全文获取类型
收费全文 | 292篇 |
免费 | 7篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 24篇 |
地球物理 | 81篇 |
地质学 | 103篇 |
海洋学 | 45篇 |
天文学 | 32篇 |
自然地理 | 8篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 12篇 |
2020年 | 8篇 |
2019年 | 5篇 |
2018年 | 10篇 |
2017年 | 8篇 |
2016年 | 24篇 |
2015年 | 16篇 |
2014年 | 9篇 |
2013年 | 14篇 |
2012年 | 14篇 |
2011年 | 21篇 |
2010年 | 19篇 |
2009年 | 19篇 |
2008年 | 25篇 |
2007年 | 13篇 |
2006年 | 17篇 |
2005年 | 10篇 |
2004年 | 13篇 |
2003年 | 7篇 |
2001年 | 2篇 |
2000年 | 9篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1960年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有301条查询结果,搜索用时 15 毫秒
1.
B. R. Johnson M. E. Abroe P. Ade J. Bock J. Borrill J. S. Collins P. Ferreira S. Hanany A. H. Jaffe T. Jones A. T. Lee L. Levinson T. Matsumura B. Rabii T. Renbarger P. L. Richards G. F. Smoot R. Stompor H. T. Tran C. D. Winant 《New Astronomy Reviews》2003,47(11-12):1067
We discuss MAXIPOL, a bolometric balloon-borne experiment designed to measure the E-mode polarization anisotropy of the cosmic microwave background radiation (CMB) on angular scales of 10′ to 2°. MAXIPOL is the first CMB experiment to collect data with a polarimeter that utilizes a rotating half-wave plate and fixed wire-grid polarizer. We present the instrument design, elaborate on the polarimeter strategy and show the instrument performance during flight with some time domain data. Our primary dataset was collected during a 26 h turnaround flight that was launched from the National Scientific Ballooning Facility in Ft. Sumner, New Mexico in May 2003. During this flight five regions of the sky were mapped. Data analysis is in progress. 相似文献
2.
Filipa Simes Brito Ferreira Oliveira 《Ocean Engineering》2007,34(2):337-342
Two numerical formulations of the breaking phenomenon were implemented in a numerical model for random wave propagation based on the elliptic formulation of the mild-slope equation. The randomness of the wave field was simulated based on a spectral component method, in which the 3-D spectrum is discretised in components of equal energy. One of the breaking process formulations is based on the concept of breaking each independent spectral component. The other is based on the distribution of the local amount of energy dissipated through the independent spectral components. The model based on the concept of breaking each independent spectral component produces the best estimates of the wave field, when the numerical results are compared with laboratory data. 相似文献
3.
V. Alves Martins C. Patinha E. Ferreira da Silva J.-M. Jouanneau O. Weber F. Rocha 《Journal of Geochemical Exploration》2006,88(1-3):408
A multiproxy approach (textural characteristics, heavy metal concentrations and benthic foraminifera data) was adopted to study the OMEX core KSGX 40, collected at the Galicia Mud Deposit (NW Iberian outer continental shelf) and recording the last ca. 4.8 ka cal BP. Geochemical profiles of Fe, Mn, Zn, Co, Cr, Cu, Ni, Pb, Al and Ca show significant temporal variations. Benthic foraminifera productivity proxy suggests that the recorded muddy events were contemporaneous of a higher Corg flux to the marine benthic environment. The higher flux of organic matter, following a long-term intensification of the upwelling and coinciding with a finer sedimentation, led to depressed levels of oxygen beneath the water-sediments interface and to early diagenetic processes of several redox-sensitive elements. 相似文献
4.
Problems associated with tourism development in Southern Africa: The case of Transfrontier Conservation Areas 总被引:2,自引:0,他引:2
Sanette Ferreira 《GeoJournal》2004,60(3):301-310
Tourism in Southern Africa is synonymous with the wildlife safari. In the post-colonial era the establishment of so-called
‘peaceparks’ that straddle the borders of states has come to be seen as a key not only to increasing tourism in the Southern
African region, but also to the modernizing of conservation policies and the development of rural economies. This paper focuses
on the global and continental presence of transfrontier conservation areas, the link between conservation and tourism development,
and the current factors that constrain and influence the realization of an ‘African Dream’ — ‘establishment of the greatest
animal kingdom’. The unstable political situation in Zimbabwe and how this negatively affects wildlife conservation and tourism
in the Gonarezhou part of the Greater Limpopo Transfrontier Park, serves as a case study.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
We describe the tidal circulation and salinity regime of a coastal plain estuary that connects to the ocean through a flood
tide delta. The delta acts as a sill, and we examine the mechanisms through which the sill affects exchange of estuarine water
with the ocean. Given enough buoyancy, the dynamics of tidal intrusion fronts across the sill and selective withdrawal (aspiration)
in the deeper channel landward appear to control the exchange of seawater with estuarine water. Comparison of currents on
the sill and stratification in the channel reveals aspiration depths smaller than channel depth during neap tide. During neap
tide and strong vertical stratification, seawater plunges beneath the less dense estuarine water somewhere on the sill. Turbulence
in the intruding bottom layer on the sill promotes entrainment of fluid from the surface layer, and the seawater along the
sill bottom is diluted with estuarine water. During ebb flow, salt is effectively trapped landward of the sill in a stagnant
zone between the aspiration depth and the bottom where it can be advected farther upstream by flood currents. During spring
tide, the plunge point moves landward and off the sill, stratification is weakened in the deep channel, and aspiration during
ebb extends to the bottom. This prevents the formation of stagnant water near the bottom, and the estuary is flooded with
high salinity water far inland. The neapspring cycle of tidal intrusion fronts on flood coupled with aspiration during ebb
interacts with the sill to play an important role in the transport and retention of salt within the estuary. 相似文献
6.
