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31.
There is a net discharge of water and nutrients through Long Key Channel from Florida Bay to the Florida Keys National Marine Sanctuary (FKNMS). There has been speculation that this water and its constituents may be contributing to the loss of coral cover on the Florida Keys Reef tract over the past few decades, as well as speculation that changes in freshwater flow in the upstream Everglades ecosystem associated with the Comprehensive Everglades Restoration Plan may exacerbate this phenomenon. The results of this study indicate that although there is a net export of approximately 3,850 (±404) ton N year?1 and 63 (±7) ton P year?1, the concentrations of these nutrients flowing out of Florida Bay are the same as those flowing in. This implies that no significant nutrient enrichment is occurring in the waters of the FKNMS in the vicinity of Long Key Channel. Because of the effect of restricted southwestward water flow through Florida Bay by shallow banks and small islands, the volume of relatively high-nutrient water from central and eastern portions of the bay exiting through the channel is small compared to the average tidal exchange. Nutrient loading of relatively enriched bay waters is mediated by tidal exchange and mixing with more ambient concentrations of the western Florida Bay and Hawk Channel. System-wide budgets indicate that the contribution of Florida Bay waters to the inorganic nitrogen pool of the Keys coral reef is small relative to offshore inputs. 相似文献
32.
Joseph Sidky Mikhail 《Earth, Moon, and Planets》1979,20(2):199-210
A study of the variation of the spectral relative ratios of reflectivity of selected mare lunar grounds between wavelengths 4000 and 8000 Å is given in comparison with lunar craters. The intensities at different wavelengths of each lunar region are corrected for the angles of illumination and viewing, and they are scaled to unity at =5538Å. Distinct variety in the spectral reflectivity values of mare grounds at short wavelengths are confirmed. The Mare Tranquillitatis type grounds (similar to Apollo-11 site), have relative ratio of reflectivity at short wavelength at =4035 Å; larger than or equal to 1.03 in addition to a bigger difference in reflectivity between the short and the long wavelength. The Mare Serenitatis type grounds (similar to Apollo-12) are characterized to give relative ratio of reflectivity less than 1.03 at =4035 Å, and smaller difference in reflectivity between short and long wavelengths. This is due to the variation in the colour of the Mare Tranquillitatis and Mare Serenitatis type ground due to compositional differences. The mare type grounds are generally different in shape than that of lunar craters grounds.Presented at the IAU-COSPAR Julian Schmidt Symposium on 100 Years of Lunar Mapping held at Lagonissi, Greece, 25–27 May, 1978. 相似文献
33.
Joseph W. Chamberlain 《Icarus》1980,44(3):651-656
An earlier paper gave solutions for the mean time rates of change of orbital elements of satellite atoms in an exosphere influenced by solar radiation pressure. Each element was assumet to beahve independently. Here the instantaneous rates of change for three elements are integrated simultaneously for the case of the inclination i = 0. The results (a) confirm the validity of using mean rates when the orbits are tightly bound to the planet and (b) serve as examples to be reproduced by the complicated numerical solutions required for arbitrary inclination. Strongly bound hydrogen atoms perturbed in Earth orbit by radiation pressure do not seem a likely cause of the geotail extending in the anti-Sun direction. Instead, radiation pressure wil cause those particles' orbits to form a broad fan-shaped tail and to deteriorate into the Earth's atmosphere. Whether loosely bound H atoms are plentiful enough to create the geotail depends on their source function versusr; that question is beyond the scope of this paper. 相似文献
34.
Mariner 9 ultraviolet spectra of the 1971 dust clouds were analyzed to obtain the phase function times single scattering albedo of the dust particles. The phase functions were matched with Mie scattering calculations for size distributions of spheres of homogeneous and isotropic material. The absorption index of the dust particles was found to increase with decreasing wavelenght from 350 nm down to about 210 nm, and drop off shortward of this wavelength. A structural shoulder occurs in the absorption spectrum between 240 and 250 nm. Titanium dioxide (anatase) has the correct transitions at 210 and 250 nm to match the absorption curve of Martian dust, and is proposed as a candidate constituent in Martian surface material. The spectral neutrality of TiO2 between 0.5 and 4 μm is consistent with visible and infrared observations of Mars. The high refractive index of TiO2 can explain the large refringence of Martian dust. The titanium dioxide content of the dust particles is estimated to be a few percent or less. Uncertainties in the results due to limitations in the model and data are discussed. 相似文献
35.
