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991.
992.
Morgan T. Jones Deborah J. Hembury Martin R. Palmer Bill Tonge W. George Darling Susan C. Loughlin 《Bulletin of Volcanology》2011,73(3):207-222
The eruptions of the Soufrière Hills volcano on Montserrat (Lesser Antilles) from 1995 to present have draped parts of the
island in fresh volcaniclastic deposits. Volcanic islands such as Montserrat are an important component of global weathering
fluxes, due to high relief and runoff and high chemical and physical weathering rates of fresh volcaniclastic material. We
examine the impact of the recent volcanism on the geochemistry of pre-existing hydrological systems and demonstrate that the
initial chemical weathering yield of fresh volcanic material is higher than that from older deposits within the Lesser Antilles
arc. The silicate weathering may have consumed 1.3% of the early CO2 emissions from the Soufrière Hills volcano. In contrast, extinct volcanic edifices such as the Centre Hills in central Montserrat
are a net sink for atmospheric CO2 due to continued elevated weathering rates relative to continental silicate rock weathering. The role of an arc volcano as
a source or sink for atmospheric CO2 is therefore critically dependent on the stage it occupies in its life cycle, changing from a net source to a net sink as
the eruptive activity wanes. While the onset of the eruption has had a profound effect on the groundwater around the Soufrière
Hills center, the geochemistry of springs in the Centre Hills 5 km to the north appear unaffected by the recent volcanism.
This has implications for the potential risk, or lack thereof, of contamination of potable water supplies for the island’s
inhabitants. 相似文献
993.
Johanna Lippmann-Pipke Jörg Erzinger Martin Zimmer Christian Kujawa Margaret Boettcher Esta Van Heerden Armand Bester Hannes Moller Nicole A. Stroncik Zeev Reches 《Applied Geochemistry》2011,26(12):2134-2146
An on-site gas monitoring study has been conducted in the framework of an earthquake laboratory (The International NELSAM–DAFGAS projects) at the TauTona gold mine, South Africa. Five boreholes up to 60 m long were drilled at 3.54 km depth into the highly fractured Pretorius Fault Zone and instruments for chemical and seismic monitoring installed therein. Over the span of 4 years sensitive gas monitoring devices were continuously improved to enable the direct observation of geogas concentration variations in the DAFGAS borehole. The major gas concentrations are constant and air-like with about 78% N2, 21% O2, 1% Ar. The geogas components CO2, CH4, He and H2 show the most interesting trends and variations on the minute-by-minute basis and significantly correlate with seismic data, while the 222Rn activity remains constant. Time series and cross correlation analysis allow the identification of different gas components (geogas and tunnel air) and the identification of two processes influencing the borehole gas composition: (1) pumping-induced tunnel air breakthrough through networks of initially water-saturated fault fractures; and (2) seismicity induced permeability enhancement of fault fractures to above ∼5 × 10-10 m2. The current set-up of the gas monitoring system is sensitive enough to quantify the resulting geogas transport during periods of intense blasting activities (including recorded blasts with seismic moment ?1 × 109 Nm, located within 1000 m of the cubby) and, it is suggested, also during induced earthquakes, a final goal of the project. 相似文献
994.
Xiang?Zhang Michael?J?Borda Martin?AA?Schoonen Daniel?R?StronginEmail author 《Geochemical transactions》2003,4(1):8
The effect of a diacetylene-containing phospholipid on the oxidation of pyrite, FeS2, was investigated. Earlier work reported by our research group showed that the adsorption of l,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine on pyrite suppressed the extent of its oxidation by about 75% over a specific time period. Results
presented here show that the pre-exposure to UV radiation of this lipid after sorption onto pyrite results in a 90% suppression.
Attenuated total reflection (ATR) Fourier transform infra-red spectroscopy (FTIR) suggests that the UV irradiation of the
lipid does not result in degradation of the adsorbed layer. It is believed that the UV exposure results in the cross-linking
and polymerization of the adsorbed phospholipid into a relatively impermeable barrier that separates the pyrite from the aqueous
phase. The results of this study might have implications for the protection of pyrite from oxidation in the environment. 相似文献
995.
