全文获取类型
收费全文 | 320篇 |
免费 | 24篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 25篇 |
地球物理 | 85篇 |
地质学 | 102篇 |
海洋学 | 35篇 |
天文学 | 31篇 |
综合类 | 4篇 |
自然地理 | 57篇 |
出版年
2024年 | 1篇 |
2023年 | 7篇 |
2022年 | 3篇 |
2021年 | 10篇 |
2020年 | 14篇 |
2019年 | 24篇 |
2018年 | 19篇 |
2017年 | 11篇 |
2016年 | 21篇 |
2015年 | 10篇 |
2014年 | 13篇 |
2013年 | 18篇 |
2012年 | 16篇 |
2011年 | 22篇 |
2010年 | 16篇 |
2009年 | 18篇 |
2008年 | 23篇 |
2007年 | 18篇 |
2006年 | 11篇 |
2005年 | 9篇 |
2004年 | 9篇 |
2003年 | 10篇 |
2002年 | 13篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有347条查询结果,搜索用时 131 毫秒
81.
82.
This paper investigates the complex demographic and social changes that have occurred in the neighborhoods of fast-growing United States metropolitan areas emerging as nodes in megapolitan regions between 1980 and 2010. A neighborhood typology is created using k-means cluster analysis to examine the demographic and housing characteristics, and geographic distribution, of neighborhoods that have existed in rapidly growing metropolitan areas. A socioeconomic index is created using principal component analysis (PCA) to analyze socioeconomic conditions within neighborhoods. Using data from the metropolitan areas of Las Vegas, Nevada; Austin, Texas; and Raleigh, North Carolina, this study identifies five neighborhood types, each of which has distinctive geographic and socioeconomic trends. The geographic orientation of each metropolitan area within their larger megapolitan region appears to have a role in the geography of neighborhood change. The results are also discussed in relation to human ecology, immigration, and economic restructuring. 相似文献
83.
AbstractTimber rattlesnakes (Crotalus horridus) are endangered throughout the northeastern United States where multiple factors contribute to population declines. Challenges exist to managing rattlesnake populations because there is little information about human dimensions of this species or other small predators that are venomous or perceived as hazardous. Our objective was to evaluate relationships between resident attitudes and behavioral intentions toward timber rattlesnakes. A mail survey (n?=?593) was used to collect data from residents who live near a rattlesnake population in central Connecticut. Two variables defined resident attitudes toward rattlesnakes: coexistence with the species and perceived threats from the species. Rattlesnake-related factors and situational factors appeared to contribute more heavily to behavioral intentions toward rattlesnakes than general wildlife value orientations. Attitudes predicted behavioral intentions toward rattlesnakes. Results will help wildlife managers incorporate human factors into appropriate management and public outreach strategies. 相似文献
84.
Brückner Florian Bahls Rebecca Alqadi Mohammad Lindenmaier Falk Hamdan Ibraheem Alhiyari Mohammad Atieh Ala’a 《Hydrogeology Journal》2021,29(8):2789-2802
Hydrogeology Journal - In 2017, a comprehensive review of groundwater resources in Jordan was carried out for the first time since 1995. The change in groundwater levels between 1995 and 2017 was... 相似文献
85.
Autumn J. Oczkowski F. Graham Lewis Scott W. Nixon H. Lee Edmiston Rebecca S. Robinson Jeffrey P. Chanton 《Estuaries and Coasts》2011,34(5):993-1005
Apalachicola Bay lies at the mouth of the Apalachicola River, where seasonally variable freshwater inflows and shifting winds
have long been thought to contribute to the support of an unusually productive and commercially important oyster fishery.
Links between the river and productivity have been shown to lie in salinity-induced reductions in oyster predators and oyster
disease as well as organic supplements from an extensive floodplain. Several studies have also indicated that nitrogen (N)
and phosphorous (P) carried by the river are important in fertilization of bay primary production. While there is concern
that upstream water withdrawals may impact the fishery, the importance of riverine N to oyster diets remains unclear. We measured
N and carbon (C) stable isotopes (δ15N, δ13C) in macroalgae, surface-water nitrate, and surface sediments, which showed a gradient from enriched riverine δ15N values to more depleted values in the Gulf of Mexico. In contrast, δ13C of particulate matter is depleted in the river and enriched offshore. Oyster stable isotope values throughout Apalachicola
Bay are more complex, but are dominated by freshwater inputs and reflect the variability and hydrodynamics of the riverine
inflows. 相似文献
86.
