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651.
652.
This letter presents some night-time observations of neutral wind variations at F2 layer levels near the dip equator, measured by the Fabry-Perot interferometer set up in 1994 at Korhogo (Ivory Coast, geographic latitude 9.25°N, longitude 355°E, dip latitude -2.5°). Our instrument uses the 630 nm (O1D) line to determine radial Doppler velocities of the oxygen atoms between 200 and 400 km altitude. First results for November 1994 to March 1995 reveal persistent eastward flows, and frequent intervals of southward winds of larger than 50 ms–1 velocity. Compared with the simultaneous ionospheric patterns deduced from the three West African equatorial ionosondes at Korhogo, Ouagadougou (Burkina-Faso, dip latitude +1.5°) and Dakar (Sénégal, dip latitude + 5°), they illustrate various impacts of the thermospheric winds on F2 layer density: (1) on the mesoscale evolution (a few 103 km and a few 100 minutes scales) and (2) on local fluctuations (hundreds of km and tens of minutes characteristic times). We report on these fluctuations and discuss the opportunity to improve the time-resolution of the Fabry-Perot interferometer at Korhogo. 相似文献
653.
A. V. Pavlov 《Annales Geophysicae》1998,16(2):176-182
In this paper we present the results of a study of the electron cooling rate, the production rates of vibrationally excited N2(v), and the production frequency of the N2 vibrational quanta arising from the collisions of electrons with unexcited N2(0) and vibrationally excited N2(1) molecules as functions of the electron temperature. The electron energy transfer rates for vibrational excitation of N2 have been calculated and fit to analytical expressions by use of the revised vibrationally excited N2 cross sections. These new analytical expressions are available to the researcher for quick reference and accurate computer modeling with a minimum of calculations. 相似文献
654.
J. Bremer 《Annales Geophysicae》1998,16(8):986-996
Continuous observations in the ionospheric E and F regions have been regularly carried out since the fifties of this century at many ionosonde stations. Using these data from 31 European stations long-term trends have been derived for different parameters of the ionospheric E layer (h E, foE), F1 layer (foF1) and F2 layer (hmF2,foF2). The detected trends in the E and F1 layers (lowering of the E region height hE; increase of the peak electron densities of the E and F1 layers, foE and foF1) are in qualitative agreement with model predictions of an increasing atmospheric greenhouse effect. In the F2 region, however, the results are more complex. Whereas in the European region west of 30° E negative trends in hmF2 (peak height of the F2 layer) and in the peak electron density (foF2) have been found, in the eastern part of Europe (east of 30° E) positive trends dominate in both parameters. These marked longitudinal differences cannot be explained by an increasing greenhouse effect only, here probably dynamical effects in the F2 layer seem to play an essential role. 相似文献
655.
Ice crystal clouds have an influence on the radiative budget of the earth; however, the exact size and nature of this influence has yet to be determined. A laboratory cloud chamber experiment has been set up to provide data on the optical scattering behaviour of ice crystals at a visible wavelength in order to gain information which can be used in climate models concerning the radiative characteristics of cirrus clouds. A PMS grey-scale probe is used to monitor simultaneously the cloud microphysical properties in order to correlate these closely with the observed radiative properties. Preliminary results show that ice crystals scatter considerably more at 90° than do water droplets, and that the halo effects are visible in a laboratorygenerated cloud when the ice crystal concentration is sufficiently small to prevent masking from multiple scattering. 相似文献
656.
G. I. Pugacheva W. N. Spjeldvik A. A. Gusev I. M. Martin N. M. Sobolevsky 《Annales Geophysicae》1998,16(8):931-939
Radial transport theory for inner radiation zone MeV ions has been extended by combining radial diffusive transport and losses due to Coulomb friction with local generation of D, T and 3He ions from nuclear reactions taking place on the inner edge of the inner radiation zone. Based on interactions between high energy trapped protons and upper atmospheric constituents we have included a nuclear reaction yield D, T and 3He flux source that was numerically derived from a nuclear reaction model code originally developed at the Institute of Nuclear Researches in Moscow, Russia. Magnetospheric transport computations have been made covering the L-shell range L=1.0–1.6. The resulting MeV energy D, T and 3He ion flux distributions show a strong influence of the local nuclear source mechanism on the inner zone energetic D, T and 3He ion content. 相似文献
657.
Some Basic Properties of the Surrogate Subgrid-Scale Heat Flux in the Atmospheric Boundary Layer 总被引:3,自引:3,他引:0
Fernando Porté-Agel Charles Meneveau Marc B. Parlange 《Boundary-Layer Meteorology》1998,88(3):425-444
The development of improved subgrid-scale (SGS) models for large-eddy simulation of scalar transport in the atmospheric boundary layer requires an improved understanding of basic properties of the SGS fluxes. High frequency atmospheric wind speed and temperature data sampled at a height of 1.7 m are used to measure SGS heat fluxes and dissipation of temperature variance, by means of one-dimensional filtering and invoking Taylor's hypothesis. Conditional averaging is used to isolate interesting features of the SGS signals, and to relate them to the large-scale characteristics of the flow, such as the presence of coherent structures. Both mean and conditionally averaged SGS quantities are compared with those obtained using a standard eddy-diffusivity model. Within the limitations imposed by the one-dimensional data analysis, we observe that the model appears unable to reproduce important features of the real signals, such as the negative dissipation of temperature variance associated with strong negative resolved temperature gradients due to the ejection of warm air under unstable atmospheric stability conditions. 相似文献
658.
Daily mean values of the Priestley-Taylor coefficient, ¯, are derived from a simple model of the daily growth of a convective boundary layer. For a particular control set of driving environmental variables, ¯ is related to the prescribed bulk surface resistance, rS by 1/¯ = 1/0 + mrS for parameters 0 and m. The dependence of the parameters 0 and m on weather is explored and a potential use of this linear relation to provide information about regional values of rS is indicated. 相似文献
659.
Aircraft measurements of potential temperature and turbulent kinetic energy are used to examine the growth of the thermal internal boundary layer (TIBL) in sea-breeze flows on four selected days of a coastal fumigation study performed in 1995 at Kwinana in Western Australia. The aircraft data, together with radiosonde measurements taken on the same days, show a multi-layered low-level onshore flow in the vertical with a superadiabatic layer extending to about 50 m above the water surface on all four days. On the first three days the layer above the superadiabatic layer was neutral, typically 200 m deep, capped by a stably stratified region, whereas on the remaining day it was fully stable. The occurrence of the neutral layer on most experimental days contrasts with the more usual situation involving an entirely stable onshore flow. A composite approach based on both temperature and turbulence data is used to provide a pragmatic but self-consistent definition of the TIBL height. The data for the first three days indicate that the TIBL grows rapidly into the neutrally stratified region to the top of the region within about 2 km from the coast, with a very slow subsequent growth into the stable stratification aloft. On the other hand, the TIBL grows only to about 200 m within a distance of 7 km from the coast on the fourth day due to a strong stable stratification.An existing numerical TIBL model based on the slab approach, capable of describing the TIBL growth in both neutral and stable environments, and a recent analytical model, more efficient for operational use, are used to simulate the aircraft TIBL observations. The predictions by both models agree reasonably well with the data. 相似文献
660.