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941.
Krzysztof Pleskot Rik Tjallingii Mirosław Makohonienko Norbert Nowaczyk Witold Szczuciński 《Journal of Paleolimnology》2018,59(4):443-459
Western Poland is located in the central European climatic transition zone, which separates the mild and humid Atlantic climate of Western Europe and the East European continental climate. This region is sensitive to lateral shifts of the European climate zones and is particularly suitable for reconstructing Holocene climate variability. This paper presents detailed analyses of the sedimentary record from Lake Strzeszyńskie since the Late Pleistocene. These include smear-slide and thin-section observations, X-ray fluorescence core scanning, magnetic susceptibility measurements, pollen analyses, and radiocarbon dating. The sediment record reveals three distinct sedimentary units consisting of: (1) an alternation of sand layers and laminated silt and clay deposits accumulated prior to 14,600 cal yr BP; (2) faintly laminated calcareous sediments intercalated with organic matter-rich layers deposited between 14,600 and 10,200 cal yr BP; and (3) massive calcareous mud deposited after 10,200 cal yr BP. The Holocene period is marked by nine phases of organic-rich sedimentation and enhanced Fe deposition, which occurred at ca. 10.1, 9.3, 6.4–6.1, 5.5–5.1, 4.7–4.5, 2.7–2.4, 1.3–1.2, 0.8–0.6, 0.4–0.2 kyr cal BP. These phases are associated with high lake levels and correspond with wet periods recognized in several other records from Poland and central Europe. These phases partly coincide with North Atlantic cold periods, which may suggest that high lake levels are triggered by an ocean-continent linking mechanism. 相似文献
942.
Solar filaments show the position of large-scale polarity-inversion lines and are used for the reconstruction of large-scale
solar magnetic field structure on the basis of Hα synoptic charts for the periods that magnetographic measurements are not
available. Sometimes crossing filaments are seen in Hα filtergrams. We analyze daily Hα filtergrams from the archive of Big
Bear Solar Observatory for the period of 1999 – 2003 to find crossing and interacting filaments. A number of examples are
presented and filament patterns are compared with photospheric magnetic field distributions. We have found that all crossing
filaments reveal quadrupolar magnetic configurations of the photospheric field and presume the presence of null points in
the corona. 相似文献
943.
Strain-rate estimation using fractal analysis of quartz grains in naturally deformed rocks 总被引:1,自引:0,他引:1
Manish A. Mamtani 《Journal of the Geological Society of India》2010,75(1):202-209
The area-perimeter fractal dimension (D) of quartz grains has earlier been proposed as a strain-rate gauge based on experimental
deformation of quartz aggregates. To test the application in naturally deformed rocks, D is calculated in (a) three quartzites
belonging to the Lunavada Group of rocks (Aravalli Mountain Belt, NW India) that developed textures between 420–600°C and
(b) one quartz reef sample from the Malanjkhand Granite (Central India), which underwent dynamic recrystallization between
250–400°C. Using the above T ranges and calculated D values, strain-rates are calculated for the two sets of samples. A 10−12.7 s−1 strain rate at 250°C is calculated for the quartz reef sample. However, at higher temperatures the calculated strain-rate
is >10−10 s−1 for the quartz reef and the quartzite samples. The quartzites show evidence of dynamic recrystallization by grain boundary
migration (GBM) and subgrain rotation (SGR), while the quartz reef is replete with evidence of bulging (BLG) recrystallization.
T and calculated strainrates are plotted on available recrystallization map of quartz. It is demonstrated that whilst the
T/strain-rate of the quartzites does not fall in the region of GBM and SGR, the T/strain-rate of the quartz reef falls in
the BLG region. The problems with strain-rate calculations using area perimeter fractal dimension are discussed. It is concluded
that the method of strain-rate calculation can be used only for lower T. 相似文献
944.
945.
We present here a numerical modelling study of dislocations in perovskite CaTiO3. The dislocation core structures and properties are calculated through the Peierls–Nabarro model using the generalized stacking
fault (GSF) results as a starting model. The GSF are determined from first-principles calculations using the VASP code. The
dislocation properties such as collinear, planar core spreading and Peierls stresses are determined for the following slip
systems: [100](010), [100](001), [010](100), [010](001), [001](100), [001](010),
and All dislocations exhibit lattice friction, but glide appears to be easier for [100](010) and [010](100).
[001](010) and [001](100) exhibit collinear dissociation. Comparing Peierls stresses among tausonite (SrTiO3), perovskite (CaTiO3) and MgSiO3 perovskite demonstrates the strong influence of orthorhombic distortions on lattice friction. However, and despite some quantitative
differences, CaTiO3 appears to be a satisfactory analogue material for MgSiO3 perovskite as far as dislocation glide is concerned. 相似文献
946.
