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401.
402.
Aerosol retrieval algorithms for the MODerate Resolution Imaging Spectroradiometer (MODIS) have been developed to estimate aerosol and microphysical properties of the atmosphere, which help to address aerosol climatic issues at global scale. However, higher spatial resolution aerosol products for urban areas have not been well-researched mainly due to the difficulty of differentiating aerosols from bright surfaces in urban areas. Here, an aerosol retrieval algorithm using the MODIS 500-m resolution bands is described, to retrieve aerosol properties over Hong Kong and the Pearl River Delta region. The rationale of our technique is to first estimate the aerosol reflectances by decomposing the top-of-atmosphere reflectances from surface reflectances and Rayleigh path reflectances. For the determination of surface reflectances, a Minimum Reflectance Technique (MRT) is used, and MRT images are computed for different seasons. For conversion of aerosol reflectance to aerosol optical thickness (AOT), comprehensive Look Up Tables specific to the local region are constructed, which consider aerosol properties and sun-viewing geometry in the radiative transfer calculations. Four local aerosol types, namely coastal urban, polluted urban, dust, and heavy pollution, were derived using cluster analysis on 3 years of AERONET measurements in Hong Kong. The resulting 500 m AOT images were found to be highly correlated with ground measurements from the AERONET (r2 = 0.767) and Microtops II sunphotometers (r2 = 0.760) in Hong Kong. This study further demonstrates the application of the fine resolution AOT images for monitoring inter-urban and intra-urban aerosol distributions and the influence of trans-boundary flows. These applications include characterization of spatial patterns of AOT within the city, and detection of regional biomass burning sources. 相似文献
403.
Franklin S. Kinnaman Justine B. Kimball Luis Busso Daniel Birgel Haibing Ding Kai-Uwe Hinrichs David L. Valentine 《Geo-Marine Letters》2010,30(3-4):355-365
The Coal Oil Point seep field located offshore Santa Barbara, CA, consists of dozens of named seeps, including a peripheral ~200 m2 area known as Brian Seep, located in 10 m water depth. A single comprehensive survey of gas flux at Brian Seep yielded a methane release rate of ~450 moles of CH4 per day, originating from 68 persistent gas vents and 23 intermittent vents, with gas flux among persistent vents displaying a log normal frequency distribution. A subsequent series of 33 repeat surveys conducted over a period of 6 months tracked eight persistent vents, and revealed substantial temporal variability in gas venting, with flux from each individual vent varying by more than a factor of 4. During wintertime surveys sediment was largely absent from the site, and carbonate concretions were exposed at the seafloor. The presence of the carbonates was unexpected, as the thermogenic seep gas contains 6.7% CO2, which should act to dissolve carbonates. The average δ13C of the carbonates was ?29.2?±?2.8‰ VPDB, compared to a range of ?1.0 to +7.8‰ for CO2 in the seep gas, indicating that CO2 from the seep gas is quantitatively not as important as 13C-depleted bicarbonate derived from methane oxidation. Methane, with a δ13C of approximately ?43‰, is oxidized and the resulting inorganic carbon precipitates as high-magnesium calcite and other carbonate minerals. This finding is supported by 13C-depleted biomarkers typically associated with anaerobic methanotrophic archaea and their bacterial syntrophic partners in the carbonates (lipid biomarker δ13C ranged from ?84 to ?25‰). The inconsistency in δ13C between the carbonates and the seeping CO2 was resolved by discovering pockets of gas trapped near the base of the sediment column with δ13C-CO2 values ranging from ?26.9 to ?11.6‰. A mechanism of carbonate formation is proposed in which carbonates form near the sediment–bedrock interface during times of sufficient sediment coverage, in which anaerobic oxidation of methane is favored. Precipitation occurs at a sufficient distance from active venting for the molecular and isotopic composition of seep gas to be masked by the generation of carbonate alkalinity from anaerobic methane oxidation. Figure
Processes modulating carbonate formation at Brian Seep (California) during times of high and low sediment burden 相似文献
404.
We studied the driving force of the Kuroshio intrusion into the South China Sea (SCS) during the winter monsoon, using satellite-tracked drifters entering the Luzon Strait (LS) through the Balintany and Babuyan Channels from the Philippine Sea. Most drifters passing through the Babuyan Channel in winter entered the interior SCS without a significant change in velocity. However, half of the drifters passing through the Balintany Channel entered the SCS at ~30 cm/s, which was faster than when they entered the LS. The other half continued moving northwestward into the Kuroshio and returned to the North Pacific. Quantitative analyses, using surface climatological wind and sea surface height anomaly (SSHa) data explained both the difference in velocity of drifters between the two channels and their acceleration through the Balintany Channel. The results suggest that the positive meridional gradient of sea surface height in the Luzon Strait, caused by the pileup of seawater driven by the Northeast monsoon, as well as Ekman flow, contribute to the Kuroshio intrusion into the SCS through the Babuyan and Balintany Channels. The former may be the main driving force. 相似文献
405.
