全文获取类型
收费全文 | 552篇 |
免费 | 32篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 13篇 |
大气科学 | 36篇 |
地球物理 | 123篇 |
地质学 | 220篇 |
海洋学 | 59篇 |
天文学 | 76篇 |
综合类 | 1篇 |
自然地理 | 62篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 5篇 |
2020年 | 14篇 |
2019年 | 14篇 |
2018年 | 13篇 |
2017年 | 19篇 |
2016年 | 25篇 |
2015年 | 26篇 |
2014年 | 19篇 |
2013年 | 24篇 |
2012年 | 28篇 |
2011年 | 38篇 |
2010年 | 42篇 |
2009年 | 39篇 |
2008年 | 25篇 |
2007年 | 32篇 |
2006年 | 24篇 |
2005年 | 26篇 |
2004年 | 28篇 |
2003年 | 20篇 |
2002年 | 13篇 |
2001年 | 8篇 |
2000年 | 13篇 |
1999年 | 6篇 |
1998年 | 15篇 |
1997年 | 8篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
排序方式: 共有590条查询结果,搜索用时 15 毫秒
521.
Intercomparison of Boron Isotope and Concentration Measurements. Part II: Evaluation of Results 总被引:3,自引:1,他引:3
Roberto Gonfiantini Sonia Tonarini Manfred Grning Alessandra Adorni‐Braccesi Assad S. Al‐Ammar Marcus Astner Sebastien Bchler Ramon M. Barnes Randy L. Bassett Alain Cocherie Annette Deyhle Andrea Dini Giorgio Ferrara Jrme Gaillardet Judith Grimm Catherine Guerrot Urs Krhenbühl Graham Layne Damien Lemarchand Anette Meixner D. Jack Northington Maddalena Pennisi Eva Reitznerov Ilia Rodushkin Naoji Sugiura Regina Surberg Sabine Tonn Michael Wiedenbeck Samuel Wunderli Yingkai Xiao Thomas Zack 《Geostandards and Geoanalytical Research》2003,27(1):41-57
The Istituto di Geoscienze e Georisorse (IGG), on behalf and with the support of the International Atomic Energy Agency (IAEA), prepared eight geological materials (three natural waters and five rocks and minerals), intended for a blind interlaboratory comparison of measurements of boron isotopic composition and concentration. The materials were distributed to twenty seven laboratories - virtually all those performing geochemical boron isotope analyses in the world -which agreed to participate in the intercomparison exercise. Only fifteen laboratories, however, ultimately submitted the isotopic and/or concentration results they obtained on the intercomparison materials. The results demonstrate that interlaboratory reproducibility is not well reflected by the precision values reported by the individual laboratories and this observation holds true for both boron concentration and isotopic composition. The reasons for the discrepancies include fractionations due to the chemical matrix of materials, relative shift of the zero position on the δ11 B scale and a lack of well characterized materials for calibrating absolute boron content measurements. The intercomparison materials are now available at the IAEA (solid materials) and IGG (waters) for future distribution. 相似文献
522.
Catherine Mriaux Amotz Agnon John R. Lister 《Earth and Planetary Science Letters》1998,160(3-4):551-562
We study the thermal structure around a cold deformable lithospheric slab as it sinks to the core–mantle boundary and migrates along it. We present analytical results for the steady thermal structure established by a steady but spatially varying motion. The analysis gives a time-like criterion for the thermal signature of a cold slab to persist by the time that the slab moves along the core–mantle boundary. The model is used to assess the feasibility of a purely thermal origin for some of the observed seismic reflectors near the core–mantle boundary. Calculations of the time-like criterion show that the dynamical conditions in our model, namely the velocity and the thickness of the descending slab, are hard to reconcile with observations of subduction and seismic features. Seismic reflections and refractions from anomalously fast regions above the core–mantle boundary could be explained as thermal slabs if the thickness of the slab at subduction was larger than 200 km or somewhat less if the slab did not split at the core–mantle boundary. A simple thermal model also predicts from mineral physics a certain correlation between S- and P-wave velocity anomalies, which is not observed. However, a purely thermal origin cannot be ruled out if the slab is buckling. This process could be in agreement with the observations: the amplitude of the seismic anomalies, the vertical extent of high-gradient zones and the P versus S comparisons. Chemical heterogeneities and phase transformations remain alternative or complementary explanations. 相似文献
523.
