimentological (mud volcanoes), and ice-related (pingos, volatile ice-block forms) mechanisms. For each broad mechanism, we present a comparative synopsis of (i) morphology and observations, (ii) physical formation processes, and (iii) published hypothesized locations on Mars. Because the morphology for MRRDs may be ambiguous, an additional tool is provided for distinguishing fields of MRRDs by origin on Mars, namely, spatial distribution analyses for MRRDs within fields on Earth. We find that MRRDs have both distinguishing and similar characteristics, and observation that applies both to their mesoscale morphology and to their spatial distribution statistics. Thus, this review provides tools for distinguishing between various MRRDs, while highlighting the utility of the multiple working hypotheses approach. 相似文献
193.
We consider the circular planar restricted three-body problem with the mass parameter μ = 5 × 10?5. Two families of periodic solutions are calculated: family c, starting from the collinear fixed point L 1, and the initial part of familyi, which begins by direct circular orbits of an infinitely small radius around the body of bigger mass. The calculated families are very close to the generating ones, which we described earlier. In particular, the existence of the predicted zigzag structure of characteristics of family iis verified. New properties of the planar and vertical traces are discovered. 相似文献
194.
The planar restricted three-body problem has an infinite number of families of symmetric periodic solutions (SPSs). The natural SPS families include certain families which are self-closed with respect to small variations in a parameter. These families remain closed for any admissible variations in the mass parameter μ. However, there are closed SRS families of another type, which exist only in bounded intervals of μ and are formed via self-bifurcations of some SPS families. This type of SPS families is poorly understude. This work describes the initial stage (4 bifurcations) of a bifurcation cascade of the natural family i and points out other closed SPS families known to date. 相似文献
195.
Fabio Orlandi Carlo Sgromo Tommaso Bonofiglio Luigia Ruga Bruno Romano Marco Fornaciari 《Theoretical and Applied Climatology》2009,97(3-4):339-347
Phenological observations of the anthesic phases of olive flowering in a central Mediterranean area were recorded over a 9-year period. The aim of this research was to compare the flowering dates in relationship to the meteorological changes. Pollen emission from anthers was monitored by remote instrumentation placed directly in olive groves and phenological data regarding daily pollen concentrations (pollen/m3) were recorded using a pollen monitoring methodology. The rhythm of the phenological phases emerged as dependent on the meteorological trend of the spring forcing temperature. Generally, the phenomenon of pollen emission occurred progressively earlier prior to 2001, while in the following 5 years, the trend seemed to be inverted, showing a progressive delay of flowering. The spring quarterly mean temperature trends registered by GISS data in Europe confirmed the presence of diverse meteorological behavior during the study period, probably causing the biological divergences that were monitored. The principal result of the present contribution is to evidence the relativity of empirical investigations and observations considering different time intervals. This is due to the partial, brief series (9 years) of flowering dates which have to be considered as part of a longer series (26 years) in order to have a complete vision of the true phenomenon. 相似文献
196.
Boundedness of Turbulent Temperature Probability Distributions,and their Relation to the Vertical Profile in the Convective Boundary Layer 总被引:3,自引:3,他引:0
Alexander Graf Dirk Schüttemeyer Heiner Geiß Axel Knaps Michael Möllmann-Coers Jan H. Schween Stefan Kollet Bruno Neininger Michael Herbst Harry Vereecken 《Boundary-Layer Meteorology》2010,134(3):459-486
Higher-order moments, minima and maxima of turbulent temperature and water vapour mixing ratio probability density functions
measured with an eddy-covariance system near the ground were related to each other and to vertical boundary-layer profiles
of the same scalars obtained through airborne soundings. The dependence of kurtosis on squared skewness showed a kurtosis
intercept below the Gaussian expectation, suggesting a compression of the probability density function by the presence of
natural boundaries. This hypothesis was corroborated by comparing actual minima and maxima of turbulent fluctuations to estimates
obtained from the first four sample moments by fitting a four-parameter beta distribution. The most sharply defined boundaries
were found for the minima of temperature datasets during the day, indicating that negative temperature fluctuations at the
sensor are limited by the availability of lower temperatures in the boundary layer. By comparison to vertical profiles, it
could be verified that the turbulent minimum of temperature near the ground is close to the minimum of potential temperature
in the boundary layer. The turbulent minimum of water vapour mixing ratio was found to be equal to the mixing ratio at a height
above the minimum of the temperature profile. This height roughly agrees with the top of the non-local unstable domain according
to bulk Richardson number profiles. We conclude that turbulence statistics measured near the surface cannot be solely explained
by local effects, but contain information about the whole boundary layer including the entrainment zone. 相似文献
197.
Stereoscopic Particle Image Velocimetry Measurements in an Urban-Type Boundary Layer: Insight into Flow Regimes and Incidence Angle Effect 总被引:1,自引:1,他引:0
An experimental investigation of the three-dimensional flow through an urban-type array (four rows of three cuboid Plexiglas
blocks) in a laboratory modelled neutrally stratified atmospheric boundary layer is presented. We concentrate on the effect
of the streamwise spacing between adjacent rows defining two different flow regimes (wake interference and skimming flow)
as well as the effect of the incident angle of the approaching boundary layer. Stereoscopic particle image velocimetry measurements
provide all three components of the velocity field in closely spaced two-dimensional planes in a region located in the middle
row downstream of the centre block. It is found that the maximal exchange rate between the fluid within the street and the
flow above is for the wake interference regime. Two regions are apparent: one influenced by streamwise velocity fluctuations,
the other by spanwise fluctuations. In addition, the incidence angle of the incoming flow has a much more dramatic effect
for the wake interference regime that would greatly favour dispersion. Coherent-structure identification tools are applied
to obtain information on the shape, extent and localisation of vortical structures. 相似文献
198.
