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71.
In recent years the use of Acoustic Doppler Current Profilers (ADCPs) to estimate Reynolds stresses, using the so-called variance
method, has become popular; and although there was great effort in studying the uncertainties on this technique, there were
no reports in the main literature of its validity using independent measurements. This work reports on the comparison of ADCP
and Acoustic Current Velocimeter (ADV) estimates of Reynolds stresses. The comparison of the ADCP and ADV is encouraging during
periods when no strong waves were present with both the explained variance of 0.8 and the slope of the regression being 0.97.
Nevertheless, when strong waves are present the method breaks down and the comparison between ADCP and ADV is very poor with
R2 =0.04. 相似文献
72.
M. Thamban S. S. Naik R. Mohan A. Rajakumar N. Basavaiah Witty D’Souza Sarita Kerkar M. M. Subramaniam M. Sudhakar P. C. Pandey 《Journal of Earth System Science》2005,114(5):443-452
Changes in the terrigenous sediment source and transport mechanisms during the late Quaternary have been investigated using
four sediment cores within the Indian sector of Southern Ocean, using the magnetic susceptibility (MS) and sedimentological
records. Sediments deposited during the Holocene and other interglacial periods were characterised by low MS, low sand content,
reduced ice-rafted detritus (IRD) input and increased illite possibly transported via hydrographic advection from the south.
The glacial intervals are characterised by high MS, high sand content, increased IRD input and reduced illite clays, derived
from both local as well as Antarctic sources. Significant reduction in clay fraction and illite content during glacials suggests
that the erosive and transporting capabilities of the deep and bottom waters could have reduced compared to the interglacial
times. The changes in terrigenous influx to this region were significantly influenced by the rhythmic glacial-interglacial
fluctuations in bottom circulation and the position of the Polar Front. 相似文献
73.
Rezende CE Lacerda LD Ovalle AR Souza CM Gobo AA Santos DO 《Marine pollution bulletin》2002,44(7):680-684
The concentrations of Al, Fe, Mn, Zn, Cu, Pb, Ni, Cr, Ba, V, Sn and As in offshore bottom sediments from the Bacia de Campos oil field, SE Brazil, were measured at the beginning and at 7 months after completion of the drilling operation. Concentrations of Al, Fe, Ba, Cr, Ni and Zn were significantly higher closer to the drilling site compared to stations far from the site. Average concentrations of Al, Cu, and in particular of Ni, were significantly higher at the end of the drilling operation than at the beginning. Comparison between drilling area sediments with control sediments of the continental platform, however, showed no significant difference in trace metal concentrations. Under the operation conditions of this drilling event, the results show that while changes in some trace metal concentrations do occur during drilling operations, they are not significantly large to be distinguished from natural variability of the local background concentrations. 相似文献
74.
Nine broadband seismograph stations in South America have provided 389 recordings of Lg coda with paths that cover most of
the continent. Lg coda Q (Q0v) and frequency dependence <(eta)> values at 1 Hz, obtained from these records, were inverted
using back-projection tomography to obtain regionalized maps of Q0 and <eta>. The entire western margin of the continent (the
active Andean mountain belt) is typified by low Q0 (250–450), whereas broad regions of high Q0 (700–1100) span the central
Brazilian shield and contiguous regions to the north and south. Intermediate Q0 (450–700) characterizes the northern Patagonia
platform and most of the Atlantic shield. Reduced Q0 in the Atlantic shield may be related to tectonic or igneous activity
that occurred during the breakup of Gondwanaland during the Jurassic period. This Q distribution is generally consistent with
earlier studies where Q0 was found to be directly proportional to the time that has elapsed since the most recent episode
of major tectonic or orogenic activity in any region. Reduced Q0 in the Patagonian platform may, however, be due to young
sediments there.
Q0 is slightly higher in two portions of the Andean belt (between latitudes 2.0°N and 10.0°S, and between latitudes 24.0°S
and 34.0°S) than in other portions of the belt. These variations are consistent with results of earlier studies of body-wave
attenuation and heat flow in the Andean mountain belt.
Spatial variations of <eta> generally vary inversely with Q0v, being low (0.0–0.2) throughout a broad region centered in the
central Brazil shield and extending to the northeastern coast. All surrounding regions except that to the northeast exhibit
intermediate to high (0.4–0.8 and possibly higher) <eta> values. Possible biasing of Lg coda Q measurements by proximity to
the transition between the South American and Pacific plates was examined using records from a station near that boundary
and was found to be small. 相似文献
75.
J. A. Souza 《Astrophysics and Space Science》1992,192(2):317-320
We have found the conditions which a background metric must obey in order that Maxwell equations have a solution depending harmonically on time in it. In particular, for the standard model, these solutions do not exist. 相似文献
76.
