全文获取类型
| 收费全文 | 69篇 |
| 免费 | 3篇 |
专业分类
| 大气科学 | 5篇 |
| 地球物理 | 14篇 |
| 地质学 | 30篇 |
| 海洋学 | 7篇 |
| 天文学 | 2篇 |
| 综合类 | 2篇 |
| 自然地理 | 12篇 |
出版年
| 2022年 | 1篇 |
| 2021年 | 2篇 |
| 2020年 | 2篇 |
| 2018年 | 3篇 |
| 2017年 | 1篇 |
| 2016年 | 1篇 |
| 2015年 | 3篇 |
| 2014年 | 2篇 |
| 2013年 | 2篇 |
| 2012年 | 3篇 |
| 2011年 | 3篇 |
| 2010年 | 4篇 |
| 2009年 | 6篇 |
| 2008年 | 5篇 |
| 2007年 | 2篇 |
| 2006年 | 8篇 |
| 2005年 | 2篇 |
| 2004年 | 3篇 |
| 2002年 | 2篇 |
| 2001年 | 1篇 |
| 2000年 | 2篇 |
| 1999年 | 2篇 |
| 1998年 | 2篇 |
| 1997年 | 1篇 |
| 1993年 | 1篇 |
| 1992年 | 1篇 |
| 1991年 | 1篇 |
| 1977年 | 1篇 |
| 1976年 | 2篇 |
| 1973年 | 1篇 |
| 1969年 | 2篇 |
排序方式： 共有72条查询结果，搜索用时 711 毫秒
1.
This paper focuses on what observers have perceived to be a failure of development leading to a ‘crisis of youth’ as increasing numbers of young people find it more difficult to gain education, access to health, a job and meet standard of living aspirations. For some, a possible escape is offered by migration to Europe, the United States or Australia, often illegally. For those remaining behind, however, international development agencies offer a ‘globalisation of solutions’ to employment, gender inequality and poverty through the millennium development goals and the programmes to attain them. In this paper we do not take the failures of development at face value but look at local contexts to present a more complex picture of the relation between education, work and social life. Based on fieldwork conducted in urban areas of The Gambia and Ghana, we argue that rather than education as a catch-all solution we need to give more attention to the costs incurred by and for young people in pursuing education and training, to the operation of and actual opportunities in labour markets, and to patterns of gender socialisation which give women limited scope to exercise agency. This paper explores key gender dimensions of work and education among low-income urban youth noting that despite on-going efforts to increase young women’s enrolment in schools and access to employment, gender inequalities have been far from eradicated. Our field interviews reveal how social expectations that women should perform the bulk of reproductive labour in their youth as well as in adulthood and constraints placed on young women’s personal freedom in respect of their social relationships reduce time dedicated to education and establish fewer contacts relevant to securing paid employment. The result is for men to end up with more educational qualifications, more skills, and higher-paying jobs, even if unemployment among young people in general remains a major problem. 相似文献
2.
Sylvia L. R. Wood John S. Richardson 《Aquatic Sciences - Research Across Boundaries》2010,72(4):499-508
A number of aquatic organisms have demonstrated an ability to modulate sediment deposition in tropical and temperate stream
systems, but little is known about the impact of similar benthic grazing processes in temperate pond systems. Using exclosure
experiments in mesocosms, we used tadpoles of the western toad (Anaxyrus boreas) to investigate two questions: (1) can grazing activities of tadpoles of the western toad in ponds reduce sediment accrual
on grazing surfaces (e.g. via bioturbation or ingestion); and (2) do these grazing activities contribute to enhanced periphyton
biomass and chlorophyll a content of benthic matter. Mesocosms received pulses of fine sediment weekly over 8 weeks to simulate allochthonous surface
inputs following rainstorms. Accumulated sediment and periphyton matter on exposed and grazing-restricted substrate surfaces
were measured weekly. Tadpole grazing activity significantly reduced the standing stock of periphyton on open grazing surfaces
by 80% in controls. Under sediment-additions, tadpoles effectively removed settled particulate matter from exposed grazing
surfaces, but no corresponding increase in periphyton biomass was observed. These results suggest that tadpoles can impact
the dynamics of sediment distribution in ponds as well as streams, providing support for a role as “ecosystem engineers” in
these habitats. 相似文献
3.
