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521.
电流线追踪电位电阻率层析成像方法初探 总被引:4,自引:3,他引:4
电阻率层析成像技术尽管已有了一些比较好的结果,但从国内外发表的文章可以看出,基本上采用的都是有限元方法,而电阻率层析成像的核心问题也就是雅可比矩阵的求取问题。有限元方法能够很好地实现该问题的求解,但需要的计算机内存及计算时间相当的大,为此我们类比地震学中走时射线追踪技术,开展了电流线追踪电位电阻率层析成像方法研究。 相似文献
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Electrical resistivity mapping was conducted to delineate boundaries and architecture of the Eumsung Basin Cretaceous. Basin boundaries are effectively clarified in electrical dipole–dipole resistivity sections as high-resistivity contrast bands. High resistivities most likely originate from the basement of Jurassic granite and Precambrian gneiss, contrasting with the lower resistivities from infilled sedimentary rocks. The electrical properties of basin-margin boundaries are compatible with the results of vertical electrical soundings and very-low-frequency electromagnetic surveys. A statistical analysis of the resistivity sections is tested in terms of standard deviation and is found to be an effective scheme for the subsurface reconstruction of basin architecture as well as the surface demarcation of basin-margin faults and brittle fracture zones, characterized by much higher standard deviation. Pseudo three-dimensional architecture of the basin is delineated by integrating the composite resistivity structure information from two cross-basin E–W magnetotelluric lines and dipole–dipole resistivity lines. Based on statistical analysis, the maximum depth of the basin varies from about 1 km in the northern part to 3 km or more in the middle part. This strong variation supports the view that the basin experienced pull-apart opening with rapid subsidence of the central blocks and asymmetric cross-basinal extension. 相似文献
524.
Geophysical methods, when integrated with soil chemical and hydrogeological methods, can be used to investigate groundwater
contamination. Direct current (DC) resistivity geo-electrical sounding and very-low-frequency electromagnetic (VLF-EM) data
were collected at an open waste site used by the municipality of the city of Isparta, Turkey. The groundwater at shallow depths
in alluvium, which is composed of gravel, sand and clay, were expected to be hazardously contaminated under and around the
open waste-disposal site, in which both household and industrial wastes are known to be disposed of improperly. In this study,
we mapped the spread of groundwater contamination using a VLF-EM method, which allows fast and inexpensive data collection.
The method complements the results of geo-electrical sounding. There is a good correlation between the results of the VLF-EM
and the DC-resistivity methods employed for the investigation of subsurface structure of the site, where soil chemical and
previous hydrogeological surveys have indicated high levels of chemical concentrations.
Received: 17 January 2000 · Accepted: 12 August 2000 相似文献
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Anthony L. Peratt 《Astrophysics and Space Science》1995,227(1-2):97-107
One of the earliest predictions about the morphology of the universe is that it be filamentary (Alfvén, 1950). This prediction followed from the fact that volumewise, the universe is 99.999% matter in the plasma state. When the plasma is energetic, it is generally inhomogeneous with constituent parts in motion. Plasmas in relative motion are coupled by the currents they drive in each other and nonequilibrium plasma often consists of current-conducting filaments.In the laboratory and in the Solar System, filamentary and cellular morphology is a well-known property of plasma. As the properties of the plasma state of matter is believed not to change beyond the range of our space probes, plasma at astrophysical dimensions must also be filamentary.During the 1980s a series of unexpected observations showed filamentary structure on the Galactic, intergalactic, and supergalactic scale. By this time, the analytical intractibility of complex filamentary geometries, intense self-fields, nonlinearities, and explicit time dependence had fostered the development of fully three-dimensional, fully electromagnetic, particle-in-cell simulations of plasmas having the dimensions of galaxies or systems of galaxies. It had been realized that the importance of applying electromagnetism and plasma physics to the problem of radiogalaxy and galaxy formation derived from the fact that the universe is largely aplasma universe. In plasma, electromagnetic forces exceed gravitational forces by a factor of 1036, and electromagnetism is 107 times stronger than gravity even in neutral hydrogen regions, where the degree of ionization is a miniscule 10–4.The observational evidence for galactic-dimensioned Birkeland currents is given based on the direct comparison of the synchrotron radiation properties of simulated currents to those of extra-galactic sources including quasars and double radio galaxies. 相似文献
528.
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
529.
Lake Algonquin, the largest glacial lake of the Great Lakes area, ended prior to 10,000 years BP by drainage to the Ottawa
Valley as the North Bay outlet was deglaciated. At that time, the outlet area was isostatically downwarped more than 100 m;
resulting low water, river-linked lakes Chippewa, Stanley, and Hough, lowstands in the basins of lakes Michigan, Huron, and
Georgian Bay respectively, were much below present lake level. While water levels were low, about half of the present lake
area was dry land. The land above the lowstands was dissected by streams and became forested. Uplift of the North Bay outlet
between 10,000 and 5,000 years BP raised lake level to above the present (the Nipissing transgression), submerging the forest
and valley system. Submerged stumps from those forests have often been encountered on the present lake floor; some stumps
have been dated.
Four sites in Ontario (Parkhill, Owen Sound, St. Joseph Island, Meaford) provide on-land evidence of pre-Nipissing drainage
and valley formation. Radiocarbon ages of valley fill organic materials range from 7,310 to 5,410 years BP. At three sites,
present drainage is known to be displaced from the pre-Nipissing drainage. Geophysical methods (EM, GPR, resistivity) have
been used to refine valley location and morphology at Parkhill and Meaford. There is the potential of tracing the valleys
down slope to the low-water shorelines with shipboard geophysics, with implications for archaeology, hydrology and hydrogeology,
paleogeography, and Great Lakes history.
This is the eighth in a series of ten papers published in this special issue of Journal of Paleolimnology. These papers were
presented at the 47th Annual Meeting of the International Association for Great Lakes Research (2004), held at the University
of Waterloo, Waterloo, Ontario, Canada. P.F. Karrow and C.F.M. Lewis were guest editors of this special issue. 相似文献
530.
Robin E. Nimmer James L. Osiensky Andrew M. Binley Kenneth F. Sprenke Barbara C. Williams 《Hydrogeology Journal》2007,15(5):877-890
Electrical resistance tomography (ERT) was used to monitor a conductive plume dilution experiment that was conducted in fractured basalt in order to assess its applications in this type of fractured-rock environment. Tap water was injected into an injection well for 34 days to dilute a pre-existing potassium chloride (KCl) plume at a site in Idaho, USA. No further fluids were introduced artificially during a 62-day monitoring period. Both surface ERT and cross-borehole ERT were used to monitor dilution and displacement of the plume. A square grid of land-surface electrodes was used with the surface ERT. Three-dimensional images of surface ERT delineated areas of increased and decreased resistivities. Increasing resistivities are attributed to dilution/displacement of the KCl solution by tap-water invasion or the influx of seasonal recharge. Decreasing resistivities resulted from redistribution of residual KCl solution. Cross-borehole ERT was conducted between the injection well and each of seven surrounding monitoring wells. Polar plots of the injection-well resistivity data in the direction of each monitoring well delineate specific locations where tap water seeped from the injection well via preferential flow paths determined by time-dependent resistivity increases. Monitoring-well data indicate locations of clustered and isolated regions of resistivity changes. 相似文献