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81.
Vadlamudi Brahmananda Rao Emanuel Giarolla Clóvis Monteiro do Espírito Santo Sergio Henrique Franchito 《Journal of Oceanography》2008,64(4):551-560
A comparison of monthly wind stress derived from winds of NCEP/NCAR (National Centers for Environmental Prediction/National
Center for Atmospheric Research) reanalysis and UWM/COADS (The University of Wisconsin-Milwaukee/Comprehensive Ocean-Atmosphere
Data Set) dataset (1950–1993), and of NCEP/NCAR reanalysis and satellite-based QuikSCAT dataset (2000–2006), is made over
the South Atlantic (10°N–40°S). On a mean seasonal scale, the comparison shows that these three wind stress datasets have
qualitatively similar patterns. Quantitatively, in general, from about the equator to 20°S in the mid-Atlantic the wind stress
values are stronger in NCEP/NCAR data than those in UWM/COADS data. On the other hand, in the Intertropical Convergence Zone
(ITCZ) area the wind stress values in NCEP/NCAR data are slightly weaker than those in UWM/COADS data. In the South Atlantic,
between 20° S–40°S, the QuikSCAT dataset presents complex circulation structures which are not present in NCEP/NCAR and UWM/COADS
data. The wind stress is used in a numerical ocean model to simulate ocean currents, which are compared to a drifting-buoy
observed climatology. The modeled South Equatorial Current agrees better with observations between March–May and June–August.
Between December–February, the South Equatorial Current from UWM/COADS and QuikSCAT experiments is stronger and more developed
than that from NCEP/NCAR experiment. The Brazil Current, in turn, is better represented in the QuikSCAT experiment. Comparison
of the annual migration of ITCZ at 20° and 30°W in UWM/COADS and NCEP/NCAR data sources show that the southernmost position
of ITCZ at 30°W in February, March and April coincides with the rainy season in NE Brazil, while the northernmost position
of ITCZ at 20°W in August coincides with the maximum rainfall of Northwest Africa. 相似文献
82.
Modelling of coupled fluid‐mechanical problems in fractured geological media using enriched finite elements 下载免费PDF全文
Jose Roberto Silvestre Euripedes do Amaral Vargas Jr. Luiz Eloy Vaz Antonio Claudio Soares 《国际地质力学数值与分析法杂志》2015,39(10):1104-1140
Geological environments, such as petroleum reservoirs, normally exhibit physical discontinuities, for example, fractures and faults. Because of the reduced thickness of these discontinuities, finite element formulations with strong discontinuity have been applied to the numerical modelling of geological environments. Until now, two relevant characteristics of petroleum reservoirs have not been addressed by these formulations. The first is the pore pressure jump in the direction normal to a discontinuity in a fluid‐mechanical coupling condition, which is present primarily in sealing faults owing to the contrast of permeability with the porous medium. The absence of this jump can affect the prediction of the deformability of a physical discontinuity. Furthermore, reservoir models frequently use coarse meshes. Thus, the method used to evaluate the pore pressure in the discontinuity may exhibit a strong dependence relative to the mesh refinement. Based on these characteristics, in this study, a formulation of an enriched finite element for application to coupled fluid‐mechanical problems with pre‐existing physical discontinuities saturated by a single fluid is presented. The formulation employs discontinuous interpolation functions and enables the reproduction of jumps of displacement and pore pressure associated with a discontinuity inside the element without the need to discretise it. An approximation to estimate the pore pressure in the discontinuity was developed, one which seeks to minimise the influence of refinement. The element's response is verified by comparison with a one‐dimensional analytical solution and simple examples that are simulated using commercial software. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
83.
Peixoto Filho Flávio Tito Vargas Junior Euripedes do Amaral Santos Erick Slis Raggio Ferreira Francisco Henriques 《Geotechnical and Geological Engineering》2021,39(6):4127-4142
Geotechnical and Geological Engineering - In coring operations, core jamming is a permanent concern, taking place when the rock core sample becomes stuck within the inner core barrel, thus... 相似文献
84.
85.
