全文获取类型
收费全文 | 1069篇 |
免费 | 54篇 |
国内免费 | 7篇 |
专业分类
测绘学 | 16篇 |
大气科学 | 76篇 |
地球物理 | 235篇 |
地质学 | 460篇 |
海洋学 | 54篇 |
天文学 | 222篇 |
自然地理 | 67篇 |
出版年
2021年 | 11篇 |
2020年 | 18篇 |
2019年 | 10篇 |
2018年 | 27篇 |
2017年 | 19篇 |
2016年 | 23篇 |
2015年 | 32篇 |
2014年 | 39篇 |
2013年 | 85篇 |
2012年 | 44篇 |
2011年 | 66篇 |
2010年 | 63篇 |
2009年 | 73篇 |
2008年 | 49篇 |
2007年 | 36篇 |
2006年 | 40篇 |
2005年 | 40篇 |
2004年 | 39篇 |
2003年 | 24篇 |
2002年 | 16篇 |
2001年 | 25篇 |
2000年 | 20篇 |
1999年 | 9篇 |
1998年 | 17篇 |
1997年 | 28篇 |
1996年 | 15篇 |
1995年 | 17篇 |
1994年 | 12篇 |
1993年 | 11篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 13篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1971年 | 9篇 |
1914年 | 7篇 |
1911年 | 4篇 |
1910年 | 5篇 |
排序方式: 共有1130条查询结果,搜索用时 31 毫秒
991.
Mu Ramkumar Doris Stüben Zsolt Berner Jens Schneider 《Journal of Earth System Science》2010,119(1):1-17
The Ariyalur-Pondicherry sub-basin of the Cauvery basin comprises a near complete stratigraphic record of Upper Cretaceous-Lower
Tertiary periods. Earlier studies have documented variations of clay mineral assemblages, change in microtexture of siliciclasts
and many geochemical and stable isotopic anomalies far below the Cretaceous-Tertiary boundary (KTB) in these strata. This
paper documents the occurrences of two positive 87Sr/86Sr anomalies preceding K-T boundary in this basin and discusses plausible causes. Analysis of trace elemental and stable isotopic
profiles, sedimentation history, petrography and mineralogy of the rocks reveal that while both the anomalies may be due to
increased detrital influx caused by sea level and climatic changes, the second anomaly might have been influenced by Deccan
volcanism which in turn predated KTB. Record of such anomalies preceding K-T boundary supports the view of multi-causal step-wise
extinction of biota across KTB. 相似文献
992.
Lassaad Mejri Vincent Regard Sébastien Carretier Stéphane Brusset Mahmoud Dlala 《Comptes Rendus Geoscience》2010,342(11):864-872
The present-day seismicity in northeastern Tunisia reported from permanent networks is of low to moderate magnitude. However, earthquakes are mentioned in the literature, specially a destructive one in the antique city of Utique. Geologic, seismic, and neotectonic investigations in this area show that the Utique fold is closely related to the recent tectonic activity in this region. Data show that the Utique fold is built on an east-west fault, and we found evidence of activity of this fault in the past 20 kyr. A seismic section and balanced cross-section show that the slip rate is of the order of 0.38 mm.yr−1. Our data show definitively the Late Pleistocene–Holocene activity of the Utique Fault; and we can predict the earthquake recurrence interval which should be of ∼103–104 yr. This high seismic risk zone deserves to be taken into account during the establishment of important regional development programs and in the application of seismic building codes. 相似文献
993.
