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151.
As a part of ESA's cornerstone mission ``ROSETTA' to comet 46P/Wirtanen a 100 kgLander will bring a scientific payload of
almost 27 kg to the surface of the nucleus.After a first scientific sequence it will operate for a considerable fraction of
thecometary orbit around the sun (between 3 AU and 2 AU). Ten experiments with a number of sub-experiments are foreseen; this
paper presents the current status of the Lander development and reviews the scientific capabilities of each of the experiments
at a time when the Flight Model (FM) of the Lander is already delivered. 相似文献
152.
In the frame of the recent worldwide activities of Lunar research, including various studies for surface stations, the aspect of longevity of such stations has been identified as a particular technical challenge. The reason for this lies in the long (about 14 days) and cold Lunar night during which it is non-trivial to keep spacecraft systems alive and sensitive equipment within an acceptable temperature range.The following paper analyzes and compares various concepts to survive Lunar night, both with and without radioisotope heater technology.The latter normally implies the use of highly toxic material (typically plutonium), which is politically problematic and a driver for cost and safety procedures.Concepts without radioisotope heating need to foresee special measures, like extremely efficient thermal insulation or sub-surface positioning of all temperature sensitive components.Special emphasis has been taken on the thermal analysis of a penetrator-type surface station. The relevant issues are discussed and results for day–night cycles are presented, assuming a typical set of engineering parameters. This concept appears to be the easiest to implement from a thermal point of view, if the use of radioisotope heaters has to be avoided. 相似文献
153.
Jens R?der Raimon Tolosana-Delgado Fred A. Hamprecht 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(7):865-879
The aim of this paper is to compare four different methods for binary classification with an underlying Gaussian process with
respect to theoretical consistency and practical performance. Two of the inference schemes, namely classical indicator kriging
and simplicial indicator kriging, are analytically tractable and fast. However, these methods rely on simplifying assumptions
which are inappropriate for categorical class labels. A consistent and previously described model extension involves a doubly
stochastic process. There, the unknown posterior class probability f(·) is considered a realization of a spatially correlated Gaussian process that has been squashed to the unit interval, and
a label at position x is considered an independent Bernoulli realization with success parameter f(x). Unfortunately, inference for this model is not known to be analytically tractable. In this paper, we propose two new computational
schemes for the inference in this doubly stochastic model, namely the “Aitchison Maximum Posterior” and the “Doubly Stochastic
Gaussian Quadrature”. Both methods are analytical up to a final step where optimization or integration must be carried out
numerically. For the comparison of practical performance, the methods are applied to storm forecasts for the Spanish coast
based on wave heights in the Mediterranean Sea. While the error rate of the doubly stochastic models is slightly lower, their
computational cost is much higher. 相似文献
154.
Bedload transport measurements with impact plate geophones: comparison of sensor calibration in different gravel‐bed streams 下载免费PDF全文
Dieter Rickenmann Jens M. Turowski Bruno Fritschi Carlos Wyss Jonathan Laronne Ronel Barzilai Ian Reid Andrea Kreisler Johann Aigner Hugo Seitz Helmut Habersack 《地球表面变化过程与地形》2014,39(7):928-942
Indirect bedload transport measurements have been made with the Swiss plate geophone system in five gravel‐bed mountain streams. These geophone sensors record the motion of bedload particles transported over a steel plate mounted flush with the channel bed. To calibrate the geophone system, direct bedload transport measurements were undertaken simultaneously. At the Erlenbach in Switzerland, a moving‐basket sampler was used. At the Fischbach and Ruetz streams in Austria, a Helley–Smith type bedload sampler provided the calibration measurements. A Bunte‐type bedload trap was used at the Rofenache stream in Austria. At the Nahal Eshtemoa in Israel, Reid‐type slot bedload samplers were used. To characterize the response of the geophone signal to bedload particles impacting on the plate, geophone summary values were calculated from the raw signal and stored at one second intervals. The number of impulses, i.e. the number of peaks above a pre‐defined threshold value of the geophone output signal, correlated well with field measured gravel transport loads and was found to be a robust parameter. The relations of impulses to gravel transport loads were generally near‐linear, but the steepness of the calibration relations differed from site to site. By comparing the calibration measurements from the different field sites and utilizing insights gained during preliminary flume experiments, it has been possible to identify the main factors that are responsible for site specific differences in the calibration coefficient. The analysis of these calibration measurements indicates that the geophone signal also contains some information about the grain size distribution of bedload. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
155.
