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141.
After World War II Saudi Arabia has experienced spectacular changes. Based on huge oil and gas revenues a particularly rapid
growth of population and a spectacular urbanization took place. One of the most booming cities in the desert environment of
the arabian peninsula is the Kingdoms capital city of Riyadh. With a built-up area of 3.5 km2 only before 1950 the city's present-day expansion reaches more than 500 km2. During the same period of time the population of Riyadh grew from less than 50,000 in 1945 to more than 1.4 Mio. in 1985.
Such an explosive development can be documented best by a satellite image. In this paper the process of urbanization of Riyadh
is presented by the interpretation of a MOMS image taken in 1984, documenting the geographic situation, urban structures,
and the city's development. 相似文献
142.
Synthetic melilites on the join Ca2MgSi2O7 (åkermanite) — Ca2FeSi2O7 (iron åkermanite) with Fe/(Fe+Mg) from 0.0 to 0.7 exhibit, at room temperature, an incommensurate phase with a rectangular modulation of a wavelength of about 19 Å in the [110] direction. Upon increase of temperature, they transform to a commensurate melilite structure at about 80° C for Fe/(Fe+Mg)=0.0 and about 250° C for Fe/(Fe+Mg)=0.6. In addition to the T(2) positions of the melilite structure filled by Si, the incommensurate phase exhibits two distinguishable T(1) sites containing the Mg and Fe2+. These two sites merge into one site during the phase transition from the incommensurate to the commensurate phase. A structural model for the incommensurate phase is based on the misfit between the tetrahedral (Mg, Fe2+)Si2O 7 4? sheets and the Ca2+ ions. 相似文献
143.
144.
Helmut Schäfer Wolfgang Friedrich Müller Ulrich Hornemann 《Physics and Chemistry of Minerals》1984,10(3):121-124
Shock recovery experiments on melilite samples in the pressure range from 11 to 50.5 GPa have been performed in order to examine the effects of shock waves on this material. The shocked samples were subsequently studied in the transmission electron microscope. All samples displayed the shock-induced amorphous areas, known as diaplectic glass. The amount of diaplectic melilite glass increased from a few percent at 11 GPa to about 85 percent at 50.5 GPa shock pressure. The shock waves also caused deformational effects as planar faults parallel to (001) and dislocations with a density in the order of 1010 cm?2. Regarding the present discussion on the origin and nature of diaplectic glass, diaplectic melilite glass is assumed to be the reversion product of a high-density phase produced in the shock front. Deformed melilites in Ca-Al-rich inclusions from chondritic meteorites studied so far do not contain diaplectic glass. It is assumed that the meteoritic melilites were hot (>1,000° C) and thus plastically deformable by shock waves of rather low amplitudes. 相似文献
145.
Summary The temperature-dependent structural and physical properties of melilites and their changes at the incommensurate-normal phase transition all are consistent with a model relating the formation of the incommensurately modulated (IC) structure to structural strain. This strain originates from an interplay between the size of the interlayer cation, its thermal vibration, and the size and deformation of the tetrahedral sheet. Consequently, the IC structure changes its properties continuously towards those of the high-temperature normal (N) phase as the IC-N phase transition is approached. Far below the transition temperature the modulation is rectangular and the structure can eventually be described by a static microdomain model. Besides chemical effects (essentially cation size), structural defects play a key role in the behaviour of the incommensurately modulated phase.
With 8 Figures 相似文献
Makroskopische und strukturelle Änderungen am inkommensurabel-normal Phasenübergang in Meliliten
Zusammenfassung Die temperaturabängigen strukturellen und physikalischen Eigenschaften der Melilite und ihre Änderungen am Phasenübergang von der inkommensurablen (IC) zur Normal(N)-Struktur sind konsistent mit einem Modell, das die Bildung der IC-Struktur durch strukturelle Verspannung erklärt. Die Verspannung entsteht durch die Wechselbeziehung zwischen der Größe des Zwischenschicht-Kations, seiner thermischen Schwingung und der Abmessung und Deformation der Tetraederschicht. Dementsprechend ändern sich die Eigenschaften der IC-Struktur bei Annäherung an den IC-N-Phasenübergang kontinuierlich in Richtung auf die Hochtemperatur-Normal-Struktur. Weit unterhalb der Übergangstemperatur ist die Modulation rechteckig und die Struktur kann durch ein statisches Mikrodomänen-Modell beschrieben werden. Neben chemischen Einflüssen (vor allem Radien der Kationen) spielen auch strukturelle Defekte eine Schlüsselrolle im Verhalten der IC-Phase.
With 8 Figures 相似文献
146.
