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201.
Jutta ZIPFEL Bradley L. JOLLIFF Ralf GELLERT Kenneth E. HERKENHOFF Rudolf RIEDER Robert ANDERSON James F. BELL III Johannes BRÜCKNER Joy A. CRISP Philip R. CHRISTENSEN Benton C. CLARK Paulo A.
De SOUZA Jr. Gerlind DREIBUS Claude
D’USTON Thanasis ECONOMOU Steven P. GOREVAN Brian C. HAHN Göstar KLINGELHÖFER Timothy J. McCOY Harry Y. McSWEEN Jr. Douglas W. MING Richard V. MORRIS Daniel S. RODIONOV Steven W. SQUYRES Heinrich WÄNKE Shawn P. WRIGHT Michael B. WYATT Albert S. YEN 《Meteoritics & planetary science》2011,46(1):1-20
Abstract– The Opportunity rover of the Mars Exploration Rover mission encountered an isolated rock fragment with textural, mineralogical, and chemical properties similar to basaltic shergottites. This finding was confirmed by all rover instruments, and a comprehensive study of these results is reported here. Spectra from the miniature thermal emission spectrometer and the Panoramic Camera reveal a pyroxene‐rich mineralogy, which is also evident in Mössbauer spectra and in normative mineralogy derived from bulk chemistry measured by the alpha particle X‐ray spectrometer. The correspondence of Bounce Rock’s chemical composition with the composition of certain basaltic shergottites, especially Elephant Moraine (EET) 79001 lithology B and Queen Alexandra Range (QUE) 94201, is very close, with only Cl, Fe, and Ti exhibiting deviations. Chemical analyses further demonstrate characteristics typical of Mars such as the Fe/Mn ratio and P concentrations. Possible shock features support the idea that Bounce Rock was ejected from an impact crater, most likely in the Meridiani Planum region. Bopolu crater, 19.3 km in diameter, located 75 km to the southwest could be the source crater. To date, no other rocks of this composition have been encountered by any of the rovers on Mars. The finding of Bounce Rock by the Opportunity rover provides further direct evidence for an origin of basaltic shergottite meteorites from Mars. 相似文献
202.
Abstract– To better understand the impact cratering process and its environmental consequences at the local to global scale, it is important to know when in the geological record of an impact crater the impact‐related processes cease. In many instances, this occurs with the end of early crater modification, leaving an obvious sedimentological boundary between impactites and secular sediments. However, in marine‐target craters the transition from early crater collapse (i.e., water resurge) to postimpact sedimentation can appear gradual. With the a priori assumption that the reworked target materials of the resurge deposits have a different chemical composition to the secular sediments we use chemostratigraphy (δ13Ccarb, %Corg, major elements) of sediments from the Chesapeake Bay, Lockne, and Tvären craters, to define this boundary. We show that the end of impact‐related sedimentation in these cases is fairly rapid, and does not necessarily coincide with a visual boundary (e.g., grain size shift). Therefore, in some cases, the boundary is more precisely determined by chemostratigraphy, especially carbonate carbon isotope variations, rather than by visual inspection. It is also shown how chemostratigraphy can confirm the age of marine‐target craters that were previously determined by biostratigraphy; by comparing postimpact carbon isotope trends with established regional trends. 相似文献
203.
