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21.
Meta-sedimentary rocks including marbles and calcsilicates in Central Dronning Maud Land (CDML) in East Antarctica experienced
a Pan-African granulite facies metamorphism with peak metamorphic conditions around 830 ± 20 °C at 6.8 ± 0.5 kbar which was
accompanied by the post-kinematic intrusion of huge amounts of syenitic (charnockitic) magmas at 4.5 ± 0.7 kbar. The marbles
and calcsilicates may represent meta-evaporites as indicated by the occurrence of metamorphic gypsum/anhydrite and Cl-rich
scapolite that formed in the presence of saline fluids with X
NaCl in the range 0.15–0.27. The marbles and calcsilicates bear biotite, tremolite and/or hornblende and humite group minerals
(clinohumite, chondrodite and humite) which are inferred to have crystallized at about 650 °C and 4.5 kbar. The syenitic intrusives
contain late-magmatic biotite and amphibole (formed between 750 and 800 °C) as well as relictic magmatic fayalite, orthopyroxene
and clinopyroxene. Two syenite and two calcsilicate samples contain fluorite. Corona textures in the marbles and calcsilicates
suggest very low fluid-rock ratios during the formation of the retrograde (650 °C) assemblages. Biotite in all but two syenite
samples crystallized at log(f
H
2
O/f
HF) ratios of 2.9 ± 0.4, while in the calcsilicates, both biotite and humite group minerals indicate generally higher log(f
H
2
O/f
HF) values of up to 5.2. A few samples, though, overlap with the syenite values. Log(f
H
2
O/f
HCl) derived from biotite covers the range 0.5–2.6 in all rock types. Within a single sample, the calculated values for both
parameters vary typically by 0.1 to 0.8 log units. Water and halogen acid fugacities calculated from biotite-olivine/orthopyroxene-feldspar-quartz
equilibria and the above fugacity ratios are 1510–2790 bars for H2O, 1.3–5.3 bars for HF and 7–600 bars for HCl. The results are interpreted to reflect the reaction of relatively homogeneous
magmatic fluids [in terms of log(f
H
2
O
/f
HF)] derived from the late-magmatic stages of the syenites with both earlier crystallized, still hotter parts of the syenites
and with adjacent country rocks during down-temperature fluid flow. Fluorine is successively removed from the fluid and incorporated
into F-bearing minerals (close to the syenite into metamorphic fluorite). In the course of this process log(f
H
2
O
/f
HF) increases significantly. Chlorine preferably partitions into the fluid and hence log(f
H
2
O
/f
HCl) does not change markedly during fluid-rock interaction.
Received: 28 November 1997 / Accepted: 27 April 1998 相似文献
22.
23.
Spijker Jeroen Recaño Joaquín Martínez Sandra Carioli Alessandra 《Journal of Geographical Systems》2021,23(2):161-207
Journal of Geographical Systems - Colombia is undergoing major changes in mortality patterns. National- and department-level cause-specific analyses have previously been carried out, but very... 相似文献
24.
Francisco Carreño Conde Sandra García Martínez Javier Lillo Ramos Raquel Fernández Martínez Ariana Mabeth-Montoya Colonia 《Environmental Earth Sciences》2014,71(1):61-66
Water resources management of protected sites requires a powerful tool to analyze the process and changes that are occurring in the environment. This paper describes a 3D geomodel design of the Jarama River Detrital Aquifer located in Madrid (Spain). That hydrogeological unit is included in the “Parque Regional de los Cursos Bajos de los Ríos Manzanares y Jarama” (Regional Park of the Lower Courses of Manzanares and Jarama Rivers). The goal of this work is to define a method by which a three-dimensional (3D) model can be created with hydrogeologic geometry real of main aquifer, to accomplish an adequate management of the groundwater resources. All data used in this study were integrated in a geographic database: geological and hydrogeological information, geological map (1:25,000), eleven cross-sections, piezometric maps and a digital elevation model. The constructed 3D model of the Jarama Aquifer shows geometric features and spatial distribution and variations of geologic units. Thus, the 3D model allows the assessment of volumes of each unit, the depth and thickness variations of the main aquifer, and the spatial and temporal variations of water tables. From the 3D model, the most suitable areas (in terms of groundwater protection) for managed recharge and mining works have been identified. 相似文献
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26.
