全文获取类型
收费全文 | 628篇 |
免费 | 21篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 17篇 |
大气科学 | 42篇 |
地球物理 | 169篇 |
地质学 | 196篇 |
海洋学 | 67篇 |
天文学 | 108篇 |
综合类 | 2篇 |
自然地理 | 50篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 9篇 |
2020年 | 10篇 |
2019年 | 17篇 |
2018年 | 21篇 |
2017年 | 30篇 |
2016年 | 31篇 |
2015年 | 20篇 |
2014年 | 30篇 |
2013年 | 34篇 |
2012年 | 29篇 |
2011年 | 39篇 |
2010年 | 35篇 |
2009年 | 32篇 |
2008年 | 36篇 |
2007年 | 30篇 |
2006年 | 31篇 |
2005年 | 25篇 |
2004年 | 21篇 |
2003年 | 18篇 |
2002年 | 18篇 |
2001年 | 12篇 |
2000年 | 12篇 |
1999年 | 13篇 |
1998年 | 9篇 |
1997年 | 8篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1970年 | 4篇 |
1966年 | 2篇 |
1963年 | 4篇 |
1961年 | 2篇 |
1940年 | 2篇 |
排序方式: 共有651条查询结果,搜索用时 31 毫秒
521.
Marta L. PATINO-DOUCE Alberto PATINO-DOUCE Mazhar QAYYUM Roger L. NIELSEN 《Geostandards and Geoanalytical Research》1994,18(2):195-198
We have developed a set of four synthetic standards for the rare earth and high field strength elements designed for use in the determination of those elements in silicates. The base material is a glass nominally at the eutectic of the MgO-Al2 O3 -SiO2 ternary system. The nominal doping level was 2 wt% of the elements as oxides. To avoid problems associated with peak interference, the elements were doped in four separate glasses. 相似文献
522.
Christian Gorini Bilal U. Haq Antonio Tadeu dos Reis Cleverson Guizan Silva Alberto Cruz Emilson Soares Didier Grangeon 《地学学报》2014,26(3):179-185
The margin of the Foz do Amazonas Basin saw a shift from predominantly carbonate to siliciclastic sedimentation in the early late Miocene. By this time, the Amazon shelf had also been incised by a canyon that allowed direct influx of sediment to the basin floor, thus confirming that the palaeo‐Amazon fan had already initiated by that time (9.5–8.3 Ma). Above this interval, during a prolonged lowstand, Messinian third‐order sequences are preserved only in the incised‐valley fills of the canyon with no equivalent strata on the shelf. Third‐ and fourth‐order sequences younger than Messinian are preserved on the shelf after sea‐level rise above the shelf by the early Pliocene. Sequences younger than 3.8 Ma often show fourth‐order cyclicity with an average duration of 400 ka (larger scale eccentricity cycles) often preserved in high‐sedimentation‐rate areas of river deltas. Mass wasting and transportation of slope sediments to the basin began to play an important role in sediment dispersal at least as far back as the mid‐Pliocene, after rapid progradation had produced steeper slopes more prone to failure. 相似文献
523.
Giuseppe A. Marzo Alfonso F. Davila Livio L. Tornabene Alberto G. Fairén Thomas Kneissl Ted L. Roush 《Icarus》2010,208(2):667-60
Several hydrated silicate deposits on Mars are observed within craters and are interpreted as excavated Noachian material. Toro crater (71.8°E, 17.0°N), located on the northern edge of the Syrtis Major Volcanic Plains, shows spectral and morphologic evidence of impact-induced hydrothermal activity. Spectroscopic observations were used to identify extensive hydrated silicate deposits, including prehnite, chlorites, smectites, and opaline material, a suite of phases that frequently results from hydrothermal alteration in terrestrial craters and also expected on Mars from geochemical modeling of hydrothermal environments. When combined with altimetry and high-resolution imaging data, these deposits appear associated predominantly with the central uplift and with portions of the northern part of the crater floor. Detailed geologic mapping of these deposits reveals geomorphic features that are consistent with hydrothermal activity that followed the impact event, including vent-like and conical mound structures, and a complex network of tectonic structures caused by fluid interactions such as fractures and joints. The crater age has been calculated from the cumulative crater size-frequency distributions and is found to be Early Hesperian. The evidence presented here provides support for impact-induced hydrothermal activity in Toro crater, that extends phyllosilicate formation processes beyond the Noachian era. 相似文献
524.
