全文获取类型
收费全文 | 1139篇 |
免费 | 78篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 13篇 |
大气科学 | 88篇 |
地球物理 | 332篇 |
地质学 | 440篇 |
海洋学 | 100篇 |
天文学 | 202篇 |
综合类 | 3篇 |
自然地理 | 43篇 |
出版年
2023年 | 9篇 |
2022年 | 7篇 |
2021年 | 13篇 |
2020年 | 16篇 |
2019年 | 11篇 |
2018年 | 44篇 |
2017年 | 43篇 |
2016年 | 68篇 |
2015年 | 41篇 |
2014年 | 67篇 |
2013年 | 91篇 |
2012年 | 61篇 |
2011年 | 54篇 |
2010年 | 56篇 |
2009年 | 67篇 |
2008年 | 45篇 |
2007年 | 34篇 |
2006年 | 28篇 |
2005年 | 48篇 |
2004年 | 35篇 |
2003年 | 30篇 |
2002年 | 22篇 |
2001年 | 18篇 |
2000年 | 11篇 |
1999年 | 11篇 |
1998年 | 15篇 |
1997年 | 18篇 |
1996年 | 14篇 |
1995年 | 19篇 |
1994年 | 12篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1985年 | 10篇 |
1984年 | 13篇 |
1983年 | 15篇 |
1982年 | 12篇 |
1981年 | 15篇 |
1980年 | 6篇 |
1979年 | 9篇 |
1978年 | 12篇 |
1977年 | 10篇 |
1975年 | 8篇 |
1974年 | 8篇 |
1973年 | 5篇 |
1972年 | 5篇 |
1969年 | 9篇 |
排序方式: 共有1221条查询结果,搜索用时 31 毫秒
991.
According to historical reports, the north-eastern coastal sector of the volcanic Pantelleria Island (Sicily Channel, Italy) was uplifted up to 1.0 m a.s.l. in the year preceding the October 1891 offshore eruptive event. To better understand the nature and timing of coastal uplift, a detailed survey of morphological and biological indicators of raised palaeo-shorelines has been carried out along the island coastline. This survey identified raised palaeo-shoreline levels at three elevation ranges: 2.5–4.2 m a.s.l. (highest), 1.5–2.7 m a.s.l. (intermediate) and 0.4–1.0 m a.s.l. (lowest). Radiocarbon dating on samples of corals and vermetids placed tight temporal constraints on the uplifting of the raised shorelines. In general, they indicate that the north-eastern sector of the island, centred on the area of Cala del Gadir, has undergone major uplifting, tilting the island towards the southwest from 900 years ago. Applying accurate corrections for sea-level variations, the total amount of volcano-tectonic uplift can be estimated. Uplift rates up to 5 mm/a suggest that the vertical deformation was caused by inflation processes related to magmatic intrusion along feeding fissures. 相似文献
992.
Hydrogeology of the Nurra Region, Sardinia (Italy): basement-cover influences on groundwater occurrence and hydrogeochemistry 总被引:2,自引:0,他引:2
Giorgio Ghiglieri Giacomo Oggiano Maria Dolores Fidelibus Tamiru Alemayehu Giulio Barbieri Antonio Vernier 《Hydrogeology Journal》2009,17(2):447-466
The Nurra district in the Island of Sardinia (Italy) has a Palaeozoic basement and covers, consisting of Mesozoic carbonates, Cenozoic pyroclastic rocks and Quaternary, mainly clastic, sediments. The faulting and folding affecting the covers predominantly control the geomorphology. The morphology of the southern part is controlled by the Tertiary volcanic activity that generated a stack of pyroclastic flows. Geological structures and lithology exert the main control on recharge and groundwater circulation, as well as its availability and quality. The watershed divides do not fit the groundwater divide; the latter is conditioned by open folds and by faults. The Mesozoic folded carbonate sequences contain appreciable amounts of groundwater, particularly where structural lows are generated by synclines and normal faults. The regional groundwater flow has been defined. The investigated groundwater shows relatively high TDS and chloride concentrations which, along with other hydrogeochemical evidence, rules out sea-water intrusion as the cause of high salinity. The high chloride and sulphate concentrations can be related to deep hydrothermal circuits and to Triassic evaporites, respectively. The source water chemistry has been modified by various geochemical processes due to the groundwater–rock interaction, including ion exchange with hydrothermal minerals and clays, incongruent solution of dolomite, and sulphate reduction. 相似文献
993.