Jörn Parplies Andreas Lücke Heinz Vos Jens Mingram Martina Stebich Ulrich Radtke Jingtai Han Gerhard H. Schleser 《Journal of Paleolimnology》2008,40(1):471-487
Total organic carbon (TOC) content, total nitrogen (TN) content, stable nitrogen isotope (δ15N) and stable organic carbon isotope (δ13Corg) ratios were continuously analysed on a high resolution sediment profile from Lake Sihailongwan (SHL), covering the time
span between 16,500 and 9,500 years BP. Strong variations of the investigated proxy parameters are attributed to great climatic
fluctuations during the investigated time period. Variations in organic carbon isotope ratios and the ratio of TOC/TN (C/N
ratio) are discussed with respect to changing proportions of different organic matter (OM) sources to bulk sedimentary OM.
Phases of high TOC content, high TN content, depleted δ13Corg values and high δ15N values are interpreted as times with increased productivity of lacustrine algae in relation to input of terrigenous organic
matter. Two distinct phases of enriched nitrogen isotope ratios from 14,200 to 13,700 and 11,550 to 11,050 years BP point
towards a reduced phytoplankton discrimination against 15N due to a diminished dissolved inorganic nitrogen pool. The combination of geochemical (TOC, TN, C/N ratio) and isotopic
(δ13Corg, δ15N) proxy parameters points to a division of climate development into four stages. A cold and dry stage before 14,200 years
BP, a warm optimum stage with high phytoplankton productivity from 14,200 to 12,450 BP, a colder and drier stage from 12,450
to 11,600 BP and a stage of climatic amelioration with high variability in TOC and TN contents after 11,600 BP. These results
are discussed in relation to monsoon variability and Northern Hemisphere climate development of the late glacial. 相似文献
156.
Diatom assemblages in the annually laminated sediments of two neighboring, pre-alpine lakes (Ammersee and Starnberger See, Southern Germany) were analyzed and compared year by year. Within both varve records of the last decades, the same 4-phase-succession of planktonic diatom species is preserved, consisting of 1. a dominance of Cyclotella species 2. assemblages of Fragilaria crotonensis, Asterionella formosa and Stephanodiscus minutulus 3. a mass bloom of Aulacoseira islandica, and 4. a dominance of Stephanodiscus species. This diatom sequence is considered as a model of a 'basic species sequence of eutrophication'. Time lags and differences in the duration of the phases between both lakes show evidence of an earlier start for nutrient loading in Starnberger See than in Ammersee, and a faster development to a higher trophic state level in the latter. The different reactions of the lakes are attributed to hydrological differences such as the existence or lack of a major tributary, the size of the catchment area, and the water residence time. The reconstruction of the eutrophication dynamics appears to be reliably hindcast by the inference of total phosphorus (TP) concentrations using weighted averaging regression and calibration techniques. Remarkable differences in the occurrence of some diatoms in both stratigraphies, which are not related to the general changes of the 'basic species sequence of eutrophication' model, may be due to the epilimnetic silica content (e.g. Fragilaria crotonensis) or competitive weaknesses (e.g. Tabellaria flocculosa). 相似文献
157.
Andreas Hartmann Martin Kralik Franko Humer Jens Lange Markus Weiler 《Environmental Earth Sciences》2012,65(8):2377-2389
For water management purposes, information about an entire aquifer system is generally more important than information about
a specific spring. Since a karstic aquifer system might drain to several outlets, conclusions derived from a single spring
can be misleading for characterization and modeling. In this study we apply a conceptual model to an Alpine dolomite karst
system in Austria. The particular challenge was that several small springs with strongly varying hydrological behavior and
diffuse flow into surrounding streams drain this system. Instead of applying the model to a single spring, it was calibrated
simultaneously to several observations within the system aiming to identify the karst system’s intrinsic hydrodynamic parameters.
Parameter identification is supported by modeling the transport of water isotopes (δ18O). The parameters were transferred to the whole system with a simple upscaling procedure and a sensitivity analysis was performed
to unfold influence of isotopic information on parameter sensitivity and simulation uncertainty. The results show that it
is possible to identify system intrinsic parameters. But the sensitivity analysis revealed that some are hardly identifiable.
Only by considering uncertainty reasonable predictions can be provided for the whole system. Including isotopic information
increases the sensitivity of some intrinsic parameters, but it goes along with a sensitivity decrease for others. However,
a possible reduction of prediction uncertainty by isotopic information is compensated by deficiencies in the transport modeling
routines. 相似文献
158.
