全文获取类型
收费全文 | 469篇 |
免费 | 15篇 |
国内免费 | 9篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 25篇 |
地球物理 | 95篇 |
地质学 | 145篇 |
海洋学 | 119篇 |
天文学 | 70篇 |
综合类 | 14篇 |
自然地理 | 22篇 |
出版年
2022年 | 3篇 |
2021年 | 6篇 |
2020年 | 15篇 |
2019年 | 5篇 |
2018年 | 8篇 |
2017年 | 15篇 |
2016年 | 8篇 |
2015年 | 7篇 |
2014年 | 19篇 |
2013年 | 22篇 |
2012年 | 18篇 |
2011年 | 17篇 |
2010年 | 14篇 |
2009年 | 25篇 |
2008年 | 29篇 |
2007年 | 17篇 |
2006年 | 23篇 |
2005年 | 29篇 |
2004年 | 13篇 |
2003年 | 14篇 |
2002年 | 16篇 |
2001年 | 6篇 |
2000年 | 17篇 |
1999年 | 13篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 8篇 |
1977年 | 2篇 |
1976年 | 5篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1971年 | 3篇 |
排序方式: 共有493条查询结果,搜索用时 390 毫秒
471.
The relationship between hard X-ray spectra and energetic electron spectra in solar X-ray bursts is investigated, and a simplified cross-section for bremsstrahlung which is applicable to the region of mildly relativistic energies is proposed. Using the proposed cross-section, we solve an integral equation to obtain the electron energy spectrum. The validity of the proposed cross-section is checked by comparing the spectrum calculated by the exact Bethe-Heitler formula. A good agreement between two calculated spectra is obtained up to 10 MeV energy with an accuracy of 20 %. 相似文献
472.
Double-planed deep seismic zone and upper-mantle structure in the Northeastern Japan Arc 总被引:6,自引:0,他引:6
Summary. The ScSp wave converted from the ScS wave at the boundary between the descending lithospheric slab and the mantle above it was clearly observed from a nearby deep earthquake with magnitude 7.7 at some stations of the seismic network of Tohoku University which covers the Tohoku District, the northeastern part of Honshu, Japan. By applying the three-dimensional seismic-ray tracing method, the location of this boundary was determined from the difference in arrival time between the ScS and ScSp waves. The result shows that the upper boundary of the descending slab lies exactly on the upper plane of the double-planed deep seismic zone found in the Northeastern Japan Arc.
There is an additional evidence that the boundary is located on the upper plane of the double-planed deep seismic zone. The hypocentre distribution of intermediate-depth earthquakes located by the small-scale seismic-array observation is extremely different from that obtained by the relatively large-scale seismic network. The discrepancy in the distribution of hypocentres of the same earthquake independently located is well explained by the inclined lithospheric slab model derived from the difference in arrival time between the ScS and ScSp waves.
The earthquakes with reverse faulting or with down-dip compressional stresses occur at the upper boundary of the descending slab. Within the descending slab, the earthquakes with down-dip extensional stresses also occur in a very narrow zone from 30 to 40 km below the dipping boundary in the depth range from 50 to about 200 km, and these shocks form the lower plane of the double-planed deep seismic zone. 相似文献
There is an additional evidence that the boundary is located on the upper plane of the double-planed deep seismic zone. The hypocentre distribution of intermediate-depth earthquakes located by the small-scale seismic-array observation is extremely different from that obtained by the relatively large-scale seismic network. The discrepancy in the distribution of hypocentres of the same earthquake independently located is well explained by the inclined lithospheric slab model derived from the difference in arrival time between the ScS and ScSp waves.
The earthquakes with reverse faulting or with down-dip compressional stresses occur at the upper boundary of the descending slab. Within the descending slab, the earthquakes with down-dip extensional stresses also occur in a very narrow zone from 30 to 40 km below the dipping boundary in the depth range from 50 to about 200 km, and these shocks form the lower plane of the double-planed deep seismic zone. 相似文献
473.
474.
Akio Suzuki Eiji Ohtani Hidenori Terasaki Ken-ichi Funakoshi 《Physics and Chemistry of Minerals》2005,32(2):140-145
In situ X-ray viscometry of the silicate melts was carried out at high pressure and at high temperature. The viscosity of the silicate melts in the diopside(Di)–jadeite(Jd) system was determined in the pressure range from 1.88 GPa to 7.9 GPa and in the temperature range from 2,003 K to 2,173 K. The viscosity of the Di 25%–Jd 75% melt decreases continuously to 5.0 GPa, whereas the viscosity of the Di 50%–Jd 50% melt increases over 3.5 GPa. The viscosity of the Di50%–Jd 50% melt reaches a minimum around 3.5 GPa. Since the amounts of silicon in the two melts are the same, the difference in the pressure dependence of the viscosity may be controlled by another network-forming element, i.e., aluminum. The difference in the pressure dependence of the viscosities in the melts with two intermediate compositions in the Di–Jd system is estimated to be due to the difference in the melt structures at high pressures and high temperatures. 相似文献
475.
