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691.
Sources of recent tectonic stress in the Pannonian region:inferences from finite element modelling 总被引:3,自引:0,他引:3
Gábor Bada Sierd Cloetingh Péter Gerner & Frank Horváth 《Geophysical Journal International》1998,134(1):87-101
We present the results of finite element modelling of the recent stress field in the Pannonian basin and surrounding Alpine orogenic belt. Our results show that the recent, predominantly compressive, stress regime in the Alpine–Pannonian–Carpathian–Dinaric system is governed by distinct tectonic factors. Of great importance is the deformation of crustal blocks with different geometries and rigidities in an overall convergent setting associated with the Africa–Europe collision. The most important stress source appears to be the counterclockwise rotation of the Adriatic microplate at the southwest boundary of the Pannonian basin. This plate tectonic unit has been interpreted as moving independently of both the European plate and the African plate. Additional boundary conditions—active shortening and compression in the Vrancea zone and the Bohemian Massif, and the effect of the immobile Moesian Platform—also significantly influence the modelling results. The incorporation of additional stress sources such as crustal thickness variation and the presence of two main fault zones separating the primary tectonic units in the study area have only locally important effects but improve the fit between the calculated results and the observed stress pattern. 相似文献
692.
Frank C. van den Bosch & Eric Emsellem 《Monthly notices of the Royal Astronomical Society》1998,298(1):267-274
We present circumstantial evidence that the central region of the edge-on S0 galaxy NGC 4570, which harbours a 150-pc scale nuclear disc in addition to its main outer disc, has been shaped under the influence of a small (∼ 500 pc) bar. This is based on the discovery of two edge-on rings, the locations of which are consistent with the inner Lindblad and ultraharmonic resonances of a rapidly tumbling triaxial potential. Observed features in the photometry and rotation curve correspond nicely with the positions of the main resonances, strengthening the case for a tumbling bar potential. The relative blue colour of the ILR ring, and the complete absence of any detected ISM, indicates that the nuclear ring is made of relatively young (≲ 2 Gyr) stars. We discuss a possible secular evolution scenario for this complex multicomponent galaxy, which may also apply to many other S0 galaxies with observed rings and/or multiple disc components. 相似文献
693.
Cecilia Scorza & Frank C. van den Bosch 《Monthly notices of the Royal Astronomical Society》1998,300(2):469-478
Hubble Space Telescope images of two early-type galaxies harbouring both nuclear and outer stellar discs are studied in detail. By means of a photometric decomposition, the images of NGC 4342 and 4570 are analysed and the photometric properties of the nuclear discs investigated. We find a continuity of properties in the parameter space defined by the central surface brightness μ0 and the scalelength R d of discs in spirals, S0s and embedded discs in ellipticals, in the sense that the nuclear discs extend the observed disc properties even further towards smaller scalelengths and brighter central surface brightnesses. When including the nuclear discs, disc properties span more than four orders of magnitude in both scalelength and central surface brightness. The nuclear discs studied here are the smallest and brightest stellar discs known, and as such, they are as extreme in their photometric properties as Malin I, when compared with typical galactic discs that obey Freeman's law. We discuss a possible formation scenario in which the double-disc structure observed in these galaxies has been shaped by now dissolved bars. Based on the fact that the black holes known to exist in some of these galaxies have masses comparable to those of the nuclear discs, we explore a possible link between the black holes and the nuclear discs. 相似文献
694.
Frank Hill 《Solar physics》1990,128(1):321-331
The first map of the horizontal flows as a function of depth and heliocentric position in the solar convection zone is presented. The map is inferred from a least-squares smoothness-constrained inversion of velocities measured from ring diagrams of the solar p-mode oscillations. The data provide information in four longitude regions at a latitude just south of the solar equator. The presence of several features is suggested by the results:
The magnitude of the flows is substantial, reaching some 450 m s–1 for the longitudinal jet, and 150 m s–1 for the latitudinal flow. Possible systematic errors and the physical consequences of the flows are discussed. 相似文献
(1) | A prograde directed longitudinal jet between the hydrogen and first helium ionization zone, reversing direction to retrograde below the second helium ionization zone. |
(2) | A equatorward directed latitudinal flow above the second helium ionization zone. |
(3) | A poleward latitudinal flow below the second helium ionization zone, but only in one of the four longitude bands. A large active region was present in this band, but not in two of the other bands, suggesting a possible relationship between the activity and the different flow pattern. |
695.
