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排序方式: 共有162条查询结果,搜索用时 46 毫秒
1.
2.
Giovanni Aloisi Klaus Wallmann Alexander Derkachev Erwin Suess 《Geochimica et cosmochimica acta》2004,68(8):1735-1748
A numerical model was applied to investigate and quantify the biogeochemical processes fueled by the expulsion of barium and methane-rich fluids in the sediments of a giant cold-seep area in the Derugin Basin (Sea of Okhotsk). Geochemical profiles of dissolved Ba2+, Sr2+, Ca2+, SO42−, HS−, DIC, I− and of calcium carbonate (CaCO3) were fitted numerically to constrain the transport processes and the kinetics of biogeochemical reactions. The model results indicate that the anaerobic oxidation of methane (AOM) is the major process proceeding at a depth-integrated rate of 4.9 μmol cm−2 a−1, followed by calcium carbonate and strontian barite precipitation/dissolution processes having a total depth-integrated rate of 2.1 μmol cm−2 a−1. At the low seepage rate prevailing at our study site (0.14 cm a−1) all of the rising barium is consumed by precipitation of barite in the sedimentary column and no benthic barium flux is produced. Numerical experiments were run to investigate the response of this diagenetic environment to variations of hydrological and biogeochemical conditions. Our results show that relatively low rates of fluid flow (<∼5 cm a−1) promote the dispersed precipitation of up to 26 wt% of barite and calcium carbonate throughout the uppermost few meters of the sedimentary column. Distinct and persistent events (several hundreds of years long) of more vigorous fluid flow (from 20-110 cm a−1), instead, result in the formation of barite-carbonate crusts near the sediment surface. Competition between barium and methane for sulfate controls the mineralogy of these sediment precipitates such that at low dissolved methane/barium ratios (<4-11) barite precipitation dominates, while at higher methane/barium ratios sulfate availability is limited by AOM and calcium carbonate prevails. When seepage rates exceed 110 cm a−1, barite precipitation occurs at the seafloor and is so rapid that barite chimneys form in the water column. In the Derugin Basin, spectacular barite constructions up to 20 m high, which cover an area of roughly 22 km2 and contain in excess of 5 million tons of barite, are built through this process. In these conditions, our model calculates a flux of barium to the water column of at least 20 μmol cm−2 a−1. We estimate that a minimum of 0.44 × 106 mol a−1 are added to the bottom waters of the Derugin Basin by cold seep processes, likely affecting the barium cycle in the Sea of Okhotsk. 相似文献
3.
The state of knowledge of the Central European water mite fauna and the research history are briefly surveyed. Several areas for which we are provided with rich data sets are of high value for the monitoring of faunistic trends on the background of local and global environmental change. The need for a database combining historical and actual faunistic information is stressed. It should facilitate the access to all data from former times, give a survey on actual activities by regular updates, and help for a better organization of future research activities. On the base of an update of the Limnofauna Europaea (K.O. Viets 1978, Gerecke in www.watermite.org) a first attempt is made to (1) recognize changes in the Central European fauna during the past 100 years; (2) emphasize species which may be endangered or have disappeared during the past 100 years. At the present state of knowledge, the degree of threat to water mite species in this area is best calculated from their preference for particular habitat types which are rare and in danger to disappear in cultivated landscapes. Our knowledge concerning neozoic water mites in the study area is discussed. 相似文献
4.
Fernando P. Siringan Erwin Don R. Racasa Carlos Primo C. David Rhodelyn C. Saban 《Estuaries and Coasts》2018,41(8):2277-2288
Mount Bulusan, the Philippines’ fourth most active volcano, erupted in February 21, 2011, sending volcanic ash and pyroclastic materials to its surrounding rivers. The waters drained into the estuary of harmful algal blooms plagued Sorsogon Bay. We aim to determine the impact of the 2011 volcanic eruption and the preceding volcanic ash emissions to the dissolved silica concentration of rivers draining the flanks of Mt. Bulusan and its possible implications to the phytoplankton assemblage of the bay. Six river water sampling periods from August 2010 to October 2012 overlapped with Mt. Bulusan’s active phase of volcanism. Our data shows that mean river silica from pre-eruption levels of ~?500 μM increased by more than 200% during and post-eruption. Highest Si concentration of 2270 μM was measured from Cadacan River in August 2011. Here, we argue that the sustained general increase of dissolved silica is due to the silica-containing materials from Mt. Bulusan’s eruption and that their concentration in river waters is also a function of watershed lithology and precipitation. Increase in dissolved silica and other nutrients caused a shift to diatom domination and, possibly, termination of Pyrodinium bahamense var. compressum blooms. Silica load increase in embayments is a natural process that controls the dominance of algae. Our study also highlights the importance of Philippine rivers to the global ocean silica budget as a function of high precipitation, tectonics in general, and volcanism in particular. 相似文献
5.
Samples of stream sediments were collected along two streams adjacent to a sanitary landfill. One of the streams drained the landfill directly. In addition, control of background samples were also analyzed from a stream not affected by the landfill. All samples were analyzed for Ag, Zn, Cu, Cd, and Pb content using atomic adsorption techniques. The pH of the three streams were monitored since pH differences in the streams may affect the quantities of metals adsorbed or precipitated on the sediments. The comparison between the content of Ag, Zn, and Cu in the sediments of the two study streams and the same metals in the control sediments indicated the landfill emitted these metals into the two adjacent streams. However, since the Cd and Pb contents in the sediments of both streams were similar to that of the control stream sediments, these metals may not be emitted into the two study streams from the landfill and they represent only background quantities. The comparisons of each metal in the sediments of each stream were made by the use of a metal trend chart, the individual calculated mean metal content values, and by the statistical two sample t-test. No decreasing trends of the quantities of Ag, Zn, or Cu as a function of increasing distance from the landfill was present in the sediments along the stream that drained the landfill directly. These sediments might have been affected by stream action and became mixed with other sediments downstream. 相似文献
6.
