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871.
Concentrations of polycyclic aromatic hydrocarbons have been determined in sediments, mussels and crustacea in the vicinity of a former gasworks site by Shoreham Harbour, UK. Very high concentrations of PAH were found in the substrate, an ash-like material deposited on the former gasworks site, which exhibited a profile consistent with the major source of contamination being coal or coke tar produced during the period of gas production at the site. Elevated PAH concentrations were also found in mussels both from the beach below the former gasworks site, and from sites further to the east in Portslade and Hove. The significance of these concentrations were assessed using an approach which involved the calculation of benzo[a]pyrene equivalent conoentrations (BaPEs), summing concentrations of individual PAH on the basis of their comparative potency as carcinogens. BaPE ranged from values of, or close to, zero for crustacea, to 336 microg kg(-1) wet weight in mussels from Southwick Beach. The contaminated mussels are not exploited commercially but may be taken by casual gatherers, and notices have been posted to warn potential consumers. 相似文献
872.
Solar magnetic and bolometric cycles recorded in sea sediments 总被引:1,自引:0,他引:1
The total carbonate and thermoluminescence (TL) profiles of the GT89-3 Ionian sea sediment core have been measured in the upper 200 cm of the core spanning the last 3100 years in order to test the presence of the Gleissberg (80–90 yr) cycle in the two different time series recorded in the same archive. Two different sampling intervals respectively of 2.5 mm and 2 mm have been chosen for the measurements in order to obtain results independent from sampling effects in the time series. We have revealed the Gleissberg cycle at 83 and 92 yr in both records. 相似文献
873.
874.
In many tidal embayments, bottom patterns, such as the channel-shoal systems of the Wadden Sea, are observed. To gain understanding
of the mechanisms that result in these bottom patterns, an idealized model is developed and analyzed for short tidal embayments.
In this model, the water motion is described by the depth- and width-averaged shallow water equations and forced by a prescribed
sea surface elevation at the entrance of the embayment. The bed evolves due to the divergence and convergence of suspended
sediment fluxes. To model this suspended-load sediment transport, the three-dimensional advection–diffusion equation is integrated
over depth and averaged over the width. One of the sediment fluxes in the resulting one-dimensional advection–diffusion equation
is proportional to the gradient of the local water depth. In most models, this topographically induced flux is not present.
Using standard continuation techniques, morphodynamic equilibria are obtained for different parameter values and forcing conditions.
The bathymetry of the resulting equilibrium bed profiles and their dependency on parameters, such as the phase difference
between the externally prescribed M2 and M4 tide and the sediment fall velocity, are explained physically. With this model, it is then shown that for embayments that
are dominated by a net import of sediment, morphodynamic equilibria only exist up to a maximum embayment length. Furthermore,
the sensitivity of the model to different morphological boundary conditions at the entrance of the embayment is investigated
and it is demonstrated how this strongly influences the shape and number of possible equilibrium bottom profiles. This paper
ends with a comparison between the developed model and field data for the Wadden Sea’s Ameland and Frisian inlets. When the
model is forced with the observed M2 and M4 tidal constituents, morphodynamic equilibria can be found with embayment lengths similar to those observed in these inlets.
However, this is only possible when the topographically induced suspended sediment flux is included. Without this flux, the
maximum embayment length for which morphodynamic equilibria can be found is approximately a third of the observed length.
The sensitivity of the model to the topographically induced sediment flux is discussed in detail. 相似文献
875.
B. C. Haimson 《Pure and Applied Geophysics》2003,160(5-6):813-831
— Vertical drilling experiments in high-porosity (22% and 25%) Berea sandstone subjected to critical true triaxial far-field stresses, in which σ H (maximum horizontal stress) >σ v (vertical stress) >σ h (least horizontal stress), revealed a new and non-dilatant failure mechanism that results in thin and very long tabular borehole breakouts that have the appearance of fractures, and which counterintuitively develop orthogonally to σ H . These breakouts are fundamentally different from those induced in crystalline rocks, as well as limestones and medium-porosity Berea sandstone. Breakouts in these rocks are typically dog-eared in shape, a result of dilatant multi-cracking tangential to the hole and subparallel to the maximum far-field horizontal stress σ H , followed by progressive buckling and shearing of detached rock flakes created by the cracks. In the high-porosity sandstone a narrow layer of grains compacted normal to σ H is observed just ahead of the breakout tip. This layer is nearly identical to “compaction bands” observed in the field. It is suggested that when a critical tangential stress concentration is reached along the σ h spring line at the borehole wall, grain bonding breaks down and a compaction band is formed normal to σ H . Debonded loose grains are expelled into the borehole, assisted by the circulating drilling fluid. As the breakout tip advances, the stress concentration ahead of it persists or may even increase, extending the compaction band, which in turn leads to breakout lengthening. 相似文献
876.