Abstract A Middle Pleistocene widespread tephra referred to here as Hakkoda–Kokumoto Tephra (Hkd–Ku) has been newly recognized. Hkd–Ku, derived from the Hakkoda Caldera located in northernmost Honshu Is. of northeast Japan, covers much of Honshu Is. At the type locality in the proximal area, Hkd–Ku comprises Plinian pumice deposits and an immediately overlying ignimbrite. The fine vitric ash nature of the distal ash‐fall deposits of Hkd–Ku suggests that they are coignimbrite ash‐fall deposits. Hkd–Ku was identified using a combination of refractive indices and chemical compositions of major, trace and rare earth elements of glass shards, heavy mineral content, refractive indices of orthopyroxene and paleomagnetic polarity. On the basis of these properties, Hkd–Ku was identified in Oga and Boso Peninsulas and Osaka Plain, 830 km southwest of the source. Stratigraphic positions in Boso Peninsula and Osaka Plain within marine sediments that have a reliable chronology based on oxygen‐isotope, and litho‐, bio‐, magneto‐ and tephrostratigraphy indicate that the age of Hkd–Ku is ca 760 ka, positioned in the transition between marine oxygen‐isotope stages 19.1 and 18.4. The widespread occurrence of Hkd–Ku providing a tie line between many different Pleistocene sections over a distance of 800 km is a key marker horizon in the early part of the Middle Pleistocene. This tephra gives a time control point of ca 760 ka to marine sediments in the Oga Peninsula – where no datum plane exists between the Brunhes–Matuyama chron boundary and oxygen‐isotope stage 12 – and to the volcanostratigraphy of the Hakkoda Caldera. The distribution of Hkd–Ku showing emplacement of coignimbrite ash‐fall deposits in the area 830 km southwest of the source emphasizes the upwind transport direction, relative to the prevailing westerly winds, typical of other coignimbrite ash‐fall deposits in the Japanese islands. 相似文献
476.
Monika Agnieszka Kusiak Artur Kdzior Mariusz Paszkowski Kazuhiro Suzuki Ignacio Gonzlez-lvarez Bolesaw Wajsprych Marek Doktor 《Lithos》2006,88(1-4):56-71
This paper reports the results of CHIME (chemical Th–U–Pb isochron method) dating of detrital monazites from Carboniferous sandstones in the Upper Silesia Coal Basin (USCB). A total of 4739 spots on 863 monazite grains were analyzed from samples of sandstone derived from six stratigraphic units in the sedimentary sequence. Age distributions were identified in detrital monazites from the USCB sequence and correlated with specific dated domains in potential source areas. Most monazites in all samples yielded ca. 300–320 Ma (Variscan) ages; however, eo-Variscan, Caledonian and Cadomian ages were also obtained. The predominant ages are comparable to reported ages of certain tectonostratigraphic domains in the polyorogenic Bohemian Massif (BM), which suggests that various crystalline lithologies in the BM were the dominant sources of USCB sediments. 相似文献
477.
The chemical Th–U total Pb isochron method (CHIME) of dating was carried out on accessory minerals in samples from the Okcheon metamorphic belt in Korea. Dated minerals include xenotime and monazite with overgrown mantles in a granitic gneiss clast from the Hwanggangri Formation, metamorphic allanite in garnet-bearing muscovite–chlorite schist of the Munjuri Formation, and polycrase and monazite in post-tectonic granite from the Hwanggangri area. Overgrowth of mantles took place at 369 ± 10 Ma on c. 1750 Ma cores of xenotime and monazite in the granitic gneiss. Allanite, occurring in textural equilibrium with peak metamorphic minerals, yields a CHIME age of 246 ± 15 Ma that is discriminably older than the polycrase (170 ± 6 Ma) and monazite (170 ± 3 Ma) ages of the post-tectonic granite. These chronological data suggest that some of the metasedimentary rocks in the belt formed through a single stage of metamorphism at c. 250 Ma from post-370 Ma sediments. Late Permian age signatures have also been reported from the Precambrian Gyeonggi and Yeongnam massifs that border the Okcheon metamorphic belt, and indicate that parts of the basement massifs and the metamorphic belt were affected by the same regional metamorphic event. 相似文献
478.
