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排序方式: 共有427条查询结果,搜索用时 15 毫秒
91.
Emmanuel Jacquet Marine Paulhiac‐Pison Olivier Alard Anton T. Kearsley Matthieu Gounelle 《Meteoritics & planetary science》2013,48(10):1981-1999
We report trace element analyses by laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) of metal grains from nine different CR chondrites, distinguishing grains from chondrule interior (“interior grains”), chondrule surficial shells (“margin grains”), and the matrix (“isolated grains”). Save for a few anomalous grains, Ni‐normalized trace element patterns are similar for all three petrographic settings, with largely unfractionated refractory siderophile elements and depleted volatile Au, Cu, Ag, S. All three types of grains are interpreted to derive from a common precursor approximated by the least‐melted, fine‐grained objects in CR chondrites. This also excludes recondensation of metal vapor as the origin of the bulk of margin grains. The metal precursors were presumably formed by incomplete condensation, with evidence for high‐temperature isolation of refractory platinum‐group‐element (PGE)‐rich condensates before mixing with lower temperature PGE‐depleted condensates. The rounded shape of the Ni‐rich, interior grains shows that they were molten and that they equilibrated with silicates upon slow cooling (1–100 K h?1), largely by oxidation/evaporation of Fe, hence their high Pd content, for example. We propose that Ni‐poorer, amoeboid margin grains, often included in the pyroxene‐rich periphery common to type I chondrules, result from less intense processing of a rim accreted onto the chondrule subsequent to the melting event recorded by the interior grains. This means either that there were two separate heating events, which formed olivine/interior grains and pyroxene/margin grains, respectively, between which dust was accreted around the chondrule, or that there was a single high‐temperature event, of which the chondrule margin records a late “quenching phase,” in which case dust accreted onto chondrules while they were molten. In the latter case, high dust concentrations in the chondrule‐forming region (at least three orders of magnitude above minimum mass solar nebula models) are indicated. 相似文献
92.
Eric Deleersnijder Emmanuel Hanert Hans Burchard Henk A. Dijkstra 《Ocean Dynamics》2008,58(3-4):237-246
Occasionally, numerical simulations using local turbulence closure schemes to estimate vertical turbulent fluxes exhibit small-scale oscillations in space, causing the eddy coefficients to vary over several orders of magnitude on short distances. Theoretical developments suggest that these spurious oscillations are essentially due to the way the eddy coefficients depend on the vertical gradient of the model’s variables. An instability criterion is derived based on the assumptions that the artefacts under study are due to the development of small-amplitude, small time- and space-scale perturbations of a smooth solution. The relevance of this criterion is demonstrated by applying it to a series a closure schemes, ranging from the Pacanowski–Philander formulas to the Mellor–Yamada level 2.5 model. 相似文献
93.
The present experimental investigation focuses on the characteristics of near bed turbulence in a fully rough, uniform open-channel
flow over a gravel-type bed. Due to bed topography small scale heterogeneity, the flow is not uniform locally in the near
bed region and a double averaging methodology is applied over a length scale much larger than the gravel size. The double-averaged
Turbulent Kinetic Energy (TKE) budget derived in the context of the present flow over a gravel bed differs from the TKE budget
written for flow over a vegetation canopy. The non-constant shape of the roughness function measured in our gravel bed leads
to an additional bed-induced production term which is null for vertical roughness elements, such as simplified vegetation
elements.
The experimental estimation of the terms of the TKE budget reveals that the maximum turbulent activity takes place away from
the reference plane, near the roughness crests. However, within the interface sublayer the work of the bed induced velocity
fluctuations against the Reynolds stress is of the same magnitude as the main turbulence production term. Consequently, the
characteristics of the TKE budget have similarities with uniform flows over canopies and strongly differ from uniform flows
over smooth and transitionally rough flows over sedimentlike beds. 相似文献
94.
Emmanuel Hinglais 《Experimental Astronomy》2005,20(1-3):435-445
This paper analyses two height energy astrophysics missions, MAX and SIMBOL-X, which have been studied in CNES in the frame of a large formation flying study program. It is particularly interesting to notice that the scientific specifications of two different missions lead to the same engineering solutions for the whole mission aspects and then advocate for a similar space segment architecture and re-use of common elements, thus allowing potential cost reductions for a second mission.In deed, the same level of data to download and a similar signal-to-noise ratio requirements leads to the same orbit and communications system, the same level of pointing precision and distance inter satellites lead to the same formation flying Guidance Navigation and Command (GNC) architecture. At the end, the same level of mass and thermal constraints leads to the same range of platform and the same propulsion systems and finally to the same launcher. 相似文献
95.
