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111.
Oxidation state of the lithospheric mantle beneath Diavik diamond mine, central Slave craton, NWT, Canada 总被引:1,自引:0,他引:1
Steven Creighton Thomas Stachel Dave Eichenberg Robert W. Luth 《Contributions to Mineralogy and Petrology》2010,159(5):645-657
Oxygen fugacity (fO2) conditions were determined for 29 peridotite xenoliths from the A154-North and A154-South kimberlites of the Diavik diamond
mine using the newly developed flank method modified specifically for measuring Fe3+ in mantle-derived pyropic garnets. The results indicate that the garnet-bearing lithospheric mantle beneath the central Slave
craton is vertically layered with respect to oxidation state. The shallow (<140 km), “ultra-depleted” layer is the most oxidized
section of garnet-bearing subcratonic mantle thus far measured, up to one log unit more oxidizing relative to the FMQ buffer
[Δlog fO2 (FMQ) + 1]. The lower, more fertile layer has fO2 conditions that extend down to Δlog fO2 (FMQ) − 3.8, consistent with xenolith suites from other localities worldwide. Based on trace element concentrations in garnets,
two distinct metasomatic events affected the mantle lithosphere at Diavik. An oxidized fluid imparted sinusoidal chondrite-normalized
REE patterns on garnets throughout the entire depth range sampled. In contrast, a reducing melt metasomatic event affected
only the lower portion of the lithospheric mantle. The fO2 state of the Diavik mantle sample suggests that diamond formation occurred by reduction of carbonate by fluids arising from
beneath the lithosphere. 相似文献
112.
Hugh Davies Paul Weber Phil Lindsay Dave Craw Barrie Peake James Pope 《Applied Geochemistry》2011,26(12):2121-2133
The Mangatini Stream drains a coal mining area in the mountains of northwestern South Island of New Zealand. Abundant rainfall on pyritic rocks yields acid mine drainage (AMD) to the stream, which flows through a steep gorge at discharges that rapidly increase from <1 to >100 m3/s during frequent rain events. The AMD is treated with finely ground limestone, which is discharged as a slurry at a point in the middle of the gorge. The limestone slurry mixes and reacts with the AMD during flow ∼4 km downstream over ∼12 h. Neutralisation reactions increase stream pH from near 3 (untreated Mangatini Stream water impacted by AMD) to 5–6 in the first 250 m downstream, although mixing is commonly incomplete in this zone. Large stream discharge volumes in rain events dilute the neutralising material input, thus driving the pH back towards 4 downstream of treatment. More complete neutralisation is achieved 4 km downstream, even in major rain events, and pH can rise to >7. Partial neutralisation is sufficient to remove most of the dissolved Fe(III) (typically ∼30 mg/L) from the Mangatini Stream in the first 10 m, and remaining dissolved Fe is essentially all Fe(II), which decreases over time as it oxidises and precipitates. Dissolved Al in the Mangatini Stream (typically ∼50 mg/L) decreases steadily downstream over ∼100 m in the limestone mixing zone. Precipitated Fe and Al form amorphous oxyhydroxides that are transported as suspended solids and deposited on the stream bed with excess limestone in zones of low flow velocity. Dissolved Zn is removed from solution by adsorption to Fe oxyhydroxide when pH reaches ∼5, but dissolved Ni remains in solution despite the neutralisation process. Gypsum precipitation occurs throughout the limestone mixing zone, resulting in at least 30% decrease in dissolved . Minor ettringite forms in the first 100 m, but then probably redissolves. The limestone dosing system is an effective method of neutralising the effects of AMD and removing most dissolved metals in a steep mountain stream with frequent rain events where this dynamic environment places many constraints on treatment options. 相似文献
113.
Place Perception and Social Interaction on an Exurban Landscape in Central Colorado* 总被引:1,自引:0,他引:1
Soren C. Larsen Curt Sorenson Dave McDermott Joshua Long Chris Post 《The Professional geographer》2007,59(4):421-433
An assumption commonly made in research on exurbanization is that the subdivision of land ownership necessarily creates a socially divisive landscape devoid of shared place perceptions and concerns. This article presents the results of an ethnography project undertaken in a former Colorado ranching valley that is currently exurbanizing. The study revealed not only the emergence of social networks and groups among new residents, but also the presence of distinct themes in place perception and assessment within these assemblages. In particular, the results indicated that concerns about natural hazards and environmental limitations have motivated new residents to interact with one another. 相似文献
114.
115.
Stephen Serjeant Steve Rawlings Stephen J. Maddox Joanne C. Baker Dave Clements Mark Lacy & Per B. Lilje 《Monthly notices of the Royal Astronomical Society》1998,294(3):494-504
Using complete samples of steep-spectrum quasars, we present evidence for a correlation between radio and optical luminosity which is not caused by selection effects, nor caused by an orientation dependence (such as relativistic beaming), nor a by-product of cosmic evolution. We argue that this rules out models of jet formation in which there are no parameters in common with the production of the optical continuum. This is arguably the most direct evidence to date for a close link between accretion on to a black hole and the fuelling of relativistic jets. The correlation also provides a natural explanation for the presence of aligned optical/radio structures in only the most radio-luminous high-redshift galaxies. 相似文献
116.
