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851.
852.
Platynereis dumerilii is found in large numbers in parchment-like tubes attached to sublittoral accumulations of detached maroalgae (principally Laminaria saccharina) in Kames Bay, Isle of Cumbrae and Lochranza, Isle of Arran. Its rôle in weed decomposition has been examined by comparing its responses (behavioural choice, growth rates, absorption efficiencies of both carbon and protein, gut retention times and rate of faecal output) to fresh and rotting weed. Worms grew significantly on either diet, with older individuals gaining more weight than small individuals. Animals of a standard size (derived from measurements of maximum bite size) feeding on fresh weed, however, grew significantly faster than those feeding on rotting weed. The former had a significantly higher protein absorption efficiency which was linearly related to protein content of ingested weed. This was not so on rotting weed. Organic carbon absorption efficiencies did not differ significantly between the two groups, neither did gut retention times nor rates of faecal output. Given a choice, Platynereis chooses to build its tube, and to feed, on fresh kelp—a strategem which ensures both maximum scope for occupancy before fronds decay and a superabundance of preferred food. Platynereis feeds around its tube entrance, recropping small areas for 2–3 days, prior to switching to another area nearby. Ciliate population densities on Platynereis faeces are much lower than on either homogenized or intact weed, associated with their lower, nutritional value (at first). Platynereis bubes act to bind kelp fronds together stabilizing the faecal input to infaunal detritivores. Platynereis is an example of a detritivore which exploits the detrital substratum directly. 相似文献
853.
Comparison of hot plasma data from ATS-6 and GEOS-1 when the satellites were near dawn L.T. conjunction reveals the presence of strong gradients separating plasmas differing by more than two orders of magnitude in keV particle fluxes. These gradients are observed at off-equatorial geomagnetic latitudes of 25–30° on field lines outside the synchronous orbit. They are associated with magnetic storms and are distinct from magnetopause crossings. Interpretation of these events in terms of a boundary between magnetospheric and polar-cap plasma leads to the following conclusions: (1) the polar cap/lobe region is essentially devoid of keV plasma at these times; (2) the field lines defining this boundary are significantly distorted from a dipolar to a more stretched form consistent with the presence of a storm-ring current, (3) smaller substorm-scale motions are superposed on the gross motion of the boundary with some evidence present for structure in the plasma spatial profile, and (4) magnetosheath-like plasma finds access to the inner magnetosphere at dawn L.T., much as it does near noon, along polar-cap boundary-layer field lines which close through the low latitude magnetospheric boundary layer. 相似文献
854.
A summary of total sulfur abundances representative of the Apollo Missions is presented. Lunar crystalline rocks range from
0 to 3100μg S g−1. Lunar soils range from 310 to 1300μg S g−1. Rock mixing models evaluate the distribution of sulfur and define indigenous rock components and extralunar contributions
of sulfur in lunar soils. Extralunar sulfur shows a positive correlation with a CC-1 like meteoritic component and solar wind
derived total carbon content in the Apollo 16 and 17 lunar soils.
Presented at the 25th International Geological Congress, Sydney, Australia, Section 15, Planetology.
Contribution No. 105 from the Center for Meteorite Studies. 相似文献
855.
Frictional heating on a fault zone with finite thickness 总被引:5,自引:0,他引:5
R. K. Cardwell D. S. Chinn G. F. Moore D. L. Turcotte 《Geophysical Journal International》1978,52(3):525-530
Summary. The problem of frictional heating on a fault of finite thickness is considered. Temperature distributions during and after faulting are obtained for faults of various thicknesses. A thick fault approximation is shown to be valid if a fault has a thickness greater than about 1 cm. The thickness of the melted zone is predicted for various frictional stress levels and displacements. The predicted thicknesses are shown to be in reasonable agreement with field observations. 相似文献
856.
Beverley J. Moore 《Geophysical Journal International》1980,63(3):671-689
b
In this paper, the method of small perturbations is applied to the ray and energy transport equations in an investigation of the effect of weak inhomogeneities on the propagation of seismic rays through a layer of fixed thickness. Just as Aki et al . have used travel-time residuals to infer first-order velocity perturbations in their block-modelling procedure, it is proposed that surface slowness and amplitude data may be used to give additional information about the structure of the velocity perturbations beneath the observer. 相似文献
In this paper, the method of small perturbations is applied to the ray and energy transport equations in an investigation of the effect of weak inhomogeneities on the propagation of seismic rays through a layer of fixed thickness. Just as Aki et al . have used travel-time residuals to infer first-order velocity perturbations in their block-modelling procedure, it is proposed that surface slowness and amplitude data may be used to give additional information about the structure of the velocity perturbations beneath the observer. 相似文献
857.
