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301.
Prof. Dr. Bernd Andreae 《GeoJournal》1978,2(4):331-342
The agricultural and pastoral development of the huge dry areas of the world are subject of this paper. The author describes the possible stages of development of the pastoral industry in accordance with the general economic development of a country or region.The development of the pastoral industry is much related to the availability of fodder during the year and over the years. Typical of the pastoral industry in the dry areas are the different ways of fodder compensation. The author points out that each development stage of a ranch has its typical way of fodder compensation in accordance with the general economic development stage of the region. 相似文献
302.
303.
Britta Lüder Gerald Kirchner Andreas Lücke Bernd Zolitschka 《Journal of Paleolimnology》2006,35(4):897-912
The history of hardwater lake Sacrower See (Brandenburg, northeastern Germany) was reconstructed back to the 17th century
based on a multi-proxy study of five short sediment cores dated by varve chronology, 210Pb and 137Cs isotopes. We were able to distinguish three main phases: The lake was mesotrophic prior to the 1830s with an oxic hypolimnion.
From the early 19th century on, δ13C of organic matter indicates that primary productivity starts to increase slowly. Between the 1830s and 1872, the lake went
through a transition towards eutrophy. Low calcite contents in the homogeneous sediment are caused by dissolution connected
to increasing primary productivity and growing importance of decomposition processes. After 1873, and accelerated since 1963,
Sacrower See is characterised by growing nutrient input, and thus further increasing primary productivity. The lake is eutrophic,
and decomposition of organic matter causes high oxygen consumption in the hypolimnion, which becomes regularly anoxic during
thermal summer stratification. Biogenic varves are preserved in the sediment, characterised by layers of autochthonous, biochemically
precipitated calcite crystals. In this study, we were able to demonstrate that Sacrower See is an example of exceptional slow
increase of anthropogenically enhanced nutrient input, and of the imprint which these processes have on sediments of a hardwater
lake. 相似文献
304.
305.
Temperature-dependent isotopic fractionation of lithium between clinopyroxene and high-pressure hydrous fluids 总被引:2,自引:1,他引:2
Bernd Wunder Anette Meixner Rolf L. Romer Wilhelm Heinrich 《Contributions to Mineralogy and Petrology》2006,151(1):112-120
The fractionation of lithium isotopes between synthetic spodumene as representative of Li-bearing clinopyroxene and Cl- and
OH-bearing aqueous fluids was experimentally determined between 500 and 900°C at 2.0 GPa. In all the experiments, 7Li was preferentially partitioned into the fluid. The fractionation is temperature dependent and approximated by the equation
Δ7Li(clinopyroxene–fluid)=−4.61×(1,000/T [K]) + 2.48; R
2=0.86. Significant Li isotopic fractionation of about 1.0‰ exists even at high temperatures of 900°C. Using neutral and weakly
basic fluids revealed that the amount of fractionation is not different. The Li isotopic fractionation between altered basalt
and hot spring water (350°C) in natural samples is in good agreement with our experimentally determined fractionation curve.
The data confirm earlier speculations drawn from the Li isotopic record of dehydrated metamorphic rocks that fluids expelled
from a dehydrating slab carry heavier Li into the mantle wedge, and that a light Li component is introduced into the deeper
mantle. Li and Li isotopes are redistributed among wedge minerals as fluids travel across the wedge into hotter regions of
arc magma production. This modifies the Li isotopic characteristics of slab-derived fluids erasing their source memory, and
explains the absence of cross-arc variations of Li isotopes in arc basalts. 相似文献
306.
Mobility and retention of trace elements in hardpan-cemented cassiterite tailings, north Queensland, Australia 总被引:1,自引:0,他引:1
This study reports on the mobility and retention of trace elements in cassiterite tailings at the inactive Jumna mill, tropical north Queensland. Since the 1980s, the uncapped tailings have developed laterally discontinuous Fe-rich hardpans, which are located in the higher parts of gently sloping tailings masses and at the top (<50 cm) of the tailings piles. Hardpan-cemented tailings comprise thin layers (typically ∼0.2–2 mm thick) of HFO (hydrous ferric oxides) and sulfate efflorescences cementing tailings grains. In comparison to the tailings, the hardpan-cemented tailings contain significantly higher median As, Ca, Cd, Co, Cu, Fe, In, Mn, Mo, Stotal, Th, U, Y and Zn values. Partial leaching studies of tailings and pond water analyses indicate that wetting and acidification of Fe-cemented tailings removes significant proportions of trace elements into pore and surface waters. Tin shows no mobility due to the presence of weathering-resistant cassiterite (SnO2) and, As and Pb display limited mobility possibly due to their coprecipitation with jarosite-type phases and HFO materials at the top of the tailings profile. By contrast, the trace elements Cd, Ce, Cu, La, Ni, Pb, U and Zn display the greatest mobility, possibly due to their incorporation in soluble sulfate efflorescences and sorption onto mineral and HFO surfaces. Hence, the Fe-rich hardpans do not protect the sulfidic tailings from further oxidation nor do they cause permanent sequestration of trace elements. 相似文献
307.