The potential consequences of bedload transport of postlarvae for patterns of distribution of marine invertebrates were explored
by developing a bedload transport model for juvenile bivalves in a small estuary in New Jersey, USA. A simple numerical model
of tidal current hydrodynamics was developed based on field measurements of shear stresses near the bottom. Burrowing behavior
of bivalves was incorporated into the model of bedload transport by using estimates of entrainment rates of Gemma gemma and Mya arenaria in a laboratory flume, and jump lengths of the bivalves were estimated by methods previously developed for noncohesive particles.
Based on the flood domination and strong gradient of shear stresses in the Navesink estuary, our model predicted that juvenile
bivalves would accumulate in the center of the estuary, traveling up to several kilometers over 30 days. Field distributions
of juvenile bivalves were consistent with the model predictions for other species of bivalves but not for G. gemma, for which field distributions of both <500- and >500-μm individuals were concentrated in the eastern end of the estuary.
Differences between the bedload model and G. gemma distributions suggest that spatial variation in burrowing behavior or biological interactions are playing an important role
in maintaining distribution patterns of this species in spite of high levels of bedload transport. This modeling approach
is applicable to other juvenile benthic invertebrates that disperse as bedload and is a useful model against which to compare
field observations of rates of transport and patterns of distribution and abundance. 相似文献
4.
Jonathan Pickering Jeffrey S. McGee Tim Stephens Sylvia I. Karlsson-Vinkhuyzen 《Climate Policy》2018,18(7):818-827
The United States’ decision to withdraw from the Paris Agreement (pending possible re-engagement under different terms) may have significant ramifications for international climate policy, but the implications of this decision remain contested. This commentary illustrates how comparative analysis of US participation in multilateral environmental agreements can inform predictions and future assessments of the decision. We compare and contrast US non-participation in the Kyoto Protocol and the Paris Agreement, focusing on four key areas that may condition the influence of US treaty decisions on international climate policy: (i) global momentum on climate change mitigation; (ii) the possibility of US non-participation giving rise to alternative forms of international collaboration on climate policy; (iii) the timing and circumstances of the US decision to exit; and (iv) the influence of treaty design on countries’ incentives to participate and comply. We find that differences across the two treaties relating to the first three factors are more likely to reduce the negative ramifications of US withdrawal from the Paris Agreement compared to the Kyoto Protocol. However, the increased urgency of deep decarbonization renders US non-participation a major concern despite its declining share of global emissions. Moreover, key design features of the Paris Agreement suggest that other countries may react to the US decision by scaling back their levels of ambition and compliance, even if they remain in the Agreement.
Key policy insights
Increasing global momentum on mitigation since 1997 means that US withdrawal from the Paris Agreement is potentially less damaging than its non-participation in the Kyoto Protocol
Despite the declining US share of global emissions, greater urgency of deep decarbonization means that the non-participation of a major player, such as the US, remains problematic for global cooperation and achieving the Paris Agreement’s goals
Differences in the design of the Kyoto Protocol and Paris Agreement suggest that US non-participation is more likely to prompt reluctant countries to stay within the Paris framework but reduce levels of ambition and compliance, rather than exit the Agreement altogether
5.
Rocky Dunlap Leo Mark Spencer Rugaber V. Balaji Julien Chastang Luca Cinquini Cecelia DeLuca Don Middleton Sylvia Murphy 《Earth Science Informatics》2008,1(3-4):131-149
The Earth System Curator is a National Science Foundation sponsored project developing a metadata formalism for describing the digital resources used in climate simulations. The primary motivating observation of the project is that a simulation/model’s source code plus the configuration parameters required for a model run are a compact representation of the dataset generated when the model is executed. The end goal of the project is a convergence of models and data where both resources are accessed uniformly from a single registry. In this paper we review the current metadata landscape of the climate modeling community, present our work on developing a metadata formalism for describing climate models, and reflect on technical challenges we have faced that require new research in the area of Earth Science Informatics. 相似文献
6.
7.
