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41.
Benthic macrophytes as a tool for delineating, monitoring and assessing ecological status: the case of Slovenian coastal waters 总被引:1,自引:0,他引:1
Benthic macrophytes from 51 sites in the upper infralittoral zone along the Slovenian rocky coast were sampled (randomly stratified) in order to (1) confirm water body (WB) boundaries, (2) select sampling points for a surveillance monitoring programme, and (3) assess preliminary Ecological Status Classes (ESC) within the European Water Framework Directive (WFD). Coverage data of macrophytes were analyzed by using cluster analysis, Simper analysis and the Ecological Evaluation Index (EEI). The vegetation was rather homogenously classified into two Cystoseiretum crinitae subassociations: Halopithetosum incurvae, and Cystoseiretosum compressae, and into Cystoseiretum barbatae association. Seven monitoring sites at a kilometer scale were selected in two significant sized WBs following the mixing zone principle and the EEI successional model. The preliminary assessment of the ESC with the EEI was in agreement with existing human pressures in the area. In view of the present results, benthic macrophytes and EEI could be valuable tools for the implementation of the WFD within the Mediterranean eco-region. 相似文献
42.
The paper presents the testing of the possibility of determining the heights of GPS points in the homogeneous field in the
new Croatian Height Reference System (HVRS71) by using the method of height transformation. The testing was made in the area
of Zagreb. As part of the field works, normal orthometric heights of 27 GPS points were determined according to the new height
system, by transferring the benchmark heights using the geometric levelling method, thus obtaining GPS/levelling points of
known ellipsoidal and normal orthometric heights. The GPS/levelling points served as the basis for determining the transformation
models that enabled the computation of normal orthometric heights from ellipsoidal heights of any GPS point in the observed
area. The empirical data used for modelling were reduced undulation dN values of GPS/levelling points. As part of the dN modelling
with parametric functions, the approximation surfaces were obtained on the basis of three polynomials: FN310, FN312 and FN318.
The transformation models were also tested using non-parametric Watson and Loess algorithms. The FN318 and Loess models yielded
the best results. 相似文献
43.
Andrea Orlando Yves Thibault Alan D. Edgar 《Contributions to Mineralogy and Petrology》2000,139(2):136-145
Experiments ranging from 2 to 3 GPa and 800 to 1300 °C and at 0.15 GPa and 770 °C were performed to investigate the stability
and mutual solubility of the K2ZrSi3O9 (wadeite) and K2TiSi3O9 cyclosilicates under upper mantle conditions. The K2ZrSi3O9–K2TiSi3O9 join exhibits complete miscibility in the P–T interval investigated. With increasing degree of melting the solid solution becomes progressively enriched in Zr, indicating
that K2ZrSi3O9 is the more refractory end member. At 2 GPa, in the more complex K2ZrSi3O9–K2TiSi3O9–K2Mg6Al2Si6O20(OH)4 system, the presence of phlogopite clearly limits the extent of solid solution of the cyclosilicate to more Zr-rich compositions
[Zr/(Zr + Ti) > 0.85], comparable to wadeite found in nature, with TiO2 partitioning strongly into the coexisting mica and/or liquid. However, at 1200 °C, with increasing pressure from 2 to 3 GPa,
the partitioning behaviour of TiO2 changes in favour of the cyclosilicate, with Zr/(Zr + Ti) of the K2(Zr,Ti)Si3O9 phase decreasing from ∼0.9 to ∼0.6. The variation in the Ti content of the coexisting phlogopite is related to its degree
of melting to forsterite and liquid, following the major substitution VITi+VI□=2VIMg.
Received: 26 January 1999 / Accepted: 10 January 2000 相似文献
44.
45.
Natural Resources Research - This study proposes an extension of a visualization approach common in biochemistry (the clustered heat maps—CHMs) to geochemical data with the main objective of... 相似文献
46.
Martina Anelli Tommaso Julitta Luca Fallati Paolo Galli Micol Rossini Roberto Colombo 《国际地球制图》2019,34(5):459-472
Photogrammetry represents a non-destructive, cost-effective tool for coral reef monitoring, able to integrate traditional remote sensing techniques and support researchers’ work. However, its application to submerged habitats is still in early stage. We present new ways to employ Structure from Motion techniques to infer properties of reef habitats. In particular, we propose the use of Digital Surface Models and Digital Terrain Models for assessing coral colonies extension and height and discriminating between seabed and coral cover. Such information can be coupled with digital rugosity estimates to improve habitat characterization. DTM, DSM and orthophotos were derived and used to compute a series of metrics like coral morphologies, reef topography, coral cover and structural complexity. We show the potentialities offered by underwater photogrammetry and derived products to provide useful basic information for marine habitat mapping, opening the possibility to extend these methods for large-scale assessment and monitoring of coral reefs. 相似文献
47.