Raphaël Pik Catherine Deniel Christian Coulon Gezahegn Yirgu Corine Hofmann Dereje Ayalew 《Journal of Volcanology and Geothermal Research》1998,81(1-2)
The extensive, complex, continental flood basalt (CFB) province which occurs in Ethiopia and Yemen consists of Oligocene prerift volcanism related to the Africa–Arabia continental break-up. Basalts from the northwestern Ethiopian Plateau exhibit a particularly large range of compositions and, for the first time in the Afro-Arabian CFB province, low-Ti basalts have been encountered. Major and some trace element data have been used to identify distinct geochemical groups and evaluate the role of differentiation processes. Three magma types have been distinguished: two high-Ti groups (HT1 and HT2) and one low-Ti group (LT). The transitional to tholeiitic LT suite exhibits low TiO2 (1–2.6%), Fe2O3* (10.5–14.8%), CaO/Al2O3 (0.4–0.75), Nb/La (0.55–0.85) and high SiO2 (47–51%). In contrast, the HT2 suite exhibits high TiO2 (2.6–5%), Fe2O3* (13.1–14.7%), CaO/Al2O3 (0.9–1.43), Nb/La (1.1–1.4) and low SiO2 (44–48.3%). The HT1 series is intermediate between the LT and HT2 groups. These three groups of lavas originated from different parental magmas. They display distinct differentiation trends, either controlled by the removal of a shallow level gabbroic (Pl+Ol+Cpx) assemblage (LT and HT1 suites) or by deeper Ol+Cpx fractionation (HT2 suite). Most of this thick continental flood lava pile was emplaced over a short time interval (about 1–2 Ma). The three contrasted magma types do not reflect a temporal evolution of their sources but rather a strong spatial control. Indeed, the northwestern Plateau may be subdivided into two different subprovinces as all the low-Ti basalts are located in the northern part of the plateau, and the high-Ti basalts are exposed in the eastern and southern parts. The LT and HT1 basalts display compositional ranges similar to those of the low- and high-Ti groups from other main CFB provinces (e.g. Parana, Deccan, Karoo, Siberia, …). However, the HT2 group exhibits extreme OIB-like compositions. This unusual geochemical signature suggests the involvement of deep mantle in the genesis of the HT2 magmas. The LT compositions rather reflect the participation of the continental lithosphere, through mantle derived melts and/or crustal contamination. 相似文献
524.
The Hasan Dagi stratovolcano (Central Anatolia, Turkey): evolution from calc-alkaline to alkaline magmatism in a collision zone 总被引:1,自引:0,他引:1
Catherine Deniel Erkan Aydar Alain Gourgaud 《Journal of Volcanology and Geothermal Research》1998,87(1-4)
The Hasan Dagi volcano is one of the two large Plio-Quaternary volcanoes in Cappadocia (Central Anatolia, Turkey). Three stages of edifice construction have been identified for this volcano: Paleovolcano, Mesovolcano and Neovolcano. Most samples from Hasan Dagi volcano are calc-alkaline and define an almost complete trend from basaltic andesite to rhyolite. However, the more recent (Neovolcano) mafic samples are alkaline basalts. The mineralogical and geochemical characteristics of the oldest lavas (Keçikalesi (13 Ma) and Paleo-Hasan Dagi (7 Ma)) are significantly different from those of the younger lavas (Meso- and Neo-Hasan Dagi (<1 Ma)). Calcic plagioclase and pigeonite are typically observed in these older lavas. The Paleovolcano basalts are depleted in alkalis and display a tholeiitic tendency whereas the differentiated lavas are depleted in Na2O but enriched in K2O compared to younger lavas. There is an evolution through time towards higher TiO2, Fe2O3*, MgO, Na2O and K2O and lower Al2O3 and SiO2 which is reflected in the basalt compositions. All the basalts display multi-element patterns typical of continental margin magmas with a significant enrichment in LILE (K, Rb, Ba and Th) and LREE and strong (Paleovolcano) to moderate (Meso- and Neovolcano) negative Nb, Zr and Ti anomalies. However, the younger basalts are the most enriched in incompatible elements, in agreement with their alkaline affinities and do not systematically display negative HFSE anomalies. REE data suggest an hydrous amphibole-bearing crystallization history for both Meso- and Neovolcano lavas. The distinction between the older and younger lavas is also apparent in trace element ratios such as Nb/Y, Ti/Y and Th/Y. These ratios indicate the role of a subducted component±crustal