H. C. Freiesleben 《Ocean Dynamics》1952,5(4):183-188
Zusammenfassung Die Arbeit will auf die heutigen funktechnischen Hilfsmittel der Navigation hinweisen und die Möglichkeit ihrer Beeinflussung durch die Ausbreitung der Funkwellen aufzeigen. Sowohl auf dem Gebiete des Funkmeßverfahrens (Radar) wie auf den weniger bekannten Gebieten der Hyperbelnavigation und der Richtfunkfeuer sind noch viele Einzelheiten über die Brechung der Funkstrahlen, über die Interferenz und Störungen durch Raumwelleneinflüsse und über die effektive Ausbreitungsgeschwindigkeit zu klären, ehe die Schiffahrt den vollen Nutzen aus allen diesen Methoden ziehen kann.
Vortrag auf der 3. Hamburger geophysikalischen Tagung, 28. 8. 1952. 相似文献
Radio direction finding and radio wave propagation
Summary The paper outlines to-day's radio aids to navigation and their eventual dependency on the propagation of radio waves. In the field of radar as well as in the less familiar fields of hyperbolic navigation and radio range many details remain to be cleared with regard to refraction of radio rays, interference and disturbance by sky waves, and the effective velocity of propagation until navigation will be able to derive the full benefit from all these methods.
Radio navigation et propagation des ondes radioélectriques
Résumé Ce travail a pour but d' exposer le radio guidage pour navigation ainsi que sa dépendance eventuelle de la propagation des ondes radioélectriques. Non seulement dans le domaine du radar mais encore dans les domaines moins connus de la navigation hyperbolique et des radiophares directionels il reste beaucoup de détails à éclaircir, détails qui se rapportent à la réfraction du rayon radioélectrique, à l'interférence et aux perturbations causées par des ondes d'espace et, enfin, à la vitesse effective de propagation. Tous ces problèmes doivent être résolus avant que la navigation puisse tirer tout le profit de ces méthodes.
Vortrag auf der 3. Hamburger geophysikalischen Tagung, 28. 8. 1952. 相似文献
877.
The impact of realistic representation of sea surface temperature (SST) on the numerical simulation of track and intensity
of tropical cyclones formed over the north Indian Ocean is studied using the Weather Research and Forecast (WRF) model. We
have selected two intense tropical cyclones formed over the Bay of Bengal for studying the SST impact. Two different sets
of SSTs were used in this study: one from TRMM Microwave Imager (TMI) satellite and other is the weekly averaged Reynold’s
SST analysis from National Center for Environmental Prediction (NCEP). WRF simulations were conducted using the Reynold’s
and TMI SST as model boundary condition for the two cyclone cases selected. The TMI SST which has a better temporal and spatial
resolution showed sharper gradient when compared to the Reynold’s SST. The use of TMI SST improved the WRF cyclone intensity
prediction when compared to that using Reynold’s SST for both the cases studied. The improvements in intensity were mainly
due to the improved prediction of surface latent and sensible heat fluxes. The use of TMI SST in place of Reynold’s SST improved
cyclone track prediction for Orissa super cyclone but slightly degraded track prediction for cyclone Mala. The present modeling
study supports the well established notion that the horizontal SST gradient is one of the major driving forces for the intensification
and movement of tropical cyclones over the Indian Ocean. 相似文献
878.
The samples for microscopic study are all collected from the Hsitsocoal field situated about 50 li northwest of the Tzuhsieh city and 40 li east ofthe Matouchen station of Pinghan Railway.In order to understand the 相似文献
879.
Mr.T.F.Hou,geologist of the National Geological Survey of Chinabrought back in 1931 from Liaoning province,a specimen of subbituminous coalin which are included patches or aggregates of small oolites.This interestingspecimen was given to the writer for microscopical investigation.Both polished 相似文献
880.
Opinions often differ among coal petrographers as to the relative ad-vantages of the thin sections and the polished sections.In reality both of themare useful and they should be used simultaneously in order to get a clear and 相似文献