M. S. Cunha C. Aerts J. Christensen-Dalsgaard A. Baglin L. Bigot T. M. Brown C. Catala O. L. Creevey A. Domiciano de Souza P. Eggenberger P. J. V. Garcia F. Grundahl P. Kervella D. W. Kurtz P. Mathias A. Miglio M. J. P. F. G. Monteiro G. Perrin F. P. Pijpers D. Pourbaix A. Quirrenbach K. Rousselet-Perraut T. C. Teixeira F. Thévenin M. J. Thompson 《Astronomy and Astrophysics Review》2007,14(3-4):217-360
Asteroseismology provides us with a unique opportunity to improve our understanding of stellar structure and evolution. Recent developments, including the first systematic studies of solar-like pulsators, have boosted the impact of this field of research within astrophysics and have led to a significant increase in the size of the research community. In the present paper we start by reviewing the basic observational and theoretical properties of classical and solar-like pulsators and present results from some of the most recent and outstanding studies of these stars. We centre our review on those classes of pulsators for which interferometric studies are expected to provide a significant input. We discuss current limitations to asteroseismic studies, including difficulties in mode identification and in the accurate determination of global parameters of pulsating stars, and, after a brief review of those aspects of interferometry that are most relevant in this context, anticipate how interferometric observations may contribute to overcome these limitations. Moreover, we present results of recent pilot studies of pulsating stars involving both asteroseismic and interferometric constraints and look into the future, summarizing ongoing efforts concerning the development of future instruments and satellite missions which are expected to have an impact in this field of research. 相似文献
77.
Kenneth Broad Alexander Pfaff Renzo Taddei A. Sankarasubramanian Upmanu Lall Franciso de Assis de Souza Filho 《Climatic change》2007,84(2):217-239
We assess the potential benefits from innovative forecasts of the stream flows that replenish reservoirs in the semi-arid
state of Ceará, Brazil. Such forecasts have many potential applications. In Ceará, they matter for both water-allocation and
participatory-governance issues that echo global debates. Our qualitative analysis, based upon extensive fieldwork with farmers,
agencies, politicians and other key actors in the water sector, stresses that forecast value changes as a society shifts.
In the case of Ceará, current constraints on the use of these forecasts are likely to be reduced by shifts in water demand,
water allocation in the agricultural Jaguaribe Valley, participatory processes for water allocation between this valley and
the capital city of Fortaleza, and risk perception. Such changes in the water sector can also have major distributional impacts.
Broad, Pfaff and Taddei equally share lead authorship. 相似文献
78.
Carlos Roberto de Souza Filho Alfredo Rossetto Nunes Emilson Pereira Leite Lena Virgínia Soares Monteiro Roberto Perez Xavier 《Surveys in Geophysics》2007,28(5-6):377-405
The Serra Leste region, located in the northeast portion of Carajás Mineral Province (PA), hosts important chrome-PGE, Au–Pd–Pt,
Cu–Mo–Au, iron, and manganese deposits and occurrences related to different geological settings. We present a regional prospective
model with focus on PGE mineralizations based on airborne geophysics (magnetometry, gamma-ray spectrometry and time domain
electromagnetometry) and geological data. Geological and geophysics data analysis indicate a plausible correspondence between
areas with meta-mafic–ultramafic rocks and low values in gamma spectrometry, mainly for the thorium channel. The meta-ultramafic
units of the complexes, the main host rock of the PGE mineralization, are well defined by analytic signal from the anomalous
magnetic field and by the apparent conductance anomalies derived from the GEOTEM system. The combination of the derivative
products with updated geological data of the Serra Leste region and PGE-Luanga deposit enable to establish a regional prospective
model for PGE and the identification of new targets within the studied area. 相似文献
79.
da Rosa CE de Souza MS Yunes JS Proença LA Nery LE Monserrat JM 《Marine pollution bulletin》2005,50(9):956-964
In January of 2003, a cyanobacterial bloom in the Patos' Lagoon (Southern Brazil) (32 degrees 05'S-52 degrees 12'W) was observed. Water samples were taken to identify the composition and abundance of the bloom, as well as the occurrence of toxins. The effects of this occurrence on the estuarine worm Laeonereis acuta (Polychaeta, Nereididae) was also evaluated. Predominance of cyanobacteria, particularly Anabaena trichomes ( approximately 2.5.10(6) individuals per liter) was observed, and low concentrations of microcystins and anticholinesterasic toxins were detected. Augmented levels of lipid hydroperoxides (LPO) and glutathione-S-transferase activity, and lowering of total protein content were also observed in organisms collected during the bloom event. Although non-toxic, the cyanobacterial bloom could augment the cycle of hyper-oxygenation and hypoxia in the water. During hyperoxia, L. acuta, an oxyconformer, should consume more oxygen, thus augmenting the rate of reactive oxygen species generation. A repeated cycle of hyper-oxygenation and hypoxia would finally induce oxidative stress, as evidenced by the high levels of LPO and glutathione-S-transferase activity. 相似文献
80.