James M. Dohm Victor R. Baker William V. Boynton Alberto G. Fairén Justin C. Ferris Michael Finch Roberto Furfaro Trent M. Hare Daniel M. Janes Jeffrey S. Kargel Suniti Karunatillake John Keller Kris Kerry Kyeong J. Kim Goro Komatsu William C. Mahaney Dirk Schulze-Makuch Lucia Marinangeli Gian G. Ori Javier Ruiz Shawn J. Wheelock 《Planetary and Space Science》2009,57(5-6):664-684
The Gamma Ray Spectrometer (Mars Odyssey spacecraft) has revealed elemental distributions of potassium (K), thorium (Th), and iron (Fe) on Mars that require fractionation of K (and possibly Th and Fe) consistent with aqueous activity. This includes weathering, evolution of soils, and transport, sorting, and deposition, as well as with the location of first-order geomorphological demarcations identified as possible paleoocean boundaries. The element abundances occur in patterns consistent with weathering in situ and possible presence of relict or exhumed paleosols, deposition of weathered materials (salts and clastic minerals), and weathering/transport under neutral to acidic brines. The abundances are explained by hydrogeology consistent with the possibly overlapping alternatives of paleooceans and/or heterogeneous rock compositions from diverse provenances (e.g., differing igneous compositions). 相似文献
525.
Lorenzo Fedele Alberto Zanetti Vincenzo Morra Michele Lustrino Leone Melluso Riccardo Vannucci 《Contributions to Mineralogy and Petrology》2009,158(3):337-356
Trace element partition coefficients between clinopyroxenes and associated glassy matrix (Cpx/L
D) have been determined for 13 REE, HFSE4+,5+, U, Th, Sr, Pb, Sc and V from combined LA-ICP-MS/EMP analyses in selected trachytes and trachyphonolites from Campi Flegrei.
Composition of clinopyroxene and glass is pretty homogeneous in the trachyphonolites, pointing to an overall attainment of
the equilibrium conditions. In trachytes, conversely, phases show some compositional heterogeneity (due to the presence of
clinopyroxene xenocrysts) that requested a more careful petrographic and geochemical inspection of the samples to assess the
equilibrium clinopyroxene composition. In the trachyte clinopyroxenes, REE are compatible from Nd to Lu (Cpx/L
D up to 2.9), like Y, Ti, Sc and V. The Cpx/L
D for Eu is lower than those of the adjacent REE, highlighting Eu2+ contribution. High D values are also shown by U, Th, Pb, Zr, Hf, Nb and Ta relatively to basaltic and andesitic systems, whereas the D
Sr is roughly similar to that found for less evolved magmas. Trachyphonolites are characterized by an overall decrease of the
Cpx/L
D for highly-charged cations (with the exception of V), and by a slight increase of D
Sr. REE are still compatible from Nd to Lu (Cpx/L
D up to 2.1), like Ti, Y, Sc and V. This variation is also predicted for REE and Y by models based on the elastic strain theory,
being consistent with the slightly lower polymerization degree estimated for the trachyphonolites. However, the observed Cpx/L
D
(REE,Y) are matched by the modelled ones only considering very low T (≤825°C), which are believed unlikely. This mismatch cannot be attributed to effects induced by the water-rich composition
of the trachyte–trachyphonolite suite, since they would lower the observed Cpx/L
D
(REE,Y). Moreover, the anomalous inflections of measured Cpx/L
D for HREE suggests some crystal-chemical control, such as the entrance of these elements in a site distinct from M2. It is
concluded that the large Cpx/L
D determined for trachytes and trachyphonolites are likely induced by hitherto unconstrained changes of the Z3+ activities related to the composition of melt and/or solid. All these considerations strongly highlight the importance of
a direct characterization of trace element partitioning in natural samples from magmatic systems poorly characterized by experimental
studies.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
526.
