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991.
Hanna Hadler Andreas Vött Timo Willershäuser Dennis Wilken Ruth Blankenfeldt Claus von Carnap-Bornheim Kurt Emde Peter Fischer Ulf Ickerodt Stefanie Klooß Bente Majchczack Lea Obrocki Wolfgang Rabbel 《地球表面变化过程与地形》2021,46(15):3228-3251
In ad 1362, a major storm surge drowned wide areas of cultivated medieval marshland along the north-western coast of Germany and turned them into tidal flats. This study presents a new methodological approach for the reconstruction of changing coastal landscapes developed from a study site in the Wadden Sea of North Frisia. Initially, we deciphered long-term as well as event-related short-term geomorphological changes, using a geoscientific standard approach of vibracoring, analyses of sedimentary, geochemical and microfaunal palaeoenvironmental parameters and radiocarbon dating. In a next step, Direct Push (DP)-based Cone Penetration Testing (CPT) and the Hydraulic Profiling Tool (HPT) were applied at vibracore locations to obtain in situ high-resolution stratigraphic data. In a last step, multivariate linear discriminant analysis (LDA) was successfully applied to efficiently identify different sedimentary facies (e.g., fossil marsh or tidal flat deposits) from the CPT and HPT test dataset, to map the facies' lateral distribution, also in comparison to reflection seismic measurements and test their potential to interpolate the borehole and CPT/HPT data. The training dataset acquired for the key site from coring and DP sensing finally allows an automated facies classification of CPT/HPT data obtained elsewhere within the study area. The new methodological approach allowed a detailed reconstruction of the local coastal landscape development in the interplay of natural marsh formation, medieval land reclamation and storm surge-related land losses. 相似文献
992.
Gerald Herrling Marius Becker Alice Lefebvre Anna Zorndt Knut Krämer Christian Winter 《地球表面变化过程与地形》2021,46(11):2211-2228
The bed of estuaries is often characterized by ripples and dunes of varying size. Whereas smaller bedforms adapt their morphological shape to the oscillating tidal currents, large compound dunes (here: asymmetric tidal dunes) remain stable for periods longer than a tidal cycle. Bedforms constitute a form roughness, that is, hydraulic flow resistance, which has a large-scale effect on tidal asymmetry and, hence, on hydrodynamics, sediment transport, and morphodynamics of estuaries and coastal seas. Flow separation behind the dune crest and recirculation on the steep downstream side result in turbulence and energy loss. Since the energy dissipation can be related to the dune lee slope angle, asymmetric dune shapes induce variable flow resistance during ebb and flood phases. Here, a noncalibrated numerical model has been applied to analyze the large-scale effect of symmetric and asymmetric dune shapes on estuarine tidal asymmetry evaluated by residual bed load sediment transport at the Weser estuary, Germany. Scenario simulations were performed with parameterized bed roughness of symmetric and asymmetric dune shapes and without dune roughness. The spatiotemporal interaction of distinct dune shapes with the main drivers of estuarine sediment and morphodynamics, that is, river discharge and tidal energy, is shown to be complex but substantial. The contrasting effects of flood- and ebb-oriented asymmetric dunes on residual bed load transport rates and directions are estimated to be of a similar importance as the controls of seasonal changes of discharge on these net sediment fluxes at the Lower Weser estuary. This corroborates the need to consider dune-induced directional bed roughness in numerical models of estuarine and tidal environments. 相似文献
993.
GOCE orbit predictions for SLR tracking 总被引:1,自引:0,他引:1
After a descent phase of about half a year, the Gravity field and steady-state Ocean Circulation Explorer (GOCE) reached the
final orbital altitude of the first measurement and operational phase (MOP-1) in September 2009. Due to this very low orbital
altitude and the inactive drag compensation during descent, the generation of reliable predictions of the GOCE trajectory
turned out to be a major challenge even for short prediction intervals. As predictions of good quality are a prerequisite
for frequent ranging from the tracking network of the International Laser Ranging Service (ILRS), Satellite Laser Ranging
(SLR) data of GOCE was very sparse at mission start and made it difficult to independently calibrate and optimize the orbit
determination based on data of the Global Positioning System (GPS). In addition to the GOCE orbit predictions provided by
the European Space Agency (ESA), the Astronomical Institute of the University of Bern (AIUB) started providing predictions
on July 22, 2009, as part of the Level 1b to Level 2 data processing performed at AIUB. The predictions based on the 12-h
ultra-rapid products of the International GNSS Service (IGS) were originally intended to primarily serve the daylight passes
in the early evening hours over Europe. The corresponding along-track prediction errors were often kept below 50 m during
the descent phase and allowed for the first successful SLR tracking of GOCE over Europe on July 29, 2009, by the Zimmerwald
observatory. Additional predictions based on the IGS 18-h ultra-rapid products are provided by AIUB since September 20, 2009,
to further optimize the GOCE SLR tracking. In this article, the development of the GOCE prediction service at AIUB is presented,
and the quality of the orbit predictions is assessed for periods with and without active drag compensation. The prediction
quality is discussed as a function of the prediction interval, the quality of the input products for the GPS satellite orbits
and clocks, and the availability of the GOCE GPS data. From the methodological point of view, different approaches for the
treatment of the non-gravitational accelerations acting on the GOCE satellite are discussed and their impact on the prediction
quality is assessed, in particular during the descent phase. Eventually, an outlook is given on the significance of GOCE SLR
tracking to identify systematic errors in the GPS-based orbit determination, e.g., cross-track errors induced by mismodeled
GOCE GPS phase center variations (PCVs). 相似文献
994.