The recent economic recession brought much university hiring to a standstill in the United States. Geography, in spite of strong prerecession growth, was no exception. Without a sense of how the academic geography job market has changed over the past decades, however, it is difficult to assess any recession-related decline or the relative strength of any recovery. This article presents an analysis of academic job postings in the field of geography from 1990 through 2011. Using data aggregated from the AAG Newsletter, which acts as an informal clearinghouse for most academic openings for geographers at four-year colleges and universities in the United States, we assess changes in the overall magnitude in numbers of academic job openings, with the particular goal of placing the recession-based paucity of openings within its broader historical context. Our results indicate that, indeed, the recession led to a very sharp decline in advertisements, but compared to previous recessions, the recovery appears to have occurred very quickly. Open-rank and temporary/non-tenure-track positions appear to have been fairly robust to the poor economic conditions, whereas assistant professor openings were particularly hard hit. 相似文献
406.
Janet M. Bradford 《新西兰海洋与淡水研究杂志》2013,47(3):287-291
The quantitative distribution of Centropages aucklandicus in summer is described. This coastal species, endemic to New Zealand, is found round the whole country except in the north. It has a northern limit coincident with the 19°c isotherm. Possible factors operating to conserve C. aucklandicus in coastal waters, temperature, salinity, food and behaviour, are discussed. 相似文献
407.
Calvin A. Whealton Jery R. Stedinger Jared D. Smith Teresa E. Jordan Franklin G. Horowitz Maria C. Richards 《International journal of geographical information science》2020,34(10):2053-2076
ABSTRACT The focus of this work is general methods for prioritization or screening of project sites based on the favorability of multiple spatial criteria. We present a threshold-based transformation of each underlying spatial favorability factor into a continuous scale with a common favorability interpretation across all criteria. We compare several methods of computing site favorability and propagating uncertainty from the data to the favorability metrics. Including uncertainty allows decision makers to determine if seeming differences among sites are significant. We address uncertainty using Taylor series approximations and analytical distributions, which are compared to computationally intensive Monte Carlo simulations. Our methods are applied to siting direct-use geothermal energy projects in the Appalachian Basin, where our knowledge about any particular site is limited, yet sufficient data exist to estimate favorability. We consider four factors that contribute to site favorability: the thermal resource described by the depth to 80°C rock, natural reservoir productivity described by rock permeability and thickness, potential for induced seismicity, and the estimated cost of surface infrastructure for heat distribution. Those factors are combined in three ways. We develop favorability uncertainty propagation and sensitivity analysis methods. All methods are general and can be applied to other multi-criteria spatial screening problems. 相似文献
408.
Structural and geochronological studies on the Liba goldfield of the West Qinling Orogen, Central China 总被引:1,自引:0,他引:1
Qingtao Zeng T. Campbell McCuaig Craig J. R. Hart Fred Jourdan Janet Muhling Leon Bagas 《Mineralium Deposita》2012,47(7):799-819
The Liba goldfield, located to the northeast of the Zhongchuan Granite in the West Qinling Orogen (WQO) of mainland China, contains the largest known gold resource of 2.8 Moz in the Zhongchuan area. Devonian metasedimentary rocks host the structurally controlled gold mineralization, which is associated with silica–sericite–chlorite–carbonate alteration. Two major styles of mineralization occurred at the goldfield, which are disseminated sediment-hosted and quartz vein hosted types. Pyrite, arsenopyrite, and arsenian pyrite are major gold carriers and gold also occurs as native gold grains and electrum spatially associated with the sulfides. Numerous felsic/intermediate dykes have a similar structural control as the mineralization, and their contacts with host rocks are recognized as favorable zones for mineralization. Detailed fieldwork in conjunction with geochronological studies has helped to define the deformation history and gold metallogenesis of the goldfield. Three major phases of deformation have been recognized in the Zhongchuan area. The first deformation (D1) event was compressional in broadly a N–S orientation, the second (D2) event was also compressional and orientated in a NE–SW direction, and the third (D3) event was post-mineralization and was associated with the emplacement of barren calcite and anhydrite veins. Compression related to D2 is the key process that controlled the distribution of igneous dykes and gold mineralization in the Liba goldfield. Both igneous and hydrothermal fluids preferentially focused along dilational jogs under local trans-extension, which took place during the late stage of D2. Precise dating with high-resolution ion microprobe (SHRIMP) U–Pb on zircon and 40Ar/39Ar on muscovite, biotite, hornblende, and plagioclase of crosscutting pre-mineralization granitic porphyry and diorite dykes have constrained the mineralization age to after ca. 227 Ma. 40Ar/39Ar analysis of minerals formed in hydrothermal alteration zones associated with gold mineralization indicates that there was a widespread ca. 216 Ma hydrothermal event that affected almost all lithologies in the area. This detailed investigation is the first study to tightly constrain the timing of gold mineralization in the WQO. The broadly overlapping timing and similar structural control of the mineralization and igneous dykes show a promising correlation, which could be potentially used to map this Late Triassic gold mineralization event in the WQO. 相似文献
409.