Dicarboxylic acids were searched for in three Sutter's Mill (SM) fragments (SM2 collected prerain, SM12, and SM41) and found to occur almost exclusively as linear species of 3‐ to 14‐carbon long. Between these, concentrations were low, with measured quantities typically less than 10 nmole g?1 of meteorite and a maximum of 6.8 nmole g?1 of meteorite for suberic acid in SM12. The SM acids' molecular distribution is consistent with a nonbiological origin and differs from those of CMs, such as Murchison or Murray, and of some stones of the C2‐ungrouped Tagish Lake meteorite, where they are abundant and varied. Powder X‐ray diffraction of SM12 and SM41 show them to be dominated by clays/amorphous material, with lesser amounts of Fe‐sulfides, magnetite, and calcite. Thermal gravimetric (TG) analysis shows mass losses up to 1000 °C of 11.4% (SM12) and 9.4% (SM41). These losses are low compared with other clay‐rich carbonaceous chondrites, such as Murchison (14.5%) and Orgueil (21.1%). The TG data are indicative of partially dehydrated clays, in accordance with published work on SM2, for which mineralogical studies suggest asteroidal heating to around 500 °C. In view of these compositional traits and mineralogical features, it is suggested that the dicarboxylic acids observed in the SM fragments we analyzed likely represent a combination of molecular species original to the meteorite as well as secondary products formed during parent‐body alteration processes, such as asteroidal heating. 相似文献
27.
28.
Stefano?ParolaiEmail author Andreas?F?cke Sandra?M.?Richwalski Lothar?Stempniwski 《Natural Hazards》2005,34(2):217-230
Ambient seismic noise measurements were conducted inside the Holweide Hospital (Cologne) for checking whether its frequencies of vibration fall into the range where soil amplification is expected. If this is the case, damage might increase in case of an earthquake due to an amplified structural response of the building. Two different techniques were used: the ratio between the horizontal and vertical components of the spectra recorded at stations located inside the building and the ratio between the corresponding components of the spectra recorded simultaneously inside the building and at a reference station placed outside. While the former method might be preferred because of less equipment involved, the latter has the advantage of producing more stable results and deleting automatically the influence of the sedimentary cover, which might obscure some eigenfrequencies of vibration of the building. An independently performed finite-element analysis of the hospital showed a good correlation between measured and calculated eigenmodes. 相似文献
29.
Wolfgang Kuhnt Florian Luderer Sandra Nederbragt Jürgen Thurow Thomas Wagner 《International Journal of Earth Sciences》2005,94(1):147-159
High sedimentation rates (up to 12 cm/kyear) of laminated organic carbon-rich biogenic limestones in the Tarfaya Basin provide an unusually high (millennial) resolution record of the late Cenomanian oceanic anoxic event (OAE-2). The global positive carbon-isotope excursion across the Cenomanian–Turonian corresponds to 11 light/dark sedimentary cycles. We interpret these cycles as a response to orbital obliquity variation and estimate the duration of the complete excursion as 440 kyear or one long eccentricity cycle. On this timescale, the main increase in 13C values occurred over a short time interval of less than 20 kyear in the late Cenomanian and reached a first maximum approximately 15 kyear prior to the bulk (mainly coccoliths) 18O-derived sea surface maximum temperature that occurs coeval to the extinction of Rotalipora cushmani. Organic carbon-accumulation rates follow obliquity cycles, reaching a maximum approximately 10 kyear after the last occurrence of R. cushmani, then slowly decreasing during the early Turonian. Thus, the maximum temperature and the maximum organic carbon accumulation in the Tarfaya Basin lagged by at least 15 kyear behind the global carbon-isotope shift and a proposed reduction of atmospheric CO2 content. The climate change across the Cenomanian/Turonian boundary probably occurred independent of CO2 levels and may have been controlled by different greenhouse gases (water vapour and methane) and changes in ocean circulation (i.e., opening of the Equatorial Atlantic gateway) 相似文献
30.