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131.
J. N. Andrews M. J. Youngman J. E. Goldbrunner W. G. Darling 《Environmental Geology》1987,10(1):43-57
The geochemistry of formation waters in the Molasse basin of Upper Austria has been investigated to ascertain the extent of
meteoric water replacement of the connate interstitial fluids in these sediments. The chemistry, isotopic composition, and
dissolved gas contents of the groundwaters and of oil and gas associated brines have been determined. The most superficial
sediments of the basin, the Innviertel (Miocene), have been completely flushed by meteoric waters within the last 200 ka.
The underlying Hall and Puchkirchen formations (Miocene/Oligocene) form gas reservoirs for biogenic methane, and the associated
formation waters are chemically and isotopically modified connate brines of the original marine deposition. In the northeastern
part of the basin, the connate brines of the deeper sediments (Cretaceous/Jurassic) have been partially or completely replaced
by meteoric waters, whereas in the south of the basin these sediments contain high salinity fluids which are substantially
of connate origin. These conclusions are supported by the stable isotope composition of the various brines. Oil-associated
brines from the Eocene sediments contain large amounts of dissolved radiogenic40Ar, which suggests that the oils have migrated from high-temperature environments. This is in contrast with the Puchkirchen,
for which the observed absence of radiogenic40Ar suggests that the biogenic methane has been formed in situ. The4He contents of these brines and of the Cretaceous/Jurassic groundwaters are, however, less than those in the overlying Puchkirchen
formation and suggest that He has been removed from the deeper sediments as a result of flushing by meteoric water. The ratios
of dissolved methane and nitrogen to argon increase with increasing ammonium content of the formation waters. All of these
parameters may be used as indices for the maturation of the system. The heavy noble gases, Kr and Xe, are abnormally abundant
in the dissolved gases, and this is attributed to geochemical concentration of these gases by adsorption onto shales in the
sediment sequence. The overall geochemical situation confirms the existence of separate hydraulic systems with little interconnection
in the several overlying geological horizons. 相似文献
132.
J.T. Andrews A. Aksu M. Kelly R. Klassen G.H. Miller W.N. Mode P. Mudie 《Quaternary Science Reviews》1985,4(4):333-355
Evidence from terrestrial sections, ice cores, and marine cores are reviewed and used to develop a scenario for environmental change in the area of the extreme northwest North Atlantic during marine isotope stages 5 and 4. The critical physical link between the landbased glacial chronology and marine events in Baffin Bay is the presence of carbonate rich drift along the Baffin Bay coast of Bylot Island and a detrital carbonate facies (Facies B) in Baffin Bay sediments. Cores from Baffin Bay/Labrador Sea can be dated by means of oxygen isotope variations and by peaks in the abundance of volcanic glass shards. One occurrence of Facies B is dated between late stage 5 and stage 4 and we correlate this event with the Eclipse Glaciation of Bylot Island and the Ayr Lake stade of the Foxe Glaciation of Baffin Island (= Kogalu aminozone). In contrast on West Greenland, amino acid racemization evidence suggests that the Greenland Ice Sheet developed throughout stage 4 and reached a maximum in stage 3 (Svartenhuk advance >40 ka). The oxygen isotope record in the Devon Island Ice Cap (northwest Baffin Bay) indicates that Baffin Bay was largely open during marine isotope stage 5. Analyses of shallow water molluscan and foraminiferal assemblages, deep-water foraminifera, pollen from Iand sections and deep-sea cores, and dinoflagellates from marine cores indicate that interglacial conditions prevailed during much of the stage
glaciation. 相似文献
133.
Some comparisons between the middle atmosphere dynamics of the Southern and Northern Hemispheres 总被引:1,自引:0,他引:1
David G. Andrews 《Pure and Applied Geophysics》1989,130(2-3):213-232
Comparisons are drawn between certain middle atmosphere dynamical processes in the Southern Hemisphere and the Northern Hemisphere. Attention is focused on the zonal-mean climatological state, stationary waves, transient waves of various types, stratospheric sudden warmings and polar ozone minima. Observations of the similarities and differences between the hemispheres are mentioned, and ways in which these comparisons may be used to enhance our dynamical knowledge of the whole middle atmosphere are discussed. 相似文献
134.