Anja M. Schleicher Laurence N. Warr Bernd Kober Emmanuel Laverret Norbert Clauer 《Contributions to Mineralogy and Petrology》2006,152(3):349-364
Episodic and localized illite mineralization is documented in the hydrothermally altered Soultz-sous-Forêts granite (Upper Rhine Graben, France). Separated grain-size fractions of altered granite and argillite vein samples contain mixtures of 2M1 and 1M trans-vacant illite varieties. The platy pseudohexagonal 2M1 illite phases dominate the vein fillings, whereas the 1M illite occurs largely as a fibrous pore-filling variety, which is particularly abundant in the granite matrix. Multiple phases of fluid injections into the granite body have resulted in different illite assemblages, each sample containing a mixture of polytype generations formed during different crystal growth events. On the basis of mineralogical and K–Ar isotopic constraints, the ages of these vein-mineralizing events are determined by plotting the K–Ar values of the various grain-size fractions against polytype abundance and the fitted volume-weighted crystallite thickness distributions. The results suggest a Permian age for the formation of the studied argillite veins, characterized by successive injections of hydrothermal fluids. Secondary episodes of illite crystallization occurred during Jurassic and Cretaceous (or even younger times) in both the veins and the granite matrix. There are indications that the polytype structure and composition of illite were strongly influenced by variations in fluid chemistry and the degree of fluid–rock interaction as the granite was progressively sealed during post-Variscan, episodic hydrothermal activity. 相似文献
308.
David L. Dettman Karl W. Flessa Bernd R. Schöne 《Geochimica et cosmochimica acta》2004,68(6):1253-1263
We describe a new method for the calculation of river flow that uses the oxygen isotope composition of bivalve mollusk shells that grew in the river-water/seawater mixing zone of the Colorado River estuary. Sclerochronological techniques are used to identify tidally-induced, fortnight-scale bundles of daily growth increments within shell cross-sections. These fortnightly markers are used to establish a chronology for samples taken for δ18O analysis. A composite seasonal δ18O profile derived from five shells that grew in the absence of river-water flow is used as a baseline against which profiles of river-influenced shells are compared. Because this comparison is between matched fortnights within a year, the temperature of shell growth is likely to be very similar. The difference in δ18O between the river-influenced shell and the “no-flow” composite shell therefore represents the change in the δ18O of the water due to the presence of river water in the mixing zone. The river water end-member is also determined within a fortnightly context so that the change in the δ18O of mixing-zone water can be used to calculate the relative proportions of seawater and fresh-water. The fresh-water end-member is calculated from the δ18O of bivalves alive prior to the emplacement of dams and water diversions on the Colorado River. The marine end-member is based on direct measurements of the δ18O of northern Gulf of California water during times of no Colorado River flow. The system has been calibrated to absolute flow amounts using recent releases of known volume and rate. 相似文献
309.
Taking varves to bits: Scanning electron microscopy in the study of laminated sediments and varves 总被引:2,自引:0,他引:2
Jean M. Dean Alan E.S. Kemp David Bull Jennifer Pike Gunilla Patterson Bernd Zolitschka 《Journal of Paleolimnology》1999,22(2):121-136
Conventional high resolution studies of varved sediments are able to identify clastic and biogenic laminae, but are often unable to resolve the nature of fine-scale lamination contained therein. This intra-annual signal provides us with the highest potential resolution from the sedimentary record and can be resolved using scanning electron microscopy (SEM). Six case studies from lacustrine and marine settings are presented to illustrate the combination of clastic and biogenic fabric types typically found in laminated sediments. Clastic laminae fabrics include those which originate through grain settling and those which are event deposits. The correct identification of event deposits is essential if varves are to be used chronologically. SEM-based biogenic laminae fabric studies have identified seasonal faunal successions where individual laminae may be less than 100 thick and most recently, deep chlorophyll maxima (DCM) summer diatom floras, providing an insight into seasonal scale processes. High resolution lamina fabric studies can provide a basis for generating records of seasonal and inter-annual variability, thus contributing to our understanding of lacustrine and marine processes and palaeoenvironmental interpretation. 相似文献
310.