全文获取类型
收费全文 | 3111篇 |
免费 | 179篇 |
国内免费 | 18篇 |
专业分类
测绘学 | 126篇 |
大气科学 | 288篇 |
地球物理 | 853篇 |
地质学 | 1105篇 |
海洋学 | 207篇 |
天文学 | 472篇 |
综合类 | 26篇 |
自然地理 | 231篇 |
出版年
2022年 | 20篇 |
2021年 | 53篇 |
2020年 | 52篇 |
2019年 | 46篇 |
2018年 | 108篇 |
2017年 | 112篇 |
2016年 | 151篇 |
2015年 | 119篇 |
2014年 | 138篇 |
2013年 | 260篇 |
2012年 | 192篇 |
2011年 | 171篇 |
2010年 | 149篇 |
2009年 | 144篇 |
2008年 | 127篇 |
2007年 | 106篇 |
2006年 | 103篇 |
2005年 | 81篇 |
2004年 | 71篇 |
2003年 | 77篇 |
2002年 | 82篇 |
2001年 | 51篇 |
2000年 | 56篇 |
1999年 | 36篇 |
1998年 | 37篇 |
1997年 | 38篇 |
1996年 | 31篇 |
1995年 | 40篇 |
1994年 | 25篇 |
1993年 | 31篇 |
1992年 | 27篇 |
1991年 | 34篇 |
1990年 | 33篇 |
1989年 | 26篇 |
1988年 | 22篇 |
1987年 | 27篇 |
1986年 | 20篇 |
1985年 | 24篇 |
1984年 | 37篇 |
1983年 | 38篇 |
1982年 | 28篇 |
1981年 | 22篇 |
1980年 | 21篇 |
1979年 | 21篇 |
1976年 | 16篇 |
1975年 | 21篇 |
1974年 | 17篇 |
1973年 | 19篇 |
1972年 | 22篇 |
1969年 | 14篇 |
排序方式: 共有3308条查询结果,搜索用时 187 毫秒
21.
22.
A densely populated soft-sediment community was experimentally analysed for interspecific competition for space in laboratory experiments. No interspecific competitive interactions leading to a decrease in survivorship could be documented over a five-week period. The four most abundant species all coexisted in laboratory microcosms. The two tube-buiding species, the tanaid Leptochelia dubia and the polychaete Rhynchospio arenincola, could not exclude the mobile bivalve Transennella tantilla or the burrowing amphipod Paraphoxus spinosus. None of the species increases its emigration frequency when other species are present. Paraphoxus is found to be a browsing predator on Phynchospio but inflicts no detectable mortality. The coexistence of these species is permitted by virtue of the fact that none of the species can alter the soft-sediment habitat sufficiently to make the habitat unsuitable for the other species. 相似文献
23.
24.
A bottom longline fishery operated in the EEZ of New Caledonia from 1988 to 1991. Fishing focused on five seamounts with summits at depths ranging from 500 to 750 m. The target species was alfonsino, Beryx splendens. As the soundings available from marine charts were not detailed enough, the fishing masters had to make their own charts in order to set the gear in the right location. A series of 11 scientific cruises devoted to a research program on alfonsino was launched in late 1991. During the first scientific cruises, several days were spent mapping the seabed to improve the existing knowledge of the topography of three seamounts by coupling the EDO echosounder depth measurements to the GPS positions. As this procedure is slow, it is applicable to limited areas or, if a wider grid is used, to large zones to locate major structures such as ridges and seamounts. The emergence of the multibeam echosounder has greatly improved seabed mapping performance. This tool seems to fit the requirement of exploratory deep-bottom fishing particularly well, as it covers large areas while providing details of the bottom. The EM 12 was used to obtain bathymetry and imagery of the SE portion of the EEZ of New Caledonia, covering an approximate area of 70,000 km2 in two weeks. For depths ranging from 500 to 4,500 m, the results were impressive. They confirmed the known major features and provided greater topographical detail, revealing fine unknown structures. They also provided information on the type of substratum, information which might influence the fishing strategy. Finally, they made it possible to obtain an accurate estimate of the exploitable area which in turn led to new stock estimates. 相似文献
25.