Smail Slimani Nicolas Massei Johanna Mesquita Danièle Valdés Matthieu Fournier Benoît Laignel Jean-Paul Dupont 《Hydrogeology Journal》2009,17(8):1823-1832
The temporal variability of water-level fluctuations in the chalk aquifer of Upper Normandy, France is constrained by natural climate fluctuations and is closely linked to the regional geological patterns. The chalk plateaus are covered with 5–50 m thick semi-permeable surficial formations; the thickness of the underlying chalk aquifer varies from 50 to 300 m. The relationship among climate oscillations, piezometric levels, and geologic structure were investigated by correlation, Fourier spectral, and continuous wavelet analyses of selected piezometric time-series data. Analysis focused on two piezometers located on the uplifted side of a major fault and two piezometers on the downthrown side. After generalization to other piezometers in the region, it was deduced that, in the downthrown compartments, a substantial aquifer and surficial formations thickness would imply a strong attenuation of annual variability, while multi-year variability is clearly expressed. Conversely, in the uplifted compartments, a thin layer of surficial formations and small thickness of the chalk authorizes strong variations on the annual mode with respect to the contribution of long-term climatic oscillations (multi-year variability). The results then demonstrated—and proposed a spatial determination of—the differential influence of geological patterns on the filtering of climate-induced oscillations in piezometric variability. 相似文献
994.
A new genus and species of percoid fish, Hendrixella grandei gen. & sp. nov. is described from the upper Ypresian limestone of Monte Bolca, Italy. It is based on four well-preserved
specimens that show an elongate and slender body and a unique combination of features, including possession of 11 + 13 vertebrae,
two series of intermuscular bones, fused haemal spine of third preural centrum, caudal fin with 17 principal rays and 11 upper
and eight lower procurrent rays, predorsal formula 0/0/1 + 1/1/, two separated dorsal fins with rayless pterygiophore in-between,
and a single supernumerary spine in both dorsal and anal fins. Due to this unique combination of features, Hendrixella cannot be placed within any existing fossil or extant percoid families and it is placed incertae sedis in the Percoidei. The possession of two series of intermuscular bones represents an unambiguous autapomorphy of Hendrixella. A comparative analysis of the distribution of intermusculars among percomorph fishes indicates that the intermuscular bones
of the upper series can be homologized with the epineurals and those of the lower series are the homologs of the epicentrals
of non-acanthomorphs. 相似文献
995.
Acknowledgement
Referees for volume 8 相似文献996.
997.
The stability of the thermohaline circulation of modern and glacial climates is compared with the help of a two dimensional ocean—atmosphere—sea ice coupled model. It turns out to be more unstable as less freshwater forcing is required to induce a polar halocline catastrophy in glacial climates. The large insulation of the ocean by the extensive sea ice cover changes the temperature boundary condition and the deepwater formation regions moves much further South. The nature of the instability is of oceanic origin, identical to that found in ocean models under mixed boundary conditions. With similar strengths of the oceanic circulation and rates of deep water formation for warm and cold climates, the loss of stability of the cold climate is due to the weak thermal stratification caused by the cooling of surface waters, the deep water temperatures being regulated by the temperature of freezing. Weaker stratification with similar overturning leads to a weakening of the meridional oceanic heat transport which is the major negative feedback stabilizing the oceanic circulation. Within the unstable regime periodic millennial oscillations occur spontaneously. The climate oscillates between a strong convective thermally driven oceanic state and a weak one driven by large salinity gradients. Both states are unstable. The atmosphere of low thermal inertia is carried along by the oceanic overturning while the variation of sea ice is out of phase with the oceanic heat content. During the abrupt warming events that punctuate the course of a millennial oscillation, sea ice variations are shown respectively to damp (amplify) the amplitude of the oceanic (atmospheric) response. This sensitivity of the oceanic circulation to a reduced concentration of greenhouse gases and to freshwater forcing adds support to the hypothesis that the millennial oscillations of the last glacial period, the so called Dansgaard—Oeschger events, may be internal instabilities of the climate system. 相似文献
998.