Extracting palaeoflood data from coarse‐grained Pleistocene river terrace archives: an example from SE Spain 下载免费PDF全文
Field‐based palaeoflood event reconstruction has the potential to contribute to the development of our understanding of long‐term landscape evolution. However, the reconstruction of past flow event histories (magnitude and frequency) over long‐term (Quaternary) timescales is fraught with difficulties. Here we make a preliminary exploration of some of the practicalities of flood reconstruction from fluvial terrace archives using commonly available sedimentological and geomorphological observations from a field perspective. We utilize Manning and palaeostage indicators to reconstruct historic events that can be used as benchmarks for a lesser used competence based approach, which is applied to coarse‐grained strath terrace deposits. We evaluate the results against gauged records for extreme and catastrophic events that affected the same region in 1973 and 2012. The findings suggest that the competence approach is most effectively applied to terrace deposits if the channel geometry is taken into account when sampling both in cross‐section and in longitudinal section and calibrated against the sedimentology for palaeo‐flow depth. Problems can arise where constrictive channel geometries allow boulder jams to develop, acting as sediment traps for the coarsest material and leading to downstream ‘boulder starvation’. Useful sites to target for palaeoflood reconstruction, therefore, would be upstream of such constrictive reaches where the coarsest transportable bedload has been effectively trapped. Sites to avoid would be downflow, where the deposited material would poorly represent palaeoflood competence. Underestimation from maximum boulder preservation and limited section exposure issues would appear to outweigh possible overestimation concerns related to fluid density and unsteady flow characteristics such as instantaneous acceleration forces. Flood data derived from river terrace deposits suggests that basal terrace geometries and coarse boulder lags common to many terrace sequences are likely the result of extreme flow events which are subsequently filled by lesser magnitude flood events, in this environmental setting. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
996.
Interaction of freshly precipitated silica gel with aqueous solutions was studied at laboratory batch experiments under ambient
and near neutral pH-conditions. The overall process showed excellent reversibility: gel growth could be considered as an opposite
process to dissolution and a linear rate law could be applied to experimental data. Depending on the used rate law form, the
resulting rate constants were sensitive to errors in parameters/variables such as gel surface area, equilibrium constants,
Si-fluxes, and reaction quotients. The application of an Integrated Exponential Model appeared to be the best approach for
dissolution data evaluation. It yielded the rate constants k
dissol ∼ (4.50 ± 0.68) × 10−12 and k
growth ∼ (2.58 ± 0.39) × 10−9 mol m−2 s−1 for zero ionic strength. In contrast, a Differential Model gave best results for growth data modeling. It yielded the rate
constants k
dissol ∼ (1.14 ± 0.44) × 10−11 and k
growth ∼ (6.08 ± 2.37) × 10−9 mol m−2 s−1 for higher ionic strength (I ∼ 0.04 to 0.11 mol L−1). The found silica gel solubility at zero ionic strength was somewhat lower than the generally accepted value. Based on the
and standard Gibbs free energy of silica gel formation was calculated as and −850,318 ± 20 J mol−1, respectively. Activation energies for silica gel dissolution and growth were determined as and respectively. An universal value for growth of any silica polymorph, is not consistent with the value for silica gel growth, which questions the hypothesis about one unique activated complex
controlling the silica polymorph growth. 相似文献
997.
