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71.
Lunar meteoroid impact flashes provide a method to estimate the flux of the large meteoroid flux and thus their hazard to
spacecraft. Although meteoroid impacts on the Moon have been detected using video methods for over a decade, the difficulty
of manually searching hours of video for the rare, extremely brief impact flashes has discouraged the technique’s systematic
implementation. A prototype has been developed for the purpose of automatically searching lunar video records for impact flashes,
eliminating false detections, editing the returned possible flashes, and archiving and documenting the results. Several utilities
for measurement, analysis, and location of the flashes on the moon included in the program are demonstrated. Application of
the program to a year’s worth of lunar observations is discussed along with examples of impact flashes. 相似文献
72.
by Xinya Li Bill X. Hu William C. Burnett Isaac R. Santos Jeffery P. Chanton 《Ground water》2009,47(4):558-568
Submarine ground water discharge (SGD) is now recognized as an important water pathway between land and sea. It is difficult to quantitatively predict SGD owing to its significant spatial and temporal variability. This study focuses on quantitative estimation of SGD caused by tidally induced sea water recirculation and a terrestrial hydraulic gradient. A two-dimensional hydrogeological model was developed to simulate SGD from a coastal unconfined aquifer in the northeastern Gulf of Mexico, where previous SGD studies were performed. A density-variable numerical code, SEAWAT2000, was applied to simulate SGD. To accurately predict discharge, various influencing factors such as heterogeneity in conductivity, uncertain boundary conditions, and tidal pumping were systematically assessed. The tidally influenced sea water recirculation zone and the fresh water–salt water mixing zone under various tidal patterns, tidal ranges, and water table heights were also investigated. The model was calibrated and validated from long-term, intensive measurements at the study site. The percentage of fresh SGD relative to total SGD ranged from 4% to 50% under normal conditions. Based on simulations of two field measurements in summer and spring, respectively, the fresh water ratios were 9% and 15%, respectively. These results support the hypothesis that the SGD induced by tidally driven sea water recirculation is much larger than terrestrial fresh ground water discharge at this site. The estimates of total and fresh SGD are at the low and high ends, respectively, of the estimation ranges obtained from geochemical tracers (e.g., 222 Rn). 相似文献
73.
Mapping gamma radiation and its uncertainty from weathering products in a Tasmanian landscape with a proximal sensor and random forest kriging 下载免费PDF全文
The radionuclides of potassium (40 K), uranium (238U) and thorium (232Th) emit from the land surface gamma radiation that is characteristic of the underlying rocks and the distribution of their weathering products in the landscape. We measured the radiation along widely separated transects using a mobile proximal sensor over a 10 000‐ha region of Tasmania. We supplemented the transect data with information from soil and geological maps and dense data from LandSat and SPOT imagery, a digital elevation model and terrain attributes on a grid at 30‐m intervals so as to map the radionuclides. We used a sequence of steps, starting with a spatial bootstrap and random forests to predict emissions across the study area and at sampling points excluded from the bootstrap samples. The predictions at the sampling points were compared with the observed values to obtain residuals, which were then used to krige them at all points on the 30 m grid. We combined the random forest and kriging predictions on the 30‐m grid to obtain our random forest kriging predictions. Repeating the procedure 100 times provided confidence limits on our results and predictions. The resulting maps of the radionuclides accord well with what we know of the soil, lithology and topography of the region from other sources. Alluvial deposits with large amounts of potassium extend from the foot slopes of the Great Western Tiers and along the flood plains of the Meander River, providing evidence of previous widespread weathering and deposition of the material. The fertile Red Ferrosols (roughly equivalent to Ferralic Nitisols in the World reference base (WRB) classification) on the extensive Tertiary basalt plateau emit little gamma radiation as a result of deep weathering and of potassium movement and accumulation down its talus slopes. The maps show the complexity of the region in terms of soil, lithology and terrain, and they show the merits of gamma radiometry for mapping and understanding the distribution of materials in such regions. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
74.
Using data assimilation method to calibrate a heterogeneous conductivity field conditioning on transient flow test data 总被引:1,自引:1,他引:0
Juxiu Tong Bill X. Hu Jinzhong Yang 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(8):1211-1223
A data assimilation method is developed to calibrate a heterogeneous hydraulic conductivity field conditioning on transient
pumping test data. The ensemble Kalman filter (EnKF) approach is used to update model parameters such as hydraulic conductivity
and model variables such as hydraulic head using available data. A synthetical two-dimensional flow case is used to assess
the capability of the EnKF method to calibrate a heterogeneous conductivity field by assimilating transient flow data from
observation wells under different hydraulic boundary conditions. The study results indicate that the EnKF method will significantly
improve the estimation of the hydraulic conductivity field by assimilating continuous hydraulic head measurements and the
hydraulic boundary condition will significantly affect the simulation results. For our cases, after a few data assimilation
steps, the assimilated conductivity field with four Neumann boundaries matches the real field well while the assimilated conductivity
field with mixed Dirichlet and Neumann boundaries does not. We found in our cases that the ensemble size should be 300 or
larger for the numerical simulation. The number and the locations of the observation wells will significantly affect the hydraulic
conductivity field calibration. 相似文献
75.
