全文获取类型
收费全文 | 378篇 |
免费 | 15篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 46篇 |
地球物理 | 88篇 |
地质学 | 168篇 |
海洋学 | 39篇 |
天文学 | 35篇 |
综合类 | 6篇 |
自然地理 | 5篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 10篇 |
2021年 | 11篇 |
2020年 | 6篇 |
2019年 | 14篇 |
2018年 | 21篇 |
2017年 | 19篇 |
2016年 | 20篇 |
2015年 | 11篇 |
2014年 | 24篇 |
2013年 | 29篇 |
2012年 | 21篇 |
2011年 | 26篇 |
2010年 | 21篇 |
2009年 | 23篇 |
2008年 | 27篇 |
2007年 | 20篇 |
2006年 | 16篇 |
2005年 | 5篇 |
2004年 | 10篇 |
2003年 | 7篇 |
2002年 | 7篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有397条查询结果,搜索用时 15 毫秒
81.
S coda wave of seventy-four local earthquakes recorded in a network of ten seismic stations were used to calculate coda Q attenuation (Qc) in the João Câmara area (northeastern Brazil). The estimates show Qc as a strong function of frequency in the range from 6.0 to 20.0 Hz. We found out that Qc in João Câmara has a functional form given by Qc= Q0 f, where Q0= 151 ± 99 and = 0.98 ± 0.05. If the standard deviations are taken into account,we conclude that there are no relevant changes in both Q0 and values from one station to another. The estimated Q0 values at the different stations suggest that the Samambaia fault is a boundary between two different seismic attenuation zones. In one side of the fault (left), where stations were installed in Pre-Cambrian terrain and thick sedimentary layer, the seismic attenuation is stronger than in the other side (stations installed in thin sedimentary layer and limestone outcrop).The anomalous Q0 values in the left side of the Samambaia fault can be explained due to the presence of a shallow conductive layer in the upper crust( 10 km), such as proposed by Padilha et al. (1992). According to our results, if there is a conductive layer in the area, it probably spreads over João Câmara city and surrounding regions.However, more detailed investigation either with seismic methods (seismic attenuation,3D tomography with P and/or S wave velocities) or with other geophysical methods is needed to interpret the observed differences in Q0 values between the two sides of the Samambaia fault. 相似文献
82.
T. S. David J. H. C. Gash F. Valente J. S. Pereira M. I. Ferreira J. S. David 《水文研究》2006,20(13):2713-2726
Redistribution of ground‐level rainfall and interception loss by an isolated Quercus ilex tree were measured over 2 years in a Mediterranean oak savannah. Stemflow, meteorological variables and sap flow were also monitored. Rainfall at ground level was measured by a set of rain‐gauges located in a radial layout centred on the tree trunk and extending beyond the crown limits. Interception loss was computed as the difference between the volume of rainwater that would reach the ground in the absence of the tree and the volume of water that actually fell on the ground sampling area (stemflow included). This procedure provided correct interception loss estimates, irrespective of rainfall inclination. Results have shown a clear non‐random spatial distribution of ground‐level rainfall, with rainwater concentrations upwind beneath the crown and rain‐shadows downwind. Interception loss amounted to 22% of gross rainfall, per unit of crown‐projected area. Stand interception loss, per unit of ground area, was only 8% of gross rainfall and 28% of tree evapotranspiration. These values reflect the low crown cover fraction of the stand (0·39) and the specific features of the Mediterranean rainfall regime (predominantly with few large storms). Nevertheless, it still is an important component of the water balance of these Mediterranean ecosystems. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
83.
84.
