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71.
The direct-push permeameter (DPP) is a promising approach for obtaining high-resolution information about vertical variations in hydraulic conductivity (K) in shallow unconsolidated settings. This small-diameter tool, which consists of a short screened section with a pair of transducers inset in the tool near the screen, is pushed into the subsurface to a depth at which a K estimate is desired. A short hydraulic test is then performed by injecting water through the screen at a constant rate (less than 4 L/min) while pressure changes are monitored at the transducer locations. Hydraulic conductivity is calculated using the injection rate and the pressure changes in simple expressions based on Darcy's Law. In units of moderate or higher hydraulic conductivity (more than 1 m/d), testing at a single level can be completed within 10 to 15 min. Two major advantages of the method are its speed and the insensitivity of the K estimates to the zone of compaction created by tool advancement. The potential of the approach has been assessed at two extensively studied sites in the United States and Germany over a K range commonly faced in practical field investigations (0.02 to 500 m/d). The results of this assessment demonstrate that the DPP can provide high-resolution K estimates that are in good agreement with estimates obtained through other means. 相似文献
72.
Arjun M. Heimsath William E. Dietrich Kunihiko Nishiizumi Robert C. Finkel 《地球表面变化过程与地形》2001,26(5):531-552
Landscapes in areas of active uplift and erosion can only remain soil‐mantled if the local production of soil equals or exceeds the local erosion rate. The soil production rate varies with soil depth, hence local variation in soil depth may provide clues about spatial variation in erosion rates. If uplift and the consequent erosion rates are sufficiently uniform in space and time, then there will be tendency toward equilibrium landforms shaped by the erosional processes. Soil mantle thickness would adjust such that soil production matched the erosion. Previous work in the Oregon Coast Range suggested that there may be a tendency locally toward equilibrium between hillslope erosion and sediment yield. Here results from a new methodology based on cosmogenic radionuclide accumulation in bedrock minerals at the base of the soil column are reported. We quantify how soil production varies with soil thickness in the southern Oregon Coast Range and explore further the issue of landscape equilibrium. Apparent soil production is determined to be an inverse exponential function of soil depth, with a maximum inferred production rate of 268 m Ma?1 occurring under zero soil depth. This rate depends, however, on the degree of weathering of the underlying bedrock. The stochastic and large‐scale nature of soil production by biogenic processes leads to large temporal and spatial variations in soil depth; the spatial variation of soil depth neither supports nor rejects equilibrium morphology. Our observed catchment‐averaged erosion rate of 117 m Ma?1 is, however, similar to that estimated for the region by others, and to soil production rates under thin and intermediate soils typical for the steep ridges. We suggest that portions of the Oregon Coast Range may be eroding at roughly the same rate, but that local competition between drainage networks and episodic erosional events leads to landforms that are out of equilibrium locally and have a spatially varying soil mantle. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
73.
Dietrich Flßner 《Limnologica》2001,31(4):303-306
A new species of Cyclops s. str. (strenuus subgroup) from a high mountain lake in Northwestern Mongolia is described. As no cytological investigations were possible, the species diagnosis and taxonomic relationships were made on the basis of morphological and morphometrical data. It is most similar to Cyclops abyssorum, but there are clear distinguishing features. 相似文献
74.
Dr. Dietrich Röder 《International Journal of Earth Sciences》1962,52(1):189-201
Between Lat. 56° N and 57° 30′ N, the Central Ranges of the Canadian Rocky Mountains contain a belt of slaty-cleaved vertical or overturned east-dipping beds which is considered as the west edge of the thrust-faulted area. Its antithetic rotation is accompanied by small-scale folding parallel to the plane of greatest shear stress, by synthetic and later antithetic movements along the plane of slaty cleavage. Reversal of movement on older reverse faults and a discordant, post-Laramide phase of synthetic normal faulting terminate the movements. Folding and rotation are contemporaneous with the thrusting to the east, and the synthetic normal faulting belongs to the grabening of the Rocky Mountain Trench adjacent to the east. Since rotation and thrusting above the uninvolved basement are contemporaneous, the rotation cannot be powered by differential movement along a stationary lineament within the basement. Its cause is suspected in the west-dipping clinoforms of the Palaeozoic sediments whose inclination placed them within the antithetic quadrant of the Laramide stress field, forcing them to continue rotation and to develop compressional folding instead of bedding-parallel elongated thrust sheets. One of two structurally analogous cases, the Swiss Massif Zone with the Helvetic nappes, shows an antithetically inclined gneissic foliation which might be a mechanical equivalent of the clinoforms in the Rocky Mountains. In the other example, from the north flank of the Hercynian Mosel syncline, a remarkably similar tectonic history and a close geographic coincidence between clinoformic sedimentation and development of an antithetic rotation zone is known. 相似文献
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Thirty-one rock samples from a Western Canada Basin well have been analysed for aromatics, using glass capillary gas chromatography with simultaneous flame ionization and sulfur-selective flame photometric detection. A uniform aromatic distribution pattern with a marked predominance of di- and tricyclic aromatic hydrocarbons was observed throughout a depth interval of 3000 meters comprising Cretaceous and Jurassic sediments. The very high relative abundance of sulfur aromatics at two narrow intervals in the Triassic and Mississippian is attributed to a major change in facies. Gradual changes with increasing depth have been observed for a series of compound ratios, which had been calculated from the isomers of methyl- and dimethylphenanthrene, and their parent compounds. These changes reflect the increasing thermal maturation of the sedimentary organic matter. A Methylphenanthrene Index (MPI) has been introduced, which exhibited a very good correlation with vitrinite reflectance data. The MPI is the first maturity parameter which is based on a series of aromatic hydrocarbons. This hydrocarbon internal maturity parameter permits the recognition and definition of maturity levels in extracts which can be compared to the maturity (e.g. vitrinite reflectance) of source rocks. 相似文献
80.
Microprobe analyses of the minerals from an unusual chloritoid-staurolite-garnet (+ muscovite + quartz + ilmenite) assemblage from the sillimanite (fibrolite) zone of Sini, India are presented and the petrological significance of the paragenesis is discussed. The X Mg in the different minerals from the chloritoid-staurolite-bearing rock varies in the order, muscovite > chlorite > chloritoid > staurolite > garnet > ilmenite, and from the associated sillimanite-bearing schists: muscovite > biotite > staurolite > garnet rim > garnet core > ilmenite. A graphical representation of the mineral compositions in an AFM projection displays a consistent topology if the effects of non-AFM components such as Zn in the staurolite and Mn in the garnet are taken into account. Petrographic and mineralogical data are consistent with a prograde formation of the chloritoid-staurolite-garnet assemblage. It is suggested that the paragenesis has been formed at similar PT conditions to the associated sillimanite (fibrolite)-staurolite-garnet-mica schists. These conditions are estimated to be 600–625°C/6±0.5 Kb. 相似文献