Lattice diffusion coefficients have been determined for 19 elements (Li, Be, Na, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y,
Zr, Eu, Gd, Lu and Hf) in a single crystal of San Carlos olivine as a function of crystallographic orientation, at 1,300°C,
1 bar and fO2 = 10−8.3 bars, by equilibration with a synthetic silicate melt. Results for Li, Na, V, Cr, Fe and Zn are from diffusion of these elements
out of the olivine, starting from their indigenous concentrations; those for all other elements are from diffusion into the
olivine, from the silicate melt reservoir. Our 25-day experiment produced diffusion profiles 50 to > 700 μm in length, which
are sufficiently long that precise analyses could be achieved by scanning laser ablation inductively coupled plasma mass spectrometry,
even at concentration levels well below 1 μg g−1. For the divalent cations Ca, Mn, Fe and Ni, profiles were also obtained by electron microprobe analysis. The results of
the two methods agree well with each other, and are consistent with divalent cation diffusion coefficients previously determined
using different experimental methodologies. Olivine/melt partition coefficients retrieved from the data are also consistent
with other published partitioning data, indicating that element incorporation and transport in olivine in our experiment occurred
via mechanisms appropriate to natural conditions. Most of the examined trace elements diffuse through olivine at similar rates
to the major octahedral cations Fe and Mg, showing that cation charge and radius have little direct influence on diffusion
rates. Aluminium and P remain low and constant in the olivine, implying negligible transport at our analytical scale, hence
Al and P diffusion rates that are at least two orders of magnitude slower than the other cations studied here. All determined
element diffusivities are anisotropic, with diffusion fastest along the [001] axis, except Y and the REEs, which diffuse isotropically.
The results suggest that element diffusivity in olivine is largely controlled by cation site preference, charge balance mechanisms
and point-defect concentrations. Elements that are present on multiple cation sites in olivine (e.g. Be and Ti) and trivalent
elements that are charge-balanced by octahedral site vacancies tend to diffuse at relatively fast rates. 相似文献
994.
Aurélie Verney-Carron Stéphane Gin Guy Libourel 《Geochimica et cosmochimica acta》2010,74(8):2291-18706
To improve confidence in glass alteration models, as used in nuclear and natural applications, their long-term predictive capacity has to be validated. For this purpose, we develop a new model that couples geochemical reactions with transport and use a fractured archaeological glass block that has been altered for 1800 years under well-constrained conditions in order to test the capacity of the model.The chemical model considers three steps in the alteration process: (1) formation of a hydrated glass by interdiffusion, whose kinetics are controlled by a pH and temperature dependent diffusion coefficient; (2) the dissolution of the hydrated glass, whose kinetics are based on an affinity law; (3) the precipitation of secondary phases if thermodynamic saturation is reached. All kinetic parameters were determined from experiments. The model was initially tested on alteration experiments in different solutions (pure water, Tris, seawater). It was then coupled with diffusive transport in solution to simulate alteration in cracks within the glass. Results of the simulations run over 1800 years are in good agreement with archaeological glass block observations concerning the nature of alteration products (hydrated glass, smectites, and carbonates) and crack alteration thicknesses. External cracks in direct contact with renewed seawater were altered at the forward dissolution rate and are filled with smectites (400−500 μm). Internal cracks are less altered (by 1 or 2 orders of magnitude) because of the strong coupling between alteration chemistry and transport. The initial crack aperture, the distance to the surface, and sealing by secondary phases account for these low alteration thicknesses. The agreement between simulations and observations thus validates the predictive capacity of this coupled geochemical model and increases more generally the robustness and confidence in glass alteration models to predict long-term behavior of nuclear waste in geological disposal or natural glass in the environment. 相似文献
995.
We have used the Krall flux-rope model (Krall and St. Cyr, Astrophys. J. 2006, 657, 1740) (KFR) to fit 23 magnetic cloud (MC)-CMEs and 30 non-cloud ejecta (EJ)-CMEs in the Living With a Star (LWS) Coordinated Data Analysis Workshop (CDAW) 2011 list. The KFR-fit results shows that the CMEs associated with MCs (EJs) have been deflected closer to (away from) the solar disk center (DC), likely by both the intrinsic magnetic structures inside an active region (AR) and ambient magnetic structures (e.g. nearby ARs, coronal holes, and streamers, etc.). The mean absolute propagation latitudes and longitudes of the EJ-CMEs (18°, 11°) were larger than those of the MC-CMEs (11°, 6°) by 7° and 5°, respectively. Furthermore, the KFR-fit widths showed that the MC-CMEs are wider than the EJ-CMEs. The mean fitting face-on width and edge-on width of the MC-CMEs (EJ-CMEs) were 87 (85)° and 70 (63)°, respectively. The deflection away from DC and narrower angular widths of the EJ-CMEs have caused the observing spacecraft to pass over only their flanks and miss the central flux-rope structures. The results of this work support the idea that all CMEs have a flux-rope structure. 相似文献
996.