This paper evaluates evidence for seasonal loess deposits in peri-Alpine Lake Constance at the end of the last Glacial (Oldest Dryas chronozone). The usefulness of such lacustrine deposits for palaeoclimatic interpretations is discussed. The sedimentology of laminated couplets comprising yellow and grey silts has been investigated to test the hypothesis that the couplets are varves (i.e. annual rhythmites) comprising alternations of loess and glacial silt and clay. The laminae are mostly less than 1 mm thick and include from bottom to top: (1) a matrix of well-sorted, non-graded fine yellow silt with sand-size intraclasts, (2) coarsening-upward grey silt with a cap of fining-upward silt to clay. The latter is typical for varves in modern proglacial lakes and reflects summer and winter deposits (silt and clay, respectively). We propose that the lack of grading and the matrix supported fabric is indicative of aeolian transport and therefore interpret the yellow laminae as loess deposits. Volcanic glass intraclasts in the loess layers are probably derived from volcanic terrain to the west of the lake, indicating an easterly palaeowind direction. Deposition of loess in the lake occurred regularly at the beginning of each annual cycle, suggesting that the palaeowinds were associated with winter and/or spring conditions. Two transport scenarios are suggested to explain the sand grains scattered in this deep-water lacustrine record. 1. The grains may have been transported as bedload over the annual winter ice-cover of the lake under moderate wind strengths, frozen into the ice, and released for deposition during spring melt. 2. The sand grains were blown directly out onto the lake water by very strong winds during spring. The first scenario is contrary to the general view that loess was transported during summer, and that loess deposits thus reflect summer conditions only. Loess input to the lake shows a transitional decrease after ca. 14.3 kyr BP and cessation at ca. 14 kyr BP, probably as a result of a change of wind behaviour, increased humidity and/or vegetational changes during the Oldest Dryas in central Europe.This paper was presented at Clima Locarno 90, the International Conference on Past and Present Climate Dynamics: Reconstruction of Rates of Change, held in Locarno, Switzerland, September 24 to 28, 1991, supported by a grant from the Swiss Academy of Sciences. It was convened jointly by the Swiss National Climate Program - ProClim, the Swiss Committee for the IGBP, the Swiss COL, the Swiss SCOPE Committee, and the Swiss CCA. Guest editor for the papers published following the conference is Dr. K. Kelts (see also Climate Dynamics 6:3/4, Jan. 1992) 相似文献
696.
Raffaello Trigila Frank J. Spera Carlo Aurisicchio 《Contributions to Mineralogy and Petrology》1990,104(5):594-608
Thermochemical calculations and laboratory phase equilibration experiments on lavas of the 131 day 1983 Mt. Etna flank eruption of 0.1 km3 were undertaken to investigate possible systematic variations in inferred melt-phenocryst equilibration conditions as a function of time. The 1983 Mt. Etna lavas are multiply saturated; plagioclase, clinopyroxene and olivine, the dominant phenocrysts, occur in the ratio 1:1/2:1/4. Melts (glasses) plot close to the plagioclase saturated olivine-clinopyroxene low pressure cotectic on a Walker-O'Hara diopside-forsterite-silica diagram suggesting equilibration of melt and phenocrysts in a high level magma reservoir. Total pressures, temperatures and dissolved H2O concentrations were calculated using the isoactivity method of Carmichael and coworkers based on about 300 elelctron microprobe analyses of coexisting olivine, clinopyroxene and plagioclase phenocrysts, microphenocrysts and groundmass microlites for samples collected 6, 46 and 125 days after the start of the eruption. Total pressures (P
t), temperatures and H2O contents based on representative olivine-clinopyroxene pairs are 140 MPa, 1105°C, 2.4 wt% H2O; 255 MPA, 1112°C, 1.0 wt% H2O and 85 MPa, 1096°C, 1.8 wt% H2O respectively for the early (283), middle (I83) and late (L83) samples. Corresponding equilibration depths are in the range 3 to 10 kilometers. Plagioclase feldspar phenocrysts, while showing more evidence of disequilibrium, provide compatible estimates of P
t and T when analysis is restricted to the low anorthite mode of the plagioclase frequency-composition histograms: 133 MPa and 1115°C; 260 MPa and 1117°C and 103 MPa and 1104°C, repectively for 283, I83 and L83. The pre-eruptive (i.e., in situ) temperature-pressure gradient calculated from olivine-clinopyroxene equilibria is 10.6 K/kbar. This compares well with independent estimates of the temperature-pressure derivative of the (pseudo) invariant point composition (10 to 12 K/kbar) in both model (e.g., diopside-forsterite-anorthite, Presnall et al. 1978) and natural (e.g., Walker et al. 1979; Grove et al. 1982) systems. Apparently, magma within the Etna reservoir was in a quasiequilibrium state buffered by its multiply-saturated character immediately preceding eruption. The temporal variation of computed P
t, T and H2O concentrations for melt-phenocryst equilibrium agrees well with predictions based on simulations of the withdrawal of magma from a body zoned with respect to dissolved H2O provided the temporal record of magma discharge is taken into account. Discharge varied by a factor of about 100 during the sample collection interval. The intermediate P
t but high H2O content inferred for sample 283 reflects the withdrawal of H2O enriched magma during an early phase of high average discharge of about (350 m3/s) before evaculation isochrons became quasistationary. The high P
t and relatively dry I83 magma reflects the deepening of the evacuation isochrons after 50 days of intermediate discharge with the development of quasi-stationary isochrons in time and space. Sample L83 from day 125 near the end of the eruption reflects the shoaling of evacuation isochrons (hence low P
t and relatively high H2O content) associated with the observed low (0.5 m3/s) discharge. Our results show that thermochemical modeling efforts provide important opportunities for testing the predictions of magma with-drawal simulations. 相似文献
697.