Many applied dispersion models require the knowledge of boundary-layer parameters such as sensible heat flux,Q
H
, friction velocity,u
*, and turbulent energy components, w and
v
. Formulas are suggested for calculating these parameters over a wide variety of types of ground surfaces, based on simple observations of wind speed near the ground and fractional cloud cover, and specification of constants such as roughness length, albedo, and soil moisture availability. Observations ofu
*,Q
H
,
w
, and
v
during field experiments in St. Louis and Indianapolis are used to test the formulas for urban sites. Relative errors of about ±20% in the predictions are seen to occur whenu
*,Q
H
,
w
, and
v
are large. However, when these quantities are small (e.g.,u
* < 0.2 m/s), the errors in the predictions are as large as the mean value of the quantity itself.In addition, it is concluded from studies of available field data and theories that the magnitude of
w
is not well-known at elevations above about 100m during the late afternoon and night. Some simple parameterizations for
w
. are suggested that are consistent with the observed steady decrease in ground-level concentration in the afternoon and the sudden increase in concentration that can occur a few hours after sunset due to wind shears associated with a low-level jet, for continuous plumes emitted from moderate to tall stacks. 相似文献
36.
Dr. Cinzia Spencer-Cervato Dr. Joseph Mullis 《International Journal of Earth Sciences》1992,81(2):347-370
In the Central Southern Alps (Feltre, Verona — Italy), a 750 m thick interval of Jurassic and Cretaceous pelagic limestones shows post-depositional partial brecciation and dolomitization. The overlying 500 m thick Tertiary sedimentary sequence is unaffected. Through the Paleogene, mostly submarine, mafic volcanism has been documented in the area. Small-scale extensional features were observed in the limestone near the contact with the dolomitized breccias. Their orientations measured in the field correspond to the tectonic framework of the area and give evidence for the contemporaneousness of the volcanic activity and the brecciation. The distribution and petrologic characteristics of the basalts, combined with the orientation of the extensional features observed in the field, allow a paleotectonic reconstruction. This tectonic scenario can be viewed as a back-arc extension, an eastward prolongation of the spreading that divided Southern France from the Sardinia-Corsica-Calabria block, generating the Ligurian-balearic basin in the Late Oligocene.The dolomite is fine-grained to sucrosic, with a microamygdaloidal porosity, partially filled with ankerite and calcite. The matrix shows a homogeneous, orange-red cathodoluminescence, indicating a single phase of iron-poor dolomite. The carbonate fraction consists of more than 90% dolomite. The dolomite is almost stoichiometric (Ca0.6Mg0.4 to Ca0.5Mg0.5). The
13C values of the dolomite are less than 1%. more negative than the unaffected limestone. The
18O values are between –5%. to –13%., with a depletion of 2–11%. relative to the undolomitized limestone. The depleted oxygen isotope ratios in the dolomitized rock can be derived either from fluids impoverished in the heavy isotopes (e.g. meteoric water) or high temperatures. The unvaried carbon isotopic ratios make the second interpretation the most acceptable. As the87Sr/86Sr values increase from a mean of 0.7077 in the unaffected limestones to 0.7085 in the dolomitized limestones, a derivation of the dolomitizing fluids from the volcanic rocks can be excluded. Comparing the obtained data with the Phanerozoic seawater isotope curve, however, the radiogenic Sr may be derived from marine waters of Late Oligocene-Early Miocene age. Microthermometric analyses of the fluid inclusions in the dolomite crystals from the bulk rocks and from the veins suggest a trapping temperature ranging from a minimum of 70°C (dolomite rock) to a maximum of 120°C (dolomite in veins). The solution contained in the inclusions is water with NaCl and MgCl2 with salinities of 46%. (dolomite bulk rock) and 17%. (dolomite in veins). The pressure correction calculated from the fluid inclusion data is about 250 bars, which roughly correspond to the lithostatic pressure over the Mesozoic limestones in the Early Miocene.These results point to a hydrothermal origin of the dolomitization during the Late Oligocene-Early Miocene, as ascertained from the strontium isotope and fluid inclusion data. The circulation of hot marine water through the brecciated limestones in convective cells, triggered by the geothermal gradient related to the volcanic activity, is the proposed hydrodynamic model. Hydrologie considerations demonstrate that the proposed model is feasible.