Ekaterina V. KOROCHANTSEVA Mario TRIELOFF Alexei I. BUIKIN Jens HOPP 《Meteoritics & planetary science》2009,44(2):293-321
Abstract— We report a high‐resolution 40Ar‐39Ar study of mineral separates and whole‐rock samples of olivine‐phyric (Dhofar 019, Sayh al Uhaymir [SaU] 005) and basaltic (Shergotty, Zagami) shergottites. Excess argon is present in all samples. The highest (40Ar/36Ar)trapped ratios are found for argon in pyroxene melt inclusions (?1500), maskelynite (?1200), impact glass (?1800) of Shergotty and impact glass of SaU 005 (?1200). A high (40Ar/36Ar)trapped component‐usually uniquely ascribed to Martian atmosphere‐can also originate from the Martian interior, indicating a heterogeneous Martian mantle composition. As additional explanation of variable high (40Ar/36Ar)trapped ratios in shocked shergottites, we suggest argon implantation from a “transient atmosphere” during impact induced degassing. The best 40Ar‐39Ar age estimate for Dhofar 019 is 642 ± 72 Ma (maskelynite). SaU 005 samples are between 700–900 Ma old. Relatively high 40Ar‐39Ar ages of melt inclusions within Dhofar 019 (1086 ± 252 Ma) and SaU 005 olivine (885 ± 66 Ma) could date entrapment of a magmatic liquid during early olivine crystallization, or reflect unrecognized excess 40Ar components. The youngest 40Ar‐39Ar age of Shergotty separates (maskelynite) is ?370 Ma, that of Zagami is ?200 Ma. The 40Ar‐39Ar chronology of Dhofar 019 and SaU 005 indicate >1 Ga ages. Apparent ages uncorrected for trapped (e.g., Martian atmosphere, mantle) argon components approach 4.5 Ga, but are not caused by inherited 40Ar, because excess 40Ar is supported by 36Artrapped. Young ages obtained by 40Ar‐39Ar and other chronometers argue for primary rather than secondary events. The cosmic ray exposure ages calculated from cosmogenic argon are 15.7 ± 0.7 Ma (Dhofar 019), 1.0–1.6 Ma (SaU 005), 2.1–2.5 Ma (Shergotty) and 2.2–3.0 Ma (Zagami). 相似文献
159.
Ilse Gräber Jørgen F. Hansen Svend E. Olesen Jens Petersen Hans S. Østergaard Lars Krogh 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):15-22
Geografisk Tidsskrift, Danish Journal of Geography 105(2):15–22, 2005 The change of Cu and Zn concentrations in Danish agricultural soils was studied in areas with intensive pig production. Cu and Zn are found in pig manure as the metals are added to pig feed as growth promoters. The changes in concentrations of total and 0.02 MEDTA extractable Cu and Zn in soils from 1986 to 1998 were determined from samples taken at two depths (0–25 cm and 25–50 cm) from 73 sites. Pig manure and mineral fertilizer was added to 60 sites whereas fertilizer only was used on 13 sites. During the survey period soil Cu concentrations increased in both depths but mostly in the sites where pig manure was added. Furthermore, the results indicated that some plant-available Cu and Zn were transported from the topsoil to the subsoil. No significant change in soil Zn concentration was found although a slight reduction was observed. Comparing soil metal concentrations observed in 1998 to the total pig manure application in a 12-year period, it was observed that application of manure caused an accumulation of Cu and of Zn in the upper 50 cm soil. The accumulation rates correspond to the Cu and Zn concentrations in the pig manure. 相似文献
160.
Werner Skrotzki Roland Tamm Carl-Georg Oertel Jens Rseberg Heinz-Günter Brokmeier 《Journal of Structural Geology》2000,22(11-12)
Lead sulfide (galena) of different purity and grain size was extruded through a round and rectangular die at temperatures between 773 and 923 K. Global and local lattice preferred orientations (here referred to as textures) were measured by neutron and electron back-scattering diffraction. Tension leads to a <100> <111> double fibre texture. Pure shear deformation yields texture components near the ideal face-centered cubic metal brass, copper, Goss and cube positions. The intensity of the components depends on the purity and/or grain size. The microstructure is partially recrystallized. Electron back-scattering diffraction indicates that in tension the <100> and in pure shear the Goss and cube components are associated with dynamic recrystallization. The deformation texture can be qualitatively explained by the full and relaxed constraints Taylor model using slip on {100}<110>, {110}<110> and {111}<110> systems. The texture formation in lead sulfide compares well with that observed for other ionic crystals with the NaCl-structure as well as for face-centered cubic metals with a high stacking fault energy. 相似文献