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81.
82.
REE chemistry and Sm-Nd systematics of late Archean weathering profiles in the Fortescue Group, Western Australia 总被引:1,自引:0,他引:1
MacFarlane AW Danielson A Holland HD Jacobsen SB 《Geochimica et cosmochimica acta》1994,58(7):1777-1794
Two weathering profiles, each consisting of an upper, sericite-rich zone and a lower, chlorite-rich zone, are preserved between flows of the Mt. Roe Basalt in the Fortescue Group, Hamersley Basin, Western Australia. REE concentrations in samples from these two profiles, which originally developed ca 2,760 Ma, show large variations depending on stratigraphic position. LREE abundances and (La/Yb)N are greatest at depths of 3-6 m below the paleosurface of the Mt. Roe #1 profile and are somewhat lower in samples above this level. The LREEs reach concentrations 6-9 times greater than in the underlying basalt, and thus appear to have been mobilized downward in the paleosol and concentrated in its middle part. LREE concentrations in the #2 profile show a similar distribution but with a sharp increase in all REE concentrations within 50 cm of the paleosurface. The distinction between the REE profiles in the two paleosols may be related to the difference in the overlying material. The #1 paleosol is overlain by a few meters of sediments and then by basalt, whereas the #2 paleosol is directly overlain by basalt. The LREEs appear to have been mobilized both during chemical weathering of the parental basalt and during later lower-greenschist-facies metamorphism and metasomatism of the paleosols. Remobilization of the REEs during the regional metamorphism of the Fortescue Group is confirmed by a whole-rock Sm-Nd reference isochron of Mt. Roe #1 samples with an age of 2,151 +/- 360 Ma. Variable initial 143Nd/144Nd values of unweathered basalt samples which may represent the paleosol protolith prevents a confident determination of the magnitude of LREE mobility. Both the initial mobilization of the REEs during weathering and the metasomatic remobilization appear to have taken place under redox conditions where Ce was present dominantly as Ce3+, because Ce anomalies are not developed within the sericite zone samples regardless of concentration. Europium anomalies in the paleoweathering profile are somewhat variable and were probably modified by mobilization of Eu2+ at metamorphic conditions. In all samples, the HREEs appear to have been relatively immobile and correlate with Al, Ti, Cr, V, Zr, and Nb. Sm-Nd systematics and REE patterns of four unweathered basalt samples indicate derivation of the Mt. Roe Basalts from a heterogeneous and enriched source having epsilon Nd between -4.0 and -7.4. Initial 143Nd/144Nd values of these basalts are even lower than those reported by NELSON et al. (1992) for Fortescue Group basalts and indicate a substantial crustal component in the generation of Mt. Roe Basalts. 相似文献
83.
84.
A diatom-based Holocene record of human impact from a coastal environment: Tuckean Swamp, eastern Australia 总被引:1,自引:0,他引:1
Kathryn H. Taffs Luc J. Farago Hendrik Heijnis Geraldine Jacobsen 《Journal of Paleolimnology》2008,39(1):71-82
Diatom-based paleolimnological studies are being increasingly used to track anthropogenic change in estuaries. Little is known,
however, about the direction and nature of long-term environmental changes in Australian estuaries. In this study, shifts
in diatom assemblages preserved in a 210Pb and C14 AMS dated sediment core from Tuckean Swamp were analysed to determine environmental changes that had taken place as a result
of changing land-use practices. Prior to European impact, the diatom assemblage remained relatively stable and was dominated
by Actinocyclus normanii and Diploneis smithii. An increasing dominance of Cyclotella meneghiniana correlates well with changed land use activities in the catchment area and indicates an increase of freshwater influence
in the swamp’s environment. A major shift in species composition began ∼1970, Eunotia flexuosa becoming dominant. The assemblage shifts recorded at this site appear to be consistent with environmental changes triggered
by human activities such as vegetation clearance, drainage and the construction of a barrage. This study demonstrates the
use of paleolimnoology in an estuarine environment to provide pre-impact data necessary for management of the aquatic environment. 相似文献
85.
86.
87.