O. C. Winter L. A. G. Boldrin E. Vieira Neto R. Vieira Martins S. M. Giuliatti Winter R. S. Gomes F. Marchis P. Descamps 《Monthly notices of the Royal Astronomical Society》2009,395(1):218-227
The triple asteroidal system (87) Sylvia is composed of a 280-km primary and two small moonlets named Romulus and Remus ( Marchis et al. 2005b ). Sylvia is located in the main asteroid belt, with semi-major axis of about 3.49 au, eccentricity of 0.08 and 11° of orbital inclination. The satellites are in nearly equatorial circular orbits around the primary, with orbital radius of about 1360 km (Romulus) and 710 km (Remus). In this work, we study the stability of the satellites Romulus and Remus. In order to identify the effects and the contribution of each perturber, we performed numerical simulations considering a set of different systems. The results from the three-body problem, Sylvia–Romulus–Remus, show no significant variation of their orbital elements. However, the inclinations of the satellites present a long-period evolution with amplitude of about 20° when the Sun is included in the system. Such amplitude is amplified to more than 50° when Jupiter is included. These evolutions are very similar for both satellites. An analysis of these results shows that Romulus and Remus are librating in a secular resonance and their longitude of the nodes are locked to each other. Further simulations show that the amplitude of oscillation of the satellites' inclination can reach higher values depending on the initial values of their longitude of pericentre. In those cases, the satellites get caught in an evection resonance with Jupiter, their eccentricities grow and they eventually collide with Sylvia. However, the orbital evolutions of the satellites became completely stable when the oblateness of Sylvia is included in the simulations. The value of Sylvia's J 2 is about 0.17, which is very high. However, even just 0.1 per cent of this value is enough to keep the satellite's orbital elements with no significant variation. 相似文献
86.
The problem of reconstructing past climates from a sparse network of noisy time-averaged observations is considered with a
novel ensemble Kalman filter approach. Results for a sparse network of 100 idealized observations for a quasi-geostrophic
model of a jet interacting with a mountain reveal that, for a wide range of observation averaging times, analysis errors are
reduced by about 50% relative to the control case without assimilation. Results are robust to changes to observational error,
the number of observations, and an imperfect model. Specifically, analysis errors are reduced relative to the control case
for observations having errors up to three times the climatological variance for a fixed 100-station network, and for networks
consisting of ten or more stations when observational errors are fixed at one-third the climatological variance. In the limit
of small numbers of observations, station location becomes critically important, motivating an optimally determined network.
A network of fifteen optimally determined observations reduces analysis errors by 30% relative to the control, as compared
to 50% for a randomly chosen network of 100 observations. 相似文献
87.
M.E.P. Gomes I.M.H.R. Antunes P.B. Silva A.M.R. Neiva F.A.L. Pacheco 《Journal of Geochemical Exploration》2010
The quartz veins containing scheelite from Fonte Santa mine cut the Lower Ordovician quartzites. A muscovite–biotite granite (G1) and a muscovite granite (G2), both S-type, crop out close to the Fonte Santa mine and are related to the Moncorvo–Bemposta shear zone. The most altered samples of G2 show intense muscovitization and microclinization and contain chlorite, columbite–tantalite, wolframite, W-ixiolite and Fe-oxides. The tin-bearing granites contain 18 ppm (G1) and 73 ppm (G2) Sn. The most altered samples of G2 correspond to a tungsten granite. The quartz veins contain muscovite, chlorite, tourmaline, scheelite, pyrrhotite, pyrite, sphalerite, chalcopyrite, galena, arsenopyrite, iron oxides, Fe sulfates, phosphates of Pb, Fe and Al. The Fonte Santa mine area was exploited for W between 1942 and 1982. At the end of November 2006, a flood event damaged the tailings dam of Fonte Santa mine, releasing contaminated material and increasing contaminant levels in water within the area of influence of the mine. The waters related to the Fonte Santa mine are poorly mineralized, with electrical conductivity of < 965 µS/cm, and of a mixed type or HCO3− and SO42− types. Most pH values (5.0−8.5) indicate that there is no significant acidic drainage in the region, as found in other areas. More acidic values (pH = 3.4) were found in the mine's lagoon. Waters associated with mineralized veins and old mine activities have Fe and Mn concentrations that forbid their use for human consumption and agriculture. Natural Na, Mg and K water contents are associated with the alteration of albite, chlorite and muscovite of country rock, while Ca with the W-bearing quartz veins. Weathering agents are carbonic and sulphuric acids and the latter has a strong influence in areas draining fine-grained mine tailings. 相似文献
88.
89.
