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51.
Monounsaturated, monoaromatic and polyaromatic hydrocarbons generated by artificial thermal alteration of young marine (Tanner basin, offshore California) kerogen were studied by computerized GC-MS. Their relative amounts changed with temperature (150–410°C) and time (5–120 hr) of heating as follows: Monounsaturates → Monoaromatics → Polyaromatics. Distribution of alkyl homologs of phenanthrene also changed with increasing degree of thermal alteration. These results are in agreement with those observed for crude oils and shales. 相似文献
52.
Hiroshi Nagasawa Kazuo Yamakoshi Tadashi Shimamura 《Geochimica et cosmochimica acta》1979,43(2):267-272
The possible existence of meteoritic spherules was investigated among several silicate spherules separated from oceanic sediments and analyzed by means of INAA (instrumental neutron activation analysis).A 0.72 mg glassy spherule was found to have uniform enrichment of 4 ~ 5 for the refractory REE (rare earth elements) and Sc with substantial depletion of Ce relative to chondritic abundances. This implies that this spherule is meteoritic in origin and that the enrichment of refractory elements was established by high temperature heating in a high O/H environment, possibly at the time of entering the Earth's atmosphere.The other three analyzed spherules showed major and trace element abundances that are consistent with an origin in the oceanic environment. 相似文献
53.
Principal fault zone width and permeability of the active Neodani fault, Nobi fault system, Southwest Japan 总被引:2,自引:0,他引:2
A. Tsutsumi S. Nishino K. Mizoguchi T. Hirose S. Uehara K. Sato W. Tanikawa T. Shimamoto 《Tectonophysics》2004,379(1-4):93-108
The internal structure and permeability of the Neodani fault, which was last activated at the time of the 1891 Nobi earthquake (M8.0), were examined through field survey and experiments. A new exposure of the fault at a road construction site reveals a highly localized feature of the past fault deformation within a narrow fault core zone. The fault of the area consists of three zone units towards the fault core: (a) protolith rocks; (b) 15 to 30 m of fault breccia, and (c) 200 mm green to black fault gouge. Within the fault breccia zone, cataclastic foliation oblique to the fault has developed in a fine-grained 2-m-wide zone adjacent to the fault. Foliation is defined by subparallel alignment of intact lozenge shaped clasts, or by elongated aggregates of fine-grained chert fragments. The mean angle of 20°, between the foliation and the fault plane suggests that the foliated breccia accommodated a shear strain of γ<5 assuming simple shear for the rotation of the cataclastic foliation. Previous trench surveys have revealed that the fault has undergone at least 70 m of fault displacement within the last 20,000 years in this locality. The observed fault geometry suggests that past fault displacements have been localized into the 200-mm-wide gouge zone. Gas permeability analysis of the gouges gives low values of the order of 10−20 m2. Water permeability as low as 10−20 m2 is therefore expected for the fault gouge zone, which is two orders of magnitude lower than the critical permeability suggested for a fault to cause thermal pressurization during a fault slip. 相似文献
54.
Keiichi Sasaki Akio Omura Kazuo Murakami Natsume Sagawa Toru Nakamori 《Quaternary International》2004,120(1):51
Coral reef terraces are one of the best recorders of relative sea-level changes during the last glacial cycle. Thus far, knowledge of relative sea-level record based on coral reefs during the marine Oxygen Isotope Stage (OIS) 3 has been limited to studies of the Huon Peninsula, Papua New Guinea. High-precision a α-spectrometric 230Th/234U dating demonstrated an offlapping sequence of five coral reef complexes, ages of which are 66, 64, 62, 55 and 52 ka, in the northern part of Kikai Island, central Ryukyus of Japan. Interstadial reefs, characterized by deepening-upward sequences of coral assemblages, recorded three hemicycles from transgression to highstand at 52, 62, and 66 ka, during which these reefs were drowned. These highstands in the relative sea-level record can be correlated with the eustatic record reconstructed from the Huon reef terraces and with the interstadials 14, 18, and 19 of the GISP 2 oxygen isotope record. This consistency confirms the Huon sea-level record of OIS 3 and implies that the eustatic sea level responded to the millennial-scale climate changes even during the glacial period of OIS 4. 相似文献
55.
The influence of intense rainfall on the activity of large-scale crystalline schist landslides in Shikoku Island, Japan 总被引:4,自引:3,他引:4
Yong Hong Hiromasa Hiura Kazuo Shino Kyoji Sassa Akira Suemine Hiroshi Fukuoka Gonghui Wang 《Landslides》2005,2(2):97-105
Many large landslides in the crystalline schist region of Shikoku Island, Japan, are susceptible to intense rainfall. Through the use of on-site monitoring systems, the activity of landslides and their meteorological triggers can be assessed. Continuous high-intensity rainfall was found to play a key role in provoking landslide movement. This paper investigates the influence of intense rainfall on the activity of crystalline schist landslides by examining rainfall and displacement of four typical landslides. By defining and calculating the effective rainfall and the relative landslide displacement, the relationship between intense rainfall and rainfall-induced landslide movement was analysed. Results indicate that the intense rainfall-induced landslide movement can be correlated with the effective rainfall. From these results, two rainfall thresholds were identified for the landslide risk management of Shikoku Island. 相似文献
56.