ICES baseline survey of trace metals in European shelf waters 总被引:1,自引:0,他引:1
Balls P.; Cofino W.; Schmidt D.; Topping G.; Wilson S.; Yeats P. 《ICES Journal of Marine Science》1993,50(4):435-444
26.
James G Wilson 《Marine environmental research》1983,8(3):129-148
The concentration of Ni in C. edule ranges from 17·8 μg/g to 53·82 μg/g with the highest concentration in the gills and mantle and the lowest in the foot and adductor muscles. The concentration does not change with either size or season.There is no significant increase in mortality even in the highest Ni concentration (100 μg/litre), nor is body condition correlated with experimental Ni concentrations. The rate of uptake of Ni (y) is described by the equation: where x1 = Ni concentration (μg/litre) and x2 = time (h).The respiration rates did not significantly change up to the highest Ni concentration used (1000 μg/litre).It is postulated that the main pathway for Ni uptake is through the gills, possibly through mucus sheet or transmembrane absorption, with a secondary uptake route via the viscera.C. edule may therefore be a suitable indicator species for Ni. 相似文献
27.
Experimental investigation of the combustive sound source 总被引:3,自引:0,他引:3
In this paper, we describe a unique low frequency underwater sound source called the combustive sound source (CSS). In this device, a combustible gas mixture is captured in a combustion chamber and ignited with a spark. The ensuing combustion produces expanding gases which in turn produce high intensity, low frequency acoustic pulses. With high-speed motion pictures of the CSS event, we relate the motion of the bubble to the acoustic waveform. We also compare the measured first bubble period in the CSS pressure signature with the predictions of the Rayleigh-Willis equation, including the dependence of the radiated acoustic waveform on the volume and depth of the bubble. Measurements of the first bubble period agree with Rayleigh-Willis theory in trend, but not in absolute value. In addition, we discuss the variation of the acoustic output with the fuel/oxygen mixture. Finally, several other factors that affect the acoustic output of CSS are discussed. These include the shape of the CSS combustion chamber, the type of oxidizer and fuel, and the ignition source 相似文献
28.
A survey of imposex in Thais orbita (Neogastropoda) along the New South Wales (NSW) coast, Australia, found imposex was still widespread 10 years after a partial ban on tributyltin (TBT) based antifouling paints. Transplant experiments also revealed that imposex was induced in T. orbita over a period of 9 weeks in Sydney Harbour, NSW. A comparison of the imposex data with that collected shortly after the introduction of restrictions on TBT revealed a general decline in imposex frequency occurring at open coast sites, an exception being the site at South West Rocks. Sites located within harbour/bay areas did not display a decline in imposex frequency but a decline in the severity of imposex was apparent. The observed decrease in imposex values in T. orbita may reflect a general decrease of butyltin contamination within the coastal environment. However, the persistence of contamination "hotspots" within harbours and bays remains a concern. 相似文献
29.
30.
Graham P. Wilson Angela L. Lamb Melanie J. Leng Silvia Gonzalez David Huddart 《Estuarine, Coastal and Shelf Science》2005,64(4):685-698
Microfossil analysis (e.g. diatoms, foraminifera and pollen) represents the cornerstone of Holocene relative sea-level (RSL) reconstruction because their distribution in the contemporary inter-tidal zone is principally controlled by ground elevation within the tidal frame. A combination of poor microfossil preservation and a limited range in the sediment record may severely restrict the accuracy of resulting RSL reconstructions. Organic δ13C and C/N analysis of inter-tidal sediments have shown some potential as coastal palaeoenvironmental proxies. Here we assess their viability for reconstructing RSL change by examining patterns of organic δ13C and C/N values in a modern estuarine environment. δ13C and C/N analysis of bulk organic inter-tidal sediments and vegetation, as well as suspended and bedload organic sediments of the Mersey Estuary, U.K., demonstrate that the two main sources of organic carbon to surface saltmarsh sediments (terrestrial vegetation and tidal-derived particulate organic matter) have distinctive δ13C and C/N signatures. The resulting relationship between ground elevation within the tidal frame and surface sediment δ13C and C/N is unaffected by decompositional changes. The potential of this technique for RSL reconstruction is demonstrated by the analysis of part of an early Holocene sediment core from the Mersey Estuary. Organic δ13C and C/N analysis is less time consuming than microfossil analysis and is likely to provide continuous records of RSL change. 相似文献