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451.
Hélène Cachier Patrick Buat-Menard Michel Fontugne Jacques Rancher 《Journal of Atmospheric Chemistry》1985,3(4):469-489
Atmospheric aerosol samples were collected in the Ivory Coast, primarily at Lamto (6°N, 5°W) between 1979 and 1981. The samples were analysed for total particulate carbon concentration and isotopic composition (13C/12C) by mass spectrometry. Observed concentrations were found high compared to values reported for temperate regions. Fine particulate carbon in the submicrometersize range accounted for 50 to 80% of the reported concentrations. At Lamto, both particulate carbon concentrations and isotopic ratios exhibit a large temporal variability which is shown to reflect the diversity of sources and their seasonal evolution. Natural emissions from the equatorial forest during the wet season, and biomass burning during the dry season, appear to be the major sources. The latter, though active during only a third of the year, is, on an annual basis, the most important source. Based on the data obtained at Lamto, an attempt has been made to estimate the flux of fine particulate carbon emitted from the tropical regions into the global troposphere. This flux, which is of the order of 20×1012 g C/yr, appears to be equivalent to the flux of fine particulate carbon emitted from industrial sources. These results suggest that the tropospheric burden of fine particulate carbon in lowlatitude regions is dominated by the long-range transport of carbonaceous aerosols originating from the Tropics. 相似文献
452.
Résumé Le gisement de fer oolithique de Mecheri Abdelaziz (Famennien terminal du bassin de Tindouf), présente des caractères morphologiques et sédimentologiques qui permettent de penser que la minéralisation s'est mise en place dans des édifices deltaïques progradants.La minéralisation est complexe et comprend trois paragenèses principales; maghémite-magnétite, bavalite-hématite, bavalite-magnétite et quatre faciès types: faciès microconglomératique (FMC), faciès à oolithes dispersées dans une matrice détritique (FOD), faciès à oolithes dispersées dans une matrice non détritique (FOND) et faciès à oolithes jointives, cimentées (FOC).Les caractères des oolithes et de la mésostase montrent que les corps minéralisés résultent de l'accumulation d'oolithes, développées essentiellement par concrétionnement intrasédimentaire et ayant subi, avant le dépôt définitif, des phases alternantes d'oolithisation et de remise en suspension.Sur l'ensemble du gisement, les teneurs moyennes sont les suivantes: Fe total: 43,49%; SiO2=13,66%; P2O5=2,31%; CaO=5,35%.En ce qui concerne la source du fer, il semble que la mise en place du minerai soit liée aux importantes réserves de quartzites ferrugineux situées dans le Précambrien du socle Réguibat, dont le stock métal initial a subi des remobilisations successives.
The Mecheri Abdelaziz oolitic iron deposit (late Famennian of Tindouf Basin) shows morphological and sedimentological features of prograding deltaic sequences.The mineralization is complex and allows the recognition of 3 types of paragenesis: maghemite-magnetite, bavalite-hematite, bavalite-magnetite; and 4 types of facies: microconglomerate facies, oolites dispersed in a matrix with detritic elements, oolites dispersed in a matrix without detritic elements and oolites with cement.The comparison of oolites and matrix suggests that the orebodies are the result of oolites deposition, developed by intrasedimentary processes and before the final deposition, by alternating phases of oolitization and suspension.For the whole ore deposit, the main composition is: total Fe=43.49%; SiO2=13.66%; P2O5=2.31%; CaO=5.35%.The major portion of iron was probably provided by continental leaching of the very important iron formations of the Precambrien Reguibat shield.相似文献
453.
A simple empirical model representing the variation of shear strain throughout a simple shear zone allows us to determine the evolution of finite strain as well as the progressive shape changes of passive markers. Theoretical strain patterns (intensity and orientation of finite strain trajectories, deformed shapes of initially planar, equidimensional and non-equidimensional passive markers) compare remarkably well with patterns observed in natural and experimental zones of ductile simple shear (intensity and orientation of schistosity, shape changes of markers, foliation developed by deformation of markers).The deformed shapes of initially equidimensional and non-equidimensional passive markers is controlled by a coefficient P, the product of
- 1. (1) the ratio between marker size and shear zone thickness
- 2. (2) the shear gradient across the zone.
454.