A method for the determination of major, minor and trace elements in silicate samples by ICP‐QMS and ICP‐SFMS applying isotope dilution‐internal standardisation (ID‐IS) and multi‐stage internal standardisation has been developed. Samples with an enriched isotope of 149Sm (spike) were decomposed by a HF/HCIO4 mixture and stepwise drying and finally diluted. In ID‐IS for trace element analyses by Q‐pole type ICP‐MS (ICP‐QMS), the Sm concentration was determined by ID, while other trace elements (Li, Be, Rb, Sr, Y, In, Cs, Ba, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Tl, Pb, Bi, Th and U) were determined using the 149Sm intensity as an internal standard. Major and minor elements were determined by multi‐stage internal standardisation, with Na, Mg, Al, P, Ca, V, Mn, Fe and Co measured by sector magnetic field type ICP‐MS (ICP‐SFMS) at middle resolution (MR; M/AM =~ 3000) using Sr determined by ICP‐QMS in the sample as the internal standard. Potassium, Sc, Ni, Cu, Zn and Ga were measured at high resolution (HR; M/ΔM ~ 7500) using the Sr concentration obtained by ICP‐QMS or the Mn concentration obtained by ICP‐SFMS at MR as internal standard. The merit of ID‐IS is that accurate dilution of the sample is not required. Matrix effects on elemental ratios down to a dilution factor (DF) of 600 were not observed in either types of mass spectrometry. Pseudo‐flow injection (FI), where transient signals were integrated, was used in ICP‐QMS, while conventional continuous sample introduction was used in ICP‐SFMS, resulting in total required sample solutions of 0.026 ml and 0.08 ml, respectively. Detection limits were low enough to determine these elements in depleted ultramafic rocks, and typical reproducibilities for basalts were 3% (Li‐Be), 1% (Rb‐U), 5% (In, Tl and Bi), 7% (Sc‐Ga) and 3% (major elements). Carbonaceous chondrites including Orgueil (Cll), Murchison (CM2) and Allende (CV3), as well as reference materials, JB‐1, ‐2, ‐3, JA‐1, ‐2, ‐3 and JP‐1 (GSJ), BHVO‐1, AGV‐1, PCC‐1 and DTS‐1 (USGS), were analysed to show the applicability of this method. Une méthode permettant la détermination des éléments majeurs, mineurs et en trace dans les echantillons silicates par ICP‐QMS et ICP‐SFMS a été développée. Elle combine la standardisation interne par dilution isotopique (ID‐IS) et la standardisation interne en deux étapes. Les échantillons, auxquels est ajouté un spike enrichi en 149 Sm, sont décomposés par une mixture HF/HCIO4′ séchés progressivement puis dilués. Dans la phase de standardisation interne par dilution isotopique avec un ICP‐MS à quadrupôle (ICP‐QMS), la concentration en Sm est déterminée par dilution isotopique tandis que les autres éléments en trace (Li, Be, Rb, Sr, Y, In, Cs, Ba, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Tl, Pb, Bi, Th et U) sont déterminés en utilisant le signal de 149 Sm comme standard interne. Les éléments majeurs et mineurs sont déterminés par standardisation interne par étapes, avec Na, Mg, Al, P, Ca, V, Mn, Fe et Co mesurés par ICP‐MS à secteur magnétique (ICP‐SFMS) en résolution intermédiaire (MR; M/ΔM =~ 3000 en utilisant Sr, mesuré par ICP‐QMS comme standard interne. Les éléments K, Sc, Ni, Cu, Zn et Ga sont mesurés en Haute Résolution (M/ΔM ~ 7500) en utilisant comme standard interne, soit la concentration en Sr obtenue par ICP‐QMS soit la concentration en Mn obtenue par ICP‐SFMS en résolution moyenne. La technique de ID‐IS a l'avantage de ne pas nécessiter la connaissance exacte du facteur de dilution de l'Schantillon. Aucun effet de matrice sur la mesure de rapports élémentaires n'a été observé sur l'un ou l'autre des spectromètres de masse, ceci jusqu'à un facteur de dilution (DF) de 600. Les analyses par ICP‐QMS ont été effectuées par pseudo injection de flux (Fl) et intégration d'un signal transitoire tandis que les analyses par ICP‐SFMS l'ont été avec un système conventionnel d'introduction. Le volume total de solution d'échantillon nécessaire etait de 0.026 ml et 0.08 ml respectivement. Les limites de détection étaient suffisamment basses pour permettre la détermination de ces éléments dans des roches ultrabasiques et les reproductibilités pour les basaltes étaient de l'ordre de 3% (Li‐Be), 1 % (Rb‐U), 5% (In, Tl et Bi), 7% (Sc‐Ga) et 3% (tous les éléments majeurs). Des chondrites carbonées dont Orgueil (Cll), Murchison (CM2) et Allende (CV3) ainsi que des matériaux de référence JB‐1, ‐2, ‐3, JA‐1, ‐2, ‐3 et JP‐1 (GSJ), BHVO‐1, AGV‐1, PCC‐1 et DTS (USGS) ont été analysés pour démontrer l'applicabilité de la méthode. 相似文献
479.
