全文获取类型
收费全文 | 732篇 |
免费 | 10篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 18篇 |
大气科学 | 108篇 |
地球物理 | 161篇 |
地质学 | 238篇 |
海洋学 | 62篇 |
天文学 | 95篇 |
综合类 | 2篇 |
自然地理 | 60篇 |
出版年
2021年 | 5篇 |
2020年 | 10篇 |
2019年 | 7篇 |
2018年 | 15篇 |
2017年 | 17篇 |
2016年 | 29篇 |
2015年 | 13篇 |
2014年 | 20篇 |
2013年 | 29篇 |
2012年 | 39篇 |
2011年 | 23篇 |
2010年 | 30篇 |
2009年 | 48篇 |
2008年 | 42篇 |
2007年 | 25篇 |
2006年 | 33篇 |
2005年 | 33篇 |
2004年 | 23篇 |
2003年 | 25篇 |
2002年 | 19篇 |
2001年 | 17篇 |
2000年 | 22篇 |
1999年 | 10篇 |
1998年 | 15篇 |
1997年 | 12篇 |
1996年 | 5篇 |
1995年 | 11篇 |
1994年 | 12篇 |
1993年 | 10篇 |
1992年 | 3篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 13篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 10篇 |
1973年 | 12篇 |
1972年 | 3篇 |
1965年 | 5篇 |
1962年 | 4篇 |
排序方式: 共有744条查询结果,搜索用时 203 毫秒
1.
Mussels, m>Mytilus edulis m> L., were exposed to elevated concentrations of copper or cadmium in the laboratory, then placed in cages in the sea (salinity 7‰). One year later maximum lengths of the mussels were measured and shells screened for deformities. Growth was 0·6 cm year?1 in the control cages and retarded in cages of exposed mussels. A total of 63% of cadmium-exposed and 46% of copper-exposed mussels had shell deformities. In the control cages 26% were deformed while in a natural population only 3% were deformed. The proportion of deformities to growth was inversely related. Low concentrations showed their injuriousness in this long-term test, probably due to the closing of the valves during exposure to high concentrations. 相似文献
2.
3.
The Nordic geological surveys: Geology for society in practice 总被引:1,自引:0,他引:1
Morten Smelror Andreas AhlstrФm Lena Ekelund Jens Morten Hansen Keijo Nenonen Anette K. Mortensen 《《幕》》2008,31(1):193-200
Since the mid-nineteenth century., when the first of the Nordic Geological Surveys were established, they have generated a substantial amount of information on the Earth's crust, its natural resources, its processes, and on the geological history of Nordic areas. The collective mission of the geological surveys is to carry out "Geology for Society", by doing research and providing services, and by making geological information and data easily accessible to all the varied end users in industry, government agencies, government institutes, public administrations, technical offices, academia and research institutes, as well as for private individuals. The present paper gives a brief overview of a few, selected, research areas and projects currently undertaken by the Nordic geological surveys. These serve as practical examples of how the Nordic geological surveys address important societal problems and challenges that require geological input for their solution. 相似文献
4.
5.
Erdal Dolu Erkan Gökaşan Engin Meriç Mustafa Ergin Tolga Görüm Hüseyin Tur Berkan Ecevitoğlu Niyazi Avşar Muhittin Görmüş Fatmagül Batuk Buğser Tok Oktay Çetin 《Geo-Marine Letters》2007,27(6):355-381
The Quaternary evolution of the Gulf of İzmit, situated on the tectonically active North Anatolian Fault Zone (NAFZ), was
investigated using seismic reflection, paleontologic, and sediment textural data. On the basis of seismic stratigraphic and
sedimentologic-paleontologic interpretations, four depositional units were distinguished within the Plio-Quaternary sequence
of the Gulf of İzmit. According to these data, Plio-Quaternary deposits supplied from the northern terrestrial area started
to accumulate during a progradational phase, in a south-facing half-graben. A coarse-grained sedimentary unit prograding into
the gulf from the south since 200 ka mall>bmall>.mall>pmall>. indicates a dramatic variation in the evolution of the gulf, with the initiation of a new strike-slip fault of the NAFZ
and a corresponding uplift of the Armutlu Peninsula in the south of the gulf. During the evolution of this fault from a wide
shear zone consisting of right-stepped strike-slip faults and pull-apart basins to a localized principal fault zone, sediments
were deposited under the influence of northerly prograding terrestrial and shallow-marine conditions due to relative sea-level
fluctuations in the Marmara Sea. During this period, the Gulf of İzmit was invaded mainly by Mediterranean and partly by Black
Sea waters. In the latest glacial period, shallow areas in the gulf became subaerially exposed, whereas the central and western
sub-basins of the gulf turned into lakes. The present evolution of the Gulf of İzmit is controlled by the after effects of
the new rupture of the NAFZ and the estuarine nature of the gulf environment. 相似文献
6.