The ion-interaction model of PITZER (1973), is very effective in deriving stability relationships at high concentrations for the system Na-Cl-HCO3-CO3-OH-H2O. The solubility products of the main sodium carbonates have been calculated from solubility data between 5 and 50°C. The stability diagram in log pco2 — temperature coordinates and the invariant points deduced from the newly determined data are in good agreement with the most recent measurements.These results are used to calculate the activities of the major dissolved species in Lake Magadi brines (Kenya). The thermodynamic treatment confirms the main conclusions reached earlier by Eugster (1970, 1980) mainly from field observations. Trona precipitation occurs at equilibrium while natron is likely to form when the temperature decreases below 25°C. After the salt deposition the CO2 supply from the atmosphere is too slow to allow equilibrium between the atmosphere and the brines. In the next stages of evaporative concentration thermonatrite and halite precipitate. The deposition of the latter salts along with the observed HCO?3 depletion suggest that fractional crystallization is likely to control trona deposition. 相似文献
455.
When compared with nearby unvergetated areas, seagrass meadows contain a dense and strikingly rich assemblage of vertebrates and invertebrates. Most recent literature has focused on evaluating the role of predation in structuring seagrass faunal communities; however, habitat complexity, abundance of food and sediment stability may also be important. This paper summarizes studies relating predator-prey relationships to different features of the seagrass system. This review suggests that the abundance of many species, both epifauna and infauna, is positively correlated with two distinct aspects of plant morphology: 1) the root-rhizome mat, and 2) the plant canopy. A scheme was developed that defines the conditions under which any particular species will be abundant or rare in a seagrass assemblage. This scheme is based on prey and predator characteristics (e.g., epifaunal vs. infaunal, tube-dweller vs. nontube dweller, burrowers vs. nonburrowers, and large vs. small as adult) and on characteristics of the seagrasses (e.g., leaf morphology, shoot density, shoot biomass, structural complexity of the meadow, and root-rhizome density and standing crop). 相似文献
456.
Jacques Demange Pierre Chovelon Pascal Puvilland 《Journal of Volcanology and Geothermal Research》1989,36(1-3)
A programme of geothermal exploration on Réunion Island resulted in the siting of an exploration geothermal borehole in Salazie Cirque. The borehole attained a depth of 2108 m and encountered temperatures of 192 ± 8°C; no aquifer was found.The geological information obtained made it possible to propose a stratigraphy for the deep underlying rocks beneath the Salazie Cirque on the Piton des Neiges and thus to interpret the events that followed the emergence of the island. A large gabbroic mass was intersected and found to comprise several successive intrusions, the principal one of which is continuously zoned from melagabbro to monzonite. Modeling of geophysical data on the drillhole results enabled the distribution of the different geological units to be interpreted.A geothermal model is proposed taking into account the dynamic evolution of the hydrothermal processes that preceded and accompanied emplacement of the gabbro responsible for the geothermal anomaly underlying the three cirques that sculpt the flanks of the Piton des Neiges. 相似文献
457.
Rou-Fei Chen Kuo-Jen Chang Jacques Angelier Yu-Chang Chan Benoît Deffontaines Chyi-Tyi Lee Ming-Lang Lin 《Engineering Geology》2006,88(3-4):160-172
The 1999 Chi–Chi earthquake triggered the catastrophic Tsaoling landslide in central Taiwan. We mapped the landslide area and estimated the landslide volume, using a high-resolution digital elevation model from airborne LiDAR (Light Detection And Ranging), aerial photographs and topographic maps. The comparison between scar and deposit volumes, about 0.126 km3 and 0.150 km3 respectively, suggests a coseismic volume increase of 19% due to decompaction during landsliding. In July 2003, the scar and deposit volumes were about 0.125 km3 and 0.110 km3 respectively. These estimates suggest that 4 years after the event, the volume of landslide debris removed by river erosion was nearly 0.040 km3. These determinations are confirmed by direct comparison between the most accurate topographic models of the post-landslide period, indicating a very high erosion rate at the local scale (0.01 km3/year) for the deposit area of the landslide. Such a large value highlights the importance of landslide processes for erosion and long-term denudation in the Taiwan mountain belt. 相似文献
458.