Zusammenfassung In den zentralen Südalpen (Feltre, Verona — Italien) findet sich eine etwa 750 m dicke Abfolge jurassischer und kretazischer pelagischer Kalke, die nach der Ablagerung zum Teil breckziert und dolomitisiert wurde, während die darüberliegenden 500 m mächtigen tertiären Sedimente keine Dolomitisierung zeigen. Im Paläogen ist im Gebiet ein mafischer, überwiegend mariner Vulkanismus dokumentiert. Kleinmaßstäbliche listrische Brüche in Kalken am Kontakt mit der dolomitisierten Breckzie entsprechen geometrisch einem großräumigen extensiven Regime im Paläogen. Sie beweisen die Gleichzeitigkeit der vulkanischen Aktivität und der Breckzierung. Die Verteilung und petrographischen Eigenschaften der Basalte, mit der Geometrie der Extensionsstrukturen, erlauben eine paläotektonische Rekonstruktion. Diese tektonische Situation entspricht einem Back-arc-basin und stellt die östliche Verlängerung des ligurisch-balearischen Beckens dar, das Südfrankreich vom Sardisch-Korsisch-Kalabrischen-Block im späten Oligozän getrennt hat.Die 13C Werte der Dolomite sind weniger als 1%. negativer als die entsprechender nicht dolomitisierter Kalke. Die 18O-Werte (relativ zum PDB Standard) variieren zwischen –5%. und –13%., das ist 2 bis 11%. negativer als die nicht dolomitisierter Kalke. Dies wird auf erhöhte Bildungstemperaturen zurückgeführt. Ein Anstieg der87Sr/86Sr-Signaturen im Mittel von 0.7077 in den nicht dolomitisierten Kalken auf 0.7085 in den dolomitisierten Kalken schließt eine Herkunft der dolomitisierenden Fluide von den vulkanischen Gesteinen aus. Beim Vergleich der Isotopensignaturen mit der phanerozoischen Meerwasser-Isotopenkurve, könnte aber das radiogene Strontium von spät oligozänem — früh miozänem Meerwasser kommen. Mikrothermometrische Analysen flüssiger Einschlüsse in Dolomitkristallen im Gestein und in Adern deutet auf eine Einschlußtemperatur von 70°C (Dolomitgestein) bzw. 120°C (Dolomit in Adern) hin. Die Lösung in den Einschlüssen ist Wasser mit NaCl und MgCl2, mit einer Salinität von 46%. (Dolomitgestein) bzw. 17%. (Adern). Die aus den Einschlüssen berechnete Druckkorrektur ist etwa 250 bar. Dies entspricht ungefähr der früh miozänen Gesteinssäule über den mesozoischen Kalken.Aufgrund dieser Daten wird eine hydrothermale Bildung der Dolomite im späten Oligozän - frühen Miozän postuliert. Es wird ein hydrodynamisches Modell vorgeschlagen, in dem aufgeheiztes Meerwasser konvektiv durch die breckzierte mesozoische Abfolge zirkuliert. Als Motor wirkt ein vulkanischer geothermischer Gradient. Dieses Modell läßt sich mit hydrologischen Betrachtungen testen und stützen.