The stratigraphic record in the James and Hudson Bay Lowlands indicates that the sequence of glacial events at the geographical center of the 12.6 × 106 km2 Laurentide Ice Sheet may have been more complex than hitherto imagined. Isoleucine epimerization ratios of in situ and transported shells recovered from till and associated marine and fluvial sediments cluster into at least 4 discrete groups. Two alternative explanations of the data are offered, of which we strongly favor the first. Hypothesis 1: Setting the age of the “last interglacial” marine incursion, the Bell Sea, at 130,000 yr B.P. results in a long-term average diagenetic temperature for the lowlands of +0.6°C. Using this temperature enables us to predict the age of shells intermediate in age between the “last interglaciation” and the incursion of the Tyrrell Sea 8000 yr ago. Between these two interglacial marine inundations, Hudson Bay is predicted to have been free of ice along its southern shore about 35,000, 75,000, and 105,000 yr ago based on amino acid ratios from shells occurring as erratics in several superimposed tills and fluvial sediments. These results suggest (1) that traditional concepts of ice-sheet build-up and decay must be reexamined; (2) that “high” sea levels may have occurred during the Wisconsin Glaciation; and (3) that a critical reappraisal is required of the open ocean δ18O record as a simple indicator of global ice volume. An alternative, Hypothesis 2, is also examined. It is based on the assumption that the 35,000-yr-old deposits calculated on the basis of Hypothesis 1 date from the “last interglaciation”; this, in effect, indicates that the Missinaibi Formation, commonly accepted as sediments of the “last interglaciation,” are about 500,000 yr old and that the effective diagenetic temperature in the lowlands during approximately the last 130,000 yr has been close to ?6°C. We argue for rejection of this alternative hypothesis. 相似文献
135.
Qin Huanhuan Andrews Charles B. Tian Fang Cao Guoliang Luo Yong Liu Jiurong Zheng Chunmiao 《Hydrogeology Journal》2018,26(4):1061-1081
Hydrogeology Journal - Beijing, in the North China plain, is one of the few megacities that uses groundwater as its main source of water supply. Groundwater accounts for about two-thirds of the... 相似文献
136.
137.
Axel K. Schmitt Kevin Konrad Graham D. M. Andrews Kenji Horie Sarah R. Brown Anthony A. P. Koppers 《International Geology Review》2018,60(8):956-976
Long-lived intra-oceanic arcs of Izu-Bonin-Marianas (IBM)-type are built on thick, granodioritic crust formed in the absence of pre-existing continental crust. International Ocean Discovery Program Expedition 350, Site U1437, explored the IBM rear arc to better understand continental crust formation in arcs. Detailed petrochronological (U–Pb geochronology combined with trace elements, oxygen and hafnium isotopes) characterizations of zircon from Site U1437 were carried out, taking care to exclude potential contaminants by (1) comparison of zircon ages with ship-board palaeomagnetic and biostratigraphic ages and 40Ar/39Ar geochronology, (2) analysing zircon from drill muds for comparison, (3) selectively carrying out in situ analysis in petrographic thin sections, and (4) minimizing potential laboratory contamination through using pristine equipment during mineral separation. The youngest zircon ages in Site U1437 are consistent with 40Ar/39Ar and shipboard ages to a depth of ~1390 m below sea floor (mbsf) where Igneous Unit Ig 1 yielded an 40Ar/39Ar age of 12.9 ± 0.3 Ma (all errors 2σ). One single zircon (age 15.4 ± 1.0 Ma) was recovered from the deepest lithostratigraphic unit drilled, Unit VII (1459.80–1806.5 mbsf). Site U1437 zircon trace element compositions are distinct from those of oceanic and continental arc environments and differ from those generated in thick oceanic crust (Iceland-type) where low-δ18O evolved melts are produced via re-melting of hydrothermally altered mafic rocks. Ti-in-zircon model temperatures are lower than for mid-ocean ridge rocks, in agreement with low zircon saturation temperatures, suggestive of low-temperature, hydrous melt sources. Zircon oxygen (δ18O = 3.3–6.0‰) and hafnium (εHf = + 10–+16) isotopic compositions indicate asthenospheric mantle sources. Trace element and isotopic differences between zircon from Site U1437 rear-arc rocks and the Hadean detrital zircon population suggest that preserved Hadean zircon crystals were probably generated in an environment different from modern oceanic convergent margins underlain by depleted mantle. 相似文献
138.
