全文获取类型
收费全文 | 433篇 |
免费 | 10篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 19篇 |
地球物理 | 100篇 |
地质学 | 159篇 |
海洋学 | 27篇 |
天文学 | 81篇 |
自然地理 | 48篇 |
出版年
2021年 | 6篇 |
2020年 | 11篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2017年 | 8篇 |
2016年 | 10篇 |
2015年 | 6篇 |
2014年 | 11篇 |
2013年 | 25篇 |
2012年 | 14篇 |
2011年 | 9篇 |
2010年 | 14篇 |
2009年 | 19篇 |
2008年 | 15篇 |
2007年 | 12篇 |
2006年 | 15篇 |
2005年 | 10篇 |
2004年 | 11篇 |
2003年 | 12篇 |
2002年 | 17篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1992年 | 8篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 9篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1970年 | 4篇 |
1962年 | 4篇 |
1961年 | 3篇 |
1960年 | 6篇 |
1959年 | 4篇 |
1956年 | 3篇 |
1955年 | 4篇 |
1952年 | 3篇 |
1940年 | 3篇 |
1937年 | 4篇 |
1936年 | 3篇 |
排序方式: 共有445条查询结果,搜索用时 0 毫秒
11.
Although meteorites are now considered as scientific objects, they still bear a strong and powerful symbolic meaning due to their extraterrestrial provenance. The present article focuses on their legal status, in other words the collection of rules, very diverse in nature, which are applicable to them. Despite a growing international market, the question of meteorites is often ignored or regarded as a detail in international relations and is rarely taken explicitly into account in negotiations and treaties. This relative neglect explains why a non‐State player, the Meteoritical Society, has taken methodological initiatives into meteoritic science and has effectively become a regulator of meteorite naming and acceptance, with a global scope. We show that to understand the legal status of meteorites, it is necessary to consider them under the prism of public international law, transnational law, and national law. We conclude that, despite the universality of meteorites as extraterrestrial objects, the variability of legal rules applicable to meteorites depending onto which territory they fall or where they are found. We note, however, that there is a trend toward regulatory uniformity in the scientific analysis of meteorites, which frames the practices of researchers and regulates traders’ activities. Finally, we contend that a meteorite remains a badly defined legal object, because it can be viewed under many angles: as an object susceptible to private appropriation, as a “common thing” (res communis), or as an element of national heritage. 相似文献
12.
Andrew J. Davies Max Wisshak James C. Orr J. Murray Roberts 《Deep Sea Research Part I: Oceanographic Research Papers》2008,55(8):1048-1062
Ecological-niche factor analysis (ENFA) was applied to the reef framework-forming cold-water coral Lophelia pertusa. The environmental tolerances of this species were assessed using readily available oceanographic data, including physical, chemical, and biological variables. L. pertusa was found at mean depths of 468 and 480 m on the regional and global scales and occupied a niche that included higher than average current speed and productivity, supporting the theory that their limited food supply is locally enhanced by currents. Most records occurred in areas with a salinity of 35, mean temperatures of 6.2–6.7 °C and dissolved oxygen levels of 6.0–6.2 ml l−1. The majority of records were found in areas that were saturated with aragonite but had low concentration of nutrients (silicate, phosphate, and nitrate). Suitable habitat for L. pertusa was predicted using ENFA on a global and a regional scale that incorporated the north-east Atlantic Ocean. Regional prediction was reliable due to numerous presence points throughout the area, whereas global prediction was less reliable due to the paucity of presence data outside of the north-east Atlantic. However, the species niche was supported at each spatial scale. Predicted maps at the global scale reinforced the general consensus that the North Atlantic Ocean is a key region in the worldwide distribution of L. pertusa. Predictive modelling is an approach that can be applied to cold-water coral species to locate areas of suitable habitat for further study. It may also prove a useful tool to assist spatial planning of offshore marine protected areas. However, issues with eco-geographical datasets, including their coarse resolution and limited geographical coverage, currently restrict the scope of this approach. 相似文献
13.
This paper analyses the extent to which specialisation gains can be achieved by liberalising access to fishing quotas within the European Union (EU). Fishing quotas are today exchanged between EU member states at a rate of 4% of total turnover in EU fisheries. Germany, Belgium, Denmark and the Netherlands are the most active. Only one fourth of these exchanges are permanent. With the management systems in EU fisheries differing among countries, comparative advantages in fisheries exist in member states with the best management practices. Hence, although positive but small specialisation gains exist in EU fisheries today, these gains might potentially be increased by liberalising access to fishing quotas and allowing transferability of quotas between individuals from different countries on a permanent basis. Increasing the gains might, however, affect relative stability. 相似文献
14.