Improved edge detection mapping through stacking and integration: a case study in the Bathurst Mining Camp 下载免费PDF全文
Airborne geophysical surveys provide spatially continuous regional data coverage, which directly reflects subsurface petrophysical differences and thus the underlying geology. A modern geologic mapping exercise requires the fusion of this information to complement what is typically limited regional outcrop. Often, interpretation of the geophysical data in a geological context is done qualitatively using total field and derivative maps. With a qualitative approach, the resulting map product may reflect the interpreter's bias. Source edge detection provides a quantitative means to map lateral physical property changes in potential and non‐potential field data. There are a number of Source edge detection algorithms, all of which apply a transformation to convert local signal inflections associated with source edges into local maxima. As a consequence of differences in their computation, the various algorithms generate slightly different results for any given source depth, geometry, contrast, and noise levels. To enhance the viability of any detected edge, it is recommended that one combines the output of several Source edge detection algorithms. Here we introduce a simple data compilation method, deemed edge stacking, which improves the interpretable product of Source edge detection through direct gridding, grid addition, and amplitude thresholding. In two examples, i.e., a synthetic example and a real‐world example from the Bathurst Mining Camp, New Brunswick, Canada, a number of transformation algorithms are applied to gridded geophysical data sets and the resulting Source edge detection solutions combined. Edge stacking combines the benefits and nuances of each Source edge detection algorithm; coincident or overlapping and laterally continuous solutions are considered more indicative of a true edge, whereas isolated points are taken as being indicative of random noise or false solutions. When additional data types are available, as in our example, they may also be integrated to create a more complete geologic model. The effectiveness of this method is limited only by the resolution of each survey data set and the necessity of lateral physical property contrasts. The end product aims at creating a petrophysical contact map, which, when integrated with known lithological outcrop information, can be led to an improved geological map. 相似文献
76.
Graham D. M. Andrews Michael J. Branney Bill Bonnichsen Michael McCurry 《Bulletin of Volcanology》2008,70(3):269-291
The 80 km long NNE-trending Rogerson Graben on the southern margin of the central Snake River Plain, Idaho, USA, hosts a rhyolitic
pyroclastic succession, 200 m thick, that records a period of successive, late-Miocene, large-volume explosive eruptions from
the Yellowstone–Snake River Plain volcanic province, and contemporaneous extension. The succession, here termed the Rogerson
Formation, comprises seven members (defined herein) and records at least eight large explosive eruptions with numerous repose
periods. Five high-grade and extremely high-grade ignimbrites are intercalated with three non-welded ignimbrites and two volcaniclastic
deposits, with numerous repose periods (palaeosols) throughout. Two of the ignimbrites are dominantly rheomorphic and lava-like
but contain subordinate non-welded pyroclastic layers. The ignimbrites are typical Snake River Plain high-silica rhyolites,
with anhydrous crystal assemblages and high inferred magmatic temperatures (≤ 1,025°C). We tentatively infer that the Jackpot
and Rabbit Springs Members may have been emplaced from the Bruneau–Jarbidge eruptive centre on the basis of: (1) flow lineation
trends, (2) crystal assemblage, and (3) radiometric age. We infer that the overlying Brown’s View, Grey’s Landing, and Sand
Springs Members may have been emplaced from the Twin Falls eruptive centre on the basis of: (1) kinematic indicators (from
the east), and (2) crystal assemblage. Furthermore, we have established the contemporaneous evolution of the Rogerson Graben
from the emplacement of the Jackpot Member onwards, and infer that it is similar to younger half-graben along the southern
margin of the Snake River Plain, formed by local reactivation of Basin and Range structures by the northeastwardly migration
of the Yellowstone hot-spot.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
77.
Sedimentary processes in the Stromboli Canyon and in the Marsili Basin are studied on the basis of side-scan sonographs.
The basin margins are characterized by slump scars, gullies, channels, and large debrites on the Calabrian slope and by straight
chutes of fast downslope sediment transport and blocky–hummocky avalanche deposits on the flanks of the Stromboli volcano.
In the Stromboli Canyon and in minor deep-sea channels, sediment transport by turbidity currents generates sediment waves.