Tony Waltham 《Geology Today》2005,21(1):22-26
The tragic scenes of human suffering in the wake of the Asian tsunami in late December 2004 have thrown into sharp relief the Earth's destructive power (Fig. 1 ). Caused by a tectonic event off the coast of Sumatra, it could be described as a very large earthquake, an unusual tsunami and a massive disaster. Or, with a longer view, it could be considered a normal feature of a convergent plate boundary. Both views are correct.
117.
Rajmal Jain Hemant Dave A. B. Shah N. M. Vadher Vishal M. Shah G. P. Ubale K. S. B. Manian Chirag M. Solanki K. J. Shah Sumit Kumar S. L. Kayasth V. D. Patel Jayshree J. Trivedi M. R. Deshpande 《Solar physics》2005,227(1):89-122
The first space-borne solar astronomy experiment of India, namely Solar X-ray Spectrometer (SOXS), was successfully launched on 08 May 2003 on board geostationary satellite GSAT-2 of India. The SOXS is composed of two independent payloads, viz. SOXS Low-Energy Detector (SLD) Payload and SOXS High-Energy Detector (SHD) Payload. The SOXS aims to study the full-disk integrated X-ray emission in the energy range from 4 keV to 10 MeV. In this paper we present the first report on the SLD instrumentation and its in-orbit performance. The SLD payload was designed and developed at the Physical Research Laboratory in collaboration with various centers of Indian Space Research Organisation (ISRO). The basic scientific aim of the SLD payload is to study solar flares in the energy range from 4 to 60 keV with high spectral and temporal resolution. To meet these requirements, the SLD payload employs state-of-the-art solid state detectors, the first time for a solar astronomy experiment, viz. Si PIN (4 –25 keV), and cadmium–zinc–telluride (4 –60 keV). With their superb high-energy resolution characteristics, SLD can observe iron and iron–nickel complex lines that are visible only during solar flares. In view of its 3.4 FOV, the detector package is mounted on a Sun Aspect System, for the first time, to get uninterrupted observations in a geostationary orbit. The SLD payload configuration, its in-flight operation, and the response of the detectors are presented. We also present the first observations of solar flares made by the SLD payload and briefly describe their temporal and spectral mode results. 相似文献
118.
B. V. Jackson A. Buffington P. P. Hick R. C. Altrock S. Figueroa P. E. Holladay J. C. Johnston S. W. Kahler J. B. Mozer S. Price R. R. Radick R. Sagalyn D. Sinclair G. M. Simnett C. J. Eyles M. P. Cooke S. J. Tappin T. Kuchar D. Mizuno D. F. Webb P. A. Anderson S. L. Keil R. E. Gold N. R. Waltham 《Solar physics》2004,225(1):177-207
We have launched into near-Earth orbit a solar mass-ejection imager (SMEI) that is capable of measuring sunlight Thomson-scattered from heliospheric electrons from elongations to as close as 18 to greater than 90 from the Sun. SMEI is designed to observe time-varying heliospheric brightness of objects such as coronal mass ejections, co-rotating structures and shock waves. The instrument evolved from the heliospheric imaging capability demonstrated by the zodiacal light photometers of the Helios spacecraft. A near-Earth imager can provide up to three days warning of the arrival of a mass ejection from the Sun. In combination with other imaging instruments in deep space, or alone by making some simple assumptions about the outward flow of the solar wind, SMEI can provide a three-dimensional reconstruction of the surrounding heliospheric density structures. 相似文献
119.
The Yaoan vein-type gold deposit is located in the Ailaoshan-Jinshajiang alkaline intrusive belt, Yunnan Province, China, and is associated both in time and space with 33.5±1.0-Ma-old alkaline intrusions. The gold mineralization is associated with potassic wall-rock alteration. The REE distribution patterns of secondary K-feldspar are generally similar to those of the igneous perthite but with about seven times higher total REE abundances. The alteration is ascribed to a high-REE magmatic fluid derived from the Yaoan alkaline intrusive suite. The hydrothermal Yaoan gold deposit formed during two gold-bearing stages, i.e. a sulfide (pyrite) stage and a sulfide-oxide stage (pyrite-specularite). The REE abundance of early stage I pyrite is relatively high with strong enrichment in LREE, (La/Yb)n of 40–290, generally positive Eu anomalies (Eu/Eu*=0.86–1.55), and REE patterns very similar to those of secondary feldspar. In contrast, the later stage II pyrite has much lower REE concentrations and lower (La/Yb)n of 5.5–11.8, Eu/Eu* of 0.49–0.76, and flat chondrite-normalized spidergram patterns. The stage I pyrite has 34S in the range of –2.2 to +3.2, and overlaps with regionally distributed pyrite in least-altered syenite porphyry. In contrast, stage II pyrite has much higher 34S values between +7.8 and +16.5. Carbon isotope data for four samples from stage II revealed 13C (PDB) values between –6 and –8. These stable isotope and REE data suggest that magmatic fluids of the alkaline intrusions caused both potassic alteration and stage I sulfide mineralization. The system evolved from stage I to stage II mineralization by influx of meteoric fluids with relatively heavier sulfur, although calcite carbon isotope data suggest that the CO2 remained dominantly of magmatic origin.Editorial handling: B. Lehmann 相似文献
120.