Janet M. Sumner 《Bulletin of Volcanology》1998,60(3):195-212
The 1986 eruption of B fissure at Izu-Oshima Volcano, Japan, produced, among other products, one andesite and two basaltic
andesite lava flows. Locally the three flows resemble vent-effused holocrystalline blocky or aa lava; however, remnant clast
outlines can be identified at most localities, indicating that the flows were spatter fed or clastogenic. The basaltic andesite
flows are interpreted to have formed by two main processes: (a) reconstitution of fountain-generated spatter around vent areas
by syn-depositional agglutination and coalescence, followed by extensional non-particulate flow, and (b) syn-eruptive collapse
of a rapidly built spatter and scoria cone by rotational slip and extensional sliding. These processes produced two morphologically
distinct lobes in both flows by: (a) earlier non-particulate flow of agglutinate and coalesced spatter, which formed a thin
lobe of rubbly aa lava (ca. 5 m thick) with characteristic open extension cracks revealing a homogeneous, holocrystalline
interior, and (b) later scoria-cone collapse, which created a larger lobe of irregular thickness (<20 m) made of large detached
blocks of scoria cone interpreted to have been rafted along on a flow of coalesced spatter. The source regions of these lava
flows are characterized by horseshoe-shaped scarps (<30 m high), with meso-blocks (ca. 30 m in diameter) of bedded scoria
at the base. One lava flow has a secondary lateral collapse zone with lower (ca. 7 m) scarps. Backward-tilted meso-blocks
are interpreted to be the product of rotational slip, and forward-tilted blocks the result of simple toppling. Squeeze-ups
of coalesced spatter along the leading edge of the meso-blocks indicate that coalescence occurred in the basal part of the
scoria cone. This low-viscosity, coalesced spatter acted as a lubricating layer along which basal failure of the scoria cone
occurred. Rotational sliding gave way to extensional translational sliding as the slide mass spread out onto the present caldera
floor. Squeeze-ups concentrated at the distal margin indicate that the extensional regime changed to one of compression, probably
as a result of cooling of the flow front. Sliding material piled up behind the slowing flow front, and coalesced spatter was
squeezed up from the interior of the flow through fractures and between rafted blocks. The andesite flow, although morphologically
similar to the other two flows, has a slightly different chemical composition which corresponds to the earliest stage of the
eruption. It is a much smaller lava flow emitted from the base of the scoria cone 2 days after the eruption had ceased. This
lava is interpreted to have been formed by post-depositional coalescence of spatter under the influence of the in-situ cooling
rate and load pressure of the deposit. Extrusion occurred through the lower part of the scoria cone, and subsequent non-particulate
flow of coalesced material produced a blocky and aa lava flow. The mechanisms of formation of the lava flows described may
be more common during explosive eruptions of mafic magma than previously envisaged.
Received: 30 May 1997 / Accepted: 19 May 1998 相似文献
410.
An archaeological geophysics investigation was conducted at the site of the Wright Brothers' 1910 hangar near Dayton, Ohio. The hangar was destroyed as part of base renovation during the buildup to World War II, and its exact location is unknown. The purpose of the investigation is to confirm the exact location of the hangar and to locate any buried artifacts from the Wright Brothers occupation of the site. Ground penetrating radar (GPR), electromagnetic, and magnetic surveys were conducted over a 68 × 100 m area, approximately centered on the suspected location of the hangar. Localized anomalies as well as areal anomalies are identified in the geophysical data. Rectangular anomalous areas are identified that are generally consistent with the suspected location of the hangar. A 1924 aerial photograph showing the hangar was digitally scanned and georeferenced to the site survey area. Two of the rectangular geophysical anomalous areas are consistent with the hangar location from the aerial photograph location. A third rectangular area, defined from GPR survey data, is immediately adjacent to the aerial photograph location. It is postulated that base engineers may have bulldozed the hangar debris onto an area adjacent to its original location and either burned it there or buried it in a trench. A prioritized exploratory program is proposed for investigating the sources of the geophysical anomalies. © 1994 John Wiley & Sons, Inc. 相似文献