Résumé Dans la partie sud des Alpes Centrales (Feltre, Verone: Italie) il existe une succession, épaisse de 750 m, de calcaires pélagiques jurassiques et crétacés, qui ont subi après leur sédimentation une bréchification et une dolomitisation partielles. Les sédiments tertiaires surincombants, épais de 500 m, ne sont pas affectés par ces phénomènes. Un volcanisme paléogène mafique, essentiellement sousmarin, a été reconnu dans la région. Dans les calcaires, au contact de la brèche dolomitisée, existent des cassures listriques de petite échelle dont la géométrie témoigne d'un régime extensif général au Paléogène. Leurs orientations, mesurées sur le terrain, indiquent la contemporanéité de l'activité volcanique et de la bréchification. La distribution et les caractères pétrologiques des basaltes, combinés à la géometrie des structures extensives, permet une reconstitution paléotectonique. Celle-ci montre une extension dans un bassin d'arrière-arc, prolongement oriental de l'expansion qui, à l'Oligocène supérieur, a séparé du sud de la France le bloc corsico-sardo-calabrais en créant le bassin liguro-baléare.La dolomie, finement grenue à saccharoïde, possède une porosité à vides micro-amygdaloïdes, partiellement occupés par de l'ankérite et de la calcite. La matrice présente une cathodoluminescence homogène rouge-orange, indiquant la présence d'une seule phase constituée de dolomite pauvre en Fe. La fraction carbonatée consiste en dolomite pour plus de 90%. Cette dolomite est à peu près stoechiométrique (Ca0,6Mg0,4 à Ca0,5Mg0,5). Les rapports 13C de la dolomie sont inférieurs de moins de 1%. à ceux du calcaire intact. Les rapports 18O sont compris entre –5%. et –13%., soit 2 à 11%. inférieurs à ceux du calcaire non dolomitisé. Cette baisse du rapport isotopique peut provenir soit de fluides appauvris en isotopes lourds (p. ex. l'eau météorique), soit d'une température élevée; la constance des rapports isotopiques du C rend cette deuxième explication la plus plausible. Le rapport87Sr/86Sr passe d'une valeur moyenne de 0,7077 dans les calcaires non affectés à 0,7085 dans les calcaires dolomitisés; cet accroissement exclut une origine volcanique pour les fluides dolomitisants. En comparant ces valeurs à la courbe isotopique du Sr de l'eau de mer au Phanérozoïque, on peut déduire que le Sr radiogénique est dérivé d'eaux marines d'âge oligocène tardif à miocène inférieur. L'analyse microthermométrique des inclusions fluides contenues dans les cristaux de dolomite suggère une température de formation qui va de 70°C (dans la roche) à 120° (dans les veines). Le contenu de ces inclusions est une solution aqueuse de NaCl et MgCl2 avec une salinité de 44%. (dans la roche) et de 17%. (dans les veines). La correction de pression calculée à partir des inclusions fluides est d'environ 250 bars, ce qui correspond grosso modo à la pression lithostatique qui s'exerçait au Miocène inférieur sur les calcaires mésozoïques.Sur la base de ces données, on conclut à une origine hydrothermale de la dolomie au cours de l'Oligocène supérieur - Miocène inférieur. Le modèle hydrodynamique proposé fait appel à la circulation convective, à travers le calcaire bréchié, d'eau marine échauffée grâce au gradient géothermique élevé dû à l'activité volcanique. Ce modèle est en accord avec des considérations hydrologiques.
(, — ) , 750 , , , , 500 , . , . , . , . . - , - . 13 , 1%. 18, PDB –5 –13%, .. 2 11% . , , . 87Sr/86Sr 0.7077 0,7085 . , - . 70° , 120° . , , 44%, 17%. , , 250 . - . , - . , . , . .相似文献
37.
