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排序方式: 共有226条查询结果,搜索用时 234 毫秒
121.
The study of sedimentary facies in the quarry of Dompcevrin (Middle Oxfordian) located northwestward of St-Mihiel (Meuse department) provides evidences of high-energy depositional conditions. The occurrence of beaches associated with hurricane coral breccias containing megaclasts is characteristic of platform edge environments. The open sea was located northeastward, in the direction of Germany, as it is indicated by the direction of progradation of beaches. It is concluded that the Oxfordian carbonate platform of Lorraine was opened to the northeast toward the Germanic Sea during the Middle Oxfordian. To cite this article: C. Carpentier et al., C. R. Geoscience 336 (2004). 相似文献
122.
Jean-Claude André Michel Déqué Philippe Rogel Serge Planton 《Comptes Rendus Geoscience》2004,336(6):491-503
The main features of the heat wave that has affected western Europe during the summer 2003 are first recalled, with particular concern to analogies and differences with previous warm-summer episodes. The skills of the various operational and pre-operational seasonal forecasting models in use at that time are evaluated. None of them has been able to consistently forecast the heat wave three month in advance. The meteorological and climatic situation prevailing during spring 2003 is then analysed. A strong sea-surface-temperature (SST) anomaly is found to have developed over North Atlantic a few months before the heat wave. The particular mechanism at work to explain the occurrence of the heat wave is not a ‘simple downwind influence’ of the SST anomaly. It very likely involves complex ocean–atmosphere interaction phenomena of a kind that is not properly taken into account in today's seasonal forecasting models. To cite this article: J.-C. André et al., C. R. Geoscience 336 (2004). 相似文献
123.
124.
Khadidja Ouzegane Serge Fourcade Jean -Robert Kienast Marc Javoy 《Contributions to Mineralogy and Petrology》1988,98(3):277-292
Several massifs of very old carbonatites have been discovered in the Archaean granulitic block of In'Ouzzal (Western Ahaggar, Algeria). These carbonatites are original since they are associated with Silica — saturated syenitic magmatism and present, in the late stages of evolution, a very uncommon mineralogy, with silicate minerals, especially wollastonite, allanite, and quartz. The mineralogy, C and O isotopes and R.E.E. distributions indicate that the late stages of crystallization occurred under high SiO2 activities, and produced the uncommon mineralogy and extremely high R.E.E. concentrations in phosphate minerals apatite and britholite. Interaction with continental crust is a possible mechanism to explain the original features of these carbonatite complexes. 相似文献
125.
In 1984–1985, the Kaiko consortium collected Seabeam, single-channel seismic and submersible sampling data in the vicinity of the Daiichi-Kashima seamount and the southern Japan trench. We performed a prestack migration of a Shell multichannel seismic profile, that crosses this area, and examined it in the light of this unusually diverse Kaiko dataset. Unlike the frontal structure of the northern Japan trench, where mass-wasting appears to be the dominant tectonic process, the margin in front of the Daiichi-Kashima shows indentation, imbrication, uplift and erosion. Emplacement of the front one-third of the seamount beneath the margin front occurs without accretion. We conclude that the Daiichi-Kashima seamount exemplifies an intermediate stage between the initial collision and subduction of a seamount at a continental margin. 相似文献
126.
Jean-Paul Cadet Kazuo Kobayashi Jean Aubouin Jacques Boulgue Christine Deplus Jacques Dubois Roland von Huene Laurent Jolivet Toshihiko Kanazawa Junzo Kasahara Kinichiro Koizumi Serge Lallemand Yasuo Nakamura Guy Pautot Kiyoshi Suyehiro Shin Tani Hidekazu Tokuyama Toshitsugu Yamazaki 《Earth and Planetary Science Letters》1987,83(1-4)
This paper presents the results of a detailed survey combining Seabeam mapping, gravity and geomagnetic measurements as well as single-channel seismic reflection observations in the Japan Trench and the juncture with the Kuril Trench during the French-Japanese Kaiko project (northern sector of the Leg 3) on the R/V “Jean Charcot”. The main data acquired during the cruise, such as the Seabeam maps, magnetic anomalies pattern, and preliminary interpretations are discussed. These new data cover an area of 18,000 km2 and provide for the first time a detailed three-dimensional image of the Japan Trench. Combined with the previous results, the data indicate new structural interpretations. A comparative study of Seabeam morphology, single-channel and reprocessed multichannel records lead to the conclusion that along the northern Japan Trench there is little evidence of accretion but, instead, a tectonic erosion of the overriding plate. The tectonic pattern on the oceanic side of the trench is controlled by the creation of new normal faults parallel to the Japan Trench axis, which is a direct consequence of the downward flexure of the Pacific plate. In addition to these new faults, ancient normal faults trending parallel to the N65° oceanic magnetic anomalies and oblique to the Japan trench axis are reactivated, so that two directions of normal faulting are observed seaward of the Japan Trench. Only one direction of faulting is observed seaward of the Kuril Trench because of the parallelism between the trench axis and the magnetic anomalies. The convergent front of the Kuril Trench is offset left-laterally by 20 km relative to those of the Japan Trench. This transform fault and the lower slope of the southernmost Kuril Trench are represented by very steep scarps more than 2 km high. Slightly south of the juncture, the Erimo Seamount riding on the Pacific plate, is now entering the subduction zone. It has been preceded by at least another seamount as revealed by magnetic anomalies across the landward slope of the trench. Deeper future studies will be necessary to discriminate between the two following hypothesis about the origin of the curvature between both trenches: Is it due to the collision of an already subducted chain of seamounts? or does it correspond to one of the failure lines of the America/Eurasia plate boundary? 相似文献
127.