Elena Chernysheva Tatiana Khomutova Flavio Fornasier Tatiana Kuznetsova Alexandr Borisov 《山地科学学报》2018,15(6):1171-1185
The chemical properties and biological activities of soils were studied in the vicinity of the medieval settlement Podkumskoe-3 in the Kislovodsk basin (Northern Caucasus, Russia). Between the 5th and 8th centuries this area was ploughed regularly, but it was then abandoned up to the present day. It has been established that past human activity leads to soil undergoing significant transformations in terms of microbial communities and enzyme activity, and that such changes are maintained over long periods. Long-term manuring in the middle of the first millennium AD led to an increase in organic carbon content and the accumulation of nitrate nitrogen. Soils of ancient abandoned fields are associated with increases in microbial biomass, number of saprotrophic bacteria, urease activity, and fungal mycelium biomass. The observed changes in the microbiological and biochemical properties of soil were conditioned by secondary anthropogenically induced succession after the abandonment of arable lands. 相似文献
947.
Shallow water flow (SWF), a disastrous geohazard in the continental margin, has threatened deepwater drilling operations. Under overpressure conditions, continual flow delivering unconsolidated sands upward in the shallow layer below the seafloor may cause large and long-lasting uncontrolled flows; these flows may lead to control problems and cause well damage and foundation failure. Eruptions from over-pressured sands may result in seafloor craters, mounds, and cracks. Detailed studies of 2D/3D seismic data from a slope basin of the South China Sea (SCS) indicated the potential presence of SWF. It is commonly characterized by lower elastic impedance, a higher Vp/Vs ratio, and a higher Poisson’s ratio than that for the surrounding sediments. Analysis of geological data indicated the SWF zone originated from a deepwater channel system with gas bearing over-pressured fluid flow and a high sedimentation rate. We proposed a fluid flow model for SWF that clearly identifies its stress and pressure changes. The rupture of previous SWF zones caused the fluid flow that occurred in the Baiyun Sag of the northern SCS. 相似文献
948.
CHEN Lei 《地球空间信息科学学报》2008,11(3):228-234
A review was conducted on the environmental evolvement and environmental archaeological research since the 1980s in the Yangtze Delta. Former environmental evolvement and environmental archaeological research results can be summed up into 4 aspects: 1) Formation and evolution of the Taihu Lake; 2) Transgression and sea-level changes in the Holocene epoch; 3) Reconstruction of the pre-historical environment; and 4) Impacts of environmental variations on the rise and fall of human civilization (formation of the cultural interruptions). Based on this review, some limitations in the present research methods and possible outcomes are pointed out in this paper. 相似文献
949.
Using the 2016 Mercury transit of the Sun, we characterize on orbit spatial point spread functions (PSFs) for the Near- (NUV) and Far- (FUV) Ultra-Violet spectrograph channels of NASA’s Interface Region Imaging Spectrograph (IRIS). A semi-blind Richardson–Lucy deconvolution method is used to estimate PSFs for each channel. Corresponding estimates of Modulation Transfer Functions (MTFs) indicate resolution of 2.47 cycles/arcsec in the NUV channel near 2796 Å and 2.55 cycles/arcsec near 2814 Å. In the short (\({\approx}\,1336~\mathring{\mathrm{A}}\)) and long (\({\approx}\,1394~\mathring{\mathrm{A}}\)) wavelength FUV channels, our MTFs show pixel-limited resolution (3.0 cycles/arcsec). The PSF estimates perform well under deconvolution, removing or significantly reducing instrument artifacts in the Mercury transit spectra. The usefulness of the PSFs is demonstrated in a case study of an isolated explosive event. PSF estimates and deconvolution routines are provided through a SolarSoft module. 相似文献
950.
Joachim Schubart 《Celestial Mechanics and Dynamical Astronomy》2017,128(2-3):295-301
The paper refers to fictitious resonant orbits of planet type that surround both components of a binary system. In case of 16 studied examples a suitable choice of the starting values leads to a process of libration of special angular arguments and to an evolution with an at least temporary stay of the planet in the resonant orbit. The ratio of the periods of revolution of the binary and a planet is equal to 1:5. Eight orbits depend on the ratio 1:5 of the masses of the binary components, but two other ratios appear as well. The basis of this study is the planar, elliptic or circular restricted problem of three bodies, but remarks at the end of the text refer to a four-body problem. 相似文献