全文获取类型
收费全文 | 377篇 |
免费 | 22篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 12篇 |
大气科学 | 24篇 |
地球物理 | 100篇 |
地质学 | 113篇 |
海洋学 | 85篇 |
天文学 | 60篇 |
综合类 | 2篇 |
自然地理 | 8篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 10篇 |
2019年 | 13篇 |
2018年 | 18篇 |
2017年 | 15篇 |
2016年 | 18篇 |
2015年 | 17篇 |
2014年 | 11篇 |
2013年 | 31篇 |
2012年 | 24篇 |
2011年 | 31篇 |
2010年 | 31篇 |
2009年 | 26篇 |
2008年 | 19篇 |
2007年 | 19篇 |
2006年 | 15篇 |
2005年 | 13篇 |
2004年 | 20篇 |
2003年 | 11篇 |
2002年 | 14篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1970年 | 2篇 |
排序方式: 共有404条查询结果,搜索用时 156 毫秒
381.
382.
We studied the dynamics of bacteria and organic matter in the Ancient Port of Genoa (Italy) during a bioremediation treatment of sediment (during summer-autumn 1998) in an area characterised by continuous sewage discharge. A strong increase in total benthic bacterial density (TBN) was recorded at the end of the study, from 14 x 10(8) to 58-172 x 10(8) cell g(-1) in different parts of the treated area. The TBN increase was linked to organic matter depletion, from more than 40 to less than 20 mg x g(-1). In order to highlight the main ecological mechanisms involved in bioremediation, a laboratory experiment based on both water and sediment from the basin studied was carried out. We observed an increase in TBN during the first 20 days and a decrease in sediment organic matter (up to about 20%). Increases of organic matter (about 2-fold) and TBN (from 21 to 33 x 10(9) cell l(-1)) occurred in the overlying water, suggesting a strong association between the sediments and water column processes. Hydrolytic activities, which double in the sediment and increase up to a 300-fold in the water, are consistent with the decrease in sediment organic matter and with the water fraction dynamics. 相似文献
383.
Fernandez Borda Roberto A. Mininni Pablo D. Mandrini Cristina H. Gómez Daniel O. Bauer Otto H. Rovira Marta G. 《Solar physics》2002,206(2):347-357
We present a new method for automatic detection of flare events from images in the optical range. The method uses neural networks for pattern recognition and is conceived to be applied to full-disk Himages. Images are analyzed in real time, which allows for the design of automatic patrol processes able to detect and record flare events with the best time resolution available without human assistance. We use a neural network consisting of two layers, a hidden layer of nonlinear neurodes and an output layer of one linear neurode. The network was trained using a back-propagation algorithm and a set of full-disk solar images obtained by HASTA (HSolar Telescope for Argentina), which is located at the Estación de Altura Ulrico Cesco of OAFA (Observatorio Astronómico Félix Aguilar), El Leoncito, San Juan, Argentina. This method is appropriate for the detection of solar flares in the complete optical classification, being portable to any Hinstrument and providing unique criteria for flare detection independent of the observer. 相似文献
384.
Stefanelli P Ausili A Di Muccio A Fossi C Di Muccio S Rossi S Colasanti A 《Marine pollution bulletin》2004,49(11-12):938-950
Polychlorobiphenyls (PCB) and organochlorine (OC) pesticides are endocrine-disrupting chemicals (EDCs). The Italian Ministry of Environment has undertaken a program (1999-2001) to measure levels of contaminants in top marine predators and to develop sensitive biomarkers for the evaluation of toxicological risk in these species. In 1999, 15 swordfishes (Xiphias gladius) taken from the Mediterranean Sea along the Sicilian coast (Strait of Messina, Italy) and in the Atlantic Ocean along the Azores Islands, and analysed for 34 congeners of PCBs and 27 organochlorine (OC) pesticides in gonad, muscle, liver and blubber tissues. In the tissues of Mediterranean swordfishes the sum of the determined PCBs congeners ranged from 4.61 to 4651.17 ng g(-1) on fresh tissue basis. Among organochlorine pesticides DDE, DDT and DDD (TDE) predominated with an overall range of 2.37-4734.56 ng(-1) w.w. In particular p,p'-DDE had concentrations appearing up to 3900 ng(-1), with the highest values found in fatty tissues, such as blubber. In the liver of Azores Island swordfishes lower levels of summation PCBs (8.43-294.17 ng/g w.w.) and summation DDTs (<0.01-217.44 ng/g w.w.) were determined. 相似文献
385.