Daniele Barroca Marra Alves Luiz Fernando Sapucci Haroldo Antonio Marques Eniuce Menezes de Souza Tayná Aparecida Ferreira Gouveia Jackes Akira Magário 《GPS Solutions》2016,20(4):677-685
The global navigation satellite system (GNSS) can provide centimeter positioning accuracy at low costs. However, in order to obtain the desired high accuracy, it is necessary to use high-quality atmospheric models. We focus on the troposphere, which is an important topic of research in Brazil where the tropospheric characteristics are unique, both spatially and temporally. There are dry regions, which lie mainly in the central part of the country. However, the most interesting area for the investigation of tropospheric models is the wet region which is located in the Amazon forest. This region substantially affects the variability of humidity over other regions of Brazil. It provides a large quantity of water vapor through the humidity convergence zone, especially for the southeast region. The interconnection and large fluxes of water vapor can generate serious deficiencies in tropospheric modeling. The CPTEC/INPE (Center for Weather Forecasting and Climate Studies/Brazilian Institute for Space Research) has been providing since July 2012 a numerical weather prediction (NWP) model for South America, known as Eta. It has yield excellent results in weather prediction but has not been used in GNSS positioning. This NWP model was evaluated in precise point positioning (PPP) and network-based positioning. Concerning PPP, the best positioning results were obtained for the station SAGA, located in Amazon region. Using the NWP model, the 3D RMS are less than 10 cm for all 24 h of data, whereas the values reach approximately 60 cm for the Hopfield model. For network-based positioning, the best results were obtained mainly when the tropospheric characteristics are critical, in which case an improvement of up to 7.2 % was obtained in 3D RMS using NWP models. 相似文献
7.
8.
Natural Hazards - Worldwide coastal zones present serious erosion problems that cause loss of territory. This phenomenon exposes people and goods to the threat, being necessary to carry out a... 相似文献
9.
Adeline Marinho Maciel Gilberto Camara Lubia Vinhas Michelle Cristina Araújo Picoli Rodrigo Anzolin Begotti Luiz Fernando Ferreira Gomes de Assis 《International journal of geographical information science》2019,33(1):176-192
Earth observation images are a powerful source of data about changes in our planet. Given the magnitude of global environmental changes taking place, it is important that Earth Science researchers have access to spatiotemporal reasoning tools. One area of particular interest is land-use change. Using data obtained from images, researchers would like to express abstractions such as ‘land abandonment’, ‘forest regrowth’, and ‘agricultural intensification’. These abstractions are specific types of land-use trajectories, defined as multi-year paths from one land cover into another. Given this need, this paper introduces a spatiotemporal calculus for reasoning about land-use trajectories. Using Allen’s interval logic as a basis, we introduce new predicates that express cases of recurrence, conversion and evolution in land-use change. The proposed predicates are sufficient and necessary to express different kinds of land-use trajectories. Users can build expressions that describe how humans modify Earth’s terrestrial surface. In this way, scientists can better understand the environmental and economic effects of land-use change. 相似文献
10.
Roberto Ventura Santos Edilton J. dos Santos João Adauto de Souza Neto Luis Christian Montreuil Carmona Alcides Nóbrega Sial Luis Henrique Mancini Lauro Cézar Montefalco de Lira Santos Gilzênia Henrique do Nascimento Lucas UpaDafubigin Santos Mendes Emerson Marcello Ferreira Anastácio 《Gondwana Research》2013,23(1):380-389
Strongly-deformed marbles may be easily confused with linear and elongated carbonatite intrusions. Both rocks may present similar texture and foliation to the host rock, or even cross cutting field relationships, which could be interpreted either as igneous or high-grade metamorphosed marble. Diagnostic criteria are even more complex when there is evidence of melting of the metasedimentary carbonate rock, such as has been described in the Himalayas and in the Eastern Ghats, India.In the Alto Moxotó Terrane, a high-grade gneissic domain of the Borborema Province, Northeastern Brazil, there are metacarbonates associated with banded gneisses and different metaplutonic rocks. Field evidence indicates the absence of other metasedimentary rocks associated with these marbles, thus suggesting that these carbonates were separated from other siliciclastic metasedimentary rocks. The presence of marble also suggests that it may represent the initial stage of a crustal carbon recycling into the mantle. These marbles present many field similarities to carbonatites (e.g., fluid-flow structure) and, together with metagranites and metamafic intrusions, may represent a major collisional tectonic suture.A detailed study of the carbon, oxygen and strontium isotopic composition of these marbles is presented. This study aims to identify the origin of the different isotopic components. It is argued that these rocks were subjected to temperature and pressure conditions that were sufficiently high to have melted them. The isotopic data presented here support this interpretation and indicate the mixing of two components: (i) one characterized by radiogenic Sr isotopes and mantle-like carbon isotopes, which is associated with the gneissic and mafic rocks, and (ii) another characterized by low 87Sr/86Sr ratios and highly positive δ13C values. Available geochemical data for the upper Paleoproterozoic indicate that the 87Sr/86Sr ratio of ocean water, varying between 0.7050 (2.25 ± 0.25 Ga) and 0.7047 (1.91 Ga), falls within the lower range of the samples from Itatuba and thus reinforces the interpretation that these marbles are sedimentary-derived and were partially contaminated by interaction with the host gneissic and mafic rocks. 相似文献