contamination in the genesis of the Hasan Dagi lavas, particularly for the oldest lavas (Keçikalesi and Paleo-Hasan Dagi). The decreasing influence of this component through time, over the last 6–7 m.y., has been accompanied by an increasing contribution of melt-enriched lithosphere. Although the range of variation of Sr, Nd and Pb isotopic ratios is small (0.70457–0.70515; 0.51262–0.51273; 18.80–18.94; 15.64–15.69; 38.87–39.10), it also reflects the evolution of the magma sources through time. Indeed, the youngest (Neovolcano) and most primitive basalts display significantly lower 87Sr/86Sr than the Paleo- and Mesovolcano basalts, whereas the Mesovolcano basalts display more radiogenic Pb than Paleovolcano samples. Magma mixing processes between initially heterogeneous and/or variably contaminated magmas may account for the genesis of the less differentiated and intermediate lavas (48–57% SiO2). Meso- and Neovolcano differentiated lavas (60–68% SiO2) are either derived from the analyzed basalts or from more primitive and more depleted magmas by fractional crystallization±some crustal contamination (AFC). Furthermore, the highly differentiated samples (72–75% SiO2) are not strongly contaminated. The strong calc-alkaline character of Hasan Dagi lavas, in the absence of contemporaneous subduction, must reflect the heritage of the early subduction of the Afro–Arabian plate under the Eurasian plate. The evolution towards alkaline compositions through time is clearly related to the development of extensional tectonics in Central Anatolia in the Late Miocene. 相似文献
525.
Ehrenfreund Pascale Krafft Catherine Kochan Hermann Pirronello Valerio 《Earth, Moon, and Planets》1998,80(1-3):1-1
Earth, Moon, and Planets - 相似文献
526.
Catherine M. Cress & Marc Kamionkowski 《Monthly notices of the Royal Astronomical Society》1998,297(2):486-492
We develop the formalism required to interpret, within a CDM framework, the angular clustering of sources in a deep radio survey. The effect of non-linear evolution of density perturbations is discussed, as is the effect of the assumed redshift distribution of sources. We also investigate what redshift ranges contribute to the clustering signal at different angular scales. Application of the formalism is focused on the clustering detected in the FIRST survey, but measurements made for other radio surveys are also investigated. We comment on the implications for the evolution of clustering. 相似文献
527.
Catherine L. Johnson Jan R. Wijbrans Catherine G. Constable Jeff Gee Hubert Staudigel Lisa Tauxe Victor-H. Forjaz Mrio Salgueiro 《Earth and Planetary Science Letters》1998,160(3-4):637-649
We present new 40Ar/39Ar ages and paleomagnetic data for São Miguel island, Azores. Paleomagnetic samples were obtained for 34 flows and one dike; successful mean paleomagnetic directions were obtained for 28 of these 35 sites. 40Ar/39Ar age determinations on 12 flows from the Nordeste complex were attempted successfully: ages obtained are between 0.78 Ma and 0.88 Ma, in contrast to published K–Ar ages of 1 Ma to 4 Ma. Our radiometric ages are consistent with the reverse polarity paleomagnetic field directions, and indicate that the entire exposed part of the Nordeste complex is of a late Matuyama age. The duration of volcanism across São Miguel is significantly less than previously believed, which has important implications for regional melt generation processes, and temporal sampling of the geomagnetic field. Observed stable isotope and trace element trends across the island can be explained, at least in part, by communication between different magma source regions at depth. The 40Ar/39Ar ages indicate that our normal polarity paleomagnetic data sample at least 0.1 Myr (0–0.1 Ma) and up to 0.78 Myr (0–0.78 Ma) of paleosecular variation and our reverse polarity data sample approximately 0.1 Myr (0.78–0.88 Ma) of paleosecular variation. Our results demonstrate that precise radiometric dating of numerous flows sampled is essential to accurate inferences of long-term geomagnetic field behavior. Negative inclination anomalies are observed for both the normal and reverse polarity time-averaged field. Within the data uncertainties, normal and reverse polarity field directions are antipodal, but the reverse polarity field shows a significant deviation from a geocentric axial dipole direction. 相似文献
528.
