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131.
The rate of accumulation of 4He in the groundwaters of the J-aquifer of the Great Artesian Basin, Australia has been determined using 14C and hydrologic ages. For groundwaters less than 50 Kyr in age, the 4He accumulation rate is 4.6 × 10?12 HeAU (where ) in close agreement with in-situ production rate of 4He (3.95 × 10?12 HeAU) based on U and Th concentrations of 1.7 and 6.1, respectively, of the sandstone. For groundwaters older than 100 Kyr, the rate of 4He accumulation is 2.91 × 10?10 HeAU based on hydrologic ages; or 74 × the rate of in-situ production. The rate of 4He “production” due to weathering of the aquifer rock is calculated to be ~10?16 HeAU, indicating that the weathering input of 4He is insignificant. If the groundwater of the GAB can be considered as a trap for the total crustal production of 4He, the rate of 4He accumulation under a steady-state flux is calculated to be 3.02 × 10?10 HeAU, in agreement with the measured accumulation rate. It is concluded that over long times the 4He accumulation rate in groundwater aquifers may be controlled by the whole crust flux of 4He. 相似文献
132.
Lou Daniel Brenton R. Clarke Drew F. Parsons 《Geostandards and Geoanalytical Research》2019,43(3):435-452
We investigate the performance of sample preparation of gold ores using vibratory (bowl, ring and puck type) mills in common use in mineral analytical laboratories. The main criteria for effective grinding are using reduced grinding charge masses ≤ ca. 50% of nominal bowl capacity and using a grinding aid to prevent caking. We show that gold particles of millimetre scale can be comminuted to ≤ 100 µm by grinding in silica flour, bauxite, synthetic carborundum, or mixtures of silica and these materials using times of up to 5 min and that 95% < 50 µm is achievable with extended grinding. This suggests that modified grinding techniques can be used to make sample masses ≤ 5 g viable for routine determination of gold in geological samples. We also demonstrate homogenisation of a gold‐bearing copper sulfide mineral flotation concentrate alone and in mixtures with silica by extended grinding at reduced charge masses. To support this work, we develop a convenient new benchmark of gold ore sample preparation performance ‘G’, an apparent maximum gold particle size interpolated from replicate analytical variance in order to overcome the limitations of laborious sieve fraction analysis of gold particle size. We show useful agreement between G and sieve fraction analysis of gold particle size in samples and test the viability of G experimentally and by analysis of literature data. 相似文献
133.
Integrated metamorphic and geochronological data place new constraintson the metamorphic evolution of a Neoproterozoic orogen in eastAntarctica. Granulite-facies rocks from a 150 km stretch ofthe Kemp Land coast reflect peak conditions involving T 870990°Cat P 7·410 kbar, with pressure increasing westwardtowards an Archaean craton. Electron microprobe-derived (Th+ U)Pb monazite ages from metapelitic assemblages indicatethat the major mineral textures in these rocks developed duringthe c. 940 Ma Rayner Orogeny. Complex compositional zoning inmonazite suggests high-T recrystallization over c. 25 Myr. Diversityin metapelitic reaction textures reflects silica and ferromagnesiancontent: Si-saturated Fe-rich metapelites contain garnet thatis partially pseudomorphed by biotite and sillimanite, whereasSi-saturated Mg-rich metapelites and Si-undersaturated metapeliticpods have reaction microstructures involving cordierite enclosingorthopyroxene, garnet and/or sapphirine, cordierite + sapphirinesymplectites around sillimanite and coarse-grained orthopyroxene+ corundum separated by sapphirine coronae. Interpretationsbased on PT pseudosections provide integrated bulk-rockconstraints and indicate a clockwise PTt pathcharacterized by a post-peak PT trajectory with dP/dT 1520 bar/ °C. This moderately sloped decompressive-coolingPT path is in contrast to near-isothermal decompressionPT paths commonly cited for this region of the RaynerComplex, with implications for the post-collisional tectonicresponse of the mid- to lower crust within this orogenic belt. KEY WORDS: electron microprobe monazite dating; granulite facies; Rayner Complex; sapphirine; THERMOCALCMinerals abbreviations: q, quartz; g, garnet; sill, sillimanite; ky, kyanite; opx, orthopyroxene; cd, cordierite; ksp, alkali feldspar; pl, plagioclase; bi, biotite; sp, spinel; ilm, ilmenite; mt, magnetite; ru, rutile; sa, sapphirine; cor, corundum; osm, osumilite; liq, silicate melt; mnz, monazite 相似文献
134.
Mark A Clilverd Ellen Clarke Henry Rishbeth Toby D G Clark Thomas Ulich 《Astronomy& Geophysics》2003,44(5):5.20-5.22
Mark A Clilverd, Ellen Clarke, Henry Rishbeth, Toby D G Clark and Thomas Ulich look forward to a little less solar activity in 2100, using direct and proxy records of past solar and geomagnetic activity. 相似文献
135.