Mi Jung Lee Jong Ik Lee Soon Do Hur Yeadong Kim Jacques Moutte Elena Balaganskaya 《Lithos》2006,91(1-4):250-261
The Sr, Nd and Pb isotopic compositions for the Kovdor phoscorite–carbonatite complex (PCC), Kola Peninsula, NW Russia, have been determined to characterize the mantle sources involved and to evaluate the relative contributions of a plume and subcontinental lithospheric mantle in the formation of the complex. The Kovdor PCC is a part of the Kovdor ultramafic–alkaline–carbonatite massif, and consists of six intrusions. The initial isotopic ratios of the analyzed samples, calculated at 380 Ma, display limited variations: εNd, + 2.0 to + 4.7; 87Sr/86Sr, 0.70319 to 0.70361 (εSr, − 12.2 to − 6.2); 206Pb/204Pb, 18.38 to 18.74; 207Pb/204Pb, 15.45 to 15.50; 208Pb/204Pb, 37.98 to 39.28. The Nd and Sr isotope data of the Kovdor PCC generally fit the patterns of the other phoscorites and carbonatites from the Kola Alkaline Province (KAP), but some data are slightly shifted from the mixing line defined as the Kola Carbonatite Line, having more radiogenic 87Sr/86Sr ratios. However, the less radiogenic Nd isotopic compositions and negative Δ7/4 values of Pb isotopes of the analyzed samples exclude crustal contamination, but imply the involvement of a metasomatized lithospheric mantle source. Isotopic variations indicate mixing of at least three distinct mantle components: FOZO-like primitive plume component, EMI-like enriched component and DMM-like depleted component. The isotopic nature of the EMI- and DMM-like mantle component observed in the Kovdor samples is considered to be inherited from metasomatized subcontinental lithospheric mantle. This supports the previous models invoking plume–lithosphere interaction to explain the origin of the Devonian alkaline carbonatite magmatism in the KAP. 相似文献
459.
Jacques Connan Arie Nissenbaum Kendra Imbus John Zumberge Stephen Macko 《Organic Geochemistry》2006,37(12):1768
Asphalts found as pure lumps or coatings on potsherds were excavated at the Philistine site of Tel Miqne-Ekron (12th to 7th century BC) in the southern Inner Coastal Plain of Israel. They were studied using the techniques of petroleum geochemistry and were compared to some natural asphalts from the area: Dead Sea floating blocks (Israel), Wadi Weida’a asphalt (Jordan) and Hasbeya (Lebanon).Tel Miqne-Ekron bitumens show evidence of weathering, indicating biodegradation and oxidation. They contain less aromatics and more asphaltenes than Dead Sea asphalt. Evaporation and biodegradation are recorded at a molecular level, especially via the phenanthrenes and dibenzothiophenes. However, several isotopic and molecular parameters allowed us to correlate the Tel Miqne-Ekron asphalt with the Dead Sea asphalt from the floating blocks. The asphalts of Hasbeya and Wadi Weida’a do not match the Tel Miqne-Ekron asphalt. The latter, in particular, is much more biodegraded, based on its steranes. The study shows that the Dead Sea asphalt was imported to Tel Miqne-Ekron over a 500 year period. This trade posed no problem in the 7th century BC when Philistia, Israel and Judah were at peace as part of the Pax Assyriaca of the Assyrian Empire. However, trade during the 12th century BC is puzzling since the asphalt had to be transported across Israelite territory that was hostile to the Philistines, as indicated in the Bible (e.g., Samson and Delilah, David and Goliath). Consequently it seems that profitable commerce surpassed ethnic, religious and political conflict, as can also be observed in the contemporary world. 相似文献
460.
A modification to the Soil Conservation Service curve number method for steep slopes in the Loess Plateau of China 总被引:9,自引:0,他引:9
The Soil Conservation Service curve number (CN) method is widely used for predicting direct runoff from rainfall. However, despite the extent of cultivation on hillslope areas, very few attempts have been made to incorporate a slope factor into the CN method. The objectives of this study were (1) to evaluate existing approaches integrating slope in the CN method, and (2) to develop an equation incorporating a slope factor into the CN method for application in the steep slope areas of the Loess Plateau of China. The dataset consisted of 11 years of rainfall and runoff measurements from two experimental sites with slopes ranging from 14 to 140%. The results indicated that the standard CN method underestimated large runoff events and overestimated small events. For our experimental conditions, the optimized and non‐optimized forms of the slope‐modified CN method of the Erosion Productivity Impact Calculator model improved runoff prediction for steep slopes, but large runoff events were still underestimated and small ones overpredicted. Based on relationships between slope and the observed and theoretical CN values, an equation was developed that better predicted runoff depths with an R2 of 0·822 and a linear regression slope of 0·807. This slope‐adjusted CN equation appears to be the most appropriate for runoff prediction in the steep areas of the Loess Plateau of China. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献