全文获取类型
收费全文 | 2080篇 |
免费 | 203篇 |
国内免费 | 322篇 |
专业分类
测绘学 | 35篇 |
大气科学 | 113篇 |
地球物理 | 399篇 |
地质学 | 474篇 |
海洋学 | 1209篇 |
天文学 | 2篇 |
综合类 | 122篇 |
自然地理 | 251篇 |
出版年
2024年 | 8篇 |
2023年 | 21篇 |
2022年 | 64篇 |
2021年 | 49篇 |
2020年 | 58篇 |
2019年 | 88篇 |
2018年 | 63篇 |
2017年 | 87篇 |
2016年 | 75篇 |
2015年 | 103篇 |
2014年 | 131篇 |
2013年 | 137篇 |
2012年 | 85篇 |
2011年 | 151篇 |
2010年 | 98篇 |
2009年 | 184篇 |
2008年 | 169篇 |
2007年 | 162篇 |
2006年 | 114篇 |
2005年 | 97篇 |
2004年 | 73篇 |
2003年 | 62篇 |
2002年 | 75篇 |
2001年 | 60篇 |
2000年 | 50篇 |
1999年 | 47篇 |
1998年 | 55篇 |
1997年 | 37篇 |
1996年 | 27篇 |
1995年 | 33篇 |
1994年 | 23篇 |
1993年 | 22篇 |
1992年 | 20篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 13篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1979年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有2605条查询结果,搜索用时 15 毫秒
61.
Access to information about past states of the environment and social systems is fundamental to understand, and cope with, the challenges of climate change and over-exploitation of natural resources at the onset of the 21st century. The loss of (old) data is a major threat to understanding better and mitigating long-term effects of human activities and anthropogenic changes to the environment. Although this is intuitively evident for old and local literature of any kind, even present-day international publishing of papers without the underlying raw data makes access to basic information a crucial issue. Here, we summarise experience resulting from a EU-funded International Science & Technology Cooperation (INCO) project (CENSOR) addressing Coastal Ecosystem Research and Management in the El Niño Southern Oscillation (ENSO) context. We show that indeed “Grey Literature” is still one of the most important sources of knowledge about natural science research and management of natural resource systems in Latin American countries. We argue that public archiving of original data of present-day research and old (Grey) Literature and easy public access are important for appreciating today's global environmental challenges caused by human activities, both past and present. 相似文献
62.
Robert S. Pomeroy Blake D. Ratner Stephen J. Hall Jate Pimoljinda V. Vivekanandan 《Marine Policy》2006,30(6):786-793
This paper examines lessons from past approaches to natural disasters, as well as early lessons from the post-2004 Asian tsunami rehabilitation, to draw out general principles for rehabilitating livelihoods in poor coastal communities. We contend that avoiding the mistakes of the past requires: (1) a framework for understanding the diversity of coastal people's livelihood strategies and the sources of their vulnerability, (2) a process for designing interventions that build on this understanding in order to strengthen and revitalize coastal communities, including a means of assessing and selecting the most promising livelihood options, and (3) a focus on the longer-term challenge of building future resilience and sustainability in the communities by addressing the root causes of vulnerability. 相似文献
63.
The properties of salinity in the South China Sea (SCS), a significant marginal sea connecting the Pacific andIndian Oceans, are greatly influenced by the transport of fresh water flux between the two oceans. However, the long-termchanges in the intermediate water in the SCS have not been thoroughly studied due to limited data, particularly in relationto its thermodynamic variations. This study utilized reanalysis data products to identify a 60-year trend of freshening in theintermediate waters of the northern South China Sea (NSCS), accompanied by an expansion of low-salinity water. Thestudy also constructed salinity budget terms, including advection and entrainment processes, and conducted an analysis ofthe salinity budget to understand the impacts of external and internal dynamic processes on the freshening trend of theintermediate water in the NSCS. The analysis revealed that the freshening in the northwest Pacific Ocean and theintensification of intrusion through the Luzon Strait at intermediate levels are the primary drivers of the salinity changes inthe NSCS. Additionally, a weakened trend in the intensity of vertical entrainment also contributes to the freshening in theNSCS. This study offers new insights into the understanding of regional deep sea changes in response to variations in boththermodynamics and oceanic dynamic processes. 相似文献
64.
H.B. Chauhan R.M. Dwivedi 《International Journal of Applied Earth Observation and Geoinformation》2008,10(2):181-1
Coastal zone assumes importance due to high productivity of ecosystems, man-made developmental activities, natural hazards and dynamic nature of the coast. As costal ecosystems are unique and fragile, understanding the impact of developmental activities on the sustainability of the coastal zone is very important. Remote sensing, because of repetitive and synoptic nature is an ideal tool for studying this. Time series data analyses for monitoring coastal zone require different type of sensors. Present study deals with atmospheric correction of satellite data, reflectance, selection of coastal features like, mudflat, mangroves, vegetated dune, coastal water, etc. and their inter-comparison using different sensor data of RESOURCESAT sensors. Reflectance values give better separateability for various coastal features in comparison to DN values. LISS IV can be used in place of LISS III or merged (LISS III + PAN) for long-term coastal zone studies. 相似文献
65.