7.
Peter Baccini Erwin Grieder Ruth Stierli Sabine Goldberg 《Aquatic Sciences - Research Across Boundaries》1982,44(1):99-116
The adsorption characteristics of sediment particles from a prealpine Swiss lake were compared with those of γ-aluminum oxide.
Under lake water conditions, i.e. with particle concentration of 2–16 mg/1 and DOC concentrations of 1–4 mg/1 at pH=8, the
adsorption of copper, zinc and orthophosphate is reduced significantly by the presence of natural organic matter (NOM). It
is postulated that the binding sites of the natural mineral surfaces are occupied almost completely by NOM under natural conditions.
A simple ligand exchange model can explain the observed phenomena. 相似文献
8.
The location requirements for emergency callers outside urban areas can hardly be fulfilled without global navigation satellite
systems (GNSS). Consequently, interest in positioning techniques based on use of a GNSS such as GPS or on the cellular network
infrastructure itself is growing rapidly in the mobile-telephone community. Moreover, the increasing demand for commercial
location-based services (LBS) has driven cellular-phone and network manufacturers to focus on positioning solutions which
are even more accurate than the regulatory mandates for positioning of emergency callers. One example of these upcoming LBS
is our PARAMOUNT project, which aims at improving user-friendly info-mobility services for hikers and mountaineers by combining
wireless communications (GMTS), satellite navigation (GNSS) and geographic information systems (GIS), based on a mobile client/server
architecture. The availability of mobile phones or PDAs with combined GNSS and cellular network-based wireless communication
on a high integration level is one primary demand of such LBS applications. Based on this, we will give some initial answers
to the question of whether mobile handset architecture synergies exist for the combination of GNSS with wireless location
in CDMA cellular wireless networks. In order to identify synergies, we will outline similarities and differences between wireless
communication and satellite navigation. In this respect, we pay particular attention to the so-called RAKE receiver architecture
employed in mobile CDMA cellular handsets. Our initial investigations will show that the RAKE receiver architecture, on which
mobile CDMA cellular handsets are based, will most likely be the one most suitable for achieving synergies between the two
positioning techniques within the same mobile handset architecture. Consequently, several receiver components could be used
to handle both types of signals (navigation and communications), resulting in a reduction of manufacturing costs and in a
decrease in energy consumption.
Electronic Publication 相似文献
9.
Erwin Nickel 《Contributions to Mineralogy and Petrology》1947,1(1):117-120
Zusammenfassung Das Periklingesetz verlangt Spiegelsymmetrie in der Zone senkrecht [010]; die kristallographische Symmetrie wiederholt sich in der Lage der Indikatrizen. Die Einmessung zeigt aber, daß (trotz normaler Verwachsung nach dem rhombischen Schnitt) die Symmetrie der verzwillingten Indikatrizen verringert ist: die (theoretische)ZE fungiert nur als Halbierungsebene der korrespondierten Mittellinien, die volle Symmetrie wird nicht verwirklicht. In unserem Falle ist die eingelagerte Zwillingspartie in bezug auf dieZE korrekter orientiert als das Hauptindividuum. - Die Konstruktion derZE nachBEREK führt auch bei der verminderten Symmetrie der verzwillingten Indikatrizen zur Auffindung der morphologisch definierten Zwillingsachse. -Man wird eben nicht vergessen dürfen, daß die Zwillingsgesetze Idealformulierungen sind, denen die Wirklichkeit nicht immer gerecht wird. 相似文献
10.
Constraining the process by which volcanoes become unstable is difficult. Several models have been proposed to explain the
driving forces which cause volcanic edifices to catastrophically collapse. These include models for destabilisation of volcanic
flanks by wedging due to dyke intrusion and the weakening of mechanical properties by pressurisation of pore fluids. It is
not known which, if any, of the models are relevant to particular sector collapse events. Recent developments in the palaeomagnetic
estimation of emplacement temperatures of volcaniclastic rocks have shown that even relatively low emplacement temperatures
can be recorded by volcaniclastics with high fidelity. We have carried out a palaeomagnetic study of emplacement temperatures
to investigate the role of igneous activity in the initiation of the 9,500 b.p. Murimotu sector collapse of Mt Ruapehu, New Zealand. This debris avalanche deposit has three fades which are stratigraphically
superimposed, and the lowermost fades contains three lithological assemblages representing different segments of the edifice
which were transported with little internal mixing within the flow. We have determined that some of the dacite-bearing assemblage
1, fades 1 was hot (∼350 °C) during transport and emplacement, whereas none of the other lithological assemblages of fades
contained hot material. Our interpretation is that a dacite dome was active on the ancient Ruapehu edifice immediately prior
to the Murimotu sector collapse. The partially cooled carapace of the dome and material shed from this part was incorporated
into the avalanche deposit, along with cold lavas and volcaniclastics. We have not found evidence for incorporation of material
at or close to magmatic temperatures, at least in the sampled locations. Our palaeomagnetic work allows us to develop a comprehensive,
new palaeomagnetic classification of volcaniclastics.
Published online: 25 January 2003
Editorial responsibility: D. Dingwell 相似文献