Raimundo Jiménez Ballesta Paz Conde Bueno Juan A. Martin Rubi Rosario Garcia Giménez 《Central European Journal of Geosciences》2010,2(4):441-454
To evaluate trace element soil contamination, geochemical baseline contents and reference values need to be established. Pedo-geochemical baseline levels of trace elements in 72 soil samples of 24 soil profiles from the Mediterranean, Castilla La Mancha, are assessed and soil quality reference values are calculated. Reference value contents (in mg kg?1) were: Sc 50.8; V 123.2; Cr 113.4; Co 20.8; Ni 42.6; Cu 27.0; Zn 86.5; Ga 26.7; Ge 1.3; As 16.7; Se 1.4; Br 20.1; Rb 234.7; Sr 1868.4; Y 38.3; Zr 413.1; Nb 18.7; Mo 2.0; Ag 7.8; Cd 4.4; Sn 8.7; Sb 5.7; I 25.4; Cs 14.2; Ba 1049.3; La 348.4; Ce 97.9; Nd 40.1; Sm 10.7; Yb 4.2; Hf 10.0; Ta 4.0; W 5.5; Tl 2.3; Pb 44.2; Bi 2.2; Th 21.6; U 10.3. The contents obtained for some elements are below or close to the detection limit: Co, Ge, Se, Mo, Ag, Cd, Sb, Yb, Hf, Ta, W, Tl and Bi. The element content ranges (the maximum value minus the minimum value) are: Sc 55.0, V 196.0, Cr 346.0, Co 64.4, Ni 188.7, Cu 49.5, Zn 102.3, Ga 28.7, Ge 1.5, As 26.4, Se 0.9, Br 33.0 Rb 432.7, Sr 3372.6, Y 39.8, Zr 523.2, Nb 59.7, Mo 3.9, Ag 10.1, Cd 1.8, Sn 75.2, Sb 9.9, I 68.0, Cs 17.6, Ba 1394.9, La 51.3, Ce 93.5, Nd 52.5, Sm 11.2, Yb 4.2, Hf 11.3, Ta 6.3, W 5.2, Tl 2.1, Pb 96.4, Bi 3.0, Th 24.4, U 16.4 (in mg kg?1). The spatial distribution of the elements was affected mainly by the nature of the bedrock and by pedological processes. The upper limit of expected background variation for each trace element in the soil is documented, as is its range as a criterion for evaluating which sites may require decontamination. 相似文献
90.
A. Alberti F. Castorina P. Censi P. Comin-Chiaramonti C.B. Gomes 《Journal of African Earth Sciences》1999,29(4):423
The Early Cretaceous (138–130 Ma) carbonatites and associated alkaline rocks of Angola belong to the Paraná-Angola-Etendeka Province and occur as ring complexes and other central-type intrusions along northeast trending tectonic lineaments, parallel to the trend of coeval Namibian alkaline complexes. Most of the Angolan carbonatite-alkaline bodies are located along the apical part of the Moçamedes Arch, a structure representing the African counterpart of the Ponta Grossa Arch in southern Brazil, where several alkaline-carbonatite complexes were also emplaced in the Early Cretaceous. Geochemical and isotopic (C, 0, Sr and Nd) characteristics determined for five carbonatitic occurrences indicate that: (1) the overall geochemical composition, including the O---C isotopes, is within the range of the Early and Late Cretaceous Brazilian occurrences from the Paraná Basin; (2) the La versus
relationships are consistent with the exsolution of COi2-rich melts from trachyphonolitic magmas; and (3) the
and
initial ratios are similar to the initial isotopic ratios (129 Ma) of alkaline complexes in northwest Namibia. In contrast, the Lupongola carbonatites have a distinctly different
initial ratio, suggesting a different source.The Angolan carbonatites have Sr---Nd isotopic compositions ranging from bulk earth to time-integrated depleted sources. Since those from eastern Paraguay (at the western fringe of the Paraná-Angola-Etendeka Province) and Brazil appear to be related to mantle-derived melts with time-integrated enriched or B.E. isotopic characteristics, it is concluded that the carbonatites of the Paraná-Angola-Etendeka Province have compositionally distinct mantle sources. Such mantle heterogeneity is attributed to ‘metasomatic processes’, which would have occurred at ca 0.6–0.7 Ga (Angola, northwest Namibia and Brazil) and ca 1.8 Ga (eastern Paraguay), as suggested by Nd-model ages. 相似文献