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341.
The Mw = 9.3 megathrust earthquake of December 26, 2004 off the northwest coast of Sumatra in the Indian Ocean generated a catastrophic
tsunami that was recorded by a large number of tide gauges throughout the World Ocean. Part 1 of our study of this event examines
tide gauge measurements from the Indian Ocean region, at sites located from a few hundred to several thousand kilometers from
the source area. Statistical characteristics of the tsunami waves, including wave height, duration, and arrival time, are
determined, along with spectral properties of the tsunami records. 相似文献
342.
Numerical Modelling of Tsunamis Generated by Hypothetical Landslides in the Strait of Georgia,British Columbia 总被引:1,自引:0,他引:1
A. B. Rabinovich R. E. Thomson B. D. Bornhold I. V. Fine E. A. Kulikov 《Pure and Applied Geophysics》2003,160(7):1273-1313
--A modified and corrected version of the viscous slide model of Jiang and LeBlond (1994) is used to assess the tsunami risk associated with hypothetical underwater slope failures in two coastal areas of British Columbia having potentially unstable sediment deposits: (a) Malaspina Strait, separating the mainland coast and Texada Island in the central Strait of Georgia; and (b) Roberts Bank on the foreslope of the Fraser River Delta in the southern Strait of Georgia. The intent of this study is to demonstrate the capability of the model for tsunami risk assessment and to improve upon previous studies of tsunami risk in the region based on reasonable submarine landslide scenarios. The potential risk from tsunamis associated with slide failures has been examined, but the likelihood of failure events themselves was not considered. For the Malaspina Strait scenarios, simulated tsunamis are generated by failure of a lobe of perched sediment situ ated on the slope of eastern Texada Island. Failure as a flow slide of the estimated 1,250,000 m3 of sediment generates wave troughs reaching ц.9 m and trough-to-crest heights of 6 to 8 m along the coast of Texada Island. At Cape Cockburn, on the opposite side of the strait, wave heights of 1.5 to 2.0 m are produced. For Roberts Bank, simulated waves are examined for two separate failure scenarios. The larger slide (Case 1) involves the failure of a sediment lobe with lateral dimensions of 7 2 3 km2 and volume of 0.75 km3 while the smaller slide (Case 2) fails a sediment lobe with dimensions of 4 2 2.6 km2 and volume of 0.23 km3. Computations were made both for high (+3 m) and low (х m) tide conditions. For both failure volumes, maximum wave amplitudes (up to 18 m for Case 1 and 8 m for Case 2) occur on the coasts of Mayne and Galiano Islands, opposite the source area. Wave amplitudes are much smaller (1 to 4 m) on the mainl and coast because of the reflection of the initial waves from Roberts Bank. Additional numerical experiments were conducted for both regions to estimate the sensitivity of the computed tsunami wave heights to input parameters, such as slide viscosity, bulk density, and slide position. 相似文献
343.
Sedimentary records of redox-sensitive trace elements hold significant potential as indicators of paleoceanographic environmental conditions. Records of Re can reveal the intensity of past reducing conditions in sediments at the time of deposition, whereas records of Ag may record the magnitude of past diatom fluxes to the seafloor. Confidence in paleoenvironmental reconstruction from records of either metal, however, requires it to have experienced negligible redistribution since deposition. This study examines diagenetic rearrangements of Re and Ag that occur in response to exposure to bottom-water O2 in environments of low sedimentation rate, including Madeira Abyssal Plain turbidites and eastern Mediterranean basin sapropels. Authigenic Re was remobilized quantitatively by oxidation but poorly retained by the underlying sediments. All records are consistent with previous work demonstrating that only a limited reimmobilization of Re occurs preferentially in Corg-rich, reducing sediments. Silver was also mobilized quantitatively by oxidation, but it was subsequently immobilized more efficiently in all cases as sharp peaks immediately into anoxic conditions below active oxidation fronts, and these peaks remain immobile in anoxic conditions during long-term burial. Comparison of Ag, S, and Se records from various cores suggests that Ag is likely to have been immobilized as a selenide, a mechanism previously proposed for Hg in similar situations (Mercone et al., 1999). Coexisting narrow peaks of Ag and Hg with Se offer a means of assessing whether oxidative burndown has ever occurred at the top of Corg- and sulfide-rich sedimentary units. Although these results suggest that caution must be used when inferring paleoenvironmental information from records of Ag and Re in cores with low sediment accumulation rates (<5 cm ka−1), they should not affect the promise that authigenic Ag and Re records hold for paleoenvironmental reconstruction in sediments with higher accumulation rates and where anoxic conditions have been maintained continuously. 相似文献
344.