The 620 M.y.-old in Hihaou (In Zize) magmatic complex located at the north-western boundary of the Archaean In Ouzzal block (western Ahaggar), is composed of massive alkaline rhyo-ignimbrites and rhyolitic domes, which are intruded by a granophyric and granitic body. The whole is preserved in a cauldron structure. Extrusive rocks are strongly 18O-depleted, with -values as low as –1.5/SMOW, while granophyres are less depleted (minimum -18O value=+2.0/SMOW. The granite has values around + 6/SMOW. D/H compositions are rather low, with D–90 to –110/SMOW. Isotopic zoning of quartz phenocrysts, 18O/16O fractionation among coexisting phases, and heterogeneity of the whole-rock -18O values, suggest that the volcanic rocks have interacted with meteoric water after the eruption. Several mechanisms of isotopic alteration are discussed. The hydrothermal alteration does not seem to have been controlled by the granitic intrusion, but rather seems to have followed the deposition of thick pyroclastic deposits on permeable arkosic sandstones and fluvio-glacial conglomerates. Pervasive circulation of water through the cooling volcanic deposits could have produced the observed 18O depletion. 相似文献
128.
Some breccias from the lunar highlands have probably trapped solar wind gases at a very early epoch in the history of the moon, as implied by their high contents of parentless fissiogenic xenon and sometimes, of parentless radiogenic129Xe. Four samples of this type, on which noble gas data already exist, have been selected for analysis of nitrogen contents and isotopic composition, by using step-wise heating techniques: 14047, 14055, 14307, 60255. Since uncertainties in the evolution of the solar wind15N/14N ratio with time are due in part to uncertainties in the measurement of the epoch of exposure, those samples provided the opportunity to measure the isotopic composition of nitrogen which has been trapped in the remote past, avoiding the problems inherent in the use of spallogenic nuclides. Results show that, in the samples studied from the Apollo 14 landing site, nitrogen is not particularly light, and has not been acquired, as a whole, in very ancient times. The conflicting presence of both parentless xenon and nitrogen of relatively “recent” isotopic signature can be explained if the hypothetical light nitrogen is diluted by more abundant, heavier nitrogen. Accordingly, the very ancient soil components which are implied in these objects by the presence of excess fission xenon have been re-exposed at a much later epoch, or mixed with some younger soil components, before the compaction event. The present data do not question the hypothesis of a secular isotopic variation of lunar trapped nitrogen, but cannot prove that very light nitrogen was trapped together with parentless fission xenon in the soil components of the highlands soil breccias. The very unusual release pattern of nitrogen in breccia 60255 can result from nitrogen isotopic homogenization with gas loss. 相似文献
129.
Lorenzo de la Fuente Yves Delage Serge Desjardins Allan MacAfee Garry Pearson Harold Ritchie 《Pure and Applied Geophysics》2007,164(6-7):1303-1325
Three cases of widespread sea fog in Lunenburg Bay, Nova Scotia were used to evaluate the suitability of operational regional
GEM forecast fields for inferring advection fog occurrences. Verification scores suggest that the objective analyses contain
significant departures from observations that will affect model accuracy, given the sensitivity of fog condensation microphysics.
Dew point depression (ES) scores show larger differences compared to temperature, with both influenced by surface characteristics.
For objective analyses and GEM forecasts ES < 2 C seems to match fog satellite images better than the physical threshold ES
≤ 0 C. In addition the GEM forecasts show a general tendency towards drier conditions near the surface, therefore reconfiguring
GEM to better represent condensation in the boundary layer is proposed. 相似文献
130.
Anna Jurado Alberto V. Borges Estanislao Pujades Pierre Briers Olha Nikolenko Alain Dassargues Serge Brouyère 《Hydrogeology Journal》2018,26(8):2739-2751
This study investigates the occurrence of greenhouse gases (GHGs) and the role of groundwater as an indirect pathway of GHG emissions into surface waters in a gaining stretch of the Triffoy River agricultural catchment (Belgium). To this end, nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) concentrations, the stable isotopes of nitrate, and major ions were monitored in river and groundwater over 8 months. Results indicated that groundwater was strongly oversaturated in N2O and CO2 with respect to atmospheric equilibrium (50.1 vs. 0.55 μg L?1 for N2O and 14,569 vs. 400 ppm for CO2), but only marginally for CH4 (0.45 vs. 0.056 μg L?1), suggesting that groundwater can be a source of these GHGs to the atmosphere. Nitrification seemed to be the main process for the accumulation of N2O in groundwater. Oxic conditions prevailing in the aquifer were not prone for the accumulation of CH4. In fact, the emissions of CH4 from the river were one to two orders of magnitude higher than the inputs from groundwater, meaning that CH4 emissions from the river were due to CH4 in-situ production in riverbed or riparian zone sediments. For CO2 and N2O, average emissions from groundwater were 1.5?×?105 kg CO2 ha?1 year?1 and 207 kg N2O ha?1 year?1, respectively. Groundwater is probably an important source of N2O and CO2 in gaining streams but when the measures are scaled at catchment scale, these fluxes are probably relatively modest. Nevertheless, their quantification would better constrain nitrogen and carbon budgets in natural systems. 相似文献