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321.
二维潮流数学模型的四边形等参单元法 总被引:4,自引:0,他引:4
本文在有限差分和有限元法的基础上,采用四边形等参单元,对在河海域进行了潮流数学模型计算,计算表明:该方法既能较好地拟合边界,又可减少网格划分等前期工作,所得结果与实测资料基本一致。 相似文献
322.
323.
As technical advances have dramatically increased our ability to analyze trace elements, the need for more reliable data on
the compositional dependence of trace element partitioning between minerals and melt has become increasingly important. The
late-Cretaceous Carmacks Group of south central Yukon comprises a succession of primitive high-Mg ankaramitic lavas characterized
by shoshonitic chemical affinities and containing large complexly zoned clinopyroxene phenocrysts. The compositional zonation
of the clinopyroxene phenocrysts is characterized by relatively Fe-rich (Mg# = Mg/(Mg + Fe) = 0.85), but mottled, cores surrounded by mantles of cyclically-zoned clinopyroxene whose Mg# varies repeatedly between 0.9 and 0.80. These cyclically zoned clinopyroxene mantles appear to record the repeated influx
and mixing of batches of primitive with more evolved magma in a deep sub-crustal (∼1.2 GPa) magma chamber(s). Laser ablation
ICP-MS was used to analyze the trace element variation in these zoned clinopyroxenes. The results indicate more than a threefold
variation in the absolute concentrations of Th, Zr, rare earth elements (REE), and Y within individual clinopyroxene phenocrysts,
with no apparent change in the degree of REE or high field strength element (HFSE) fractionation. The variation in absolute
abundances of trace elements correlates closely with the major element composition of the clinopyroxene, with the most enriched
clinopyroxene having the lowest Mg# and highest Al contents. The problem is that the amount of crystal fractionation required to explain the major element variation
(∼20%) in these clinopyroxene phenocrysts cannot explain the increase in the abundance of the incompatible trace elements,
which would require more than 70% crystal fractionation, if constant partition coefficients are assumed. The anomalous increase
in incompatible trace elements appears to reflect an increase in their partition coefficients with increasing AlIV in the clinopyroxene; with an increase in Al2O3 from 1.5 to 4.0 wt.% during ∼20% crystal fractionation over a temperature decrease of ∼100°C being associated with more that
a threefold increase in the partition coefficients of Th, Zr, REE, and Y. The magnitude of these increases may indicate that
the substitution of these trace elements into clinopyroxene is better modeled in some natural systems by a local charge balance
model, rather than the distributed charge model that better replicates the results of annealed experiments. These findings
indicate that the effect of Al on the partition coefficients of incompatible trace elements in clinopyroxene may be under
appreciated in natural magmatic systems and that the application of experimentally determined clinopyroxene partition coefficients
to natural systems must be done with caution. 相似文献
324.
Peter Caccetta Simon Collings Andrew Devereux Kassell Hingee Don McFarlane Anthony Traylen 《International Journal of Digital Earth》2016,9(5):457-475
This paper describes the development of a system for decimetre-scale monitoring of land-surface and land-cover in urban and peri-urban environments. We describe our methodology that comprises the application of highly automated processing and analysis methods to digital aerial photography. The approach described in this paper addresses a monitoring need by providing the ability to generate change information at a spatial resolution suitable for urban, peri-urban and coastal areas, where an increasing percentage of the worlds’ population dwells. These areas are dynamic, with many environmental issues associated with planning, service provision, resource management and allocation, as well as monitoring regulatory compliance. We present a system based on standardised data and methods, which is able to track and communicate changes in features of interest in a way that has not been previously possible. We describe the methodology and then demonstrate its feasibility by applying it to geographic areas of planning and policy relevant size (the order of tens of thousands of square kilometres). We demonstrate the approach by applying it to the problem of urban forest assessment. 相似文献
325.
Glen T. Shen Edward R. Sholkovitz Don R. Mann 《Earth and Planetary Science Letters》1983,64(3):437-444
A mixing experiment, using large volumes (100 l) of filtered (< 1 μm) freshwater and seawater end-members, was performed to simulate and investigate the chemical reactivity of239, 240Pu during estuarine mixing. An organic-rich freshwater with a relatively high concentration (0.8 dpm/100 l) of dissolved239, 240Pu was used as one end-member; Buzzards Bay seawater (dissolved239, 240Pu= 0.04dpm/100l) was the other. The results demonstrate that dissolved239, 240Pu in the freshwater undergoes extensive and rapid coagulation under simulated estuarine conditions. There is a strong correlation between the amount of coagulation of dissolved239, 240Pu, humic acids (HA), and Fe. The extent of coagulation of all three constituents increases with increasing salinity and the net extent of their removal is 53%, 57%, and 100% for Pu, HA, and Fe respectively. As has been documented for Fe in freshwater, dissolved239, 240Pu appears to be stabilized by naturally occurring humic substances to form negatively charged colloids which are then coagulated by seawater cations. The extrapolation of these experimental results to real estuaries will require additional research. 相似文献
326.
Encapsulated embryos and free-living larvae of Ilyanassa obsoleta were exposed to concentrations of No. 2 fuel oil (water-accommodated fraction, WAF) up to 1.0 ppm. Development of velum pigmentation and release of larvae from egg capsules were delayed in the presence of 1.0 ppm WAF, but exposure to the oil did not increase developmental mortality of encapsulated individuals. Individuals which were prematurely removed from egg capsules and exposed to oil directly suffered no mortality until yolk reserves were depleted and feeding on phytoplankton commenced. Feeding, free-living larvae suffer high mortality at 1.0 ppm WAF. The reduced susceptibility of encapsulated embryos to the oil stress may therefore reflect the importance of toxicant uptake by ingestion (as opposed to diffusion) rather than the degree of protection afforded by encapsulation. 相似文献
327.