Patrick Lajeunesse Guillaume St‐Onge Jacques Locat Mathieu J. Duchesne Michael D. Higgins Richard Sanfaçon Joseph Ortiz 《Meteoritics & planetary science》2013,48(12):2542-2558
We report on a 4.1 (±0.2) km diameter and 185 m deep circular submarine structure exposed on the seabed in >40 m water depths in the northwestern Gulf of St. Lawrence (Eastern Canada) from the analysis of high‐resolution multibeam bathymetric and seismic data. The presence of a circular form characterized by a central uplift and concentric rings resembles the morphology and geometry of complex meteorite impact structures. Also, other origins, such as kimberlites, intrusions, karsts, or diapirs, can be eliminated on geological criteria. A single 4 cm long breccia fragment recovered from the central uplift has numerous glassy droplets of fluorapatite composition, assumed to be impact melts, and a single quartz grain with planar intersection features thought to be shock‐induced planar deformation features (PDFs). The absolute age of this possible impact structure is unknown, but its geological setting indicates that it was formed long after the Mid‐Ordovician and before regional pre‐Quaternary sea‐level lowstands. Present results outline the need for further examination to confirm an impact origin and to precisely date the formation of the structure. 相似文献
997.
J. Luterbacher S. J. Koenig J. Franke G. van der Schrier E. Zorita A. Moberg J. Jacobeit P. M. Della-Marta M. Küttel E. Xoplaki D. Wheeler T. Rutishauser M. Stössel H. Wanner R. Brázdil P. Dobrovolný D. Camuffo C. Bertolin A. van Engelen F. J. Gonzalez-Rouco R. Wilson C. Pfister D. Limanówka Ø. Nordli L. Leijonhufvud J. Söderberg R. Allan M. Barriendos Rüdiger Glaser D. Riemann Z. Hao C. S. Zerefos 《Climatic change》2010,101(1-2):201-234
We use long instrumental temperature series together with available field reconstructions of sea-level pressure (SLP) and three-dimensional climate model simulations to analyze relations between temperature anomalies and atmospheric circulation patterns over much of Europe and the Mediterranean for the late winter/early spring (January–April, JFMA) season. A Canonical Correlation Analysis (CCA) investigates interannual to interdecadal covariability between a new gridded SLP field reconstruction and seven long instrumental temperature series covering the past 250 years. We then present and discuss prominent atmospheric circulation patterns related to anomalous warm and cold JFMA conditions within different European areas spanning the period 1760–2007. Next, using a data assimilation technique, we link gridded SLP data with a climate model (EC-Bilt-Clio) for a better dynamical understanding of the relationship between large scale circulation and European climate. We thus present an alternative approach to reconstruct climate for the pre-instrumental period based on the assimilated model simulations. Furthermore, we present an independent method to extend the dynamic circulation analysis for anomalously cold European JFMA conditions back to the sixteenth century. To this end, we use documentary records that are spatially representative for the long instrumental records and derive, through modern analogs, large-scale SLP, surface temperature and precipitation fields. The skill of the analog method is tested in the virtual world of two three-dimensional climate simulations (ECHO-G and HadCM3). This endeavor offers new possibilities to both constrain climate model into a reconstruction mode (through the assimilation approach) and to better asses documentary data in a quantitative way. 相似文献
998.