Lithium isotopes in island arc geothermal systems: Guadeloupe, Martinique (French West Indies) and experimental approach 总被引:1,自引:0,他引:1
We report lithium (Li) isotopic measurements in seawater-derived waters that were discharged from geothermal wells, thermal springs, and sub-marine springs located in volcanic island arc areas in Guadeloupe (the Bouillante geothermal field) and Martinique (Lamentin plain and the Diamant areas). While Li isotopic signatures of the geothermal fluids collected from deep reservoirs were found to be homogeneous for a given site, the δ7Li signatures for each of these reservoirs were significantly different. The first low temperature (25-250 °C) experiments of Li isotope exchange during seawater/basalt interaction confirmed that Li isotopic exchange is strongly temperature dependent, as previously inferred from natural studies. Li isotopic fractionation ranged from +19.4‰ (Δsolution-solid) at 25 °C to +6.7‰ at 250 °C. These experiments demonstrated the importance of Li isotopic fractionation during the formation of Li-bearing secondary minerals and allowed us to determine the following empirical relationship between isotopic fractionation and temperature: Δsolution-solid = 7847/T − 8.093. Application of experimental results and literature data to the Bouillante area suggested that geothermal water was in equilibrium at 250-260 °C. It likely has a deep and large reservoir located in the upper sheeted dike complex of the oceanic crust, just below the transition zone between andesite volcanic flows and the basaltic dikes. The upper dike section, from which Li is extracted by hydrothermal fluids, was characterized by light Li isotopic values in the rocks, indicating retention of 6Li by the altered rocks. For the Lamentin and Diamant areas, the geothermal fluids appeared to be in equilibrium with reservoir volcano-sedimentary rocks at 90-120 °C and 180 °C, respectively. Further evidence for this argument is provided by the fact that only the Na/Li thermometric relationship determined for sedimentary basins yielded temperature values in agreement with those measured or estimated for the reservoir fluids. This suggests the importance of a sedimentary signature in these reservoir rocks. Altogether, this study highlights that the use of Li isotopic systematics is a powerful tool for characterizing the origin of geothermal waters as well as the nature of their reservoir rocks. 相似文献
199.
Laurent Jolivet Fabien Trotet Patrick Monié Olivier Vidal Bruno Goffé Loïc Labrousse Philippe Agard Bad'r Ghorbal 《Tectonophysics》2010,480(1-4):133-148
Syn-orogenic detachments in accretionary wedges make the exhumation of high-pressure and low-temperature metamorphic rocks possible with little erosion. The velocity of exhumation within the subduction channel or the accretionary complex, and thus the shape of P–T paths, depend upon the kinematic boundary conditions. A component of slab retreat tends to open the channel and facilitates the exhumation. We document the effect of slab retreat on the shape of P–T paths using the example of the Phyllite–Quartzite Nappe that has been exhumed below the Cretan syn-orogenic detachment during the Miocene in Crete and the Peloponnese. Data show a clear tendency toward colder conditions at peak pressure and during exhumation where the intensity of slab retreat is larger. This spatial evolution of P–T gradient is accompanied with an evolution from a partly coaxial regime below the Peloponnese section of the detachment toward a clearly non-coaxial regime in Crete. 相似文献
200.
Sandrine Guerlet Thierry Fouchet Bruno Bézard Leigh N. Fletcher F. Michael Flasar 《Icarus》2010,209(2):682-7965
Limb and nadir spectra acquired by Cassini/CIRS (Composite InfraRed Spectrometer) are analyzed in order to derive, for the first time, the meridional variations of diacetylene (C4H2) and methylacetylene (CH3C2H) mixing ratios in Saturn’s stratosphere, from 5 hPa up to 0.05 hPa and 80°S to 45°N. We find that the C4H2 and CH3C2H meridional distributions mimic that of acetylene (C2H2), exhibiting small-scale variations that are not present in photochemical model predictions. The most striking feature of the meridional distribution of both molecules is an asymmetry between mid-southern and mid-northern latitudes. The mid-southern latitudes are found depleted in hydrocarbons relative to their northern counterparts. In contrast, photochemical models predict similar abundances at north and south mid-latitudes. We favor a dynamical explanation for this asymmetry, with upwelling in the south and downwelling in the north, the latter coinciding with the region undergoing ring shadowing. The depletion in hydrocarbons at mid-southern latitudes could also result from chemical reactions with oxygen-bearing molecules.Poleward of 60°S, at 0.1 and 0.05 hPa, we find that the CH3C2H and C4H2 abundances increase dramatically. This behavior is in sharp contradiction with photochemical model predictions, which exhibit a strong decrease towards the south pole. Several processes could explain our observations, such as subsidence, a large vertical eddy diffusion coefficient at high altitudes, auroral chemistry that enhances CH3C2H and C4H2 production, or shielding from photolysis by aerosols or molecules produced from auroral chemistry. However, problems remain with all these hypotheses, including the lack of similar behavior at lower altitudes.Our derived mean mixing ratios at 0.5 hPa of (2.4 ± 0.3) × 10−10 for C4H2 and of (1.1 ± 0.3) × 10−9 for CH3C2H are compatible with the analysis of global-average ISO observations performed by Moses et al. (Moses, J.I., Bézard, B., Lellouch, E., Gladstone, G.R., Feuchtgruber, H., Allen, M. [2000a]. Icarus 143, 244-298). Finally, we provide values for the ratios [CH3C2H]/[C2H2] and [C4H2]/[C2H2] that can constrain the coupled chemistry of these hydrocarbons. 相似文献