首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   82篇
  免费   4篇
测绘学   2篇
大气科学   6篇
地球物理   20篇
地质学   36篇
海洋学   7篇
天文学   3篇
综合类   1篇
自然地理   11篇
  2023年   1篇
  2022年   2篇
  2021年   5篇
  2020年   1篇
  2019年   5篇
  2018年   5篇
  2017年   4篇
  2016年   1篇
  2015年   3篇
  2014年   6篇
  2013年   1篇
  2012年   3篇
  2011年   8篇
  2010年   2篇
  2009年   2篇
  2008年   5篇
  2007年   2篇
  2006年   2篇
  2004年   4篇
  2003年   1篇
  2002年   1篇
  2001年   2篇
  2000年   1篇
  1997年   1篇
  1995年   1篇
  1991年   2篇
  1989年   3篇
  1988年   1篇
  1987年   2篇
  1986年   2篇
  1985年   1篇
  1983年   1篇
  1982年   2篇
  1981年   1篇
  1978年   1篇
  1970年   1篇
排序方式: 共有86条查询结果,搜索用时 15 毫秒
51.
ABSTRACT

Based on research into multiple types of climate change mitigation and adaptation (CCMA) projects and policies in Cambodia, this paper documents intersecting social and environmental conflicts that bear striking resemblance to well-documented issues in the history of development projects. Using data from three case studies, we highlight the ways that industrial development and CCMA initiatives are intertwined in both policy and project creation, and how this confluence is creating potentials for maladaptive outcomes. Each case study involves partnerships between international institutions and the national government, each deploys CCMA as either a primary or supporting legitimation, and each failed to adhere to institutional and/or internationally recognized standards of justice. In Cambodia, mismanaged projects are typically blamed on the kleptocratic and patrimonial governance system. We show how such blame obscures the collusion of international partners, who also sidestep their own safeguards, and ignores the potential for maladaptation at the project level and the adverse social and environmental impacts of the policies themselves.

Key policy insights
  • Initiatives to mitigate or adapt to climate change look very much like the development projects that caused climate change: Extreme caution must be exercised to ensure policies and projects do not exacerbate the conditions driving climate change.

  • Safeguards ‘on paper’ are insufficient to avoid negative impacts and strict accountability mechanisms must be put in place.

  • Academic researchers can be part of that accountability mechanism through case study reports, policy briefs, technical facilitation to help ensure community needs are met and safeguards are executed as written.

  • Impacts beyond the project scale must be assessed to avoid negative consequences for social and ecological systems at the landscape level.

  相似文献   
52.
由中国地震局、全国人大教科文卫委员会、国务院法制办公室、国家质量技术监督局有关人员组成的防震减灾法制管理考察代表团一行8人 ,于 2 0 0 0年 4月 1 2~ 2 8日赴美国进行了防震减灾法制管理考察。代表团在美国期间 ,访问了美国联邦紧急事务管理局 (FEMA)、美国地质调查局 (USGS) ,考察了美国建设工程抗震设防的情况 ,特别与旧金山市政府进行了学术交流。双方主要就旧金山市政府自 1 989年洛马普列塔 7.1级地震后 ,在地震灾害防御方面所采取的对策措施进行了研讨和交流。美国是世界上地震多发、地震灾害严重的国家之一。因此 ,美国…  相似文献   
53.
54.

Globally, coral reefs are threatened by ocean warming and acidification. The degree to which acidification will impact reefs is dependent on the local hydrodynamics, benthic community composition, and biogeochemical processes, all of which vary on different temporal and spatial scales. Characterizing the natural spatiotemporal variability of seawater carbonate chemistry across different reefs is critical for elucidating future impacts on coral reefs. To date, most studies have focused on select habitats, whereas fewer studies have focused on reef scale variability. Here, we investigate the temporal and spatial seawater physicochemical variability across the entire Heron Island coral reef platform, Great Barrier Reef, Australia, for a limited duration of six days. Autonomous sensor measurements at three sites across the platform were complemented by reef-wide boat surveys and discrete sampling of seawater carbonate chemistry during the morning and evening. Variability in both temporal and spatial physicochemical properties were predominantly driven by solar irradiance (and its effect on biological activity) and the semidiurnal tidal cycles but were influenced by the local geomorphology resulting in isolation of the platform during low tide and rapid flooding during rising tides. As a result, seawater from previous tidal cycles was sometimes trapped in different parts of the reef leading to unexpected biogeochemical trends in space and time. This study illustrates the differences and limitations of data obtained from high-frequency measurements in a few locations compared to low-frequency measurements at high spatial resolution and coverage, showing the need for a combined approach to develop predictive capability of seawater physicochemical properties on coral reefs.