R. Friedrich B. Wickert P. Blank S. Emeis W. Engewald D. Hassel H. Hoffmann H. Michael A. Obermeier K. Schäfer T. Schmitz A. Sedlmaier M. Stockhause J. Theloke F.-J. Weber 《Journal of Atmospheric Chemistry》2002,42(1):179-206
Measurements and model developments with the objective to improve the quality and resolution of estimations of anthropogenic emissions are described. Measurement results on a chassis dynamometer were used to determine VOC profiles for exhaust gas emissions of passenger cars for different vehicle and fuel types and different driving modes. Further measurements resulted in emission factors and VOC profiles for lignite burning in residential stoves. Using remote sensing techniques benzene emission factors of gas stations and the efficiency of gasoline vapour recovery systems were measured.To improve the quality and the spatial and temporal resolution of emission data, emission models were improved or modified. This was done by elaborating and applying new methods for important emission source categories (e.g., solvent use, road traffic, small combustion) as well as including new data sources in the calculation routines (e.g. emission statements, land use data, import/export indices of solvents). Simultaneously considerable progress was made improving temporal and spatial allocation functions and VOC profiles. With these improvements a large number of anthropogenic emission data sets for 14 different grid projections in Germany and Europe have been generated. An emission scenario for Germany for 2010 suggests that considering air quality directives from the EU and Germany which are in force or in pipeline, German emissions of VOC and NOx will decrease, but still exceed the national emission ceilings of the EU-NEC directive. 相似文献
147.
Cation ordering in omphacite and effect on deformation mechanism and lattice preferred orientation (LPO) 总被引:1,自引:0,他引:1
We present microstructural data and lattice preferred orientations (LPOs) of omphacites from a suite of eclogites, from the Adula/Cima Lunga nappe (Central Alps). Our work shows a surprisingly strong correlation between the measured LPO and the ordering state of cations in omphacite. Estimates of deformation temperature from metamorphic petrology, together with measured omphacite compositions and LPOs, determine the field (ordering state), on the omphacite phase diagram, into which each sample falls. LPOs dominated by L-type and S-type signatures are developed in samples that fall in the P2/n field (ordered structure) and C2/c field (disordered structure), respectively.Dislocations with b=1/2−110 or b=[001] are observed in the transmission electron microscope (TEM) in all samples. The former change from a perfect dislocation in the C2/c structure to a partial in P2/n. Any movement of a partial dislocation requires the formation or growth of a stacking fault. Furthermore, in order to pass an obstacle a partial dislocation has to constrict to a unit dislocation. The energy to form a constriction is high in omphacite due to the large separation width. Thus, the activity of the b=1/2−110 dislocation is hindered in the P2/n structure relative to the C2/c structure, which change the balance between the two and might give rise to the different LPOs. 相似文献
148.
正The papers in this issue stem from the 13th International Symposium on River Sedimentation held in September 2016 at the University of Stuttgart,Germany.The Symposiums on River Sedimentation aim to provide a platform for scientists and engineers for fruitful and in-depth knowledge exchange.The objectives are to develop sustainable revitalization and management strategies that address the ongoing negative effects of anthropogenic activities,whilst improving river systems toward a healthy ecological status.The fundamental research and understanding of interactive 相似文献
149.
V. V. Adushkin B. B. Chen S. I. Popel A. Yu. Dubinskii P. G. Weidler F. Friedrich 《Izvestiya Physics of the Solid Earth》2018,54(2):330-335
An experimental study of small-scale mineral particles in the atmosphere over Kyrgyzstan is carried out. It is shown that the substance of the studied particles corresponds to quartz-enriched minerals, feldspars, layered silicates, minerals containing lime carbonate, etc. Overall, there is a definite correspondence between the mineral particle compositions in the atmosphere of Kyrgyzstan and in the other regions of Central Asia. The constructed size-distribution functions of the particles agree with the results of studying the dust aerosol properties in the deserts of Central Asia obtained in the southwestern part of Tajikistan in 1989. 相似文献
150.
Climate change effects on hydrological system conditions influencing generation of storm runoff in small Alpine catchments 总被引:1,自引:0,他引:1
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Gertraud Meißl Herbert Formayer Klaus Klebinder Florian Kerl Friedrich Schöberl Clemens Geitner Gerhard Markart David Leidinger Axel Bronstert 《水文研究》2017,31(6):1314-1330
Floods and debris flows in small Alpine torrent catchments (<10 km2) arise from a combination of critical antecedent system state conditions and mostly convective precipitation events with high precipitation intensities. Thus, climate change may influence the magnitude–frequency relationship of extreme events twofold: by a modification of the occurrence probabilities of critical hydrological system conditions and by a change of event precipitation characteristics. Three small Alpine catchments in different altitudes in Western Austria (Ruggbach, Brixenbach and Längentalbach catchment) were investigated by both field experiments and process‐based simulation. Rainfall–runoff model (HQsim) runs driven by localized climate scenarios (CNRM‐RM4.5/ARPEGE, MPI‐REMO/ECHAM5 and ICTP‐RegCM3/ECHAM5) were used in order to estimate future frequencies of stormflow triggering system state conditions. According to the differing altitudes of the study catchments, two effects of climate change on the hydrological systems can be observed. On one hand, the seasonal system state conditions of medium altitude catchments are most strongly affected by air temperature‐controlled processes such as the development of the winter snow cover as well as evapotranspiration. On the other hand, the unglaciated high‐altitude catchment is less sensitive to climate change‐induced shifts regarding days with critical antecedent soil moisture and desiccated litter layer due to its elevation‐related small proportion of sensitive areas. For the period 2071–2100, the number of days with critical antecedent soil moisture content will be significantly reduced to about 60% or even less in summer in all catchments. In contrast, the number of days with dried‐out litter layers causing hydrophobic effects will increase by up to 8%–11% of the days in the two lower altitude catchments. The intensity analyses of heavy precipitation events indicate a clear increase in rain intensities of up to 10%. 相似文献