全文获取类型
收费全文 | 1528篇 |
免费 | 73篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 20篇 |
大气科学 | 98篇 |
地球物理 | 379篇 |
地质学 | 732篇 |
海洋学 | 130篇 |
天文学 | 177篇 |
综合类 | 5篇 |
自然地理 | 64篇 |
出版年
2024年 | 3篇 |
2023年 | 5篇 |
2022年 | 18篇 |
2021年 | 26篇 |
2020年 | 24篇 |
2019年 | 34篇 |
2018年 | 54篇 |
2017年 | 60篇 |
2016年 | 62篇 |
2015年 | 56篇 |
2014年 | 77篇 |
2013年 | 116篇 |
2012年 | 57篇 |
2011年 | 120篇 |
2010年 | 94篇 |
2009年 | 111篇 |
2008年 | 91篇 |
2007年 | 56篇 |
2006年 | 62篇 |
2005年 | 58篇 |
2004年 | 53篇 |
2003年 | 42篇 |
2002年 | 42篇 |
2001年 | 23篇 |
2000年 | 23篇 |
1999年 | 15篇 |
1998年 | 14篇 |
1997年 | 15篇 |
1996年 | 13篇 |
1995年 | 10篇 |
1994年 | 19篇 |
1993年 | 9篇 |
1992年 | 14篇 |
1991年 | 14篇 |
1990年 | 6篇 |
1989年 | 15篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1977年 | 5篇 |
1975年 | 7篇 |
1974年 | 5篇 |
1973年 | 4篇 |
排序方式: 共有1605条查询结果,搜索用时 15 毫秒
71.
China Ocean Engineering - Turkey has announced its plan to construct a new waterway, Canal Istanbul, parallel to the Bosphorus. In this study, the influence of Canal Istanbul on salinity... 相似文献
72.
Pedro S.B.REYES Mauricio E.VALAREZO Jenry CóRDOVA Fran?ois A.MICHAUD Camilo ZAPATA 《山地科学学报》2018,15(5):966-975
The longitudinal profile of a river channel can be described in function of mathematical expressions. The logarithmic fit is the most used method to describe the relative equilibrium of a channel elevation profile. Rivers showing zones of high channel gradient and convex-upward profiles can be evaluated in function of the offset distance with respect to the logarithmic curve. The Jama River profile has been constructed using differential GPS data for the downstream reach and 4-m-grid DEM data base for the remaining headward profile. The resulting longitudinal profile shows a prominent knickpoint of about 80 m in elevation characterized by sharp local convexity. The offset distance in vertical direction from the logarithmic plot is interpreted as the successive accumulation of multiple uplift episodes associated with the Jama Fault System activity. The horizontal offset is suggested to represent the remaining retreated distance for the upstream propagation of the Jama knickpoint. The highly resistant Cretaceous rocks outcropping along the Jama knickpoint reach acts as an inflection point between two subprofiles that show well-fitted logarithmic curves, thereby representing a temporary partitioned equilibrium along the Jama River profile. 相似文献
73.
74.
François Baudin Jean-Robert Disnar Philippe Martinez Bernard Dennielou 《Marine and Petroleum Geology》2010
The quantity and the source of organic matter preserved in the Recent turbiditic channel-levees systems around 4000 m-depth off the Congo River were determined using bulk geochemical approaches (Rock-Eval, elemental and isotopic analyses) as well as molecular and optical analyses on selected samples. These mud-rich sediments contain high amount of organic matter (3% Corg on average), the origin of which is a mixture of terrestrial higher-plant debris and deeply oxidized phytoplanktonic material. Although the relative contribution of continental source versus marine source of the organic matter cannot be precisely quantified, the continental fraction appears significant (at least 70–80%) especially for such depths and distances from the coast. The organic matter distribution appears very homogeneous at different scales, from the single turbiditic event to the entire levee, and changes in accumulation rates have a little impact on the quantity and quality of preserved organic matter. 相似文献
75.