Contributions of boron isotopes to understanding the hydrogeochemistry of the coastal detritic aquifer of Castellón Plain,Spain 总被引:1,自引:0,他引:1
The Castellón Plain alluvial aquifer, Spain, is intensively exploited to meet the demand for agricultural irrigation and industrial water supply. The geochemistry of its groundwater shows complex salinization in the northern and southern parts of the aquifer, with significant pollution from human origin in the central portion. Boron content and B isotope geochemistry are useful for distinguishing between various sources of pollution and their relative importance in different parts of this aquifer. Boron concentrations in the groundwater vary between 0.01 and 0.85 mg/L. In the more saline groundwaters, found at the northern and southern ends of the study area, the presence of B is linked to inputs from seawater and water with a calcium-magnesium sulphate facies, which feed the aquifer and clearly influence the chemistry of its waters. Evidence of B adsorption processes in some samples is shown by the low B/Cl ratios and the high values of δ11B. In the central portion of the aquifer, the high B/Cl ratios and the strongly negative δ11B are related to pollution of human origin. 相似文献
66.
Definition and measurement of salinity in salt lakes 总被引:4,自引:0,他引:4
Salinity is the most important chemical attribute of athalassic salt lakes. Even so, some confusion persists of what salinity means and how to measure it. For sal lakes, salinity is best defined as the sum total of all ion concentrations, or total ion concentration. Ideally, it is recommended that salinities be expressed on a mass per mass basis and as ppt (parts per thousand). Direct measurements of salinity can only be derived from full ionic analyses. Indirect measurements can be derived by determinations of density, conductivity, freezing point depression and total dissolved solids or matter. 相似文献
67.
The Oso Bay, Texas, sediments from nine sites were analyzed by GC-MS for organics to measure contamination in the bay. In most of the sites sediments contained tetrachloroethene (87–1433 g/kg), bis (2-ethylhexyl)phthalate (40–193 g/kg), and aliphatic hydrocarbons, C8-C13 (720–2491 g/kg). Sources of these contaminants include a landfill, military facilities, and municipal and industrial discharges. Size analysis of the sediments indicates they contain a high percentage of muddy sand (50–75 percent), which suggests that Oso Bay consists of common bay margin sediments. 相似文献
68.
Paleoenvironmental records of water level and climatic changes from the middle to late Holocene at a Lake Erie coastal wetland, Ontario, Canada 总被引:2,自引:0,他引:2
Pollen and diatom assemblages, and peat stratigraphies, from a coastal wetland on the northern shore of Lake Erie were used to analyze water level and climatic changes since the middle Holocene and their effects on wetland plant communities. Peat deposition began 4700 cal yr B.P. during the Nipissing II transgression, which was driven by isostatic rebound. At that time, a diatom-rich wild rice marsh existed at the site. Water level dropped at the end of the Nipissing rise at least 2 m within 200 yr, leading to the development of shallower-water plant communities and an environment too dry for most diatoms to persist. The sharp decline in water level was probably driven primarily by outlet incision, but climate likely played some role. The paleoecological records provide evidence for post-Nipissing century-scale transgressions occurring around 2300, 1160, 700 and 450 cal yr B.P. The chronology for these transgressions correlates with other studies from the region and implies climatic forcing. Peat inception in shallow sloughs across part of the study area around 700 cal yr B.P. coincides with the Little Ice Age. These records, considered alongside others from the region, suggest that the Little Ice Age may have resulted in a wetter climate across the eastern Great Lakes region. 相似文献
69.
海滨湿地生态系统的热点研究 总被引:1,自引:1,他引:1
海滨湿地具有强大的生态服务功能,然而由于人类活动的长期和强烈干扰,导致该系统严重受损和退化。海滨湿地生态系统的严重退化引起国内外学术界的高度关注。有关其退化及生态恢复的研究热点涉及该系统的演化与机制、对外来种入侵的响应与生态控制、退化海滨湿地生态系统的修复、生态系统健康的评估及其保护与利用平衡的研究。本文综述了上述热点研究的进展,有利于把握国际前沿研究动态,借鉴最新研究方法和经验,推动我国在这一领域的研究尽快赶上国际先进水平。 相似文献
70.
The formation and evolution of the barrier islands of Inhaca and Bazaruto, Mozambique 总被引:1,自引:0,他引:1
S.J. Armitage G.A. Botha G.A.T. Duller A.G. Wintle L.P. Rebêlo F.J. Momade 《Geomorphology》2006,82(3-4):295-308
The barrier islands of Inhaca and Bazaruto are related to the extensive coastal dune system of the Mozambican coastal plain, south-east Africa. Optically stimulated luminescence (OSL) dating of key stratigraphic units indicates that accretion of sediment within these systems is episodic. Both islands appear to have been initiated as spits extending from structural offsets in the coastline. Superposition of significant quantities of sediment upon these spits during subsequent sea-level highstands formed the core of the islands, which were anchored and protected by beachrock and aeolianite formation. At least two distinct dune-building phases occurred during Marine Oxygen Isotope Stage (MIS) 5, tentatively attributed to marine transgressions during sub-stages 5e and 5c. Although some localized reactivation of dune surfaces occurred prior to the Holocene, large quantities of sediment were not deposited on either island during the low sea-levels associated with MIS 2. Significant dune-building and sediment reworking occurred immediately prior to and during the Holocene, though it is not clear whether these processes were continuous or episodic. Significant erosion of the eastern shoreline of Bazaruto suggests that it is far less stable than Inhaca and may suffer further large-scale erosion. A model is presented for the formation of barrier islands along the Mozambican coastal plain. 相似文献