Fluid inclusion and stable isotope (O, H, C, and S) constraints on the genesis of the Serrinha gold deposit, Gurupi Belt, northern Brazil 总被引:1,自引:0,他引:1
Evandro L. Klein Chris Harris Christophe Renac André Giret Candido A. V. Moura Kazuo Fuzikawa 《Mineralium Deposita》2006,41(2):160-178
The Serrinha gold deposit of the Gurupi Belt, northern Brazil, belongs to the class of orogenic gold deposits. The deposit is hosted in highly strained graphitic schist belonging to a Paleoproterozoic (∼2,160 Ma) metavolcano-sedimentary sequence. The ore-zones are up to 11 m thick, parallel to the regional NW–SE schistosity, and characterized by quartz-carbonate-sulfide veinlets and minor disseminations. Textural and structural data indicate that mineralization was syn- to late-tectonic and postmetamorphic. Fluid inclusion studies identified early CO2 (CH4-N2) and CO2 (CH4-N2)-H2O-NaCl inclusions that show highly variable phase ratios, CO2 homogenization, and total homogenization temperatures both to liquid and vapor, interpreted as the product of fluid immiscibility under fluctuating pressure conditions, more or less associated with postentrapment modifications. The ore-bearing fluid typically has 18–33mol% of CO2, up to 4mol% of N2, and less than 2mol% of CH4 and displays moderate to high densities with salinity around 4.5wt% NaCl equiv. Mineralization occurred around 310 to 335°C and 1.3 to 3.0 kbar, based on fluid inclusion homogenization temperatures and oxygen isotope thermometry with estimated oxygen fugacity indicating relatively reduced conditions. Stable isotope data on quartz, carbonate, and fluid inclusions suggest that veins formed from fluids with δ18OH2O and δDH2O (310–335°C) values of +6.2 to +8.4‰ and −19 to −80‰, respectively, which might be metamorphic and/or magmatic and/or mantle-derived. The carbon isotope composition (δ13C) varies from −14.2 to −15.7‰ in carbonates; it is −17.6‰ in fluid inclusion CO2 and −23.6‰ in graphite from the host rock. The δ34S values of pyrite are −2.6 to −7.9‰. The strongly to moderately negative carbon isotope composition of the carbonates and inclusion fluid CO2 reflects variable contribution of organic carbon to an originally heavier fluid (magmatic, metamorphic, or mantle-derived) at the site of deposition and sulfur isotopes indicate some oxidation of the originally reduced fluid. The deposition of gold is interpreted to have occurred mainly in response to phase separation and fluid-rock interactions such as CO2 removal and desulfidation reactions that provoked variations in the fluid pH and redox conditions. 相似文献
57.
58.
Abstract K-Ar age studies in the Ashigawa and the southern part of the Tokuwa granodioritic bodies, which consist of the southern part of the Kofu plutonic complex, revealed that they formed between 12 and 9 Ma. Quite a narrow range of ages obtained from the Ashigawa southernmost part of the Tokuwa pluton implies that they cooled rapidly. The southern part of the Tokuwa pluton, as a whole, shows a systematic age distribution with a decrease in age to the north. Compilation of currently available plutonic ages in the South Fossa Magna suggests that the plutonic activities occurred three times in this region. Episodic activity like this could be argued in relation to the tectonic development of this region. 相似文献
59.
Abstract Recent paleomagnetic studies are reviewed in an effort to clarify the relationship between the intra-arc deformation of central Japan and the collision tectonics of the Izu-Bonin Arc. The cusp structure of the pre-Neogene terranes of central Japan, called the Kanto Syntaxis, suggests a collisional origin with the Izu-Bonin Arc. The paleomagnetic results and newly obtained radiometric ages of the Kanto Mountains revealed the Miocene rotational history of the east wing of the Kanto Syntaxis. More than 90° clockwise rotation of the Kanto Mountains took place after deposition of the Miocene Chichibu Basin (planktonic foraminiferal zone of N.8: 16.6–15.2 Ma). After synthesizing the paleomagnetic data of the Japanese Islands and collision tectonics of central Japan, it appears that approximately a half rotation (40–50°) probably occurred at ca 15 Ma in association with the rapid rotation of Southwest Japan. The remainder (50-40°) continued until 6 Ma, resulting in the sharp bent structure of the pre-Neogene accretionary complexes (Kanto Syntaxis). The latter rotation seems to have been caused by the collision of the Izu-Bonin Arc on the northwestward migrating Philippine Sea Plate. 相似文献
60.
Recent structural, tephrochronologic and magnetostratigraphic studies conducted along the northernmost border of the Philippine Sea (PHS) plate enable us to reconstruct the precise tectonic evolution along the convergent boundary between the PHS plate and the Northeast Japan (NEJ) plate or the North American (NAM) plate since about 1 Ma. The authors of the present study split the tectonic evolution into five stages and present the characteristics of each stage. A plate tectonic interpretation is proposed, based upon the tectonic evolution, with special reference to the mode of convergent motion. In brief, our interpretations are as follows: the relative motion between the PHS and the NEJ plates was not recognized geologically within the area studied from about 1.0 to 0.9 Ma (Stage 1), suggesting either none or small influence from the coupling between the two plates during that period of time. Convergence between the PHS and the NEJ plates was possibly in N-S direction from 0.9 to 0.5 Ma (Stage II), and probably north-northwestward since 0.5 Ma (Stages III to V). The mode of the convergent motion was that of buoyant subduction in Stages II and III. The mode changed gradually from buoyant subduction during Stage IV to collision in Stage V (0.07 Ma to the present). 相似文献