全文获取类型
收费全文 | 639篇 |
免费 | 30篇 |
国内免费 | 11篇 |
专业分类
测绘学 | 38篇 |
大气科学 | 86篇 |
地球物理 | 151篇 |
地质学 | 274篇 |
海洋学 | 62篇 |
天文学 | 34篇 |
综合类 | 5篇 |
自然地理 | 30篇 |
出版年
2022年 | 6篇 |
2021年 | 26篇 |
2020年 | 9篇 |
2019年 | 15篇 |
2018年 | 32篇 |
2017年 | 24篇 |
2016年 | 34篇 |
2015年 | 29篇 |
2014年 | 38篇 |
2013年 | 44篇 |
2012年 | 35篇 |
2011年 | 54篇 |
2010年 | 44篇 |
2009年 | 33篇 |
2008年 | 37篇 |
2007年 | 33篇 |
2006年 | 40篇 |
2005年 | 18篇 |
2004年 | 14篇 |
2003年 | 15篇 |
2002年 | 13篇 |
2001年 | 13篇 |
2000年 | 10篇 |
1999年 | 5篇 |
1998年 | 9篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1973年 | 1篇 |
1969年 | 1篇 |
1965年 | 1篇 |
1955年 | 1篇 |
1953年 | 1篇 |
1940年 | 1篇 |
1939年 | 3篇 |
排序方式: 共有680条查询结果,搜索用时 31 毫秒
61.
62.
Gomez-Tuena Arturo; Langmuir Charles H.; Goldstein Steven L.; Straub Susanne M.; Ortega-Gutierrez Fernando 《Journal of Petrology》2007,48(3):537-562
Geochemical studies of Plio-Quaternary volcanic rocks from theValle de BravoZitácuaro volcanic field (VBZ) incentral Mexico indicate that slab melting plays a key role inthe petrogenesis of the Trans-Mexican Volcanic Belt. Rocks fromthe VBZ are typical arc-related high-Mg andesites, but two differentrock suites with distinct trace element patterns and isotopiccompositions erupted concurrently in the area, with a traceelement character that is also distinct from that of other Mexicanvolcanoes. The geochemical differences between the VBZ suitescannot be explained by simple crystal fractionation and/or crustalassimilation of a common primitive magma, but can be reconciledby the participation of different proportions of melts derivedfrom the subducted basalt and sediments interacting with themantle wedge. Sr/Y and Sr/Pb ratios of the VBZ rocks correlateinversely with Pb and Sr isotopic compositions, indicating thatthe Sr and Pb budgets are strongly controlled by melt additionsfrom the subducted slab. In contrast, an inverse correlationbetween Pb(Th)/Nd and 143Nd/144Nd ratios, which extend to lowerisotopic values than those for Pacific mid-ocean ridge basalts,indicates the participation of an enriched mantle wedge thatis similar to the source of Mexican intraplate basalts. In addition,a systematic decrease in middle and heavy rare earth concentrationsand Nb/Ta ratios with increasing SiO2 contents in the VBZ rocksis best explained if these elements are mobilized to some extentin the subduction flux, and suggests that slab partial fusionoccurred under garnet amphibolite-facies conditions. KEY WORDS: arcs; mantle; Mexico; sediment melting; slab melting 相似文献
63.
Vulnerability assessment in a volcanic risk evaluation in Central Mexico through a multi-criteria-GIS approach 总被引:1,自引:1,他引:1
José Fernando Aceves-Quesada Jesús Díaz-Salgado Jorge López-Blanco 《Natural Hazards》2007,40(2):339-356
The Valley of Toluca is a major industrial and agricultural area in Central Mexico, especially the City of Toluca, the capital
of The State of Mexico. The Nevado de Toluca volcano is located to the southwest of The Toluca Basin. Results obtained from
the vulnerability assessment phase of the study area (5,040 km2 and 42 municipalities) are presented here as a part of a comprehensive volcanic risk assessment of The Toluca Basin. Information
has been gathered and processed at a municipal level including thematic maps at 1:250,000 scale. A database has been built,
classified and analyzed within a GIS environment; additionally, a Multi-Criteria Evaluation (MCE) approach was applied as
an aid for the decision-making process. Cartographic results were five vulnerability maps: (1) Total Population, (2) Land
Use/Cover, (3) Infrastructure, (4) Economic Units and (5) Total Vulnerability. Our main results suggest that the Toluca and
Tianguistenco urban and industrial areas, to the north and northeast of The Valley of Toluca, are the most vulnerable areas,
for their high concentration of population, infrastructure, economic activity, and exposure to volcanic events. 相似文献
64.