Efficient testing of earthquake forecasting models 总被引:1,自引:0,他引:1
David A. Rhoades Danijel Schorlemmer Matthew C. Gerstenberger Annemarie Christophersen J. Douglas Zechar Masajiro Imoto 《Acta Geophysica》2011,59(4):728-747
Computationally efficient alternatives are proposed to the likelihood-based tests employed by the Collaboratory for the Study of Earthquake Predictability for assessing the performance of earthquake likelihood models in the earthquake forecast testing centers. For the conditional L-test, which tests the consistency of the earthquake catalogue with a model, an exact test using convolutions of distributions is available when the number of earthquakes in the test period is small, and the central limit theorem provides an approximate test when the number of earthquakes is large. Similar methods are available for the R-test, which compares the likelihoods of two competing models. However, the R-test, like the N-test and L-test, is fundamentally a test of consistency of data with a model. We propose an alternative test, based on the classical paired t-test, to more directly compare the likelihoods of two models. Although approximate and predicated on a normality assumption, this new T-test is not computer-intensive, is easier to interpret than the R-test, and becomes increasingly dependable as the number of earthquakes increases. 相似文献
136.
Katherine?CalvinEmail author Marshall?Wise Patrick?Luckow Page?Kyle Leon?Clarke Jae?Edmonds 《Climatic change》2016,136(1):57-68
The magnitude and character of the global resource base of fossil fuels is a key determinant of the evolution of the future global energy system and corresponding fossil fuel carbon emissions. What is less well understood is the potential magnitude of impact of the availability of fossil fuels, due to the interaction with biomass energy, on agriculture, land use, ecosystems and therefore carbon emissions from land-use change. This paper explores these links and implications. We show that if oil resources are limited, then the consequently higher price for liquids induces both the use of coal-to-liquids technology deployment, but also enhanced production of bioenergy crops particularly in a business-as-usual scenario. This in turn implies greater pressure to convert unmanaged ecosystems to produce bioenergy, and higher rates of terrestrial carbon emissions from land use. 相似文献
137.
The spatial variation of the nocturnal urban boundary-layer structure is described and the time variation of the mixing height, and the nocturnal inversion top and strength after sunrise is presented for urban sites located upwind, downwind, and near the center of the heat island, and at an upwind rural site. Observations were derived from high resolution temperature profiles obtained by a helicopter during 35 intensive morning experiments in St. Louis, Missouri.The nocturnal urban boundary layer increased in depth from the upwind edge of the urban area. Far downwind, in suburban and rural areas, a remnant of the urban boundary layer existed between a stable surface-based layer and an upper inversion that resembled the upwind rural inversion.The mixing height (base of the inversion) evolved in a parabolic manner after sunrise at the urban locations. A rise in the inversion top after sunrise at the urban locations is believed to be due to low-level convergence which caused the entire inversion layer to be lifted. Due to large horizontal temperature gradients associated with the urban heat island, cold air advection tended to counteract the urban-induced lifting effect by inhibiting mixing-height growth at urban locations upwind of the heat-island center. Advection also caused the maximum height and fastest growth rate of the urban mixed layer to be shifted downwind of the urban area with time. However, mean mixing-height growth rates at various urban locations did not differ significantly. The rural mixing-height growth rate was about twice as large as urban values for up to 3 hr after sunrise. Spatial differences in the mixing height became small near the time of inversion dissipation, which appeared to occur at about the same time at all locations.On assignment from the National Oceanic and Atmospheric Administration, U.S. Department of Commerce. 相似文献
138.
139.
A programme of aerosol sampling by dichotomous sampler has been undertaken with analysis of soluble ions plus carbonate. The technique for carbonate involved release of CO2 by HCl vapour and quantitative measurement of the CO2 by FTIR spectroscopy. The method is suitable for amounts down to below 10g CO3
2- per filter. The prevailing atmospheric levels in an urban area were found to be below 1g m-3. Information on the particle size from the dichotomous sampler was supplemented by use of a cascade impactor. Although CaCO3 is clearly the dominant species initial analyses demonstrated higher carbonate levels than could be accounted for on the basis of the concentrations of calcium and magnesium ions which are the most likely cations in mineral carbonates. Analysis with and without heating to 100°C in a vacuum oven demonstrates the presence of carbonate in volatile form. This could be due to carbon dioxide adsorbed onto particulate matter such as soot. 相似文献
140.
Antomy D. Clarke 《Journal of Atmospheric Chemistry》1992,14(1-4):479-488
During May-June of 1990 an extensive flight series to survey aerosol present in the upper-troposphere was undertaken aboard the NASA DC-8 as part of the CLObal Backscatter Experiment (GLOBE). About 50,000 km were characterized between 8–12 km altitude and between 70°N and 58°S. Aerosol with diameters greater than 3nm were counted and sized with a combination of condensation nuclei counters and optical particle counters. Aerosol number and mass concentrations were separately identified with regard to both refractory and volatile components. Regions of the free-troposphere with the lowest mass concentrations were generally found to have the highest number concentrations and appeared to be effective regions for new particle production. These new particle concentrations appear inversely related to available aerosol surface area and their volatility suggests a sulfuric acid composition. The long lifetime of these new particles aloft can result in their growth to sizes effective as CN and CCN that can be mixed throughout the troposphere. 相似文献