Benjamin J. Andrews James E. GardnerTodd B. Housh 《Journal of Volcanology and Geothermal Research》2008
Compositional and isotopic zoning patterns in plagioclase and amphibole phenocrysts from El Chichón record multiple cycles of country rock assimilation, magma injection, hybridization, and mixing. Laser ablation ICP-MS and electron microprobe analyses of plagioclase crystals from 7 eruptions spanning 3100 years reveal four types of zoning. These compositional and isotopic zones are often associated with textural changes observed in the crystals in thin section (e.g. sieved or patchy regions). Amphiboles are frequently zoned in Al and Si, and, in two magmas, may have clinopyroxene rims. Interestingly, most plagioclase show multiple and repeated zoning patterns. Moreover, all magmas contain all zoning patterns and textures, and crystals with substantially different sequences of zones occur within mm of one another. The most reasonable explanation for the origin of these textures is a frequently recharged chamber. Plagioclase zones with increasing anorthite contents (An) and decreasing 87Sr/86Sr ratios record injection by a hotter, possibly wetter, and more primitive magma (lower 87Sr/86Sr ratio). Zones with decreasing An and increasing 87Sr/86Sr ratios record assimilation of country rock and/or hybridization of the host and injected magmas; injection of hot magma may provide the heat for country rock assimilation. Changes in An without corresponding changes in 87Sr/86Sr ratio likely record slight variations in pressure or temperature during crystallization, or the far-field thermal effects of magma injection. Variations in 87Sr/86Sr ratio unaccompanied by Anzoning record assimilation of country rock. Amphibole zoning patterns also record periodic heating events; amphibole with clinopyroxene rims record episodes where the magma was heated beyond the amphibole stability field. Bulk compositional homogeneity and the juxtaposition of many crystals with disparate zoning patterns in single pumice require the magmatic system to be well mixed. Strontium diffusion rates indicate that the plagioclase zoning patterns cannot have persisted at magmatic pressures and temperatures for more than ~ 500 years, thus cycles of injection and assimilation occur on timescales equal to or shorter than the eruption recurrence interval. Long-term compositional and isotopic homogeneity indicate that there is a balance between recharge, assimilation, and crystallization. 相似文献
139.
D.P. Patil J.R.G. Andrews P.H.T. Uhlherr 《International Journal of Mineral Processing》1997,50(4):289-306
In the shear flocculation process, flocculation of ultrafine (size < 10 μm) hydrophobic particle occurs in the presence of a high shear field. Hence, it is necessary to consider both processes of coalescence and breakage, while modelling shear flocculation.In this paper, a lumped discrete population balance model is presented considering both processes of coalescence and breakage of flocs. A method is also proposed to convert discrete kernels to lumped discrete kernels by satisfying the constraints on them. The numerical solution of the model is compared with some special analytical solutions of the continuous population balance model, with which it is observed to be in agreement. The model equations are derived in such a way that it predicts correctly both the rate of change of number and the total volume of the flocs. The size distribution of a flocculating suspension can be predicted by this model. 相似文献
140.
Mathias J. Collins Noah P. Snyder Graham Boardman William S.L. Banks Mary Andrews Matthew E. Baker Maricate Conlon Allen Gellis Serena McClain Andrew Miller Peter Wilcock 《地球表面变化过程与地形》2017,42(11):1636-1651
Dam removals with unmanaged sediment releases are good opportunities to learn about channel response to abruptly increased bed material supply. Understanding these events is important because they affect aquatic habitats and human uses of floodplains. A longstanding paradigm in geomorphology holds that response rates to landscape disturbance exponentially decay through time. However, a previous study of the Merrimack Village Dam (MVD) removal on the Souhegan River in New Hampshire, USA, showed that an exponential function poorly described the early geomorphic response. Erosion of impounded sediments there was two‐phased. We had an opportunity to quantitatively test the two‐phase response model proposed for MVD by extending the record there and comparing it with data from the Simkins Dam removal on the Patapsco River in Maryland, USA. The watershed sizes are the same order of magnitude (102 km2), and at both sites low‐head dams were removed (~3–4 m) and ~65 000 m3 of sand‐sized sediments were discharged to low‐gradient reaches. Analyzing four years of repeat morphometry and sediment surveys at the Simkins site, as well as continuous discharge and turbidity data, we observed the two‐phase erosion response described for MVD. In the early phase, approximately 50% of the impounded sediment at Simkins was eroded rapidly during modest flows. After incision to base level and widening, a second phase began when further erosion depended on floods large enough to go over bank and access impounded sediments more distant from the newly‐formed channel. Fitting functional forms to the data for both sites, we found that two‐phase exponential models with changing decay constants fit the erosion data better than single‐phase models. Valley width influences the two‐phase erosion responses upstream, but downstream responses appear more closely related to local gradient, sediment re‐supply from the upstream impoundments, and base flows. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献