Marla H. Moore 《Icarus》1984,59(1):114-128
The infrared absorption spectrum from 3.3 to 27 μm (3030-370 cm?) of SO2 ice films has been measured at 20 and 88°K before and after 1-MeV proton irradiation. The radiation flux was chosen to simulate the estimated flux of Jovian magnetospheric 1-MeV protons incident on Io. After irradiation, SO3 is identified as the dominant molecule synthesized in the SO2 ice. This is also the case after irradiation of composite samples of SO2 with sulfur, or disulfites. Darkening was observed in irradiated SO2 ice and in irradiated S8 pellets. Photometric and spectral measurements of the thermoluminescence of irradiated SO2 have been made during warming. The spectrum appears as a broad band with a maximum at 4450 Å. Analysis of the luminescence data suggests that, at Ionian temperatures, irradiated SO2 ice would not be a dominant contributor to posteclipse brightening phenomena. After warming to room temperature, a form of SO3 remains along with a sulfate and S8. Based on these experiments, it is reasonable to propose that small amounts of SO3 may exist on the surface of Io as a result of irradiation synthesis in SO2 frosts. 相似文献
858.
859.
Effects of buoyancy and mechanical layering on collisional deformation of continental lithosphere: Results from physical modeling 总被引:1,自引:0,他引:1
We use two suites of lithospheric-scale physical experiments to investigate the manner in which deformation of the continental lithosphere is affected by both (1) variations of lithospheric density (quantified by the net buoyant mass per area in the lithospheric mantle layer, MB), and (2) the degree of coupling between the crust and lithospheric mantle (characterized by a modified Ampferer ratio, Am). The dynamics of the experiments can be characterized with a Rayleigh–Taylor type ratio, CLM. Models with a positively buoyant lithospheric mantle layer (MB > 0 and CLM > 0) result in distributed root formation and a wide deformation belt. In contrast, models with a negatively buoyant lithospheric mantle layer strongly coupled to the crust (MB < 0, 0 > CLM > ≈ − 0.2, and Am > ≈ 10− 3) exhibit localized roots and narrow deformation belts. Syncollisional delamination of the model lithospheric mantle layer and a wide deformation belt is exhibited in models with negatively buoyant lithospheric mantle layers weakly coupled to the crust (MB < 0, CLM < 0, and Am < ≈ 10− 3). Syncollisional delamination of the continental lithosphere may initiate due to buoyancy contrasts within the continental plate, instead of resulting from wedging by the opposing plate. Rayleigh–Taylor instabilities dominate the style of deformation in models with a negatively buoyant lithospheric mantle layer strongly coupled to the crust and a slow convergence rate (MB < 0 and CLM > ≈ − 0.2). The degree of coupling (Am) between the model crust and lithospheric mantle plays a lesser role in both the style of lower-lithospheric deformation and the width of the crustal deformed zone with increasing density of the lithospheric mantle layer. 相似文献
860.
Edward M. Ripley Nur Iskandar Taib Chusi Li Craig H. Moore 《Contributions to Mineralogy and Petrology》2007,154(1):35-54
Copper–nickel sulfide mineralization in the Partridge River Intrusion of the 1.1 Ga Duluth Complex is restricted primarily
to a 100 m thick zone near the base of the intrusion, which is heterogeneous at meter scales in terms of both sulfide contents
and rock types, which include dunite, melatroctolite, troctolite, leucotroctolite, gabbro, olivine gabbro, gabbronorite, and
rare norite. Olivine-rich troctolites and melatroctolites appear to have required mineral accumulation on a substrate, whereas
augite troctolite and gabbros are thought to have formed via in situ crystallization of magmas ranging in composition from
high-Al olivine tholeiite to high-Ti tholeiite. δ18O values of orthopyroxene-poor rocks in the Partridge River Intrusion range from 5.2 to 6.7‰. δ18O values of 6.7‰ are consistent with less than 20% contamination by high-18O metasedimentary country rock, either via devolatilization or local partial melting. Rocks with greater than ∼15% orthopyroxene,
gabbronorites, and norites, are characterized by δ18O values in excess of 6.9‰, and required the assimilation of larger amounts of siliceous country rocks. Sulfur isotopic values
in leucotroctolitic rocks that contain less than ∼400 ppm S and that overlie the basal zone range between −1.5 and 2‰, values
that are consistent with those of mantle-derived sulfur. In contrast, δ34S values in the basal zone range from −1.4 to 10.5‰, where the 34S-enriched samples require an input of sulfur from metasedimentary country rocks. δ34S values of the rocks in the basal zone correlate with variations in olivine Fo content but not with S abundance. The wide
range in δ34S values of rocks in the basal zone strongly suggests that magmas interacted with layers in the sedimentary country rocks
that were themselves characterized by variable sulfide contents and δ34S values. The S isotopic data suggest that the heterogeneity observed in the basal zone results from the emplacement of relatively
thin sheets of compositionally distinct magma. All rock types present in the basal zone can be produced as a result of variable
degrees of fractionation of a parental high-Al olivine tholeiite, followed by varying degrees of contamination of derivative
liquids by country rocks. The S-contamination process was essential for the development of Cu–Ni mineralization, and was restricted
to the earliest stages in the development of the Duluth Complex at a time when volatile species such as S and H2O, and low-T partial melts of country rocks, were available to magmas.
Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users. 相似文献