Two mantle sources, two plumbing systems: tholeiitic and alkaline magmatism of the Maymecha River basin, Siberian flood volcanic province 总被引:2,自引:0,他引:2
Nicholas Arndt Catherine Chauvel Gerald Czamanske Valeri Fedorenko 《Contributions to Mineralogy and Petrology》1998,133(3):297-313
Rocks of two distinctly different magma series are found in a ∼4000-m-thick sequence of lavas and tuffs in the Maymecha River
basin which is part of the Siberian flood-volcanic province. The tholeiites are typical low-Ti continental flood basalts with remarkably restricted, petrologically evolved compositions. They have basaltic
MgO contents, moderate concentrations of incompatible trace elements, moderate fractionation of incompatible from compatible
elements, distinct negative Ta(Nb) anomalies, and Nd values of 0 to +2. The primary magmas were derived from a relatively shallow mantle source, and evolved in large crustal
magma chambers where they acquired their relatively uniform compositions and became contaminated with continental crust. An
alkaline series, in contrast, contains a wide range of rock types, from meymechite and picrite to trachytes, with a wide range of compositions
(MgO from 0.7 to 38 wt%, SiO2 from 40 to 69 wt%, Ce from 14 to 320 ppm), high concentrations of incompatible elements and extreme fractionation of incompatible
from compatible elements (Al2O3/TiO2∼1; Sm/Yb up to 11). These rocks lack Ta(Nb) anomalies and have a broad range of Nd values, from −2 to +5. The parental magmas are believed to have formed by low-degree melting at extreme mantle depths (>200 km).
They bypassed the large crustal magma chambers and ascended rapidly to the surface, a consequence, perhaps, of high volatile
contents in the primary magmas. The tholeiitic series dominates the lower part of the sequence and the alkaline series the
upper part; at the interface, the two types are interlayered. The succession thus provides evidence of a radical change in
the site of mantle melting, and the simultaneous operation of two very different crustal plumbing systems, during the evolution
of this flood-volcanic province.
Received: 6 January 1998 / Accepted: 29 June 1998 相似文献
529.
Jane Southworth Harini Nagendra Laura A. Carlson Catherine Tucker 《Applied geography (Sevenoaks, England)》2004,24(4):303-322
The effectiveness of parks as management regimes is much in debate. This study examines the effect of establishment of the Celaque National Park, Honduras, in 1987, on limiting deforestation through a comparison with the surrounding landscape using remote sensing, GIS and landscape pattern analysis. Pressure on the park region is found to relate spatially to the locations of towns and roads, with increasing deforestation in the landscape surrounding the park. In contrast, the park has been largely successful in maintaining forest cover. Although the extent of change within the park is not pronounced, the pattern of change is. Expansion of agriculture and coffee production have led to increasing pressure on the park boundaries, with as much as 25% of the landscape surrounding the park experiencing land cover change between 1996 and 2000. This has significant implications for the future of the park. 相似文献
530.
Catherine A. Hier Majumder David A. Yuen Erik O. Sevre John M. Boggs Stephen Y. Bergeron 《Visual Geosciences》2002,7(1):1-53
Finite Prandtl number thermal convection is important to the dynamics of planetary bodies in the solar system. For example,
the complex geology on the surface of the Jovian moon Europa is caused by a convecting, brine-rich global ocean that deforms
the overlying icy “lithosphere”. We have conducted a systematic study on the variations of the convection style, as Prandtl
numbers are varied from 7 to 100 at Rayleigh numbers 106 and 108. Numerical simulations show that changes in the Prandtl number
could exert significant effects on the shear flow, the number of convection cells, the degree of layering in the convection,
and the number and size of the plumes in the convecting fluid. We found that for a given Rayleigh number, the convection style
can change from single cell to layered convection, for increasing Prandtl number from 7 to 100. These results are important
for determining the surface deformation on the Jovian moon Europa. They also have important implications for surface heat
flow on Europa, and for the interior heat transfer of the early Earth during its magma ocean phase. Electronic Supplementary
Material is available if you access this article at . On that page (frame on the left side), a link takes you directly to the supplementary material.
Electronic Supplementary Material is available if you access this article at . On that page (frame on the left side), a link takes you directly to the supplementary material. 相似文献