Zoltn Vci Carl B. Agee Christopher D. K. Herd Erin Walton Oliver Tschauner Karen Ziegler Vitali B. Prakapenka Eran Greenberg Sylvia Monique‐Thomas 《Meteoritics & planetary science》2020,55(5):1011-1030
Hydrous alteration of olivine macrocrysts in a Martian olivine phyric basalt, NWA 10416, and a terrestrial basalt from southern Colorado are examined using SEM, EPMA, TEM, and µXRD techniques. The olivines in the meteorite contain linear nanotubes of hydrous material, amorphous areas, and fluid dissolution textures quite distinct from alteration identified in other Martian meteorites. Instead, they bear resemblance to terrestrial deuteric alteration features. The presence of the hydrous alteration phase Mg‐laihunite within the olivines has been confirmed by µXRD analysis. The cores of the olivines in both Martian and terrestrial samples are overgrown by unaltered rims whose compositions match those of a separate population of groundmass olivines, suggesting that the core olivines are xenocrysts whose alteration preceded crystallization of the groundmass. The terrestrial sample is linked to deep crustal metasomatism and the “ignimbrite flare‐up” of the Oligocene epoch. The comparison of the two samples suggests the existence of an analogous relatively water‐rich magmatic reservoir on Mars. 相似文献
8.
In order to better model the fate and transport of material in a combined sewer overflow (CSO), hydrologic and geochemical measurements were made during a storm event in Flushing Bay, NY, USA. Particle size, total suspended solids concentrations, and CSO solid density are used to calculate the settling velocity of aggregates of the CSO material. Roughly half of the material that is discharged from the outfall sinks rapidly to the bottom, while the other half forms a turbid surface plume in fresher water. The dry solid density of the CSO material was 1589 kg m(-3) and the volume fraction of solid material to total aggregate volume ranged from 0.1 to 1.0. The settling velocity estimates of aggregated material in the surface plume ranged from about 0.5 to 9.0 mm s(-1) with a median settling velocity of 2.9 mm s(-1). A strong inverse relationship between the size of the aggregates and the aggregate density resulted in a fractal dimension of the aggregates of 2.3. 相似文献
9.
10.
Nagel Karl -Heinz Schütz Karsten -Ingo Schütz Sylvia Wilmers Wilhelm Zeil Werner 《International Journal of Earth Sciences》1976,65(1):536-557
Zusammenfassung Die Thiersee- und die Karwendelmulde in den Nördlichen Kalkalpen sind als zwei getrennte, E-W-verlaufende Synklinen entwickelt. Ihre Länge zwischen Kufstein und Mittenwald beträgt über 70 km.Systematische geologische Aufnahmen — Kartierung, Stratigraphie, Sedimentologie und Gefügekunde — ergaben, daß die Thierseemuide im Raum von Achenkirch nicht — wie früher vermutet wurde — in die Karwendelmulde umbiegt. Die Auswertung von mehr als 45 000 Gefügemessungen mit Hilfe eines EDV-Programms bewies vielmehr, daß Thierseemuide und Karwendelmulde zwei parallele, unabhängige Strukturen sind, die durch die komplizierte tektonische Zone von Achenkirch getrennt werden.Die paläogeographische Entwicklung und der Ablauf der Bewegungen werden im Überblick skizziert.
Systematic geological survey showed that the Thiersee and Karwendel synclines in the Northern Calcareous Alps are two parallel structures, separated by a slightly folded intersection. The synclines do not turn into each other, as was presumed by earlier workers.The tectonic situation in the area of Achenkirch was cleared by evaluation of more than 45,000 field texture data by a computer program. Mapping as well as stratigraphical and sedimentological analysis supports the tectonic model. The paleogeographic development and tectonic history are briefly described.
Résumé Les dépressions du «Thiersee» et du «Karwendel», dans les Alpes calcaires du Nord, sont deux synclinaux indépendants de direction Est-Ouest. Elles font 70 km de long entre Kufstein et Mittenwald.Des relevés géologiques systématiques — levés géologiques, stratigraphie, sédimentologie et structurologie — démontrèrent que, dans la région d'Achenkirch, la dépression du «Thiersee» ne contourne pas la dépression du «Karwendel» (comme on l'a longtemps supposé!). L'exploitation par ordinateur de plus de 45.000 mesures structurales révéla au contraire, que ces dépressions sont deux structures parallèles et indépendantes, séparées par la zone tectonique complexe d'Achenkirch.Le développement paléogéographique et le déroulement des mouvements font l'objet d'une vue d'ensemble.
, . 70 . , - , , — , , . EDV 45 000 , , . .相似文献