This paper presents a numerical investigation on the effects of thermal shock as a pretreatment of rock prior to comminution. More specifically, the effect of heat shock-induced cracks on the uniaxial compressive strength of rock is numerically studied. The chosen constitutive model of rock employs a (strong) embedded discontinuity finite element formulation to describe cracks. The thermomechanical problem that governs the heat shock pretreatment of rocks is considered as an uncoupled problem because of a highly dominating role of the external heat influx. Two solution methods of the global problem are presented: an explicit-explicit dynamic scheme and an implicit-implicit quasi-static scheme. The model performance is tested in simulations on heterogeneous numerical rock samples subjected first to a heat shock pretreatment and then to a mechanical compression test. According to the results, the compressive strength of intact granite rock having the axial splitting failure mode can be substantially reduced by heat shock pretreatment. 相似文献
48.
William M. Jackson Victor Blunt Hua Lin Martina Green Gregory Olivera William H. Fink Yihan Bao Randall S. Urdahl Fida Mohammad Mansour Zahedi 《Astrophysics and Space Science》1996,236(1):29-47
A unified picture of the photodissociation of theC
2
H radical has been developed using the results from the latest experimental and theoretical work. This picture shows that a variety of electronic states ofC
2 are formed during the photodissociation of theC
2
H radical even if photoexcitation accesses only one excited state. This is because the excited states have many avoided corssings and near intersections where two electronic states come very close to one another. At these avoided crossings and near intersections, the excited radical can hop from one electronic state to another and access new final electronic states of theC
2 radical. The complexity of the excited state surfaces also explains the bimodal rotational distributions that are observed in all of the electronic states studied. The excited states that dissociate through a direct path are limited by dynamics to produceC
2 fragments with a modest amount of rotational energy, whereas those that dissociate by a more complex path have a greater chance to access all of phase space and produce fragments with higher rotational excitation. Finally, the theoretical transition moments and potential energy curves have been used to provide a better estimate of the photochemical lifetimes in comets of the different excited states of theC
2
H radical. The photochemically active states are the 22+, 22II, 32II, and 32+, with photodissociation rate constants of 1.0×10–6, 4.0×10–6, 0.7×10–6, and 1.3×10–6s–1, respectively. These rate constants lead to a total photochemical lifetime of 1.4×105 s. 相似文献
49.
Jacopo Baima Matteo Ferrabone Roberto Orlando Alessandro Erba Roberto Dovesi 《Physics and Chemistry of Minerals》2016,43(2):137-149
The phonon dispersion and thermodynamic properties of pyrope (\(\hbox {Mg}_3\hbox {Al}_2\hbox {Si}_3\hbox {O}_{12}\)) and grossular (\(\hbox {Ca}_3\hbox {Al}_2\hbox {Si}_3\hbox {O}_{12}\) ) have been computed by using an ab initio quantum mechanical approach, an all-electron variational Gaussian-type basis set and the B3LYP hybrid functional, as implemented in the Crystal program. Dispersion effects in the phonon bands have been simulated by using supercells of increasing size, containing 80, 160, 320, 640, 1280 and 2160 atoms, corresponding to 1, 2, 4, 8, 16 and 27 \(\mathbf {k}\) points in the first Brillouin zone. Phonon band structures, density of states and corresponding inelastic neutron scattering spectra are reported. Full convergence of the various thermodynamic properties, in particular entropy (S) and specific heat at constant volume (\(C_\mathrm{{V}}\)), with the number of \(\mathbf {k}\) points is achieved with 27 \(\mathbf {k}\) points. The very regular behavior of the S(T) and \(C_\mathrm{{V}}(T)\) curves as a function of the number of \(\mathbf {k}\) points, determined by high numerical stability of the code, permits extrapolation to an infinite number of \(\mathbf {k}\) points. The limiting value differs from the 27-\(\mathbf {k}\) case by only 0.40 % at 100 K for S (the difference decreasing to 0.11 % at 1000 K) and by 0.29 % (0.05 % at 1000 K) for \(C_\mathrm{{V}}\). The agreement with the experimental data is rather satisfactory. We also address the problem of the relative entropy of pyrope and grossular, a still debated question. Our lattice dynamical calculations correctly describe the larger entropy of pyrope than grossular by taking into account merely vibrational contributions and without invoking “static disorder” of the Mg ions in dodecahedral sites. However, as the computed entropy difference is found to be larger than the experimental one by a factor of 2–3, present calculations cannot exclude possible thermally induced structural changes, which could lead to further conformational contributions to the entropy. 相似文献
50.