Prawn postlarvae fishing in coastal Bangladesh: Challenges for sustainable livelihoods 总被引:1,自引:0,他引:1
Fishing for prawn (Macrobrachium rosenbergii) postlarvae is a major contributor to the livelihoods of the coastal poor in Bangladesh, including women. A study of coastal livelihoods along the lower Pasur River in southwest Bangladesh indicates that on average 40% of total annual income comes from postlarvae fishing during the few months involved. However, indiscriminate fishing of wild postlarvae, with high levels of by-catch, has an impact on biodiversity in coastal ecosystems. This has provoked imposition of restrictions on postlarvae collection. The ban has, however, not been firmly enforced because of the lack of alternative livelihoods for coastal poor. A conceptual framework, drawn from an approach to poverty reduction known as the sustainable livelihoods approach, is applied to understanding the role of prawn postlarvae fishing. Evidence from this study suggests that postlarvae fishers faced a number of livelihood constraints, including poor livelihood assets. This paper concludes that wider livelihood options need to be found for postlarvae fishers to support their livelihoods. 相似文献
15.
Biased estimation: a simple framework for inversion and uncertainty analysis with prior information 总被引:1,自引:0,他引:1
Max A. Meju 《Geophysical Journal International》1994,119(2):521-528
16.
Barbara B. Prézelin Max M. Tilzer Oscar Schofield Clivia Haese 《Aquatic Sciences - Research Across Boundaries》1991,53(2-3):136-186
This tutorial was designed for nonbiologists requiring an introduction to the nature and general timescales of phytoplankton responses to physical forcing in aquatic environments. As such, an effort was made to highlight biological markers which might assist in identifying, measuring and/or validating physical processes controlling the variability in the distribution, abundance, composition and activity of phytoplankton communities. Given the recent advances in environmental optics and remote sensing capabilities, a special emphasis was placed on the nature and utility of phytoplankton optical properties in current bio-optical modelling efforts to predict temporal and spatial variability in phytoplankton productivity and growth. 相似文献
17.
This synthesis of detailed geological and geophysical information relates deep crustal structure to deformation and the emplacement of granites in the South Armorican Massif and the adjacent continental shelf. Near the continental margin a zone of geophysical anomalies is regarded as a nearly complete line of suture between a southern continent and America. A major mafic body in the trace of the supposed suture in interpreted as a relic of probable oceanic crust which has apparently acted as a deflector of regional strain.It is proposed that late in the Hercynian collision history, during late Carboniferous time, compressional strain acted across the mafic body and can be directly related to generation of younger regional structures in the metasediments and to localization of granite emplacement. 相似文献
18.
The arrival time difference for the AB branch of PKP from deep Tonga earthquakes is constant over years with a standard deviation
of ±0.05 seconds at seismographs located 10 to 50 km from each other. If published travel time curves are used to calculate
the relative residuals of PKP the standard deviation from the constant mean is improved by approximately 0.01 seconds for
AB branch data. For the BC branch, standard deviations of relative travel times of ±0.06 seconds are reduced to less than
±0.05 seconds by calculating relative residuals. We conclude that changes of crustal transit time forP-waves could be resolved, based on careful PKP arrival time measurement at two or more neighboring stations if the changes
exceed 0.05 sec and last for more than one year. The conditions for achieving this result are that PKP from Tonga earthquakes
is clearly recorded, and that time-keeping is accurate. The data on which these conclusions are based were obtained from the
Graefenberg seismograph array, which is located in West Gemany and consists of 13 stations separated by distances of 10 km
to 100 km. We propose that relative arrival times of PKP from Tonga could be used in the Mediterranean - Middle East area
to search for precursory travel time changes before large earthquakes. 相似文献
19.
Measurement of 17 laboratories on the stable isotope reference materials, NBS 22 lubricating oil and NBS 21 graphite, resulted in a revised calibration on the PDB scale. NBS 22 13C/12C ratios of all laboratories did not demonstrate a gausssian distribution. Therefore, values which resulted from direct comparison with NBS 20 carbonate standards were selected the mean value of which is ; this value is recommended as new value for NBS 22. The reported variations in δ13C for NBS 21 were consistent within the accuracies for single meaurements; the mean value is ?28.16 ± 0.01. The variations of D/H ratios of NBS 22 also were consistent with the accuracy quoted, with a mean value of ?119?. 相似文献
20.
Comment on 'The magnetotelluric phase tensor' by T. Grant Caldwell, Hugh M. Bibby and Colin Brown 总被引:1,自引:0,他引:1
Max Moorkamp 《Geophysical Journal International》2007,171(2):565-566
We demonstrate a minor inconsistency in the appendix of 'The magnetotelluric phase tensor' by Caldwell et al. that can lead to incorrect results, and provide a simple solution for this problem. 相似文献