C. M. Holl J. R. Smyth H. M. S. Laustsen S. D. Jacobsen R. T. Downs 《Physics and Chemistry of Minerals》2000,27(7):467-473
Natural witherite (Ba0.99Sr0.01CO3) has been studied by single-crystal X-ray diffraction in the diamond anvil cell at eight pressures up to 8 GPa. At ambient pressure, cell dimensions are a?=?5.3164(12) Å, b?=?8.8921(19) Å, c?=?6.4279(16) Å, and the structure was refined in space group Pmcn to R(F)?=?0.020 from 2972 intensity data. The unit cell and atom position parameters for the orthorhombic cell were refined at pressures of 1.2, 2.0, 2.9, 3.9, 4.6, 5.5, 6.2, and 7.0 GPa. The volume-pressure data are used to calculate equation of state parameters K T0?=?50.4(12) GPa and K′?=?1.9(4). At approximately 7.2 GPa, a first-order transformation to space group P3¯1c was observed. Cell dimensions of the high-pressure phase at 7.2 GPa are a?=?5.258(6) Å, c?=?5.64(1) Å. The high pressure structure was determined and refined to R(F)?=?0.06 using 83 intensity data, of which 15 were unique. This high-pressure phase appears to be more compressible than the orthorhombic phase with an estimated initial bulk modulus (K 7.2GPa) of 10 GPa. 相似文献
88.
Thomas P. Kersten Gürcan Büyüksalh brahm Baz Karsten Jacobsen 《The Photogrammetric Record》2009,24(126):122-138
Although the Historic Peninsula of old Istanbul was added to the UNESCO World Heritage List in 1985, complete documentation of this important area has not yet been carried out. In 2006 the Istanbul Metropolitan Municipality's Historical Environment Protection Directorate initiated the "Historic Peninsula Project", which covers an area of 1500 ha and includes approximately 48 000 buildings in crowded and frequently narrow streets. BİMTAŞ, a company owned by the Municipality, immediately started the documentation of all buildings in the project area using terrestrial laser scanning. This created the challenge of building up an efficient production environment with new high-end technology to fulfil the requirements of this project in a very short timeframe of 2 years. This paper describes the entire production environment for documentation of all buildings, detailing the frequent adaptations of the process resulting from learning on the job. Although the data acquisition and mapping environment was established in the course of production, it was always essential to optimise the technical solutions in order to meet the requirements for data quality and delivery deadlines. Only 80 ha of the required 1500 ha was completed using static scanning during the first 6 months, thus requiring a change from static to mobile terrestrial laser scanning in order to accelerate the work and to conclude the scanning phase for the remaining major area within 3 months. 相似文献
89.
Transfer of zoonotic bacterial pathogens through intact soil columns was monitored in an outdoor lysimeter over 36 d. Manure spiked with Salmonella enterica serovar Senftenberg was applied to either the soil surface or injected 0.08 m into the soil to compare leaching associated with the two manure application methods. The highest concentrations of S. enterica (up to 60,000 S. enterica CFU/mL) were detected on Day 1 in the first drainage samples, with measurable but declining concentrations persisting for 10 to 36 d depending on replicate columns. The total recovery of leached S. enterica in drainage samples ranged from 0.08% to 13.8%. When comparing the two application methods, there was no statistically significant difference in the leaching concentration of S. enterica at each sampling time during the study period. In addition, comparison of enumerations by selective plating and real-time polymerase chain reaction yielded similar concentrations of S. enterica, indicating that mainly viable and culturable cells were leached from the columns. When the experiment was terminated, the fluorescent dye Acid Yellow was applied to four selected columns and the distribution of dye and size of active (dye-stained) pores were measured with a digital camera and visualization software. The profiles showed that the area covered by active pores ranged from 0.1% to 3.6%. The relatively small fraction of active pores in the soil profile was consistent with the evidence of rapid transport of S. enterica and chloride in the columns. 相似文献
90.
The size of various Phanerozoic paleoceans, determined from paleogeographic maps, provides a framework for assigningεNd measurements of primary authigenic marine minerals to individual paleoceans and for establishing theirεNd versus age curves. We report newεNd data (in the range from 80 to 750 Ma) for the largest Phanerozoic and Late Precambrian paleocean, the Pacific/Panthalassa Ocean (PPO), and limited data on some small Paleozoic paleoceans. These new data and all other published data on paleoceanεNd values are used to determine the trends through time ofεNd in seven Phanerozoic paleoceans. The variations in paleoceanεNd curves are due to changes in the rate of crustal additions and in paleoceanic geometry. From these data we can calculate a meanεNd curve and a mean Nd model age curve for Phanerozoic seawater. These curves show large variations with age and reflect the variations ofεNd in erosion products from the continents as a function of age. The high erosion rates of young, uplifted areas enhanceεNd and Nd model age variations of Phanerozoic seawater. This makes it difficult to quantitatively recover crustal addition rates from these curves; however, it makes the episodic nature of continental additions more evident. 相似文献