Vladimir A. Krasnopolsky Jean Pierre Maillard Tobias C. Owen Robert A. Toth Michael D. Smith 《Icarus》2007,192(2):396-403
Oxygen and carbon isotope ratios in the martian CO2 are key values to study evolution of volatiles on Mars. The major problems in spectroscopic determinations of these ratios on Mars are uncertainties associated with: (1) equivalent widths of the observed absorption lines, (2) line strengths in spectroscopic databases, and (3) thermal structure of the martian atmosphere during the observation. We have made special efforts to reduce all these uncertainties. We observed Mars using the Fourier Transform Spectrometer at the Canada–France–Hawaii Telescope. While the oxygen and carbon isotope ratios on Mars were byproducts in the previous observations, our observation was specifically aimed at these isotope ratios. We covered a range of 6022 to 6308 cm−1 with the highest resolving power of ν/δν=3.5×105 and a signal-to-noise ratio of 180 in the middle of the spectrum. The chosen spectral range involves 475 lines of the main isotope, 184 lines of 13CO2, 181 lines of CO18O, and 119 lines of CO17O. (Lines with strengths exceeding 10−27 cm at 218 K are considered here.) Due to the high spectral resolution, most of the lines are not blended. Uncertainties of retrieved isotope abundances are in inverse proportion to resolving power, signal-to-noise ratio, and square root of the number of lines. Laboratory studies of the CO2 isotope spectra in the range of our observation achieved an accuracy of 1% in the line strengths. Detailed observations of temperature profiles using MGS/TES and data on temperature variations with local time from two GCMs are used to simulate each absorption line at various heights in each part of the instrument field of view and then sum up the results. Thermal radiation of Mars' surface and atmosphere is negligible in the chosen spectral range, and this reduces errors associated with uncertainties in the thermal structure on Mars. Using a combination of all these factors, the highest accuracy has been achieved in measuring the CO2 isotope ratios: 13C/12C = 0.978 ± 0.020 and 18O/16O = 1.018 ± 0.018 times the terrestrial standards. Heavy isotopes in the atmosphere are enriched by nonthermal escape and sputtering, and depleted by fractionation with solid-phase reservoirs. The retrieved ratios show that isotope fractionation between CO2 and oxygen and carbon reservoirs in the solid phase is almost balanced by nonthermal escape and sputtering of O and C from Mars. 相似文献
204.
Pablo Samaniego Claude Robin Gilles Chazot Erwan Bourdon Joseph Cotten 《Contributions to Mineralogy and Petrology》2010,160(2):239-260
Geochemical studies of long-lived volcanic complexes are crucial for the understanding of the nature and composition of the
subduction component of arc magmatism. The Pichincha Volcanic Complex (Northern Andean Volcanic Zone) consists of: (1) an
old, highly eroded edifice, the Rucu Pichincha, whose lavas are mostly andesites, erupted from 1,100 to 150 ka; and (2) a
younger, essentially dacitic, Guagua Pichincha composite edifice, with three main construction phases (Basal Guagua Pichincha,
Toaza, and Cristal) which developed over the last 60 ka. This structural evolution was accompanied by a progressive increase
of most incompatible trace element abundances and ratios, as well as by a sharp decrease of fluid-mobile to fluid-immobile
element ratios. Geochemical data indicate that fractional crystallization of an amphibole-rich cumulate may account for the
evolution from the Guagua Pichincha andesites to dacites. However, in order to explain the transition between the Rucu Pichincha
andesites and Guagua Pichincha dacites, the mineralogical and geochemical data indicate the predominance of magma mixing processes
between a mafic, trace-element depleted, mantle-derived end-member, and a siliceous, trace-element enriched, adakitic end-member.
The systematic variation of trace element abundances and ratios in primitive samples leads us to propose that the Rucu Pichincha
magmas came from a hydrous-fluid metasomatized mantle wedge, whereas Guagua Pichincha magmas are related to partial melting
of a siliceous-melt metasomatized mantle. This temporal evolution implies a change from dehydration to partial melting of
the slab, which may be associated with an increase in the geothermal gradient along the slab due to the presence of the subducted
Carnegie Ridge at the subduction system. This work emphasizes the importance of studying arc-magma systems over long periods
of time (of at least 1 million of years), in order to evaluate the potential variations of the slab contribution into the
mantle source of the arc magmatism. 相似文献
205.
Marlon M. Jean John W. Shervais Sung-Hi Choi Samuel B. Mukasa 《Contributions to Mineralogy and Petrology》2010,159(1):113-136
The middle Jurassic Coast Range Ophiolite (CRO) is one of the most important tectonic elements in western California, cropping
out as tectonically dismembered elements that extend 700 km from south to north. The volcanic and plutonic sections are commonly
interpreted to represent a supra-subduction zone (SSZ) ophiolite, but models specifying a mid-ocean ridge origin have also
been proposed. These contrasting interpretations have distinctly different implications for the tectonic evolution of the
western Cordillera in the Jurassic. If an SSZ origin is confirmed, we can use the underlying mantle peridotites to elucidate
melt processes in the mantle wedge above the subduction zone. This study uses laser ablation–inductively coupled plasma–mass
spectrometry (LA–ICP–MS) to study pyroxenes in peridotites from four mantle sections in the CRO. Trace element signatures
of these pyroxenes record magmatic processes characteristic of both mid-ocean ridge and supra-subduction zone settings. Group
A clinopyroxene display enriched REE concentrations [e.g., Gd (0.938–1.663 ppm), Dy (1.79–3.24 ppm), Yb (1.216–2.047 ppm),
and Lu (0.168–0.290 ppm)], compared to Group B and C clinopyroxenes [e.g., Gd (0.048–0.055 ppm), Dy (0.114–0.225 ppm), Yb
(0.128–0.340 ppm), and Lu (0.022–0.05 ppm)]. These patterns are also evident in orthopyroxene. The differences between these
geochemical signatures could be a result of a heterogeneous upper mantle or different degrees of partial melting of the upper
mantle. It will be shown that CRO peridotites were generated through fractional melting. The shapes of REE patterns are consistent
with variable degrees of melting initiated within the garnet stability field. Models call for 3% dry partial melting of MORB-source
asthenosphere in the garnet lherzolite field for abyssal peridotites and 15–20% further partial melting in the spinel lherzolite
field, possibly by hydrous melting for SSZ peridotites. These geochemical variations and occurrence of both styles of melting
regimes within close spatial and temporal association suggest that certain segments of the CRO may represent oceanic lithosphere,
attached to a large-offset transform fault and that east-dipping, proto-Franciscan subduction may have been initiated along
this transform. 相似文献
206.