K. Simon 《Contributions to Mineralogy and Petrology》1990,105(2):177-196
Hercynian S-type granites from the southeastern Schwarzwald granite series represent cogenetic biotite-and two-mica granites. Oxygen- and hydrogen-isotope data show that hydrothermal alteration invoking isotopically light surface waters resulted in a drastic reduction in 18O and D and pronounced disequilibrium between the minerals. Effective water-rock ratios are calculated to be high, about 0.8 vol units. A shift in the18O/16O and the chemical composition of the fluid due to water-rock interaction is continuously traced from pure H2O with meteoric isotopic character in the deep-seated biotite granites to slightly saline water with rock-equilibrated isotopic composition in the two-mica granites at a shallower level. Substantial retrograde hydrometamorphism in the temperature range 500° to 200° C resulted mineralogically in high-temperature chloritization of biotite, and low-temperature muscovitization as well as feldspar alteration, respectively. Another result of the re-equilibration of cations is strong disturbance of the Rb–Sr system which affects measured ages and initial87Sr/86Sr values. Hydrothermal differentiation and alteration probably overlap to a very large extent magmatic differentiation processes. 相似文献
38.
Darren F. Mark John Parnell Simon P. Kelley Sarah C. Sherlock 《Journal of Geochemical Exploration》2006,89(1-3):259
Integration of fluid inclusion analysis with high spatial resolution Ar–Ar dating of K-feldspar cements has been used to resolve and reconstruct palaeo-fluid flow. Fluid inclusion analysis allows discrimination of distinct cement phases, thereby identifying discrete episodes of fluid flow. Ar–Ar dating of the same cements via high spatial resolution laserprobe establishes absolute age constraints on the framework previously constructed. Integration of these two datasets yields temperature–composition–time data. 相似文献
39.
Nicolas Pouvreau Belén Martin Miguez Bernard Simon Guy Wöppelmann 《Comptes Rendus Geoscience》2006,338(11):802-808
The work of searching, recovering and quality control of ancient sea-level measurements at Brest is presented. This work enables us to complete a study carried out by Cartwright in 1972, which showed a decrease in the tidal M2 semi-diurnal amplitude of 1% per century. After including these ancient data, as well as the last four decades of observations in the analysis, our results show an increase of the amplitude of M2 after 1960 and a decrease before 1880, suggesting a long-period oscillation rather than a steady secular trend. To cite this article: N. Pouvreau et al., C. R. Geoscience 338 (2006). 相似文献
40.
Integrated, in situ textural, chemical and electron microprobe age analysis of monazite grains in a migmatitic metapelitic gneiss from the western Musgrave Block, central Australia has identified evidence for multiple events of growth and recrystallisation during poly-metamorphism in the Mesoproterozoic. Garnet + sillimanite-bearing metapelite underwent partial melting and segregation to palaeosome and leucosome during metamorphism between 1330 and 1296 Ma, with monazite grains in leucosome recording crystallisation at 1300 Ma. Monazite breakdown during melting is inferred to have occurred in the palaeosome. During a subsequent granulite facies event at 1200 Ma, deformation and metamorphism of leucosome and palaeosome resulted in partial disturbance of ages and potential minor growth on 1300 Ma monazite in leucosome. Growth of new, high-Y (+HREE) monazite in palaeosome domains occurred during garnet breakdown in the presence of sillimanite to cordierite and spinel, as a result of post-peak isothermal decompression. Diffusive enrichment of resorbed garnet rims in Y + HREE suggests garnet breakdown occurred slower than volume diffusion of REE. Monazite in both palaeosome and leucosome were subsequently partially to penetratively recrystallised during a retrogression event that is suggested to have occurred at 1150–1130 Ma. The intensity of recrystallisation and disturbance of ages appears linked to proximity to retrogressed garnet porphyroblasts and their occurrence in the relatively reactive or ‘fertile’ local environments provided by the palaeosome/mesosome volumes, which caused localised changes in retrogressive fluids towards compositions more aggressive to monazite. Like reaction textures, it is apparent that domainal equilibrium and reaction may control or at least strongly influence monazite REE and U–Th–Pb chemistry and hence ages. 相似文献