  相似文献   
55.
56.
 Multibeam bathymetric data collected in St. George’s Bay, Newfoundland, show glacial and postglacial landforms in a 100-m-deep basin offshore from a barrier. Back-scatter data provide information on sediment lithology. Features undetected by previous conventional surveys include large bedforms on the surface of a barrier platform and submarine fans on its flanks. The data demonstrate that sediment transport processes are more complex than was previously believed. Multibeam bathymetric images are the sea-floor equivalents of air photographs. They can be used effectively to plan conventional acoustic surveys. Received: 16 February 1996 / Revision received: 4 September 1996  相似文献   
57.
Erodibility of cohesive sediment in the Sacramento-San Joaquin River Delta (Delta) was investigated with an erosion microcosm. Erosion depths in the Delta and in the microcosm were estimated to be about one floc diameter over a range of shear stresses and times comparable to half of a typical tidal cycle. Using the conventional assumption of horizontally homogeneous bed sediment, data from 27 of 34 microcosm experiments indicate that the erosion rate coefficient increased as eroded mass increased, contrary to theory. We believe that small erosion depths, erosion rate coefficient deviation from theory, and visual observation of horizontally varying biota and texture at the sediment surface indicate that erosion cannot solely be a function of depth but must also vary horizontally. We test this hypothesis by developing a simple numerical model that includes horizontal heterogeneity, use it to develop an artificial time series of suspended-sediment concentration (SSC) in an erosion microcosm, then analyze that time series assuming horizontal homogeneity. A shear vane was used to estimate that the horizontal standard deviation of critical shear stress was about 30% of the mean value at a site in the Delta. The numerical model of the erosion microcosm included a normal distribution of initial critical shear stress, a linear increase in critical shear stress with eroded mass, an exponential decrease of erosion rate coefficient with eroded mass, and a stepped increase in applied shear stress. The maximum SSC for each step increased gradually, thus confounding identification of a single well-defined critical shear stress as encountered with the empirical data. Analysis of the artificial SSC time series with the assumption of a homogeneous bed reproduced the original profile of critical shear stress, but the erosion rate coefficient increased with eroded mass, similar to the empirical data. Thus, the numerical experiment confirms the small-depth erosion hypothesis. A linear model of critical shear stress and eroded mass is proposed to simulate small-depth erosion, assuming that the applied and critical shear stresses quickly reach equilibrium.  相似文献   
58.
The EDdy Dynamics, mixing, Export, and Species composition (EDDIES) project provided a unique opportunity to evaluate the response of the microbial community and further understand the biological and biogeochemical consequences of mesoscale perturbation events in an oligotrophic system. In order to characterize microbial dynamics, we performed measurements of bacterial biomass (BB) and production (BP) and phytoplankton pigment analyses in two upwelling eddies in the Sargasso Sea sampled in 2004 and 2005. We also observed a 3-fold increase in BP at the Bermuda Atlantic Time-series Study (BATS) site during the passage of a cyclonic eddy in 2003. Although the integrated BB and BP over 140 m in 2004 and 2005 eddies remained within the climatological range measured at the BATS site, there was systematic variability in bacterioplankton dynamics across both eddies. Cyclonic eddy C1 demonstrated decreased BP at the feature's center relative to its periphery, and BP was not correlated with total chlorophyll a (TChl a) variability. However, BP correlated with prymnesiophyte pigments throughout the feature. In contrast, mode-water eddy A4 showed an enhancement in BP at the eddy center (EC) relative to its edges and was coincident with elevated TChl a, high primary production measurements, and a high concentration of diatoms. In eddy A4, the tight relationship between enhanced BP, TChl a and specific phytoplankton taxa implies that the phytoplankton community structure was an important factor influencing BP variability. While the heterotrophic bacterial response in C1 and A4 was not enhanced relative to BATS summer climatology, these data and the presence of similar nutrient fields across both eddies suggest that BP and BB were influenced by the eddy perturbations and responded to changes in the phytoplankton community.  相似文献   
59.
Titan, Saturn's largest moon, has a thick nitrogen/methane atmosphere. The temperature and pressure conditions in Titan's atmosphere are such that the methane vapor should condense near the tropopause to form clouds. Several ground-based measurements have observed sparse cloud-like features in Titan's atmosphere, while the Cassini mission to Saturn has provided large scale images of the clouds. However, Titan's cloud formation conditions remain poorly constrained. Heterogeneous nucleation (from the vapor phase onto a solid or liquid aerosol surface) greatly enhances cloud formation relative to homogeneous nucleation. In order to elucidate the cloud formation mechanism near the tropopause, we have performed laboratory measurements of the adsorption of methane and ethane onto solid organic particles (tholins) representative of Titan's photochemical haze. We find that monolayers of methane adsorb onto tholin particles at saturation ratios less than unity. We also find that solid methane nucleates onto the adsorbed methane at a saturation ratio of S=1.07±0.008. This implies that Titan's methane clouds should form easily. This is consistent with recent measurements of the column of methane ruling out excessive methane supersaturation. In addition, we find ethane adsorbs onto tholin particles in a metastable phase prior to nucleation. However, ethane nucleation onto the adsorbed ethane occurs at a relatively high saturation ratio of S=1.36±0.08. These findings are consistent with the recent report of polar ethane clouds in Titan's lower stratosphere.  相似文献   
60.
In both nature and synthetic experiments, the common iron oxide haematite (α‐Fe2O3) can incorporate significant amounts of U into its crystal structure and retain radiogenic Pb over geological time. Haematite is a ubiquitous component of many ore deposit types and, therefore, represents a valuable hydrothermal mineral geochronometer, allowing direct constraints to be placed on the timing of ore formation and upgrading. However, to date, no suitable natural haematite reference material has been identified. Here, a synthetic haematite U‐Pb reference material (MR‐HFO) is characterised using LA‐ICP‐MS and ID‐TIMS. Centimetre‐scale ‘chips’ of synthesised α‐Fe2O3 were randomly microsampled via laser ablation‐extraction and analysed using ID‐TIMS. Reproducible U/Pb and Pb/Pb measurements were obtained across four separate chips (n = 13). Subsequently, an evaluation of the suitability MR‐HFO in constraining U‐Pb data via LA‐ICP‐MS is presented using a selection of natural samples ranging from Cenozoic to Proterozoic in age. The MR‐HFO normalised U‐Pb ratios are more concordant and ages more accurate versus the same LA‐ICP‐MS spot analyses normalised to zircon reference material, when compared with independently acquired ID‐TIMS data from the same natural haematite grains. Results establish MR‐HFO as a suitable reference material for LA‐ICP‐MS haematite U‐Pb geochronology.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号