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931.
A finite element method for dynamic analysis of long slender marine structures under combined parametric and forcing excitations 总被引:2,自引:0,他引:2
This paper presents a numerical analysis of lateral responses of a long slender marine structure under combined parametric and forcing excitations. In the development of the 3-D numerical program, a finite element method is implemented in the time domain using the Newmark constant acceleration method. Some example studies are performed for various water depths, environmental conditions and vessel motions. The relative amplitudes of combined excitations to a conventional forcing excitation are examined. The response amplitude of a combined excitation is much greater than that of a forcing excitation in the even number of instability regions of the Mathieu stability chart. The results demonstrate that a combined excitation needs to be considered for the accurate dynamic analysis of long slender marine structures subjected to a surface vessel motion. 相似文献
932.
Dae Choul Kim Gwang Hoon Lee Young Kyo Seo Gil Young Kim Seok Yun Kim Jeong Chang Kim Soo Chul Park Roy Wilkens 《Marine Georesources & Geotechnology》2004,22(1):21-31
Shallow gas in the Korea Strait shelf mud (KSSM) off SE Korea, revealed by high-resolution subbottom profiles, is associated with acoustic blanking, acoustic turbidity, seepages with plumes in the water column, and seafloor depressions. The acoustic blanking, characterized by strong, consistent top reflection and wipeout below, is most dominant. The seaward edge of the acoustic blanking zone generally coincides with the 100-m water-depth contour, suggesting that the water depth (the pressure) may control the distribution of shallow gas. The acoustic turbidity, characterized by diffuse top reflection, is a dark smear, partially blanking the data below. The seepages with plumes, characterized by vertical smearing and disturbed seafloor, are seen only along the shallowest, landward edge of the acoustic blanking zone. This may suggest that the decreased gas solubility at shallow water depths, caused by the lowered pressure, increases the volume of free gas in the sediments, facilitating the gas escape. The seafloor depressions, interpreted as pockmarks, are accompanied by cone-shaped acoustic masking, which is probably the reflection from a narrow vent of gas. The gas-related acoustic anomalies appear to occur mostly in the upper, recent mud of the KSSM. Neither permeable beds nor faults, which can act as vertical migration pathways for deep thermogenic gas, are evident in the recent mud. We interpret that the bacterial degradation of organic matter in situ is the main source for the gas in the KSSM. The upwelling off SE Korea may be an important source for the increased organic matter in the area. 相似文献
933.
The wide area of the Korea Strait shelf is covered by a thin veneer of gravelly sands, sands, or muddy sands. Most gravels are sub- to well-rounded and their content reaches up to 25%. These sediments were derived from the Korean Peninsula through the paleochannel of the Nakdong River, which extended onto the mid-shelf during late Pleistocene low sea level. The gravel distribution pattern suggests reworking and transport of the sediments by strong currents during times of low sea level. 相似文献
934.
Computer simulation of coastal acoustic tomography with four, five, seven and nine stations was applied to two-dimensional
vortex fields of horizontal domain 5 km × 5 km. Travel time data obtained in reciprocal directions between all pairs of acoustic
stations were analyzed to reconstruct the vortex fields by the stochastic inverse method, reduced to the damped least squares
method. The weighting factor appearing in the inverse analysis was determined by applying the L-curve method, in which a point
making both the size of estimated error ‖y - Ex‖ and solution ‖x‖ as small as possible in a balance is specified as an optimum.
The performance of this method was examined using two-dimensional vortex models which have different wavenumber spectra and
adding the random error of different levels to the travel time difference data y. This study suggests that in the selection
of the optimal weighting factor the horizontal section of the simulated tidal vortex fields can be well reconstructed by the
coastal acoustic tomography system composed of five to seven acoustic stations located in the periphery of the vortex fields.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
935.
Clay minerals of the surface sediments of Bransfield Strait, Antarctica, exhibit distinctive geographical distributions: kaolinite has the highest concentration near the shore of the South Shetland Islands in the northern strait (20%); chlorite, near Smith Island in the northwestern strait; illite, on the continental shelf off the Antarctic Peninsula in the southern strait (80%); and smectite, close to the Penguin and Bridgeman islands in the northeastern strait (25%). This distribution pattern, combined with hydrographic and climatic data for the strait, are used to infer clay mineral provenance and dispersal patterns. 相似文献
936.
Synoptic distributions of thermal surface mixed layer and thermocline were identified using four airborne expendable bathythermograph
(AXBT) surveys (September 1992 and February, May, and September 1993) in the southern Yellow and East China Seas. Seasonality
and a dominant driving mechanism of the surface mixed layer were examined. The dominant driving mechanisms differ between
seasons and between on-shelf and off-shelf regimes. Currents, eddies, and migration of bottom cold waters (on the shelf) also
affect the surface mixed layer. Thermocline thickness, temperature difference from thermocline top to bottom, and thermocline
intensity in warm seasons were measured, and their synoptic features were also discussed. 相似文献
937.