The 9th-Generation International Geomagnetic Reference Field 总被引:5,自引:0,他引:5
International Association of Geomagnetism Aeronomy Division V Working Group Participating members: S. Macmillan S. Maus T. Bondar A. Chambodut V. Golovkov R. Holme B. Langlais V. Lesur F. Lowes H. Lühr W. Mai M. Mandea N. Olsen M. Rother T. Sabaka A. Thomson I. Wardinski 《Geophysical Journal International》2003,155(3):1051-1056
345.
We present kinematic observations of NGC 3923, one of the best-known examples of an elliptical galaxy with shells. Although NGC 3923 has no rotation on its major axis, it has minor axis rotation with an amplitude of some 20 km s−1 out to 25 arcsec radius. This is possibily the result of a kinematically decoupled core, but we present arguments against this hypothesis, and if the core were formed by a merger, this must have been a different merger from that which gave rise to the shells. The minor axis rotation suggests that NGC 3923 is prolate or triaxial, at least in the inner region. A prolate geometry for the whole galaxy would favour the merger model over the interaction model for the shell formation mechanism. There is other evidence, however, that the shape of the underlying galaxy changes with radius, in which case it is possible that the minor axis rotation could be confined to the galaxy core. The kinematics could reflect a triaxial mass distribution, in which the long and short axes are aligned with the photometric major and minor axes, and the axial ratios change such that the galaxy is near-prolate in the inner regions and near-oblate at larger radii. Measuring the rotation curve to about double this radius along the minor axis, as well as offset from the nucleus along the major axis at the radius of the innermost shells, would enable the true extent of the minor axis rotation to be determined. 相似文献
346.
347.
Keith W. Gates Brian E. Perkins Jackie G. EuDaly Amanda S. Harrison Wayne A. Bough 《Estuaries and Coasts》1985,8(2):244-251
A study to determine the impact of seafood packing and processing effluents discharged to southeastern estuarine waters was conducted in July and August of 1979. The environmental impact of current seafood processing wastes on Georgia’s estuaries appears to be minimal when compared with the natural organic load. One large estuary demonstrated a high residual capacity to receive processing effluents without significant change. The BOD load from shrimp thawing, peeling, sorting, and cleaning operations at a large seafood processing plant was shown to be equivalent to the organic material generated by a 302 m2 plot (57 ft×57 ft) of salt marsh. NH4?N levels were greater than, but the same order of magnitude as, natural runoff from marsh land. 相似文献
348.
An increase in the transmission of solar radiation in the UV-B region (specifically, 290–320 nm) is expected to occur as a result of anthropogenic degradation of stratospheric ozone. The potential impact of increased levels of UV-B radiation upon the biosphere is of ecological concern. In a previous study a community of estuarine organisms received a daily exposure to a simulated solar spectrum enhanced in UV-B radiation for a period of six weeks. A dominant species of diatom growing at the surface of these communities was isolated and identified to beMelosira nummuloides. Short chains of this diatom were irradiated for a four-hour period on each of three consecutive days. Fluorescent sunlamps filtered by a 290 nm cut-off filter (0.13–0.50 mm cellulose acetate) or a 315 nm cut-off filter (0.13mm Mylar ‘S’) provided a range of fluence which closely approximated natural fluence levels. A least squares regression analysis of the number of cell divisions on the biologically weighted fluence indicated a significant depression in the growth of this species by radiation in the 290–320 nm waveband. 相似文献
349.
Peter M. D. Bradshaw Ian Thomson Barry W. Smee Jan O. Larsson 《Journal of Geochemical Exploration》1974,3(3):209-225
This paper deals briefly with the principles of geochemical migration in the secondary (soil, sediment) environment, a knowledge of which is essential to a correct interpretation of exploration geochemical data. Examples are given which illustrate that the principles which apply in the more easily interpreted tropical areas, also apply in the more complicated glaciated regions. Any person employing exploration geochemistry in geomorphologically complicated areas, is well advised to study data from strictly residual soil areas where the fundamentals of geochemical migration are more easily observed. From this base it is easier to understand the additional complications of geochemistry in mountainous and glaciated terrain. Of the variety of exploration geochemical techniques which can be used, this paper deals specifically with two: soil profile sampling, and different strengths of acid extraction of metal from samples. Examples from the different environments are compared and contrasted. 相似文献
350.
H.W. Dosso V. Ramaswamy F.W. Jones D.J. Thomson 《Physics of the Earth and Planetary Interiors》1974,9(2):108-110
This work compares experimental analogue model measurements and finite-difference numerical calculations of the electric and magnetic fields for the cases of induction in a highly conducting plate and wedge embedded in a poorly conducting host earth. The results indicate very good agreement between the experimental and theoretical results and confirm the validity of the analogue and numerical methods for studying complex induction problems. 相似文献