Astrid Schnetzer Stefanie D. MoorthiPeter D. Countway Rebecca J. GastIlana C. Gilg David A. Caron 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(1):16-26
Protistan community structure was examined from 6 depths (1.5, 20, 42, 150, 500, 880 m) at a coastal ocean site in the San Pedro Channel, California. A total of 856 partial length 18S rDNA protistan sequences from the six clone libraries were analyzed to characterize diversity present at each depth. The sequences were grouped into a total of 259 Operational Taxonomic Units (OTUs) that were inferred using an automated OTU calling program that formed OTUs with approximately species-level distinction (95% sequence similarity). Most OTUs (194 out of 259) were observed at only one specific depth, and only two were present in clone libraries from all depths. OTUs were obtained from 21 major protistan taxonomic groups determined by their closest BLAST matches to identified protists in the NCBI database. Approximately 74% of the detected OTUs belonged to the Chromalveolates, with Group II alveolates making up the largest single group. Protistan assemblages at euphotic depths (1.5, 20 and 42 m) were characterized by the presence of clades that contained phototrophic species (stramenopiles, chlorophytes and haptophytes) as well as consumers (especially ciliates). Assemblages in the lower water column (150, 500 and 800 m) were distinct from communities at shallow depths because of strong contributions from taxa belonging to euglenozoans, acantharians, polycystines and Taxopodida (Sticholonche spp. and close relatives). Species richness (Chao I estimate) and diversity (Shannon index) were highest within the euphotic zone and at 150 m, and lowest for protistan assemblages located in the oxygen minimum zone (500 and 880 m). Multivariate analyses (Bray-Curtis coefficient) confirmed that protistan assemblage composition differed significantly when samples were grouped into shallow (≤150 m) and deep water assemblages (≥150 m). 相似文献
87.
Galloway TS Brown RJ Browne MA Dissanayake A Lowe D Jones MB Depledge MH 《Marine environmental research》2004,58(2-5):233-237
The ECOMAN project was initiated from an awareness of the complexity of the functioning of coastal marine systems and the clear need for more pragmatic environmental assessment techniques linking environmental degradation with its causes. The aim of the project is to develop a suite of easy to use, cost effective and environmentally valid biological responses (biomarkers) to assess the general health of coastal systems, including estuaries. To achieve this aim, various sublethal endpoints are being measured and evaluated from a range of common coastal organisms showing different feeding types (filter feeding, grazing and predation) and habitat requirements (estuary and rocky shore) and at different levels of biological response (cellular, physiological and behavioural). This holistic integrated approach is essential to identify the full impact of chemical contamination on organisms, and enables the sensitivity of organisms to be ranked and key sentinel species for specific habitats to be identified. 相似文献
88.
89.
Marine protected areas (MPAs) are among the most widely accepted methods of marine management. MPAs are not, however, always placed such that they can maximize impact on conservation and livelihoods. Current MPA guidelines fall short in focusing primarily on biophysical criteria, overlooking interrelated socioeconomic factors. We identified 32 socioeconomic factors that influence whether MPA placement has an impact on biodiversity and/or livelihoods and weighted the quality of evidence using a novel “Evidence for Impact” Score. Results suggest that stakeholder engagement, poverty, population density, and strong leadership have most potential to positively impact biodiversity and/or livelihoods, but the direction of impact (i.e., positive or negative) can be context-dependent. We found a generally poor evidence base for impact evaluation of socioeconomic factors: though some factors were highly cited, few studies actually evaluate impact. Results indicate the need for a more interdisciplinary approach to MPA placement and more empirical studies that assess impact. 相似文献
90.
The period 1996-2001 has witnessed a refocusing of population growth on Sydney and Melbourne as both cities have developed significant concentrations of so-called 'new economy' jobs and taken on, to greater or lesser extents, the characteristics of global cities. The consequence of these trends, for Sydney most particularly, is population growth. This paper establishes this demographic reality by describing recent demographic trends in Sydney and possible future scenarios for Sydney's population, given differing levels of fertility, internal migration and international migration. A related future trend is also traced--that the number of households in Sydney will grow more rapidly than the population due to changes in household structure. This raises the issue of how and where these households will be accommodated, given the relative land shortage in the Sydney Statistical Division and given that there is no doubt that planners in New South Wales will be attempting to maintain and enhance Sydney's status as a global city. In sum, the paper argues that Sydney planners should be preparing for growth of around one million people in the next 20 years and a further one million in the following 30 years. To maintain that potential future residents of Sydney can be redirected to other parts of New South Wales is a vain hope. 相似文献