Petrology and CHIME geochronology of Pan-African high K and Sr/Y granitoids in the Nkambe area, Cameroon 总被引:1,自引:1,他引:0
The Central African Belt in the Nkambe area, northwestern Cameroon represents a collisional zone between the Saharan metacraton and the Congo craton during the Pan-African orogeny, and exposes a variety of granitoids including foliated and massive biotite monzogranites in syn- and post-kinematic settings. Foliated and massive biotite monzogranites have almost identical high-K calc-alkaline compositions, with 73–67 wt.% SiO2, 17–13 wt.% Al2O3, 2.1–0.9 wt.% CaO, 4.4–2.7 wt.% Na2O and 6.3–4.4 wt.% K2O. High concentrations of Rb (264–96 ppm), Sr (976–117 ppm), Ba (3680–490 ppm) and Zr (494–99 ppm), with low concentrations of Y (mostly< 20 ppm with a range 54–6) and Nb (up to 24 ppm) suggest that the monzogranites intruded in collisional and post-collisional settings. The Sr/Y ratio ranges from 25 to 89. K, Rb and Ba resided in a single major phase such as K-feldspar in the source. Garnet was present in the source and remained as restite at the site of magma generation. This high K2O and Sr/Y granitic magma was generated by partial melting of a granitic protolith under high-pressure and H2O undersaturated conditions where garnet coexists with K-feldspar, albitic plagioclase. CHIME (chemical Th–U-total Pb isochron method) dating of zircon yields ages of 569 ± 12–558 ± 24 Ma for the foliated biotite monzogranite and 533 ± 12–524 ± 28 Ma for the massive biotite monzogranite indicating that the collision forming the Central African Belt continued in to Ediacaran (ca 560 Ma). 相似文献
480.
Contrasting ages between isotopic chronometers in granulites: monazite dating and metamorphism in the Higo Complex, Japan 总被引:1,自引:1,他引:0
The Higo Complex of west-central Kyushu, western Japan is a 25 km long body of metasedimentary and metabasic lithologies that increase in metamorphic grade from schist in the north to migmatitic granulite in the south, where granitoids are emplaced along the southern margin. The timing of granulite metamorphism has been extensively investigated and debated. Previously published Sm–Nd mineral isochrons for garnet-bearing metapelite yielded ca.220–280 Ma ages, suggesting high-grade equilibration older than the lower grade schist to the north, which yielded ca.180 Ma K–Ar muscovite ages. Ion and electron microprobe analyses on zircon have yielded detrital grains with rim ages of ca.250 Ma and ca.110 Ma. Electron microprobe ages from monazite and xenotime are consistently 110–130 Ma. Two models have been proposed: 1) high-grade metamorphism and tectonism at ca.115 Ma, with older ages attributed to inheritance; and 2) high-grade metamorphism at ca.250 Ma, with resetting of isotopic systems by contact metamorphism at ca.105 Ma during the intrusion of granodiorite. These models are evaluated through petrographic investigation and electron microprobe Th–U–total Pb dating of monazite in metapelitic migmatites and associated lithologies. In-situ investigation of monazite reveals growth and dissolution features associated with prograde and retrograde stages of progressive metamorphism and deformation. Monazite Th–U–Pb isochrons from metapelite, diatexite and late-deformational felsic dykes consistently yield ca.110–120 Ma ages. Earlier and later stages of monazite growth cannot be temporally resolved. The preservation of petrogenetic relationships, coupled with the low diffusion rate of Pb at < 900 °C in monazite, is strong evidence for timing high-temperature metamorphism and deformation at ca.115 Ma. Older ages from a variety of chronometers are attributed to isotopic disequilibrium between mineral phases and the preservation of inherited and detrital age components. Tentative support is given to tectonic models that correlate the Higo terrane with exotic terranes between the Inner and Outer tectonic Zones of southwest Japan, possibly derived from the active continental margin of the South China Block. These terranes were dismembered and translated northeastwards by transcurrent shearing and faulting from the beginning to the end of the Cretaceous Period. 相似文献