The lake Hunnebotn (A=1 km2, zmax=11 m) has become separated from the sea by isostasis, but a 1.5-m-deep channel is held open by periodic dredging. Water exchange is minor due to the small tidal range (21 cm) and the length of the channel (1.8 km), but there may be an inflow of seawater at spring tides. The terrestrial watershed runoff may be fertilized by sewage and agricultural runoff despite some measures taken to prevent this. Historical and new records of biological communities indicate variations in sensitivity to different phases of the isolation and eutrophication process. The native oyster was most sensitive and disappeared first. Later, the eelgrass disappeared possibly due to overgrowth by epiphytic algae, and finally there was a massive littoral–sublittoral invasion of green algae. The lake should not be left in this condition, for aesthetic reasons and because marine inlets and eutrophic brackish water may serve as refugia for spore populations of toxic microalgae. Improving surface water quality will require better control of anthropogenic sources, but bursts and leaks of nutrients from the anoxic monimolimnion cannot be controlled. 相似文献
7.
Multi-proxy evidence of long-term changes in ecosystem structure in a Danish marine estuary, linked to increased nutrient loading 总被引:3,自引:0,他引:3
Marianne Ellegaard Annemarie L. Clarke Nina Reuss Simon Drew Kaarina Weckstrm Stephen Juggins N. John Anderson Daniel J. Conley 《Estuarine, Coastal and Shelf Science》2006,68(3-4):567
This paper presents a study of changes in eutrophication over the past 100 years in a fertile estuary. The Danish estuary Mariager Fjord is a long, narrow sill-fjord with a permanently anoxic basin. In 1997 anoxia spread from the basin to the entire inner estuary, killing almost all eukaryotes and prompting debate on the causes. This paper reports a multi-proxy survey of 210Pb-dated sediment cores from the anoxic basin. Analyses of diatoms, dinoflagellates, pigments and geochemical proxies were used to determine changes in ecosystem structure over the past 100 years. The aim was to establish ‘base-line conditions’, for management purposes, of the biological structure prior to 1900, and to examine possible causes of changes observed. Geochemical proxies total nitrogen (TN), total carbon (TC) and biogenic silica (BSi) were consistently high throughout the sediment record. Increased concentrations of pigments and natural isotopes (δ13C, δ15N) suggested increasing production and nutrient loading. The main changes in the biological proxies occurred between 1915 and the 1940s, and indicated that the estuary has been somewhat eutrophic since 1900, but that the eutrophication process increased over the past 100 years. A reconstruction of TN concentration by a diatom-based transfer function supports this interpretation, with inferred TN ca. 1900 around 60 μmol l−1, and an increase in TN concentration over the past century to ca. 130 μmol l−1 by 1995. Inferred TN decreased to ca. 100 μmol l−1 by 2001, similar to present day monitoring data. 相似文献
8.
