全文获取类型
收费全文 | 315篇 |
免费 | 24篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 26篇 |
地球物理 | 64篇 |
地质学 | 102篇 |
海洋学 | 54篇 |
天文学 | 41篇 |
综合类 | 3篇 |
自然地理 | 47篇 |
出版年
2022年 | 2篇 |
2021年 | 9篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 11篇 |
2017年 | 9篇 |
2016年 | 14篇 |
2015年 | 9篇 |
2014年 | 9篇 |
2013年 | 35篇 |
2012年 | 18篇 |
2011年 | 14篇 |
2010年 | 22篇 |
2009年 | 17篇 |
2008年 | 12篇 |
2007年 | 11篇 |
2006年 | 9篇 |
2005年 | 9篇 |
2004年 | 8篇 |
2003年 | 10篇 |
2002年 | 7篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 8篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有342条查询结果,搜索用时 31 毫秒
41.
Ann E. Reynolds Gail B. Mackiernan Shirley D. Van Valkenburg 《Estuaries and Coasts》1978,1(3):192-196
Evans blue and neutral red were tested as mortal and vital stains respectively for eight estuarine algal species which had been exposed to chlorine-produced oxidants in a continuous-flow system. The effect of CPO on staining with Evans blue was negligible. High concentrations of CPO affected staining with neutral red in several instances; this is probably due to CPO-induced mortality of test organisms during the exposure or staining period. Neutral red leached fromSkeletonema costatum andOlisthodiscus luteus before the end of the staining period. Staining ofDunaliella tertiolecta with neutral red proceeded more slowly. Evens blue, which was incorporated quickly and remained in the cells, is recommended for live-dead determinations for all species examined exceptNitzschia closterium, for which neutral red should be used. Neither stain was effective onMychonastes ruminatus (Simpson and Van Valkenburg 1978). 相似文献
42.
Macrofauna along the Sudanese Red Sea coast: potential effect of mangrove clearance on community and trophic structure 下载免费PDF全文
Mangroves along the Sudanese Red Sea coast are under constant anthropogenic pressure. To better understand the influence of mangrove clearance on the intertidal benthic community, we investigated the composition, biodiversity and standing stock of the macrofauna communities at high‐, mid‐ and low‐water levels in three contrasting habitats: a bare sand flat, a cleared mangrove and an intact mangrove. In addition, a community‐wide metric approach based on taxon‐specific carbon and nitrogen isotope values was used to compare the trophic structure between the three habitats. The habitats differed significantly in terms of macrofaunal standing stock, community composition and trophic structure. The high‐ and mid‐water levels of the intact mangroves showed a distinct macrofaunal community characterized by elevated densities and biomass, largely governed by higher decapod and gastropod abundances. Diversity was similar for cleared and intact mangroves, but much lower for the bare sand flat. Community‐wide metrics indicated highest trophic diversity and community niche breadth in the intact mangroves. Differences between the cleared and intact mangroves can be partly attributed to differences in sediment characteristics resulting from mangrove clearance. These results suggest a significant impact of mangrove clearance on the macrofaunal community and trophic structure. This study calls for further investigations and management actions to protect and restore these habitats, and ensure the survival of this ecologically valuable coastal ecosystem. 相似文献
43.
44.
Eric F. Lambin Sarah Ann Lise D’haen Ole Mertz Jonas Østergaard Nielsen Kjeld Rasmussen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2014,114(1):76-83
In an attempt to anticipate possible futures of drylands of West Africa in the face of rapid socio-economic and environmental changes, we developed four scenarios based on recent survey data, the literature and our knowledge of the region. The four scenarios are inspired by those developed by the Millennium Ecosystem Assessment: (1) ‘downward spiral’ characterized by rapid climate change, expansion of agriculture and chaotic urban growth; (2) ‘integrated economy’ with integrated land management, food production for local markets and rural–urban exchanges; (3) ‘open doors’ characterized by large-scale out-migrations, land grabbing by foreign companies and development aid and (4) ‘climate change mitigation’ with an increase in biofuel crops, land management for carbon capture and development of off-farm activities. We conclude that the Sahel region is most likely moving away from being a highly climate-dependent region based on agriculture towards a more open and diversified economy. West African countries have to find a balance between the new opportunities and risks created by economic globalization. 相似文献
45.
Jean‐Charles Leclerc Pascal Riera Laure M.‐L. J. Noël Cédric Leroux Ann C. Andersen 《Marine Ecology》2014,35(2):261-270
The diet of Pomatoschistus microps has been studied using both gut content and stable isotope analyses. In the Roscoff Aber Bay (Brittany, France), this fish is commonly found on sandy muddy intertidal flats. Gut content analyses were also interpreted using trophic indices. Owing to the large diversity of prey consumed, these indices emphasised the opportunistic feeding behaviour of P. microps. Here, this species fed mainly on endofauna with meiofauna being of high relative importance. The main biotic components of its trophic habitat, characterized by δ13C and δ15N, provided evidence of a major trophic pathway based on drift Enteromorpha sp. Trophic positions estimated by both diet analyses and isotopic analyses led to similar results. In this bay, P. microps is a first‐order predator with a low degree of omnivory. Despite a preferential consumption of the amphipod Corophium arenarium, we assumed that this goby behaves as a generalist feeding on a uniform variety of endofauna taxa. 相似文献
46.