Between the basin margins and the abyssal plain, the outcropping volcanic basement traps part of the sediment coming from
the marginal areas. The abyssal plain is characterized by low relief lobes and ponded sediments. 相似文献
78.
Susan Ringrose Bill Downey Dane Genecke Francis Sefe Bernard Vink 《Journal of Arid Environments》1999,43(4):375
Quaternary sedimentation in the western Makgadikgadi basin of north central Botswana is evaluated on the basis of new evidence from satellite imagery and sedimentological analyses. Thematic Mapper imagery interpretation, combined with field evidence, has led to the identification of geomorphological features which are mainly composed of light grey calcareous sandstones (formerly calcretes) overlain by dark grey sands. The literature suggests that palaeolake Makgadikgadi I formed and developed intermittently after initial downwarping in the early–mid Pleistocene. The calcareous sandstones were formed when calcium carbonate precipitation took place in pre-existing Kalahari sands along the western shoreline of Makgadikgadi I. Field evidence, supported by X-ray diffraction and SEM analyses, indicates that CaCO3precipitated mainly in marshy conditions around plant roots and stems and in association with bacteria in embayments along the lakeshore. The sandstones thickened and became partially indurated as a result of increasing palaeolake levels. Deposition was terminated by renewed tectonism which uplifted the shoreline zone relative to the lake basin, leading to falling palaeolake levels. Post-uplift reworking led to case hardening and pedogenic calcrete formation in the upper sections of the calcareous sandstones. Sedimentary conditions altered during the late Pleistocene. Extensive distributaries from the proto-Okavango system incised the shoreline ridge contributing to the filling of Makgadikgadi II. Satellite data suggest that the proto-Okavango rivers formed a series of fan deltas at this time along the western Makgadikgadi basin. Widespread dispersal of fluvial grey sands took place as a result of basin tilting which led to anastomosing channels flowing southward possibly around 18,000 B.P. These results, although preliminary in nature, augment previous geomorphological analyses by adding some detail in terms of depositional environments and by providing a tentative age and origin for the ubiquitous grey sands. 相似文献
79.
Multi-gas Emissions Pathways to Meet Climate Targets 总被引:1,自引:1,他引:1
Malte Meinshausen Bill Hare Tom M. M. Wigley Detlef Van Vuuren Michel G. J. Den Elzen Rob Swart 《Climatic change》2006,75(1-2):151-194
So far, climate change mitigation pathways focus mostly on CO2 and a limited number of climate targets. Comprehensive studies of emission implications have been hindered by the absence
of a flexible method to generate multi-gas emissions pathways, user-definable in shape and the climate target. The presented
method ‘Equal Quantile Walk’ (EQW) is intended to fill this gap, building upon and complementing existing multi-gas emission
scenarios. The EQW method generates new mitigation pathways by ‘walking along equal quantile paths’ of the emission distributions
derived from existing multi-gas IPCC baseline and stabilization scenarios. Considered emissions include those of CO2 and all other major radiative forcing agents (greenhouse gases, ozone precursors and sulphur aerosols). Sample EQW pathways
are derived for stabilization at 350 ppm to 750 ppm CO2 concentrations and compared to WRE profiles. Furthermore, the ability of the method to analyze emission implications in a
probabilistic multi-gas framework is demonstrated. The probability of overshooting a 2 ∘C climate target is derived by using different sets of EQW radiative forcing peaking pathways. If the probability shall not
be increased above 30%, it seems necessary to peak CO2 equivalence concentrations around 475 ppm and return to lower levels after peaking (below 400 ppm). EQW emissions pathways
can be applied in studies relating to Article 2 of the UNFCCC, for the analysis of climate impacts, adaptation and emission
control implications associated with certain climate targets. See for EQW-software and data. 相似文献
80.
青藏高原西部的抬升速率:叶城—狮泉河花岗岩^40Ar—^39Ar年龄的地质解释 总被引:17,自引:2,他引:17
通过对叶城-狮泉河剖面花岗岩中黑云母40Ar-39Ar法年龄研究,获得西昆仑北岩带库地岩体海拔高度2950m和2850m黑云母的封闭年龄分别为396.9Ma和388.9Ma,西昆仑南岩带塔西土路克、三十里营房和奇台大坂岩体黑云母的封闭年龄为195.8~183.9Ma,班公湖-喀喇昆仑北岩带日土岩体黑云母封闭年龄为80.3~79.6Ma,其时代分别为加里东期、印支期和燕山晚期。年龄结果表明,同一岩体海拔高的黑云母封闭年龄大于海拔低的黑云母封闭年龄,根据海拔高程差和坪年龄差计算出岩体的抬升速率,表明青藏高原西部从加里东期到燕山晚期,隆起速度有增大的趋势,而且具脉动性。 相似文献