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721.
The magnetic fields of a sample of chemically peculiar stars, in which they had not been detected earlier, are reinvestigated on the basis of our own measurements and literature data. Despite the considerably higher measurement accuracy, again no magnetic fields were detected in any of them. An upper limit on the field of HD 10221 of 40 G was obtained. Despite the weakness of the fields, the parameters characterizing an anomaly in chemical composition correspond to those for strong fields. The same parameters in stars with strong fields generally correspond in value, although they are lower than expected in the case of HD 47152. 相似文献
722.
Coronal Magnetic Flux Rope Equilibria and Magnetic Helicity 总被引:1,自引:0,他引:1
1 INTRODUCTIONObservations show that the magnetic helicity of solar magnetic structures has a predominantsign in each hemisphere of the Sun, positive in the southern hemisphere and negative in thenorthern, regardless of the solar cycle (Rust, 1994). The magnetic helicity is strictly conservedin the frame of ideal MHD (WOltjer, 1958), and approximately conserved in the presence ofresistive dissipation and magnetic reconnection in a highly conductive plajsma (Taylor, 1974;Berger, 1984; H… 相似文献
723.
724.
725.
James H. Shirley 《Monthly notices of the Royal Astronomical Society》2006,368(1):280-282
The orbital motion of the Sun has been linked with solar variability, but the underlying physics remains unknown. A coupling of the solar axial rotation and the barycentric orbital revolution might account for the relationships found. Some recent published studies addressing the physics of this problem have made use of equations from rotational physics in order to model particle motions. However, our standard equations for rotational velocity do not accurately describe particle motions due to orbital revolution. The Sun's orbital motion is a state of free fall; in consequence, aside from very small tidal motions, the associated particle velocities do not vary as a function of position on or within the body of the Sun. In this note, I describe and illustrate the fundamental difference between particle motions in rotation and revolution, in order to dispel some part of the confusion that has arisen in the past and that which may yet arise in the future. This discussion highlights the principal physical difficulty that must be addressed and overcome by future dynamical spin–orbit coupling hypotheses. 相似文献
726.
727.
Denise C. Gabuzda Elizaveta A. Rastorgueva Paul S. Smith Shane P. O'Sullivan 《Monthly notices of the Royal Astronomical Society》2006,369(4):1596-1602
We investigate the relationship between the optical and radio emission of active galactic nuclei (AGN) by analysing optical and 15+22+43 GHz Very Long Baseline Array (VLBA) polarization observations simultaneous to within a day for 11 BL Lacertae (BL Lac) objects and the blazar 3C279. We have determined and corrected for the Faraday rotation measures in the very long baseline interferometry (VLBI) cores, enabling us to compare the intrinsic (zero-wavelength) VLBI-core polarization angles and the optical polarization angles χopt . A clear alignment between these two angles emerges in the transition toward higher radio frequencies, and a prominent peak at 0° is visible in the distribution of |χopt −χ43 GHz |. This correlation implies that the magnetic-field orientations in the regions giving rise to the optical and radio polarization are the same, and can be easily understood if the radio and optical polarization are roughly cospatial. It is difficult to rule out the possibility that they arise in different regions in a straight jet with a uniform magnetic-field structure, but this seems less likely, since the VLBI jets of AGN are often bent on parsec-scales. This may suggest that much or all of the strong optical polarization in these sources arises in the inner radio jets, possibly associated with the formation and emergence of compact new VLBI components. 相似文献
728.
Y. Soobiah A.J. Coates D.O. Kataria R.A. Frahm J.R. Scherrer R. Lundin H. Andersson A. Grigoriev H. Koskinen T. Säles W. Schmidt J. Luhmann D. Williams C.C. Curtis B.R. Sandel M. Carter A. Fedorov S. McKenna-Lawler R. Cerulli-Irelli P. Wurz N. Krupp M. Fränz C. Dierker 《Icarus》2006,182(2):396-405
Mars Express (MEX) Analyser of Space Plasmas and Energetic Atoms (ASPERA-3) data is providing insights into atmospheric loss on Mars via the solar wind interaction. This process is influenced by both the interplanetary magnetic field (IMF) in the solar wind and by the magnetic ‘anomaly’ regions of the martian crust. We analyse observations from the ASPERA-3 Electron Spectrometer near to such crustal anomalies. We find that the electrons near remanent magnetic fields either increase in flux to form intensified signatures or significantly reduce in flux to form plasma voids. We suggest that cusps intervening neighbouring magnetic anomalies may provide a location for enhanced escape of planetary plasma. Initial statistical analysis shows that intensified signatures are mainly a dayside phenomenon whereas voids are a feature of the night hemisphere. 相似文献
729.
The star HD220825 is studied as part of a program to investigate the chemical abundance of CP stars with weak magnetic fields.
Its magnetic field is found to be Be < 100 G. The chemical abundance appears to correspond to that of CP stars with high magnetic
fields. The present results and other data imply that the magnetic field has little effect on the degree of anomaly in the
chemical abundance, although it undoubtedly has an effect. The rotation speed of the star is 37.5 km/s, substantially lower
than for normal stars with the same temperature. The weak magnetic field raises difficulties for the hypothesis that the loss
of angular momentum involves the magnetic field.
__________
Translated from Astrofizika, Vol. 49, No. 4, pp. 585–594 (November 2006). 相似文献
730.
We use the mapping-phase high-altitude magnetic measurements provided by Mars Global Surveyor (MGS) between March 1999 and April 2003 to model nine relatively isolated magnetic anomalies of Mars. Each anomaly is modeled with an elliptical prism. Each component of the observed magnetic field is modeled independently using an elliptical prism in order to assess the reliability of the results and suppress non-crustal and nearby crustal source contaminations. The paleomagnetic pole positions are obtained from the magnetization vectors of the model source bodies. We clean the data by removing the bad tracks and then divide the entire data into two sets that are measured at different times. Applying covariance analysis in the Fourier domain to two maps of the same magnetic component that are derived from the two sets provides a means to extract the most common features of the maps. The quality of a model is evaluated and only good models are used in the final geophysical interpretation. Most poles that come from good models cluster in the Tharsis region, suggesting that Mars experienced polar motion since the magnetic source bodies were magnetized. 相似文献