Theresa?M.?KayzarEmail author Bruce?K.?Nelson Olivier?Bachmann Ann?M.?Bauer Pavel?E.?Izbekov 《Contributions to Mineralogy and Petrology》2014,168(4):1067
The Klyuchevskoy group of volcanoes in the Kamchatka arc erupts compositionally diverse magmas (high-Mg basalts to dacites) over small spatial scales. New high-precision Pb isotope data from modern juvenile (1956–present) erupted products and hosted enclaves and xenoliths from Bezymianny volcano reveal that Bezymianny and Klyuchevskoy volcanoes, separated by only 9 km, undergo varying degrees of crustal processing through independent crustal columns. Lead isotope compositions of Klyuchevskoy basalts–basaltic andesites are more radiogenic than Bezymianny andesites (208Pb/204Pb = 37.850–37.903, 207Pb/204Pb = 15.468–15.480, and 206Pb/204Pb = 18.249–18.278 at Bezymianny; 208Pb/204Pb = 37.907–37.949, 207Pb/204Pb = 15.478–15.487, and 206Pb/204Pb = 18.289–18.305 at Klyuchevskoy). A mid-crustal xenolith with a crystallization pressure of 5.2 ± 0.6 kbars inferred from two-pyroxene geobarometry and basaltic andesite enclaves from Bezymianny record less radiogenic Pb isotope compositions than their host magmas. Hence, assimilation of such lithologies in the middle or lower crust can explain the Pb isotope data in Bezymianny andesites, although a component of magma mixing with less radiogenic mafic recharge magmas and possible mantle heterogeneity cannot be excluded. Lead isotope compositions for the Klyuchevskoy Group are less radiogenic than other arc segments (Karymsky—Eastern Volcanic Zone; Shiveluch—Northern Central Kamchatka Depression), which indicate increased lower-crustal assimilation beneath the Klyuchevskoy Group. Decadal timescale Pb isotope variations at Klyuchevskoy demonstrate rapid changes in the magnitude of assimilation at a volcanic center. Lead isotope data coupled with trace element data reflect the influence of crustal processes on magma compositions even in thin mafic volcanic arcs. 相似文献
47.
The Las Campanas/AAT rich cluster survey – I. Precision and reliability of the photometric catalogue
Kevin A. Pimbblet Ian Smail Alastair C. Edge Warrick J. Couch Eileen O'Hely Ann I. Zabludoff 《Monthly notices of the Royal Astronomical Society》2001,327(2):588-600
The Las Campanas Observatory and Anglo-Australian Telescope Rich Cluster Survey (LARCS) is a panoramic imaging and spectroscopic survey of an X-ray luminosity-selected sample of 21 clusters of galaxies at . Charge-coupled device (CCD) imaging was obtained in B and R of typically 2° wide regions centred on the 21 clusters, and the galaxy sample selected from the imaging is being used for an on-going spectroscopic survey of the clusters with the 2dF spectrograph on the Anglo-Australian Telescope. This paper presents the reduction of the imaging data and the photometric analysis used in the survey. Based on an overlapping area of 12.3 deg2 we compare the CCD-based LARCS catalogue with the photographic-based galaxy catalogue used for the input to the 2dF Galaxy Redshift Survey (2dFGRS) from the APM, to the completeness of the GRS/APM catalogue, . This comparison confirms the reliability of the photometry across our mosaics and between the clusters in our survey. This comparison also provides useful information concerning the properties of the GRS/APM. The stellar contamination in the GRS/APM galaxy catalogue is confirmed as around per cent, as originally estimated. However, using the superior sensitivity and spatial resolution in the LARCS survey evidence is found for four distinct populations of galaxies that are systematically omitted from the GRS/APM catalogue. The characteristics of the 'missing' galaxy populations are described, reasons for their absence examined and the impact they will have on the conclusions drawn from the 2dF Galaxy Redshift Survey are discussed. 相似文献
48.
Preserving coastal natural character: Court interpretations of a long‐standing New Zealand policy goal 下载免费PDF全文
Victoria Ann Froude 《New Zealand geographer》2015,71(1):45-55
New Zealand's policy goal to preserve coastal natural character was first incorporated into planning legislation in 1973 and protected area legislation in 1977. An evaluation of 100 relevant Resource Management Act Court decisions determined the Courts' interpretations of this policy goal. The Courts have repeatedly found that natural character is of nature (not culture), including natural elements, patterns, and processes. There is a continuum of naturalness from pristine indigenous ecosystems to the urban environment. A 2014 Supreme Court decision has upheld the use of environmental bottom lines for natural character and the importance of protection as part of sustainable management. 相似文献
49.
50.
Lunar near-terminator and high-resolution panoramic camera photographs were searched for flow fronts, the edges of flow units in mare areas. Data for twenty areas, including fifteen previously unmeasured areas, are summarized. Height measurements of flow scarps present on the Moon range from 1 to 96 m. More than half (57%) of all flow fronts measured are less than 15 m thick. These observations agree well with other photogeological and experimental observations of flow unit thicknesses on the Moon. 相似文献