Hae-Hoon Park 《Ocean Engineering》1993,20(2)
An indirect tension measurement method of a towing cable in midwater or a buoy cable is proposed using underwater acoustic positioning systems, etc., to give the in-water cable tension. The most simple and traditional cable tension measurement method is to apply a mechanical tension meter at the one end of the cable, but the method has limits in the aspects of continuous monitoring and manual operation. However, the technique in this study is to apply the Pode's analysis of the equilibrium configuration and tension of a flexible twine, in which the cable tension is given as a function of the geometric positions of both ends of the cable. A set of nonlinear integral equations is formulated and solved numerically by the Newton-Raphson method. Then the inclination angles and the tensions at the lower and the upper ends of the cable could be obtained. The derived method enables us to track a towed object, to measure the tension of a towing cable or a buoy cable and is also applicable to the remotely operated vehicle (ROV) tethered to a mother ship. 相似文献
938.
E. R. Rene Ph.D. M. S. Jo S. H. Kim H. S. Park Ph.D. 《International Journal of Environmental Science and Technology》2007,4(2):177-182
Biodegradation has proved to be a versatile technique to remediate benzene, toluene, ethyl benzene and xylene mixtures in contaminated soil and groundwater. In this study, a mixed microbial culture obtained from a wastewater treatment plant was used to degrade liquid phase ethyl benzene and xylene, at initial concentrations varying between 15 to 75 mg/l. Experiments were conducted according to the 2k?1 fractional factorial design to identify the main and interaction effects of parameters and their influence on biodegradation of individual ethyl benzene and xylene compounds in mixtures. The removal efficiencies of these compounds varied between 2 to 90% depending on the concentration of other compounds and also on their interaction effects. A statistical interpretation of the results was done based on the Fishers variance ratio (F) and probability (P) values. Though all the main effects were found significant (P < 0.05) at the 5% confidence level, the interactions between benzene and toluene and benzene and xylene concentrations were also found to be statistically significant and play a major role in affecting the total ethyl benzene and xylene removal. 相似文献
939.
To delineate spatial extent of seawater intrusion in a small experimental watershed in the coastal area of Byunsan, Korea,
electrical resistivity surveys with some evaluation core drillings and chemical analysis of groundwaters were conducted. The
vertical electrical sounding (VES) method was applied, which is useful to identify variations in electrical characteristics
of layered aquifers. The drilling logs identified a three-layered subsurface including reclamation soil, weathered layer and
relatively fresh sedimentary bedrock. The upper two layers are the main water-bearing units in this area. A total of 30 electrical
sounding curves corresponded mostly to the H type and they were further divided into three classes: highly conductive, intermediate,
and low conductive, according to the observed resistivity values of the most conductive weathered layer. In addition, groundwater
samples from 15 shallow monitoring wells were analyzed and thus grouped into two types based on HCO3/Cl and Ca/Na molar ratios with TDS levels, which differentiated groundwaters affected by seawater intrusion from those not
or less affected. According to relationships between the three classes of the sounding curves and groundwater chemistry, locations
of the monitoring wells with low HCO3/Cl and Ca/Na ionic ratios coincided with the area showing the highly conductive type curve, while those with the high ratios
corresponded to the area showing low conductive curve type. Both the low electrical resistivity and the low ionic ratios indicated
effects of seawater intrusion. From this study, it was demonstrated that the VES would be useful to delineate seawater intrusion
in coastal areas. 相似文献
940.
Detecting areal changes in tidal flats after sea dike construction using Landsat-TM images 总被引:1,自引:0,他引:1
Moon Seong Kang Sang June Im Tae Il Jang Seung Woo Park Sang Min Kim 《Journal of Earth System Science》2007,116(6):561-573
The main objective of this study was to estimate changes in the area of tidal flats that occurred after sea dike construction
on the western coast of South Korea using Landsat-TM images. Applying the ISODATA method of unsupervised classification for
Landsat-TM images, the tidal flats were identified, and the resulting areas were quantified for each image. The area of tidal
flats from a topographic map published in one year differs significantly from that shown in another, which appears to be attributable
to the tide levels at the time of aerial photography. During the study period, the area of tidal flats, as estimated from
Landsat-TM images, increased by 4.57 km2 per year in the study areas. The tidal flats in the inner sea of Chunsu Harbor area increased by 200 m2 per zone, while the accumulation for a number of inner sea areas within Asan Harbor area occurred at over 50m2 per zone. The results of this research may serve as the basis of an environmentallyfriendly development plan for tidal flats. 相似文献