H. Rönkkömäki Ph.D. R. Pöykiö Ph.D. H. Nurmesniemi Ph.D. K. Popov D.Sc. E. Merisalu Dr. T. Tuomi PhD I. Välimäki M.Sc. 《International Journal of Environmental Science and Technology》2008,5(4):485-494
The particles in the examined cyclone fly ash were all smaller than 0.25 mm. in diameter, and particles smaller than 0.075 mm. in diameter accounted for 88.4 % of the ash weight. This result indicates that cyclone fly ash consists of particles with a small diameter. The metals in the cyclone fly ash were enriched in small particles. The highest concentrations for zinc, copper, lead, cadmium and molybdenum in the cyclone fly ash were found in the smallest particle size fraction (< 0.075 mm.) and for Barium, chromium, nickel, Vanadium and Cobalt in the second to smallest particle size fraction (0.075-0.125 mm.). From an environmental and toxicological standpoint, the smallest particles are of the greatest concern when ash is handed at landfill disposal sites (transport and disposal especially in stormy weather conditions), and some studies have reported risks to workers from prolonged exposure to ash. The results of the comparison of various dissolution methods for metals showed that the digestion procedures with nitric acid alone (USEPA 3051) or with a mixture of nitric acid + hydrogen peroxide (USEPA 3050B) slightly underestimated the metal concentrations in the cyclone fly ash. Although the use of hydrofluoric acid is often necessary for the determination of a number of elements associated with siliceous minerals, its use can result in loss of trace elements during dissolution. 相似文献
9.
Seismic hazard of Egypt 总被引:1,自引:0,他引:1
Earthquake hazard parameters such as maximum expected magnitude,M
max, annual activity rate,mg src="/content/q1v37n747442h4hn/xxlarge955.gif" alt="lambda" align="BASELINE" BORDER="0">, andb value of the Gutenberg-Richter relation have been evaluated for two regions of Egypt. The applied maximum likelihood method permits the combination of both historical and instrumental data. The catalogue used covers earthquakes with magnitude mg src="/content/q1v37n747442h4hn/xxlarge8805.gif" alt="ge" align="MIDDLE" BORDER="0">3 from the time interval 320–1987. The uncertainties in magnitude estimates and threshold of completeness were taken into account. The hazard parameter determination is performed for two study areas. The first area, Gulf of Suez, has higher seismicity level than the second, all other active zones in Egypt.b-values of 1.2 ± 0.1 and 1.0 ± 0.1 are obtained for the two areas, respectively. The number of annually expected earthquakes with magnitude mg src="/content/q1v37n747442h4hn/xxlarge8805.gif" alt="ge" align="MIDDLE" BORDER="0">3 is much larger in the Gulf of Suez, 39 ± 2 than in the other areas, 6.1 ± 0.5. The maximum expected magnitude is calculated to be 6.5 ± 0.4 for a time span of 209 years for the Gulf of Suez and 6.1 ± 0.3 for a time span of 1667 years for the remaining active areas in Egypt. Respective periods of 10 and 20 years were reported for earthquakes of magnitude 5.0 for the two subareas. 相似文献
10.
Planar deformation features in quartz grains from the resurge deposit of the Lockne structure,Sweden
Abstract— Microscopic planar deformation features (PDFs) in quartz grains are diagnostic of shock meta-morphism during hypervelocity impact cratering. Measurements of the poles of sets of PDFs and the optic axis of 25 quartz grains were carried out for a sample of the Loftarsten deposit from the Lockne area, Sweden. The most abundant PDFs observed in the sample from the Lockne area correspond to those found at known impact craters (i.e., ω (10mg loading="lazy" alt="inline image" class="section_image" src="/cms/asset/2b52e7e6-1e65-478d-bfef-1dd7d1a5b89c/j.1945-5100.1995.tb01167.x_fu1.gif">13} and π (10mg loading="lazy" alt="inline image" class="section_image" src="/cms/asset/a1f1ac6c-053d-4384-a030-a0f316c6e0d5/j.1945-5100.1995.tb01167.x_fu2.gif">12). This study confirms the previous suggestion that the Lockne structure is an impact crater. The Loftarsten is, therefore, interpreted as the final stage of resurge deposition after a marine impact at Lockne in the Middle Ordovician. 相似文献