Lithic artifacts buried in the soil profile may be transported to the surface during tillage‐induced kinetic sieving, differential erosion, or swell–shrink cycles of clays and become part of a rock fragment mulch. Archaeologically, these manifestations are recognized as surface scatters. Although artifacts at the soil surface are difficult to relate to the local stratigraphic context, surface assemblages may provide information on lithic industries and the archaeological significance of sparsely explored regions. Through in situ investigation of surface material in 60 1 × 1 m2 plots in the Tembien district in the northern Ethiopian highlands, we show that rock fragment mulches can contain a significant number of lithic artifacts and we provide evidence for mid‐Pleistocene occupation of a site. Considering that severe rill and gully erosion may be a threat to the archaeological heritage and that well‐dated African Middle Stone Age sites are rare, we conclude that the region deserves more attention for archaeological research. © 2009 Wiley Periodicals, Inc. 相似文献
207.
208.
Adnand Bitri Jean-Pierre Brun Denis Gapais Florence Cagnard Charles Gumiaux Jean Chantraine Guillaume Martelet Catherine Truffert 《Comptes Rendus Geoscience》2010,342(6):448-452
We present results and interpretation of a 72 km long deep seismic reflection profile acquired across the internal zone of the Hercynian belt of South Brittany. The profile is of excellent quality, most of the crust being highly reflective. The “ARMOR 2 South” profile, is correlated with the “ARMOR 2 North” profile that was published in 2003. Correlation of the main subsurface reflections with surface geological and structural data provides important information about the crustal structure that resulted from thickening during Late Devonian and regional-scale extension during Late Carboniferous. In particular, seismics image shows a very high reflectivity zone, lying flat over more than 40 km at about 10–12 km depth. This zone is interpreted as a major zone of ductile crustal thinning. 相似文献
209.
Jean Ferrandini Michelle Ferrandini Philippe Rossi Brengre Savary-Sismondini 《Comptes Rendus Geoscience》2010,342(12):921-929
Priabonian age is highlighted for the first time in Corsica in the Venaco Formation using the presence of specific microfauna (in particular some representatives of Turborotalia cerroazulensis lineage). This silicoclastic formation is mainly represented by coarse facies. It is composed of three members from south to north and from oldest towards youngest: member of Uboli, Cardo and Orsu. The sedimentologic analysis reveals a gravity depositional environment, involving different type of currents. Sedimentologic and chronologic characteristics make the Venaco Formation and the Annot Formation (p.p.) equivalent. Dating the Venaco Fm. brings confirmation that the green schist metamorphism of the Variscan batholith and the related deformation are from the pre-Priabonian period. 相似文献
210.
Heat exchange during laminar flow in an open fracture is studied numerically on the basis of the Stokes equation in the limit of hydrothermal lubrication. We examine the influence of fracture roughness on hydraulic permeability and heat flux through the fracture sides when a cold fluid is injected into a homogeneous hot host rock. Spatial temperature fluctuations inside the fluid are studied assuming the temperature of the rock to be constant and the fracture aperture to be self-affine. An application to the case study at the deep geothermal reservoir of Soultz-sous-Forêts, France, is presented. Finally, a thermal model based on sparse spatial information of the geometrical aperture is successfully proposed to reproduce the response of the fracture. 相似文献