Guilherme Mallmann Hugh St. C. O’Neill Stephan Klemme 《Contributions to Mineralogy and Petrology》2009,158(4):485-504
The major- and trace-element abundances of the coexisting phases of four metasomatized spinel peridotite xenoliths from the
Anakies locality (SE Australia) were determined by electron microprobe and laser-ablation ICP-MS. The compositions of all
phases are remarkably homogeneous, with the exception of phosphorus (P), lithium (Li) and sodium (Na) in olivine. These three
elements are enriched in large parts of most olivine crystals due to a second metasomatic episode. Apart from these elements,
all phases are in mutual equilibrium with respect to both their major- and trace-element compositions. Li and Na show a strong
correlation with P in olivine, although molar Li + Na are an order of magnitude less than molar P, indicating that the substitution
mechanism of these elements is more complex than the simple charge-balanced coupled exchange IVSi4+ + VI(FeMg)2+ = IVP5+ + VI(LiNa)+. We suggest that Li and Na are decorating octahedral-site cation vacancies formed by the original incorporation of P. Elemental
maps revealed that the P zoning patterns are concentric in a few large olivine porphyroblasts, but form irregular patches
in most crystals. This distribution of P is proposed to be the result of a two-stage process, whereby the initial concentric
zoning, caused by its exceptionally sluggish diffusion after metasomatic influx, is broken up by extensive sub-solidus deformation
and recrystallization, attesting to large grain-scale strains even within the lithosphere. Such strains must be an efficient
means of ensuring trace-element equilibrium during partial melting. The association of Li with P in olivine may help to explain
the variability of Li abundances in mantle minerals and to interpret Li diffusion experiments and Li isotopic fractionation. 相似文献
999.
The abundances of 30 trace elements, including the volatile chalcophile/siderophile elements As, Cd, Ga, In and Sn were determined by laser ablation ICP-MS in minerals of 19 anhydrous and 5 hydrous spinel peridotite xenoliths from three continents. The majority of samples were fertile lherzolites with more than 5% clinopyroxene; several samples have major element compositions close to estimates of the primitive mantle. All samples have been previously analysed for bulk-rock major, minor and lithophile trace elements. They cover a wide range of equilibration temperatures from about 850 to 1250 °C and a pressure range from 0.8 to 3.0 GPa. A comparison of results from bulk-rock analyses with concentrations obtained from combining silicate and oxide mineral data with modal mineralogy, gave excellent agreement, with the exception of As. Arsenic is the only element analysed that has high concentrations in sulphides. For all other elements sulphides can be neglected as host phases in these mantle rocks. The major host phase for Cd, In and Sn is clinopyroxene and if present, amphibole. Cadmium and In appear to behave moderately incompatibly during mantle melting similar to Yb.The data yield new and more reliable mantle abundances for Cd (35 ± 7 ppb), In (18 ± 3 ppb) and Sn (91 ± 28 ppb). The In value is similar to the Mg and CI-normalized Zn abundance of the mantle, although In is cosmochemically more volatile than Zn. The high In content suggests a high content of volatile elements in general in proto-Earth material. The lower relative abundances of volatile chalcophile elements such as Cd, S, Se and Te might be explained by sulphide segregation during core formation. The very low relative abundances of volatile and highly incompatible lithophile elements such as Br, Cl and I, and also C, N and rare gases, imply loss during Earth accretion, arguably by collisional erosion from differentiated planetesimals and protoplanets. 相似文献
1000.
P. Kallioglou Th. Tika G. Koninis St. Papadopoulos K. Pitilakis 《Geotechnical and Geological Engineering》2009,27(2):217-235
The paper presents results from a laboratory investigation into the dynamic properties of natural intact and model organic
soils by means of resonant-column tests. The natural intact organic soils were sands, cohesive soils and peats with varying
content of calcium carbonate. The model organic soils were formed in laboratory by mixing kaolinite and paper pulp. The influence
of various soil parameters, such as strain level, confining stress, void ratio, plasticity index, organic content and secondary
consolidation time on shear modulus, G, and damping ratio, DT, is presented and discussed. The test results on natural organic
soils show that only high organic contents (OC ≥ 25%) have significant influence on G and DT at both small and high shear
strains. For the model organic soils, however, a significant influence of even lower values of organic content (5% ≤ OC ≤ 20%)
on G at small strains and DT at both small and high strains is observed. 相似文献