386.
387.
388.
Maria Li. Calleja Cristina Barrón Jason A. Hale Thomas K. Frazer Carlos M. Duarte 《Estuaries and Coasts》2006,29(6):1255-1264
The effects of light reduction on community metabolism and sediment sulfate reduction rates (SRR) were assessed experimentally
in a shallow (<2.0 m) seagrass (Thalassia testudinum) meadow along Florida's north-central Gulf coast. Nine experimental plots (1.5 m×1.5 m) were shaded differentially to achieve
a 0–90% gradient in light reduction within the seagrass meadow. Gross primary production and net community production (NCP),
estimated with in situ benthic chamber incubations, decreased with increasing light reduction. The compensation irradiance
for community metabolism, i.e., the shading level at which NCP shifted from net autotrophic to net heterotrophic, was determined
to be 52.5% of the incoming irradiance at canopy height in the seagrass bed (308.7 μE m−2 s−1 PAR at noon). Sediment SRR, determined with the use of a35S−SO4
2− radiotracer technique, increased quickly (within 5 d) and markedly with increased shade, i.e., simulated light reduction.
SRR increased 50-fold when shading exceeded the light compensation point for the seagrass community, rendering the community
net heterotrophic. Five days after restoring ambient light conditions, SRR had decreased sharply for all shading treatments.
The observed decrease in NCP, coincident with the increase in the SRR with light reduction, suggests that light reduction
has an indirect influence on sediment SRR mediated through its effect on seagrass metabolism. 相似文献
389.
Cristina Barrón Carlos M. Duarte Michel Frankignoulle Alberto Vieira Borges 《Estuaries and Coasts》2006,29(3):417-426
We measured monthly dissolved oxygen (DO) changes in situ benthic incubations from March 2001 to October 2002 in aPosidonia oceanica meadow and unvegetated sediments of Magalluf Bay (Mallorca Island, Spain) to determine gross primary production (GPP), community
respiration (R), and net community production (NCP). From June 2001 to October 2002, we also measured fluxes of dissolved
inorganic carbon (DIC) and total alkalinity (TAlk). The yearly integrated metabolic rates based on DO changes show that theP. oceanica communities are net autotrophic while the metabolic rates in the unvegetated benthic communities are nearly balanced. Higher
calcium carbonate (CaCO3) cycling, both in terms of production and dissolution, was observed inP. oceanica communities than in unvegetated benthic communities. In theP. oceanica meadow, the annual release of CO2 from net CaCO3 production corresponds to almost half of the CO2 uptake by NCP based on DIC incubations. In unvegetated benthic communities, the annual uptake of CO2 from net CaCO3 dissolution almost fully compensates the CO2 release by NCP based on DIC incubations. CaCO3 dynamics is potentially a major factor in CO2 benthic fluxes in seagrass and carbonate-rich temperate coastal ecosystems. 相似文献
390.
Different types of free water have been analysed for their deuterium and chemical composition in order to evaluate their source, mixing phenomena, and the underground dynamics. All types of ground water (mineral, geothermal and wellhead water) display δD values (− 82.6‰ to − 72.6‰) similar to surface waters from the studied area (− 77.1‰ to − 73.6‰). The global salt content varies from 1102 to 8707 mg/l for the groundwater, and from 46 to 392 mg/l for the surface water. From the co-variation between the δD values and the chemical composition of the waters, as well as from the seasonal variation of these two parameters, it is evident that the free water from Tuşnad Băi are meteoric in origin. The mineralization of the mineral water took place by means of an intense underground circulation, probably in the fault system developed within the Neogene magmatites. 相似文献