David Schmidt Susanne T. Schmidt Joseph Mullis Rafael Ferreiro Mählmann Martin Frey 《Contributions to Mineralogy and Petrology》1997,129(4):385-403
The andesitic early Oligocene Taveyanne metagreywacke of the Helvetic nappes of western Switzerland shows an increase of
metamorphic grade from zeolite facies through lower greenschist facies. Electron microprobe analysis, fluid inclusion thermometry,
stable isotope analysis, coal rank, illite and chlorite crystallinity and thermodynamic calculations were carried out to determine
metamorphic conditions. Evaluation of all techniques used in this study suggest that only combinations of different parameters
yield reliable information to constrain very low-grade metamorphic conditions. Electron microprobe analyses are presented
for actinolite, chlorite, epidote, phengite, laumontite, prehnite, pumpellyite, and titanite. With increasing metamorphic
grade, chlorite is enriched in tetrahedral Al, pumpellyite becomes poorer in Fetot and more homogeneous in chemical composition, and titanite tends to incorporate Ti at the expense of Al and Fe3+. Metamorphic P-T conditions were determined by a combination of fluid inclusion microthermobarometry, stable isotope thermometry on quartz-calcite
veins, chlorite “geothermometry” and thermodynamic calculations. Peak temperatures range from 210–250 °C for zeolite facies
to 270–300 °C for prehnite-pumpellyite facies to 300–360 °C for pumpellyite-actinolite facies. An evaluation of 289 chlorite
analyses indicates that the tetrahedral Al content is negatively correlated with the saponite component. Temperatures derived
from chlorite “geothermometry” match maximum temperature conditions mentioned above. Illite crystallinity data for shales
and slates intercalated with the Taveyanne metagreywacke indicate that the diagenetic zone correlates with the zeolite facies,
the upper anchizone with the prehnite-pumpellyite facies, and the lower epizone with the pumpellyite-actinolite facies. A
comparison of coal rank and illite crystallinity data (n=12,r=0.91) yielded R
max values of 2.9 and 5.5% for the lower and upper boundary of the anchizone, respectively.
Received: 2 August 1996 / Accepted: 16 July 1997 相似文献
998.
The Rattlesnake Tuff of eastern Oregon comprises >99% ofhigh-silica rhyolite glass shards and pumices representing 280km3 of magma. Glassy, crystal-poor, high-silica rhyolite pumicesand glass shards cluster in five chemical groups that rangein color from white to dark gray with increasing Fe concentration.Compositional clusters are defined by Fe, Ti, LREE, Ba, Eu,Rb, Zr, Hf, Ta, and Th. Progressive changes with increasingdegree of evolution of the magma occur in modal mineralogy,mineral composition, and partition coefficients. Partition coefficientsare reported for alkali feldspar, clinopyroxene, and titanomagnetite.Models of modal crystal fractionation, assimilation, successivepartial melting, and mixing of end members cannot account forthe chemical variations among rhyolite compositions. On theother hand, 50% fractionation of observed phenocryst compositionsin non-modal proportions agrees with chemical variations amongrhyolite compositions. Such non-modal fractionation might occuralong the roof and margins of a magma chamber and would yieldcompositions of removed solids ranging from syenitic to granitic.A differentiation sequence is proposed by which each more evolvedcomposition is derived from the previous, less evolved liquidby fractionation and accumulation, occurring mainly along theroof of a slab-like magma chamber. As a layer of derivativemagma reaches a critical thickness, a new layer is formed, generatinga compositionally and density stratified magma chamber. KEY WORDS: high-silica rhyolite; partition coefficients; differentiation; zoned ash-flow tuff; layered convection 相似文献
999.
1000.
Martin Sharp 《Quaternary Research》1985,24(3):268-284
A model for sedimentation by surging glaciers is developed from analysis of the debris load, sedimentary processes, and proglacial stratigraphy observed at the Icelandic surging glacier, Eyjabakkajökull. Three aspects of the behavior of surging glaciers explain the distinctive landformsediment associations which they may produce: (a) sudden loading of proglacial sediments during rapid glacier advances results in the buildup of excess pore pressures, failure, and glacitectonic deformation of the overridden sediments; (b) reactivation of stagnant marginal ice by the downglacier propagation of surges is associated with large longitudinal compressive stresses. These induce intense folding and thrusting during which basal debris-rich ice is elevated into an englacial position in a narrow marginal zone. As the terminal area of the glacier stagnates between surges, debris from this ice is released supraglacially and deposited by meltout and sediment flows; (c) local variations in overburden pressure beneath stagnant, crevassed ice cause subglacial lodgement tills, which are sheared during surges, to flow into open crevasses and form “crevasse-fill” ridges. 相似文献