A parallelizable, semi‐implicit numerical method is proposed for the study of naturally‐fractured reservoir systems. It has proved to be computationally efficient in producing accurate numerical solutions for the dual‐porosity model for immiscible, two‐phase flow in such reservoirs. The method combines hybridized mixed finite elements, a new version of the modified method of characteristics, a sophisticated operator‐splitting procedure for separating the pressure calculation in the fractures from that of the saturation, another operator splitting to handle the interaction of the matrix blocks and the fractures, and domain decomposition iterative procedures for both the pressure and the saturation. It permits moderately long time steps for the pressure and the saturation in the fractures and matrix blocks by using short, inexpensive microsteps to treat the transport portion of the saturation equation in the fractures. This paper is devoted to the formulation of the method and a discussion of numerical results for five‐spot and vertical cross‐section examples. 相似文献
85.
The transition between blueschists and lawsonite-bearing eclogites based on observations from Corsican metabasalts 总被引:2,自引:0,他引:2
Syntectonic eclogites, associated with blueschist parageneses, have recrystallized in metabasalts from eastern Corsica under very low temperatures (420°C). The evolution of these eclogites is recorded by the order of development of metamorphic minerals, as demonstrated by helicitic inclusions of lawsonite and actinolite in Fe-rich garnets, and the occurrence of fibrous Na-pyroxenes in the pressure shadows and cracks of boudinaged garnets, within a foliated matrix composed of glaucophane, Ca---Fe garnets and lawsonite.
A Schreinemakers analysis has been completed on the lawsonite-ferroglaucophane-actinolite-almandine-grossular-ferro-omphacite-chlorite system in a (T,P,μH2O)-space. The resulting three-dimensional relationships are applied to the studied samples. They are consistent with a prograde increase in temperature at low μH2O, producing eclogites from blueschists, and with a subsequent retrogressive decrease in pressure. 相似文献
86.
A. M. de S. Bueno C. A. de B. Pereira M. N. Rabello-Gay J. M. Stern 《Stochastic Environmental Research and Risk Assessment (SERRA)》2002,16(4):267-278
The data analyzed in this paper are part of the results described in Bueno et al. (2000). Three cytogenetics endpoints were
analyzed in three populations of a species of wild rodent – Akodon montensis – living in an industrial, an agricultural, and
a preservation area at the Itajaí Valley, State of Santa Catarina, Brazil. The polychromatic/normochromatic ratio, the mitotic
index, and the frequency of micronucleated polychromatic erythrocites were used in an attempt to establish a genotoxic profile
of each area. It was assumed that the three populations were in the same conditions with respect to the influence of confounding
factors such as animal age, health, nutrition status, presence of pathogens, and intra- and inter-populational genetic variability.
Therefore, any differences found in the endpoints analyzed could be attributed to the external agents present in each area.
The statistical models used in this paper are mixtures of negative-binomials and Poisson variables. The Poisson variables
are used as approximations of binomials for rare events. The mixing distributions are beta densities. The statistical analyzes
are under the bayesian perspective, as opposed to the frequentist ones often considered in the literature, as for instance
in Bueno et al. (2000). 相似文献
87.
Jos Manuel Piarra Michel Robardet Ahmed Bourahrouh Florentin Paris Zlia Pereira Jean Le
Menn Rmy Gourvennec Toms Oliveira Hubert Lardeux 《Comptes Rendus Geoscience》2002,334(16)
A new section in the Silurian graptolitic ‘phtanites’ (black cherts) of Les Fresnaies at Chalonnes-sur-Loire (SE Armorican Massif) shows for the first time that these rocks (1) succeed conformably to Uppermost Ordovician (Hirnantian) glaciomarine deposits and (2) contain successive graptolite assemblages that characterise the base of the Silurian, the whole Rhuddanian and Aeronian stages and the lower part of the Telychian. To cite this article: J.M. Piçarra et al., C. R. Geoscience 334 (2002) 1177–1183. 相似文献
88.