Ramón de Elía Daniel Caya Hélène Côté Anne Frigon Sébastien Biner Michel Giguère Dominique Paquin Richard Harvey David Plummer 《Climate Dynamics》2008,30(2-3):113-132
This work is a first step in the analysis of uncertainty sources in the RCM-simulated climate over North America. Three main
sets of sensitivity studies were carried out: the first estimates the magnitude of internal variability, which is needed to
evaluate the significance of changes in the simulated climate induced by any model modification. The second is devoted to
the role of CRCM configuration as a source of uncertainty, in particular the sensitivity to nesting technique, domain size,
and driving reanalysis. The third study aims to assess the relative importance of the previously estimated sensitivities by
performing two additional sensitivity experiments: one, in which the reanalysis driving data is replaced by data generated
by the second generation Coupled Global Climate Model (CGCM2), and another, in which a different CRCM version is used. Results
show that the internal variability, triggered by differences in initial conditions, is much smaller than the sensitivity to
any other source. Results also show that levels of uncertainty originating from liberty of choices in the definition of configuration
parameters are comparable among themselves and are smaller than those due to the choice of CGCM or CRCM version used. These
results suggest that uncertainty originated by the CRCM configuration latitude (freedom of choice among domain sizes, nesting
techniques and reanalysis dataset), although important, does not seem to be a major obstacle to climate downscaling. Finally,
with the aim of evaluating the combined effect of the different uncertainties, the ensemble spread is estimated for a subset
of the analysed simulations. Results show that downscaled surface temperature is in general more uncertain in the northern
regions, while precipitation is more uncertain in the central and eastern US. 相似文献
999.
Exhumation of eclogite and blueschist (Cyclades,Greece): Pressure–temperature evolution determined by thermobarometry and garnet equilibrium modelling 下载免费PDF全文
Valentin Laurent Pierre Lanari Inès Naïr Romain Augier Abdeltif Lahfid Laurent Jolivet 《Journal of Metamorphic Geology》2018,36(6):769-798
High‐P rocks such as eclogite and blueschist are metamorphic markers of palaeo‐subduction zones, and their formation at high‐P and low‐T (HP–LT) conditions is relatively well understood since it has been the focus of numerous petrological investigations in the past 40 years. The tectonic mechanisms controlling their exhumation back to the surface are, however, diverse, complex and still actively debated. Although the Cycladic Blueschist Unit (CBU, Greece) is among the best worldwide examples for the preservation of eclogite and blueschist, the proposed P–T evolution followed by this unit within the Hellenic subduction zone is quite different from one study to another, hindering the comprehension of exhumation processes. In this study, we present an extensive petrological data set that permits refinement of the shape of the P–T trajectory for different subunits of the CBU on Syros. High‐resolution quantitative compositional mapping has been applied to support the thermobarometric investigations, which involve semi‐empirical thermobarometry, garnet equilibrium modelling and P–T isochemical phase diagrams. The thermodynamic models highlight the powerful use of reactive bulk compositions approximated from local bulk compositions. The results are also combined with Raman spectrometry of carbonaceous material (RSCM) to retrieve the metamorphic peak temperature distribution at the scale of the island. A major result of this study is the good agreement between all the independent thermobarometric methods, permitting reconstruction of the prograde and retrograde P–T trajectories. Garnet compositional zoning was used to retrieve prograde, peak and retrograde growth stages in line with the results of the P–T isochemical phase diagrams, RSCM temperature and peak‐pressure crystallization of the garnet–omphacite–phengite assemblage. Our results are consistent with previous thermobarometric estimates from other occurrences of CBU rocks (Tinos, Andros), suggesting a multistage exhumation process with (1) early syn‐orogenic exhumation within the subduction channel, (2) isobaric heating at mid‐crustal depths (~10–12 kbar) following thermal re‐equilibration of the lithosphere from a cold syn‐orogenic regime in the subduction zone to a warmer post‐orogenic regime in the back‐arc domain and (3) exhumation and cooling related to a post‐orogenic phase of extension following slab retreat. Expanding to the general aspects of subduction zones, we suggest that such metamorphic evolution of HP–LT units should be regarded as a characteristic feature of exhumation driven by slab rollback. 相似文献
1000.