B. John Makario Londoño A. John Jairo Sanchez E. Luis Eduardo Toro Fernando Gil Cruz Olga Patricia Bohorquez 《Bulletin of Volcanology》1998,59(8):556-561
Coda Q–1 was calculated at Nevado del Ruiz Volcano (NRV) before and after two phreatomagmatic eruptions (November 1985, September
1989) and for a period of stability (May 1987) using a functional form for coda derived from a single scattering model (Sato
1977). Substantial changes were found before and after the eruptions. The highest value of Q–1 was found during the November 1985 eruption, an intermediate value for the September 1989 eruption, and the lowest value
for May 1987. It seems that the changes in coda Q–1 at NRV have a still-unknown relationship with the volume or magnitude of the eruption. A relatively strong frequency dependence
was found for all periods. Also Q–1 clearly changed with time, suggesting that the scattering was strong for the eruption of November 1985 and decreased for
the eruption of September 1989, and that the intrinsic absorption probably increased. This suggests the possibility that crystallization
is taking place in the NRV magma. The clear change of coda Q–1 before and after the eruptions at NRV also suggests the possibility that coda Q–1 is a premonitory tool of activity at this volcano.
Received: 25 October 1996 / Accepted: 21 January 1998 相似文献
65.
Johildo Salomo Figueirêdo Barbosa Fernando Alves daSilva Najara Santos Sapucaia Sundaram S. Iyer 《Gondwana Research》1998,1(3-4):343-356
New petrological and geochemical characteristics of the Brejtes region, situated in the south of Bahia, Brazil are discussed. The region forms a part of the most important and extensive granulite facies terrain in Brazil of Archean/Paleoproterozoic age. Five groups of rock types all equilibrated in the granulite facies are identified in this region. They are: i) supracrustal and related rocks, ii) undifferentiated granulites, iii) hornblende bearing enderbite-charnockites, iv) hornblende free enderbite-charnockites, v) charnockites. The first group appears to be the oldest in the region as they form enclaves in the 2.9 Ga old undifferentiated granulites. The third and fourth group are enderbite-charnockites, whose protoliths constitute two series of calc-alkaline rocks, one titanium poor (hornblende free) and another titanium rich (hornblende bearing). U/Pb zircon SHRIMP dates indicate ages of formation at 2.81 Ga (hornblende free) and 2.69 Ga (hornblende bearing) for the two groups. The fifth group of rocks have charnockitic affinity and are present in the center of the Brejtes Dome. These rocks are also have calc-alkaline affinity, but show petrographic and geochemical characteristics distinct from those of other groups. Preliminary geochronological investigations by zircon Pb-Pb evaporation method yielded 2.6 Ga and 2.0 Ga for the charnockites from the inner core of the Brejtes Dome. These age data suggest that the circular structure was formed by the re-fusion of the 2.6 Ga old deep crustal material generating younger charnockites at 2.0 Ga. 相似文献
66.
Fernando Corfu 《Lithos》1980,13(4):305-323
U---Pb analyses of zircon, monazite and sphene as well as Rb---Sr analyses of whole rocks and minerals have been carried out in an attempt to elucidate the evolution of the Precambrian shield underlying the Caledonian Jotun-nappe in central southern Norway. The earliest event recognized in the area is a high grade metamorphism at 1518 ± 17 m.y. which followed intense magma formation, igneous activity, erosion and sedimentation over a period of maximum 300 m.y. The Sveconorwegian cycle is characterized by the intrusion of two anatectic magma generations at 1014 ± 35 m.y. and 930±10 m.y. that disturbed and partly reset the isotopic systems of the country rocks. A post-magmatic fracturing stage at 875 m.y. concludes this cycle. Rb---Sr mineral systems were not completely equilibrated in the undeformed shield during the Caledonian event in contrast to new grown minerals in strongly deformed overlying Lower Paleozoic sediments which record the main deformation at 384±18 m.y. Zircon lower intercept ages ranging between 330–370 m.y. show that lead loss of zircon in rocks subjected to low grade metamorphic conditions may be the result of such processes as annealing, alteration, dilation or a combination of them. 相似文献
67.
68.