Joaquín Guerrero-Campo Francisco Alberto Melchor Maestro John Hodgson Gabriel Montserrat-Martí 《Journal of Arid Environments》1999,41(4):411
A model, based on the physico-chemical properties of gypsum, is postulated in order to interpret the regular distribution of plant communities associated with the topography and the main environmental stresses to which each vegetation type is subjected in a landscape unit.The leaf chemical composition of 28 representative plant species supports the main predictions of the model: species from low areas present large concentrations of Na, N and ash but low contents of Ca. It is demonstrated that the strong nutrient and salt downwashing in the hilly terrain is an important cause of the vegetation segregation observed on a large spatial scale. 相似文献
527.
We analyzed the instrumental seismicity of Southern Italy in the area including the Lucanian Apennines and Bradano foredeep, making use of the most recent seismological data base available so far. P- and S-wave arrival times, recorded by the Italian National Seismic Network (RSNC) operated by the Istituto Nazionale di Geofisica e Vulcanologia (INGV), were re-picked along with those of the SAPTEX temporary array deployed in the region in the period 2001–2004. For some events located in the upper Val d'Agri, we also used data from the Eni-Agip oil company seismic network. We examined the seismicity occurred during the period between 2001 and 2006, considering 514 events with magnitudes M ≥ 2.0. We computed the VP/VS ratio obtaining a value of 1.83 and we carried out an analysis for the one-dimensional (1D) velocity model that approximates the seismic structure of the study area. Earthquakes were relocated and, for well- recorded events, we also computed 108 fault plane solutions. Finally, using 58 solutions, the most constrained, we computed regional stress field in the study area.Earthquake distribution shows three main seismic regions: the westernmost (Lucanian Apennines) characterized by high background seismicity, mostly with shallow hypocenters, the easternmost below the Bradano foredeep and the Murge with deeper and more scattered seismicity, and finally the more isolated and sparse seismicity localized in the Sila Range and in the offshore area along the northeastern Calabrian coast. Focal mechanisms computed in this work are in large part normal and strike-slip solutions and their tensional axes (T-axes) have a generalized NE–SW orientation. The denser station coverage allowed us to improve hypocenters determination compared to those obtained by using only RSNC data, for a better characterization of the crustal and subcrustal seismicity in the study area. 相似文献
528.
Probability-weighted hazard maps for comparing different flood risk management strategies: a case study 总被引:5,自引:1,他引:4
Giuliano Di Baldassarre Attilio Castellarin Alberto Montanari Armando Brath 《Natural Hazards》2009,50(3):479-496
The study proposes an original methodology for producing probability-weighted hazard maps based on an ensemble of numerical
simulations. These maps enable one to compare different strategies for flood risk management. The methodology was applied
over a 270-km2 flood-prone area close to the left levee system of a 28-km reach of the river Reno (Northern Central Italy). This reach is
characterised by the presence of a weir that allows controlled flooding of a large flood-prone area during major events. The
proposed probability-weighted hazard maps can be used to evaluate how a structural measure such as the mentioned weir alters
the spatial variability of flood hazard in the study area. This article shows an application by constructing two different
flood hazard maps: a first one which neglects the presence of the weir using a regular levee system instead, and a second
one that reflects the actual geometry with the weir. Flood hazard maps were generated by combining the results of several
inundation scenarios, simulated by coupling 1D- and 2D-hydrodynamic models. 相似文献
529.
530.
On the Impact of Anthropogenic Heat Fluxes on the Urban Boundary Layer: A Two-Dimensional Numerical Study 总被引:2,自引:1,他引:1
Andrea Krpo Francisco Salamanca Alberto Martilli Alain Clappier 《Boundary-Layer Meteorology》2010,136(1):105-127
The heat generated in buildings and the manner in which this heat is exchanged with the ambient environment can play an important
role in urban climate. Recent studies have shown that anthropogenic heat from air-conditioning facilities can increase the
exterior ambient temperature and should be taken into account for a more complete urban heat island (UHI) mitigation study.
For this purpose, the first part of the present work is focused on the coupling of a new building energy model (BEM) and an
urban canopy parameterisation (UCP). The new scheme is implemented in a finite volume mesoscale model (MM) and tested in a
two-dimensional (2D) configuration of a city over flat terrain. A sensitivity study is performed with respect to different
parameters in order to test the simulation system and enhance the understanding of the possible impacts of the BEM on the
exterior microclimate. 相似文献