A hydrodynamic model which takes into account the aquitard storage effect was developed for the deep multilayered system including the Dogger aquifer and its surroundings in the Paris Basin. It provides a good explanation for a series of observations in the Dogger concerning, for instance, the hydraulic head, the salinity and the transmissivity. The calibration of the model also makes it possible to estimate some unmeasured parameters such as the aquifer and aquitard storage coefficients. Finally, the results of simulations of the transport of 4He and 14C strengthen the representativeness of the model. The Darcy average horizontal velocity in the Dogger, obtained with the model, is of the order of 0.33m year−1. 相似文献
96.
Index overlay and Boolean logic are two techniques customarily applied for knowledge-driven modeling of prospectivity for mineral deposits, whereby weights of values in evidential maps and weights of every evidence map are assigned based on expert opinion. In the Boolean logic technique for mineral prospectivity modeling (MPM), threshold evidential values for creating binary maps are defined based on expert opinion as well. This practice of assigning weights based on expert opinion involves trial-and-error and introduces bias in evaluating relative importance of both evidential values and individual evidential maps. In this paper, we propose a data-driven index overlay MPM technique whereby weights of individual evidential maps are derived from data. We also propose a data-driven Boolean logic MPM technique, whereby thresholds for creating binary maps are defined based on data. For assigning weights and defining thresholds in these proposed data-driven MPM techniques, we applied a prediction-area plot from which we can estimate the predictive ability of each evidential map with respect to known mineral occurrences, and we use that predictive ability estimate to assign weights to evidential map and to select thresholds for generating binary predictor maps. To demonstrate these procedures, we applied them to an area in the Kerman province in southeast Iran as a MPM case study for porphyry-Cu deposits. 相似文献
97.
98.
Scriven Blair William Gerald McGrath Heather Stefanakis Emmanuel 《Natural Hazards》2021,108(2):1629-1657
Natural Hazards - Acknowledging the devastating consequences of past earthquakes, current research efforts focus on the development of tools for assessing and controlling the risk and losses... 相似文献
99.
Genetic structure of the reef grouper Epinephelus merra in the West Indian Ocean appears congruent with biogeographic and oceanographic boundaries 下载免费PDF全文
The reef fauna connectivity of the West Indian Ocean (WIO) is one of the least studied globally. Here we use genetic analyses of the grouper Epinephelus merra (Bloch 1793) to determine patterns of connectivity and to identify barriers to dispersal in this WIO marine area. Phylogeographic and population‐level analyses were conducted on cytochrome b sequences and microsatellites (13 loci) from 557 individuals sampled in 15 localities distributed across the West Indian Ocean. Additional samples from the Pacific Ocean were used to benchmark the WIO population structure. The high level of divergence revealed between Indian and Pacific localities (of about 4.5% in sequences) might be the signature of the major tectonic and climatic changes operating at the Plio‐Pleistocene transition, congruently with numerous examples of Indo‐Pacific speciation. In comparison, the E. merra sequences from the Indian Ocean constitute a monophyletic clade with a low average genetic distance (d < 0.5%). However both genetic markers indicated some structure within this ocean. The main structure revealed was the isolation of the Maldives from the WIO localities (a different group signature identified by clustering analysis, great values of differentiation). Both marker types reveal further significant structure within the WIO, mainly the isolation of the Mascarene Islands (significant AMOVA and isolation‐by‐distance patterns) and some patchy structure between the northernmost localities and within the Mozambique Channel. The WIO genetic structure of E. merra appeared congruent with main biogeographic boundaries and oceanographic currents. 相似文献
100.
Priscilla Pareuil François Bordas Emmanuel Joussein Philippe Vieillard Jean-Claude Bollinger 《Applied Geochemistry》2010
Square sections of a Mn-rich slag from an alkaline battery recycling plant were submitted to 6-month batch leaching procedures. High-Purity Water (HPW), acidic (pH 4) and alkaline (pH 12) conditions were used in order to observe the behavior of primary solid phases as well as the constituent elements (Mn, Mg, Al, Si, Ca). The experiments were coupled with both KINDIS(P) modeling and mineralogical study (SEM-EDS). Experimental results showed that the Mn-rich slag was sensitive to acidic conditions which induced the dissolution of primary phases. Moreover, pH 4 conditions did not result in the formation of newly formed solid products, leading to the greatest mobilization of metallic elements (especially Mn). Alkaline conditions favored the precipitation of secondary phases, especially rhodochrosite, calcite and Mg-saponite, inducing low mobilization of the contained elements. The KINDIS(P) modeling allowed the stability of primary phases and newly formed products to be predicted. Although the modeled results have to be considered with caution, they allow the assessment and understanding of future environmental behavior of the solid material in given conditions. In this case, the reuse of Mn-rich slag in acidic conditions has to be avoided because of the acidic dissolution of the primary phases. 相似文献