Marcos Almeida Bezerra Ricardo Erthal Santelli Valfredo Azevedo Lemos Juscelia Pereira dos Santos Alves Bernardo Ferreira Braz Luana Bastos Santos 《洁净——土壤、空气、水》2020,48(7-8)
The implementation of flow injection analysis (FIA) systems and correlated techniques in the laboratory routine provides an increase of analytical throughput and the reduction of risks of analyte losses and contamination. Naturally, it contributes to the reduction of reagent consumption and minimization of waste generation. This paper presents and discusses an overview of the main strategies adopted to make methods based on FIA systems more environmentally friendly, and offers a review of these methods that covers the period from January 2002 to December 2019. Strategies based on reagent management (adoption of procedures without reagents, replacement of toxic reagents, recycling and reuse of reagents and, use of immobilized reagents), the online waste treatment, and the improvements of FIA systems (flow system configurations that avoid reagent wastage, use of green detectors, automation, and miniaturization) are approached in this perspective. 相似文献
89.
Henrique Patricio Prado Pereira Nelson Violante-Carvalho Izabel Christina Martins Nogueira Alexander Babanin Qingxiang Liu Uggo Ferreira de Pinho Fabio Nascimento Carlos Eduardo Parente 《Ocean Dynamics》2017,67(12):1577-1591
It is well known that the majority of buoy measurements are located around the US coast and along some Europeans countries. The lack of long-term and densely spaced in situ measurements in the Southern Hemisphere in general, and the South Atlantic in particular, hinders several investigations due to the lack of detailed metocean information. Here, we present an effort to overcome this limitation, with a dense network of buoys along the Brazilian coast, equipped with several meteorological and oceanographic sensors. Out of ten currently operational buoys, three are employed to present the main characteristics of waves in the Southern part of the network. For the first time, sensor characteristics and settings are described, as well as the methods applied to the raw wave data. Statistics and distributions of wave parameters, swell propagating events, comparison with a numerical model and altimeters and a discussion about the occurrence of freak waves are presented. 相似文献
90.
Natalia Hauser Wolf Uwe Reimold Aaron J. Cavosie Alvaro P. Crsta Winfried H. Schwarz Mario Trieloff Carolinna Da Silva Maia de Souza Luciana A. Pereira Eduardo N. Rodrigues Matthews Brown 《Meteoritics & planetary science》2019,54(10):2286-2311
A silicious impact melt rock from polymict impact breccia of the northern part of the alkali granite core of the Araguainha impact structure, central Brazil, has been investigated. The melt rock is thought to represent a large mass of impact‐generated melt in suevite. In particular, a diverse population of zircon grains, with different impact‐induced microstructures, has been analyzed for U‐Pb isotopic systematics. Backscattered electron and cathodoluminescence images reveal heterogeneous intragrain domains with vesicular, granular, vesicular plus granular, and vesicular plus (presumably) baddeleyite textures, among others. The small likely baddeleyite inclusions are not only preferentially located along grain margins but also occur locally within grain interiors. LA‐ICP‐MS U‐Pb data from different domains yield lower intercept ages of 220, 240, and 260 Ma, a result difficult to reconcile with the previous “best age” estimate for the impact event at 254.7 ± 2.7 Ma. SIMS U‐Pb data, too, show a relatively large range of ages from 245 to 262 Ma. A subset of granular grains that yielded concordant SIMS ages were analyzed for crystallographic orientation by EBSD. Orientation mapping shows that this population consists of approximately micrometer‐sized neoblasts that preserve systematic orientation evidence for the former presence of the high‐pressure polymorph reidite. In one partially granular grain (#36), the neoblasts occur in linear arrays that likely represent former reidite lamellae. Such grains are referred to as FRIGN zircon. The best estimate for the age of the Araguainha impact event from our data set from a previously not analyzed type of impact melt rock is based on concordant SIMS data from FRIGN zircon grains. This age is 251.5 ± 2.9 Ma (2σ, MSWD = 0.45, p = 0.50, n = 4 analyses on three grains), indistinguishable from previous estimates based on zircon and monazite from other impact melt lithologies at Araguainha. Our work provides a new example of how FRIGN zircon can be combined with in situ U‐Pb geochronology to extract an accurate age for an impact event. 相似文献