Frank Bradshaw Wood 《Astrophysics and Space Science》1985,110(1):137-141
Triple star systems, especially those in which one star has very small mass may be more common than has been generally considered. Here is summarized some of the recent evidence supporting this possibility.Communication presented at the International Conference on Astrometric Binaries, held on 13–15 June, 1984, at the Remeis-Sternwarte Bamberg, Germany, to commemorate the 200th anniversary of the birth of Friedrich Wilhelm Bessel (1784–1846) 相似文献
698.
699.
Frank?McDermottEmail author Francisco?G.?Delfin?Jr. Marc?J.?Defant Simon?Turner Rene?Maury 《Contributions to Mineralogy and Petrology》2005,150(6):652-670
Pliocene to recent volcanic rocks from the Bulusan volcanic complex in the southern part of the Bicol arc (Philippines) exhibit
a wide compositional range (medium- to high-K basaltic-andesites, andesites and a dacite/rhyolite suite), but are characterised
by large ion lithophile element enrichments and HFS element depletions typical of subduction-related rocks. Field, petrographic
and geochemical data indicate that the more silicic syn- and post-caldera magmas have been influenced by intracrustal processes
such as magma mixing and fractional crystallisation. However, the available data indicate that the Bicol rocks as a group
exhibit relatively lower and less variable 87Sr/86Sr ratios (0.7036–0.7039) compared with many of the other subduction-related volcanics from the Philippine archipelago. The
Pb isotope ratios of the Bicol volcanics appear to be unlike those of other Philippine arc segments. They typically plot within
and below the data field for the Philippine Sea Basin on 207Pb/204Pb versus 206Pb/204Pb and 208Pb/204Pb versus 206Pb/204Pb diagrams, implying a pre-subduction mantle wedge similar to that sampled by the Palau Kyushu Ridge, east of the Philippine
Trench. 143Nd/144Nd ratios are moderately variable (0.51285–0.51300). Low silica (<55 wt%) samples that have lower 143Nd/144Nd tend to have high Th/Nd, high Th/Nb, and moderately low Ce/Ce* ratios. Unlike some other arc segments in the Philippines
(e.g. the Babuyan-Taiwan segment), there is little evidence for the involvement of subducted terrigenous sediment. Instead,
the moderately low 143Nd/144Nd ratios in some of the Bicol volcanics may result from subduction of pelagic sediment (low Ce/Ce*, high Th/Nd, and high
Th/Nb) and its incorporation into the mantle wedge via a slab-derived partial melt. 相似文献
700.
Real-Time Tsunami Forecasting: Challenges and Solutions 总被引:8,自引:0,他引:8
Vasily?V.?TitovEmail author Frank?I.?Gonzalez E.?N.?Bernard Marie?C.?Eble Harold?O.?Mofjeld Jean?C.?Newman Angie?J.?Venturato 《Natural Hazards》2005,35(1):35-41
A new method for real-time tsunami forecasting will provide NOAAs Tsunami Warning Centers with forecast guidance tools during an actual tsunami event. PMEL has developed the methodology of combining real-time data from tsunameters with numerical model estimates to provide site- and event-specific forecasts for tsunamis in real time. An overview of the technique and testing of this methodology is presented. 相似文献