New stacked central configurations for the planar 5-body problem 总被引:1,自引:0,他引:1
Jaume Llibre Luis Fernando Mello Ernesto Perez-Chavela 《Celestial Mechanics and Dynamical Astronomy》2011,110(1):43-52
A stacked central configuration in the n-body problem is one that has a proper subset of the n-bodies forming a central configuration. In this paper we study the case where three bodies with masses m
1, m
2, m
3 (bodies 1, 2, 3) form an equilateral central configuration, and the other two with masses m
4, m
5 are symmetric with respect to the mediatrix of the segment joining 1 and 2, and they are above the triangle generated by
{1, 2, 3}. We show the existence and non-existence of this kind of stacked central configurations for the planar 5-body problem. 相似文献
69.
Günther J. Redhammer Fernando Cámara Matteo Alvaro Fabrizio Nestola Gerold Tippelt Sebastian Prinz Jan Simons Georg Roth Georg Amthauer 《Physics and Chemistry of Minerals》2010,37(10):685-704
A synthetic clinopyroxene with composition LiFe3+Ge2O6, monoclinic s.g. P21/c, a = 9.8792(7), b = 8.8095(5), c = 5.3754(3) Å, β = 108.844(6)°, V = 442.75(16) Å3, has been studied by in situ low- and high-temperature single-crystal X-ray diffraction. The variation of lattice parameters and the intensity of the b-type reflections (h + k = 2n + 1, only present in the P-symmetry) with increasing temperature showed a displacive phase transition from space group P21/c to C2/c at a transition temperature T tr = 789 K, first order in character, with a sudden volume increase of 1.6% and a decrease of β by 1° at the transition. This spontaneous dilatation is reversible, shows a limited hysteresis of ±10°C, and corresponds to the vanishing of the b-type reflections, thus indicating a symmetry increase to space group C2/c. Below T tr an expansion is observed for all the cell parameters, while the β angle remained almost constant; at T > T tr the thermal volume expansion is due to dilatation of the structure in the $(\bar{1}\,0\,1) A synthetic clinopyroxene with composition LiFe3+Ge2O6, monoclinic s.g. P21/c, a = 9.8792(7), b = 8.8095(5), c = 5.3754(3) ?, β = 108.844(6)°, V = 442.75(16) ?3, has been studied by in situ low- and high-temperature single-crystal X-ray diffraction. The variation of lattice parameters
and the intensity of the b-type reflections (h + k = 2n + 1, only present in the P-symmetry) with increasing temperature showed a displacive phase transition from space group P21/c to C2/c at a transition temperature T
tr = 789 K, first order in character, with a sudden volume increase of 1.6% and a decrease of β by 1° at the transition. This spontaneous dilatation is reversible, shows a limited hysteresis of ±10°C, and corresponds
to the vanishing of the b-type reflections, thus indicating a symmetry increase to space group C2/c. Below T
tr an expansion is observed for all the cell parameters, while the β angle remained almost constant; at T > T
tr the thermal volume expansion is due to dilatation of the structure in the ([`1] 0 1)(\bar{1}\,0\,1) plane, mostly along [0 1 0], and pure shear in the (0 1 0) plane due to the decrease of β. From comparison with silicate analogues, the germanate clinopyroxenes are more expansible, while the P21/c expands more than the C2/c phase. The evolution of Q
2 (calculated as the normalized intensity of b-type reflections) with T in the framework of the Landau theory has been done using a standard expression for a first order phase transition. We observe
a jump of Q
02 = 0.538(2) at T
tr, with T
c of 481(7) K, b/a = −2,290 K, and c/a = 3,192 K, and thus far from being tri-critical point. A closely related composition (LiFe3+Si2O6) shows an equivalent phase transition at 228 K, which is very close to the tri-critical point and 561 K cooler. This result
indicates that a change in the composition of tetrahedral sites can have dramatic effects on the P21/c ↔ C2/c displacive phase transition in clinopyroxenes. The major changes observed in the evolution of the crystal structure with
T are observed in the M2 polyhedron, with a volume decrease by ca. 13.3%, compared to ca. 1.3% observed in the M1 polyhedron.
The tetrahedra behave as rigid units with neither a significant change of volume at T > T
tr (<1‰), nor a change of tilting of the basal plane. No change in coordination is observed at T > T
tr in the M2 polyhedron, which remains sixfold coordinated although a strong deformation of this polyhedron is observed. This
deformation is related to a strong change by 51.4° at T
tr of the kinking angle (O3–O3–O3 angle) of the B-chain of tetrahedra, which switches from O-rotated to S-rotated [from 143.3(5)°
to 194.7(6)°]. The A-chain is S-rotated at T < T
tr [206.8(5)° at 703 K] and extends by 12° at the transition. 相似文献
70.