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421.
422.
Phillip L. Hellman Raymond E. Smith Paul Henderson 《Contributions to Mineralogy and Petrology》1977,65(2):155-164
The effect of low grade hydrous burial metamorphism (prehnite-pumpellyite facies) upon the rare earth elements (REE) has been studied by using samples from the Cliefden Outcrop, New South Wales. The REE, together with other reputedly immobile elements, have been mobilised during the metamorphism. Although mobile, the REE have behaved remarkably coherently with little light rare earth (LREE) fractionation. This is reflected in the chondrite normalised patterns which are sub-parallel to parallel in shape. High correlations of REE with other elements can be used to predict the maximum likely variation of these elements in the studied outcrop. The high correlations do not necessarily mean that, for similarly metamorphosed terrains, crystallisation-differentiation processes have operated but may rather have resulted from strong geochemical coherence during post-crystallisation elemental redistribution. The REE do not appear to be strongly domain controlled within the Cliefden Outcrop. 相似文献
423.
Raymond A. Scheinfeld John B. Robertson Todd G. Schwendeman 《Ground Water Monitoring & Remediation》1986,6(4):49-55
A growing number of state and local governments and petroleum-related companies require the use of release detection systems for underground petroleum storage tanks. This has resulted in a confusing array of commercially available petroleum product detection devices, many of which have not been extensively field-tested. These systems, which are installed in ground water observation wells, vapor wells or U-tubes, include hydrocarbon-detecting paste, bailers, interface probes, electrical resistivity sensors, thermal-conductivity sensors, hydrocarbon-soluble devices, hydrocarbon-permeable materials and vapor detectors. This paper describes the available state-of-the-art technology for leak detection and the application for which each system is best suited. 相似文献
424.
Michel Dagbert Raymond Pertsowsky Michel David Guy Perrault 《Geochimica et cosmochimica acta》1975,39(11):1499-1504
An attempt is made to describe global variations in the geochemistry of major and minor elements within a population of nepheline syenite samples defined by mineralogical criteria.Using correspondence analysis, a new pattern recognition procedure, it is possible to define a few trends of common behaviour which reflect most of the initial dispersion.As Al and Na participate in the scattering along the two main trends, agpaicity is recorded by them. However, the traditional form of the coefficient which measures it is proved to be unsatisfactory as variations of K are not significant. 相似文献
425.
We have relocated the twenty-eight largest magnitude (4.3M
s
7.3) historical (1922–1963) earthquakes of the southeastern Caribbean. We also present new focal mechanisms for seven of these events. The relocations are based on reported ISSP andS arrival times that we analyzed using generalized linear inversion techniques. The new focal mechanisms were constrained by first motionP polarities as reported by the ISS and as picked by us where records were available, and by the polarities and ratios ofSH andsSH, andSV andsSV arrivals that we determined from seismograms. The results of the relocations are commensurate with the distribution of seismicity observed in the recent era: hypocenters are shallow and intermediate in depth (0–200 km), and the events occur almost exclusively in areas known to be currently seismic. The frequent seismic activity in the vicinity of the Paria Peninsula, Venezuela, is clearly a persistent feature of the regional earthquake pattern; intermediate depth earthquakes indicative of subduction beneath the Caribbean plate occur here and along the Lesser Antilles arc. The Grenadines seismic gap is confirmed as an area of low seismic moment release throughout the historical era. Trinidad and the eastern Gulf of Paria were also largely quiescent.The new focal mechanisms, despite being a sparse data set, give significant insight into both subduction processes along the Lesser Antilles arc and into the shallow deformation of the Caribbean-South America plate boundary zone. The largest earthquake to have occurred in this region, the 19 March 1953 event (M
m
=7.01), is a Lesser Antilles slab deformation event, and another earthquake in this region of the Lesser Antilles is probably a rarely-observed interplate thrust event. Shallow deformation in the plate boundary zone is complex and, near the Paria Penninsula, involves mixed southeastward thrusting and dextral strike-slip on east-striking faults, and secondarily, normal faulting. Bending of the subducting Atlantic-South American plate also seems to generate seisms. The rather high ratio of intraplate deformation to interplate deformation observed along the Lesser Antilles subduction zone in the more recent era seems to have been operative in the historical era as well. 相似文献
426.