Jari Syväranta Pia Högmander Tapio Keskinen Juha Karjalainen Roger I. Jones 《Aquatic Sciences - Research Across Boundaries》2011,73(1):79-89
We used carbon and nitrogen stable isotope analyses to assess the relative contributions from pelagic and littoral energy sources to higher trophic levels in a lake ecosystem before and after a major food web perturbation. The food web structure of the lake was altered when the population sizes of the most abundant fish species (small perch, roach and bream) were reduced during an attempt to improve water quality by biomanipulation. Fish removal was followed by dense year classes of young fish, which subsequently increased the utilisation of pelagic resources. This was reflected as a decrease in relative energy contribution from littoral sources and also led to more distinct pelagic and littoral food chains after fish removal. Community metrics calculated from stable isotope data indicated increased trophic diversity and occupied niche area, and reduced trophic redundancy in the food web. However, only minor changes were observed in fish trophic positions, although roach and pike occupied slightly lower trophic positions after fish removal. Despite the Jyväsjärvi ecosystem becoming more dependent on pelagic energy after fish removals, the littoral energy contribution was still substantial, particularly to certain fish species. Hence, our results support recent arguments for the importance of benthic production in lake ecosystems. More generally, our results illustrate how large-scale perturbations of food web structure can alter energy flow patterns through an entire ecosystem. 相似文献
995.
The study of infrasound is experiencing a renaissance in recent years since it was chosen as a verification technique for
the Comprehensive Nuclear-Test-Ban Treaty. Currently, 60 infrasound arrays are being installed to monitor the atmosphere for
nuclear tests as part of the International Monitoring System (IMS). The number of non-IMS arrays also increases worldwide.
The experimental ARCES infrasound array (ARCI) is an example of such an initiative. The detectability of infrasound differs
for each array and is a function of the array location and configuration, the state of the atmosphere, and the presence of
natural and anthropogenic sources. In this study, a year of infrasound data is analyzed as recorded by ARCI. Contributions
of the atmosphere and the sources are evaluated in both a low- (0.1–1.0 Hz) and high-frequency (1.0–7.0 Hz) pass-band. The
enormous number of detections in the low-frequency band is explained in terms of the stratospheric wind and ocean wave activity
and compared with the detection of microseism. Understanding the detectability in the low-frequency band is of utmost importance
for successfully applying infrasound as a verification technique since small-sized nuclear test will show up in this frequency
range. 相似文献
996.
Bastian Baranski Theodor Foerster Bastian Schäffer Kristof Lange 《Transactions in GIS》2011,15(Z1):125-142
A lot of effort has been invested in Spatial Data Infrastructures (SDIs) during the last decade regarding interoperable standards for services and data. But still the scalability and performance of SDI services is reported to be crucial especially if they are accessed concurrently by a high number of users. Furthermore, laws and provisions such as the INSPIRE directive specify challenging requirements regarding the performance, availability and scalability of SDI services. This article presents a Hybrid Cloud architecture for matching INSPIRE‐related Quality of Service (QoS) requirements, without investing in rarely used hardware in advance, by occupying external third‐party resources on a pay‐as‐you‐go basis. The presented Hybrid Cloud is a composition of a local IT‐infrastructure (Private Cloud) and the computational resources of third‐party vendors (Public Cloud). The local infrastructure is laid out to handle the average main load of a service and in lasting peak times additional resources of external providers are allocated and integrated on demand into the local infrastructure to provide sufficient service quality automatically. A proof‐of‐concept implementation of the proposed Hybrid Cloud approach is evaluated and benchmarked with respect to INSPIRE‐related QoS requirements. 相似文献
997.
998.