Graça Cabeçadas M. José Brogueira M. Gelena Cavaco Célia Gonçalves 《Journal of Oceanography》2010,66(2):201-210
Although the circulation of intermediate water masses in the eastern North Atlantic remains poorly defined, the presence of
fresher intermediate waters, the Sub-Artic (SAIW) and the Antarctic Intermediate Water (AAIW), as well the saline intermediate
Mediterranean Water (MW), has been tracked using biogeochemical properties. Here we assess the hydrographic and chemical structures
of intermediate waters along the western Portuguese margin by examining the vertical distributions and property-property plots
of chemical tracers (oxygen and nutrients). AAIW was traced by low oxygen and high nutrients, while SAIW was recognized by
low nutrients. The Mediterranean Water (MW) undercurrent is shown to spread towards the eastern flank of Gorringe bank. Concurrently,
the fresher waters gained salt by direct incorporation of MW, while this water was enriched in nutrients on its way northward
and westward owing, to a great extent, to the entrainment of an AAIW branch. The distributions of nutrients and apparent oxygen
utilization are discussed in terms of regional ocean circulation. Our analysis suggests a circulation pattern of the various
intermediate waters along the western Portuguese margin: MW extends all over the area, but its presence is more pronounced
around cape St. Vincent; SAIW apparently moves southward, reaching the Gorringe bank region, and AAIW flows northward along
the coast and around the bank. 相似文献
76.
Mélina C.Z. Laurent Olivier Gros Jean-Pierre Brulport Françoise Gaill Nadine Le Bris 《Marine environmental research》2009,67(2):83-88
Large organic falls to the benthic environment, such as dead wood or whale bones, harbour organisms relying on sulfide-oxidizing symbionts. Nothing is known however, concerning sulfide enrichment at the wood surface and its relation to wood colonization by sulfide-oxidizing symbiotic organisms.In this study we combined in situ hydrogen sulfide and pH measurements on sunken wood, with associated fauna microscopy analyses in a tropical mangrove swamp. This shallow environment is known to harbour thiotrophic symbioses and is also abundantly supplied with sunken wood. A significant sulfide enrichment at the wood surface was revealed. A 72 h sequence of measurements emphasized the wide fluctuation of sulfide levels (0.1–>100 μM) over time with both a tidal influence and rapid fluctuations. Protozoans observed on the wood surface were similar to Zoothamnium niveum and to vorticellids. Our SEM observations revealed their association with ectosymbiotic bacteria, which are likely to be sulfide-oxidizers. These results support the idea that sunken wood surfaces constitute an environment suitable for sulfide-oxidizing symbioses. 相似文献
77.
Jannet Elloumi Jean-François CarriasHabib Ayadi Télesphore Sime-NgandoAbderrahmen Bouaïn 《Estuarine, Coastal and Shelf Science》2009
The composition and distribution of the main planktonic halophilic micro-organisms (heterotrophic and autotrophic picoplankton, nanoplankton, phytoplankton, ciliates) and metazooplankton were investigated in six ponds of increasing salinity in the solar salt works of Sfax, Tunisia, from January to December 2003. Marked changes in the composition and biomass of the communities were found along the salinity gradient, especially at salinities of 150 and 350. Autotrophic picoplankton, nanoplankton, diatoms, dinoflagellates and ciliates characterized the less salted ponds. Planktonic biomass was the highest at intermediate salinity as a consequence of a bloom of Ochromonas. Species richness of phytoplankton, ciliates and zooplankton greatly decrease above a salinity of 150 and typical halophiles (Dunaliella salina, cyanobacteria, Fabrea salina and Artemia salina) were found between 150 and 350 salinity. In this environment, F. salina appeared more adapted than the brine shrimp to survive during phytoplankton blooms. The halophilic plankton was however almost entirely composed of heterotrophic prokaryotes in the crystallizers. We thus observed a progressive disappearance of the autotrophic planktonic communities along the salinity gradient. Multivariate analysis of the communities provides evidence that ponds represent discrete aquatic ecosystems within this salt works. 相似文献
78.
This paper presents an estimation of the economic effects of the Prestige oil spill in Galicia, focusing on the Death Coast fisheries and using fish landings as a market technique. Examining the evolution of landings in the Death Coast before and after the accident, the analysis reveals two opposing trends, with landings of some species increasing and those of other species diminishing. 相似文献
79.
80.