An important ecological role ascribed to oysters is the transfer of materials from the water column to the benthos as they
feed on suspended particles (seston). This ecosystem service has been often touted as a major reason for many oyster restoration
efforts, but empirical characterization and quantification of seston removal rates in the field have been lacking. Changes
in chlorophyll a (chl a) concentrations in the water column were measured in May 2005 and June 2006 in South Carolina using in situ fluorometry and
laboratory analysis of pumped water samples taken upstream and downstream as water flowed over natural and constructed intertidal
oyster reefs. Both methods gave similar results overall, but with wide variability within individual reef datasets. In situ
fluorometer data logged at 10 to 30-s intervals for up to 1.3 h over eight different reefs (three natural and five constructed)
showed total removal (or uptake) expressed as % removal of chl a ranging from −9.8% to 27.9%, with a mean of 12.9%. Our data indicate that restored shellfish reefs should provide water-quality
improvements soon after construction, and the overall impact is probably determined by the size and density of the resident
filter feeder populations relative to water flow characteristics over the reef. The measured population-level chl a removal was converted to mean individual clearance rates to allow comparison with previous laboratory studies. Although direct
comparisons could not be made due to the small size of oysters on the study reefs (mean shell height, 36.1 mm), our calculated
rates (mean, 1.21 L h−1) were similar to published laboratory measured rates for oysters of this size. However, the wide variability in measured
removal by the oyster reefs suggests that individual oyster feeding rates in nature may be much more variable than in the
laboratory. The proliferation of ecosystem-level models that simulate the impacts of bivalves on water quality based only
on laboratory-feeding measurements underscores the importance of further research aimed at determining ecologically realistic
feeding rates for oysters in the field. Because in situ methods provide many replicate measurements quickly, they represent
a potentially powerful tool for quantifying the effects of oyster reefs, including all suspension-feeding taxa present, on
water quality. 相似文献
427.
Richard H. Guthrie Peter J. Deadman A. Raymond Cabrera Stephen G. Evans 《Landslides》2008,5(1):151-159
Landslide magnitude–frequency curves allow for the probabilistic characterization of regional landslide hazard. There is evidence
that landslides exhibit self-organized criticality including the tendency to follow a power law over part of the magnitude–frequency
distribution. Landslide distributions, however, also typically exhibit poor agreement with the power law at smaller sizes
in a flattening of the slope known as rollover. Understanding the basis for this difference is critical if we are to accurately
predict landslide hazard, risk or landscape denudation over large areas. One possible argument is that the magnitude–frequency
distribution is dominated by physiographic controls whereby landslides tend to a larger size, and larger landslides are landscape
limited according to a power law. We explore the physiographic argument using first a simple deterministic model and then
a cellular automata model for watersheds in coastal British Columbia. The results compare favorably to actual landslide data:
modeled landslides bifurcate at local elevation highs, deposit mass preferentially where the local slopes decrease, find routes
in confined valley or channel networks, and, when sufficiently large, overwhelm the local topography. The magnitude–frequency
distribution of both the actual landslides and the cellular automata model follow a power law for magnitudes higher than 10,000–20,000 m2 and show a flattening of the slope for smaller magnitudes. Based on the results of both models, we argue that magnitude–frequency
distributions, including both the rollover and the power law components, are a result of actual physiographic limitations
related to slope, slope distance, and the distribution of mass within landslides. The cellular automata model uses simple
empirically based rules that can be gathered for regions worldwide. 相似文献
428.
Song Fu Maha Ashour-Abdalla XiaoHua Deng Mostafa El-Alaoui Meng Zhou Robert L. Richard Raymond J. Walker ZhiGang Yuan 《中国科学:地球科学(英文版)》2014,57(10):2543-2551
We report where and how ions are accelerated in the proximity of earthward propagating dipolarization fronts(DFs) in the magnetotail during a magnetospheric substorm on February 15, 2008. Two DFs were observed by multiple THEMIS spacecraft in the near-Earth magnetotail(~?10 Re). We studied the ion dynamics associated with these DFs by comparing observed results with large scale kinetic(LSK) simulation results. The LSK simulation reproduced the sudden ion energy flux enhancement concurrent with the arrival of the DF at the satellite locations. We found that ions can be accelerated to more than 100 keV energy at the DF. These ions were initially non-adiabatically accelerated near magnetic reconnection site and then still non-adiabatically accelerated at the DF structure. 相似文献
429.
Raymond M. Caron Claire Samson Paul Straznicky Stephen Ferguson Luise Sander 《Geophysical Prospecting》2014,62(2):352-363
Carleton University and Sander Geophysics are developing an unmanned aircraft system (UAS) for aeromagnetic surveying. As an early indication of the expected performance of the unmanned aircraft system, a simulated unmanned aircraft system (sUAS) was built. The simulated unmanned aircraft system is a T‐shaped structure configured as a horizontal gradiometer with two cesium magnetometers spaced 4.67 m apart, which is the same sensor geometry as planned for the unmanned aircraft system. The simulated unmanned aircraft system is flown suspended beneath a helicopter. An 8.5 km2 area in the Central Metasedimentary Belt of the Grenville Province, near Plevna, Ontario, Canada, was surveyed with the simulated unmanned aircraft system suspended 50 m above ground. The survey site was chosen on the basis of its complex geological structure. The total magnetic intensity (TMI) data recorded were compared to that obtained during a conventional fixed‐wing survey and a ground survey. Transverse magneto‐gradiometric data were also recorded by the simulated unmanned aircraft system. The simulated unmanned aircraft system total magnetic intensity data have a higher resolution than the conventional fixed‐wing data and were found to have a similar resolution to that of the ground survey data. The advantages of surveying with the simulated unmanned aircraft system were: (1) the acquisition of a detailed data set free of gaps in coverage at a low altitude above the terrain and (2) substantial saving of time and effort. In the survey site, the 4.67 m simulated unmanned aircraft system gradiometer measured the transverse magnetic gradient reliably up to an altitude of 150 m above ground. 相似文献