Dust deposition in the Aral Sea: implications for changes in atmospheric circulation in central Asia during the past 2000 years 总被引:1,自引:0,他引:1
Xiangtong Huang Hedi Oberhänsli Hans von Suchodoletz Philippe Sorrel 《Quaternary Science Reviews》2011,30(25-26):3661-3674
We investigated mineral aerosol (dust) deposition in the Aral Sea with intention to understand the variability of dust in central Asia and its implications for atmospheric circulation change in the late Holocene. Using an 11.12-m sediment core of the lake, we calculated bulk sediment fluxes at high time-resolution and analyzed grain-size distributions of detrital sediments. A refined age-depth model was established by combined methods of radiocarbon dating and archeological evidence. Besides, a principal component analysis (PCA) of grain-size fractions and elements (Fe, Ti, K, Ca, Sr) was used to assess the potential processes controlling detrital inputs. The results suggest that two processes are mainly relevant for the clastic input as the medium silt fractions and Ti, Fe and K are positively correlated with Component 1 (C1), and the fine size fractions (<6 μm) are positively correlated with Component 2 (C2). Taking the results of the PCA, geological backgrounds, clastic input processes into account, we propose that the medium silt fractions and, in particular, the grain-size fraction ratio (6–32 μm/2–6 μm), can serve as indicators of the variability of airborne dust in the Aral Sea region. On the contrary, the fine size fractions appear to be contributed mainly by the sheetwash processes. The bulk sediment deposition fluxes were extremely high during the Little Ice Age (LIA; AD 1400–1780), which may be related to the increased dust deposition. As indicated by the variations of grain-size ratio and Ti, the history of dust deposition in central Asia can be divided into five distinct periods, with a remarkably low deposition during AD 1–350, a moderately high value from AD 350–720, a return to relatively low level between AD 720 and AD 1400 (including the Medieval Warm Period (MWP, AD 755–1070)), an exceptionally high deposition from AD 1400 to 1940s and an abnormally low value since 1940s. The temporal variations in the dust deposition are consistent with the changes in the Siberian High (SH) and mean atmospheric temperature of the northern hemisphere during the past 2000 years, with low/high annual temperature anomalies corresponding to high/low dust supplies in the Aral Sea sediments, respectively. The variations in the fine size fraction also show a broadly similarity to a lacustrine δ18O record in Turkey (Jones et al., 2006), implying that there was less moisture entering western central Asia from the Mediterranean during the LIA than during the MWP. 相似文献
999.
Jürgen Schäfer 《Geodinamica Acta》2013,26(4):125-136
AbstractDetrital amphiboles from the Famennian, Saxothuringian greywackes of the “Erbendorf Paleozoic” in Bavaria were analysed with an electron microprobe. The results were compared with recalculated literature data of amphiboles from potential source rocks to obtain more detailed information about the provenance of the oldest preserved synorogenic sediments in the Saxothuringian belt.All of the detrital amphiboles show very similar, homogeneous chemical compositions. All of them are Ca-amphiboles (with (Ca+Na)B ≥: 1.34; NafB < 0.67; (Na+K)A < 0.50 and Ti < 0.50), mostly inagnesio-hornblende and tschermakitic hornblende. The comparison with amphiboles from rocks of potential provenance areas reveals that the Randamphibolit-Series of the Miinchberg Massif – or an equivalent, already eroded unit – can be regarded as source rock of the detrital amphiboles.The presented data are the first evidence, that the Randamphibolit of the Miinchberg Massif was exhumed as early as in the Famennian, shortly after its metamorphism. It can be concluded that before Famennian time the complete Saxothuringian oceanic crust and large parts of the Saxothuringian continental crust had been subducted at the active margin. This implies that the collision of the Saxothuringian plate with the Tepla-Barrandian microplate, leading to the accretion of the Saxothuringian plate, happened 15–20 Ma earlier than previous authors had supposed. Accordingly, the collisional stage must have been reached not later than in the middle Devonian (approx. 380 Ma). 相似文献
1000.
Sedimentary evolution of Lake Van (Eastern Turkey) reconstructed from high-resolution seismic investigations 总被引:1,自引:0,他引:1
Deniz Cukur Sebastian Krastel Filiz Demirel-Schlüter Emin Demirbağ Caner Imren Frank Niessen Mustafa Toker 《International Journal of Earth Sciences》2013,102(2):571-585
This paper presents results of a multi-channel seismic reflection survey at Lake Van and provides constraints on the sedimentary evolution of the lake. The geophysical data of the lake confirm the existence of three physiographic provinces: a shelf, a slope, and a deep, relatively flat basin. The most prominent features identified on the shelf and slope are clinoforms, submerged channels, as well as closely spaced lake floor depressions, reflecting a highly variable lake-level history. The morphological depressions are interpreted as resulting from subaquatic erosion by channelized, sediment-laden currents into horizontally bedded fan sediments. Submerged channels on the eastern shelf are interpreted as meandering-slope channels, probably as a consequence of a lake-level fall that exposed the shelf area. Clinoforms on the Eastern fan may represent relict deltas formed during stationary or slightly rising lake-level intervals. Merging subsurface imaging interpretation with morphological studies of exposed sediments reveals lake-level fluctuations of several hundreds of meters during the past ca. ~550 ka. The lake has three prominent basins (Tatvan, Deveboynu, and the Northern basin) separated by basement ridges (e.g., the Northern ridge). The seismic units in the Tatvan and Northern basins are dominated by alternations of well-stratified and chaotic reflections, while the Deveboynu basin subsurface consists mainly of chaotic units. The chaotic seismic facies are interpreted as mass-flow deposits, probably triggered by earthquakes and/or rapid lake-level fluctuations. The moderate-to-high-amplitude, well-stratified facies seen in the deeper parts of the basins are interpreted as lacustrine deposits intercalated with tephra layers. The occurrence of a clinoform in the deepest part of the lake suggests a major flooding stage of Lake Van more than ~400 ka ago. Seismic profiles from the deepest part of the lake basin show remarkably uniform and continuous stratigraphic units without any major erosional feature following the flooding event, indicating that the lake was never completely dry afterward and therefore significantly older than previously suggested. 相似文献