New data on the U, Pu, and P distributions in less metamorphosed H-chondrites (type 3–5), coupled with literature results, permit a provisional picture to be assembled of the chemistry of these elements and for the rare earth elements in ordinary chondrites and the changes brought about by chondritic metamorphism. Preferential associations of phosphates with metals and/or sulndes in all chondrites strongly indicate an “initially” siderophile or conceivably chalcophile character for P in ordinary chondrite precursor materials with phosphate subsequently formed by oxidation. This oxidation occurred prior to or during chondritic metal-silicate fractionation. Uranium is initially concentrated in chondrule glass at ~ 100 ppb levels with phosphates (primarily merrillite) in H-3 chondrites being essentially U-free (<20 ppb). As chondrule glass devitrified during metamorphism, U migrated into phosphates reaching ~ 50 ppb in Nadiabondi (H-5) merrillite and 200–300 ppb in merrillite from equilibrated chondrites but “froze out” before total concentration in phosphates occurred. Relative 244Pu fission track densities in the outer 5 μm of olivine and pyroxene grains in contact with merrillite and with chondrule mesostasis in Bremervörde (H-3) give Pu(mesostasis)/Pu(merrillite) <0.01, implying total concentration of Pu in phosphates. Similarly, no detectable Pu (<0.1 ppb) was found in chondrule mesostasis in Tieschitz and Sharps; whereas, direct measurements of tracks in phosphates in H-3 chondrites are consistent with high (?10 ppb) Pu concentrations. Thus, a strong Pu-P correlation is indicated for ordinary chondrites. There is variable Pu/U fractionation in all chondritic phosphates reaching an extreme degree in the unequilibrated chondrites; therefore, the Pu/U ratio in phosphates appears relatively useless for relative meteorite chronology. Literature data indicate that the REE are located in chondrules in unequilibrated chondrites, most likely in glass; thus there may also be strong Pu/Nd fractionation within these meteorites. Like U, the REE migrate into phosphates during metamorphism but, unlike U, appear to be quantitatively concentrated in phosphates in equilibrated chondrites. Thus relative ages, based on Pu/Nd, may be possible for equilibrated chondrites, but the same chronological conclusions are probably obtainable from Pu concentrations in phosphates, i.e., on the Pu/P ratio. However, Pu/P chronology is possible only for ordinary chondrites; so there appears to be no universal reference element to cancel the effects of Pu chemical fractionation in all meteorites. Available data are consistent with — but certainly do not prove-that variations in Pu/P represent age differences, but if these age differences do not exist, then it is conceivable that the solar system ratio, important for cosmochronology, is still lower than the presently accepted value of 0.007. 相似文献
328.
Jane E. Denne Harold L. Yarger P. Allen Macfarlane Ralph W. Knapp Marios A. Sophocleous James R. Lucas Don W. Steeples 《Ground water》1984,22(1):56-65
Aquifers found in glacial buried valleys are a major source of good-quality ground water in northeastern Kansas. The extent and character of many of these deposits are not precisely known, so a detailed study of the buried valleys was undertaken. Test drilling, Landsat imagery, shallow-earth temperature measurements, seismic refraction, surface electrical resistivity, and gravity data were used to evaluate two sites in Nemaha and Jefferson Counties. Tonal patterns on springtime Landsat imagery and winter/summer anomalies in shallow-earth temperatures were quick and inexpensive methods for locating some glacial buried aquifers and suggested areas for more intensive field studies. Reversed seismic refraction and resistivity surveys were generally reliable indicators of the presence or absence of glacial buried valleys, with most depth determinations being within 25% of test-drilling results. The effectiveness of expensive test-hole drilling was greatly increased by integrating remote sensing, shallow-earth temperature, seismic, and resistivity techniques in the two buried valley test areas. A gravity profile allowed precise definition of the extent of one of the channels after the other techniques had been used for general information. 相似文献
329.
226Ra and other uranium-series radionuclides have been measured in a suite of marine phosphorite samples from the upwelling area off Peru/Chile by gamma-ray spectrometry and radiochemical techniques. Our results lead to the following conclusions: (1) phosphorite nodules typically show unidirectional growth at rates of 1 to 10 mm/Kyr; (2) very young samples (less than a few thousand years) contain slight excess amounts of 226Ra probably derived from pore fluids; and (3) slow but persistent leakage of 226Ra out of phosphate nodules occurs resulting in systematically lower 226Ra ages compared to 230Th ages for samples older than about twenty thousand years. Radium fluxes from these phosphate nodules appear to be 1 to 3 orders of magnitude less than those calculated for deep-sea sediments and ferromanganese nodules. 相似文献
330.
Free oscillation and body wave data are used to construct average Q models for the earth. The data set includes fundamental and overtone observations of the radial, spheroidal and toroidal modes, ScS observations and amplitudes of body waves as a function of distance. The preferred model includes a low-Q zone at both the top and the bottom of the mantle. In these regions the seismic velocities are likely to be frequency dependent in the “seismic” band. Absorption in the mantle is predominantly due to losses in shear. Compressional absorption may be important in the inner core.A grain-boundary relaxation model is proposed that explains the dominance of shear over compressional dissipation, the roughly frequency independent average values for Q and the variation of Q with depth. In the high-Q regions, the lithosphere and the midmantle (200–2000 km), Q is predicted to be frequency dependent. However, the low-Q regions of the earth, where Q is roughly frequency independent, dominate the observations of attenuation. 相似文献