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141.
Jacqueline H. Carrillo Scott E. Emert D. Eli Sherman Pierre Herckes Jeffrey L. Collett Jr. 《Atmospheric Research》2008,87(3-4):259
A new, relatively low cost instrument has been developed to detect the presence of fog or cloud for fog/cloud sampling applications. The instrument uses attenuation of an 880 nm light emitting diode signal to detect cloud/fog drops in the optical path between a sending and receiving arm. Laboratory and field testing under a variety of conditions and fog types were carried out to determine the ability of the optical fog detector (OFD) to accurately detect cloud/fog presence as well as to provide some measure of liquid water content. Results indicated that the OFD provided a reliable estimate of fog presence as well as a reasonable estimate of liquid water content (LWC) under several different conditions. The OFD does appear to have an interference from rain, resulting in an overestimation of LWC during rainfall. This may occasionally give a false positive indication of fog presence. 相似文献
142.
This paper summarises the development and principal results of fifty years of research on aerosols in the marine atmosphere at Mace Head Atmospheric Research Station on the west coast of Ireland. It concentrates on the sources, physico-chemical properties, number and mass concentrations, size range, volatility and chemical composition of aerosols in different air masses. It also examines optical properties of the aerosols and their long-range transport. 相似文献
143.
144.
Timothy J. Stubbs David A. Glenar Anthony Colaprete Denis T. Richard 《Planetary and Space Science》2010,58(5):830-1934
The Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft will orbit the Moon at an altitude of ≈50 km with a payload that includes the Ultraviolet Spectrometer (UVS) instrument, which will obtain high spectral resolution measurements at near-ultraviolet and visible wavelengths (≈231-826 nm). When LADEE/UVS observes the lunar limb from within the shadow of the Moon it is anticipated that it will detect a lunar horizon glow (LHG) due to sunlight scattered from submicron exospheric dust, as well as emission lines from exospheric gases (particularly sodium), in the presence of the bright coronal and zodiacal light (CZL) background. A modularized code has been developed at NMSU for simulations of scattered light sources as observed by orbiting instruments in lunar shadow. Predictions for the LADEE UVS and star tracker cameras indicate that LHG, sodium (Na) emission lines, and CZL can be distinguished based on spatial morphology and spectral characteristics, with LHG dominant at blue wavelengths (∼250-450 nm) and small tangent heights. If present, LHG should be readily detected by LADEE/UVS and distinguishable from other sources of optical scattering. Observations from UVS and the other instruments aboard LADEE will significantly advance our understanding of how the Moon interacts with the surrounding space environment; these new insights will be applicable to the many other airless bodies in the solar system. 相似文献
145.
Fifteen samples of (Mg,Fe)SiO3 majorite with varying Fe/Mg composition and one sample of (Mg,Fe)(Si,Al)O3 majorite were synthesized at high pressure and temperature under different conditions of oxygen fugacity using a multianvil press, and examined ex situ using X-ray diffraction and Mössbauer and optical absorption spectroscopy. The relative concentration of Fe3+ increases both with total iron content and increasing oxygen fugacity, but not with Al concentration. Optical absorption spectra indicate the presence of Fe2+–Fe3+ charge transfer, where band intensity increases with increasing Fe3+ concentration. Mössbauer data were used in conjunction with electron microprobe analyses to determine the site distribution of all cations. Both Al and Fe3+ substitute on the octahedral site, and charge balance occurs through the removal of Si. The degree of Mg/Si ordering on the octahedral sites in (Mg,Fe)SiO3 majorite, which affects both the c/a ratio and the unit cell volume, is influenced by the thermal history of the sample. The Fe3+ concentration of (Mg,Fe)(Si,Al)O3 majorite in the mantle will reflect prevailing redox conditions, which are believed to be relatively reducing in the transition zone. Exchange of material across the transition boundary to (Mg,Fe) (Si,Al)O3 perovskite would then require a mechanism to oxidize sufficient iron to satisfy crystal-chemical requirements of the lower-mantle perovskite phase. 相似文献
146.
Geochemical characterization, correlation, and optical dating of tephra in alluvial sequences of central western Argentina 总被引:1,自引:0,他引:1
The synthesis of paleoclimatic archives provided by loess and alluvial sequences of central Argentina has been hindered by the lack of a cohesive lithostratigraphic framework extending across the Chaco-Pampean plains and catchments of the Rios Desaguadero, Colorado, and Negro. This condition originates in part from the dearth of absolute chronological controls. The occurrence of discrete tephra layers across this region may provide an opportunity to address this deficiency if a tephrochronological framework can be established. The potential of such a project is assessed within the context of a pilot study constrained within alluvial sequences of central western Argentina proximal to potential source vents in the Southern Volcanic Zone. The intersite discrimination and correlation of tephra layers on a geochemical basis is examined, with indirect chronological control for the eruption of each generated by optical dating. Alluvial sediments on either side of each of five tephra units at a type site were dated using the optically stimulated luminescence of fine-silt-sized quartz, thus providing an age control on each tephra (ca. 24,000, 30,000, 32,000, 39,000, and 48,000 yr). The geochemical composition of each tephra was derived. Using these data, tephra layers at other sites in the study area were geochemically analyzed and, in instances of statistical concordance in major oxide structure, correlated to the type site and therefore ascribed ages. This methodology identified a further sixth volcanic event between ca. 24,000 and 30,000 yr not registered by type-site tephras. The extension of this initial tephrochronological framework beyond the alluvial sequences of central western Argentina is encouraged by the occurrence of geochemically distinct tephra verified and dated in this study. 相似文献
147.
本文扼要介绍了PMOE行星历表研究当前的进展和工作 ,给出了PMOE2 0 0 2与DE40 5历表的比较。 相似文献
148.
V. P. Solntsev E. G. Tsvetkov A. I. Alimpiev R. I. Mashkovtsev 《Physics and Chemistry of Minerals》2006,33(5):300-313
We have studied the polarized optical absorption and the EPR spectra of Ni-doped beryls grown by hydrothermal, flux and gas-transport methods, and chrysoberyl grown by the Czochralski and flux methods. In beryls, three groups of bands belonging to three various Ni centres were distinguished by analysis of the absorption band intensities. The first group, bands with maximums at 21740 (E ⊥ c), 17240 (E || c) and 9260 (E ⊥ + || c), 7140 (E || + ⊥ c) cm−1, are due to Ni3+ in octahedral Al3+ site. The second group is bands at 25640 (E ⊥ c), 22220 (E || c) and 13520 (E || + ⊥ c), 13160 (E ⊥+ || c) cm−1 and 8930 (E ⊥ + || c), 7460 (E || c) cm−1, which are caused by Ni2+ in octahedral Al3+ site. Weak wide bands at 17540 (E ⊥ c), 15500 (E || c) cm−1 and 6580 (E || + ⊥ c), 5950 (E || c) cm−1 are related to Ni2+ in tetrahedral Be2+ site. The occurrence of Ni ions in Be2+ site is proved by the EPR spectra of 1VNi+ in γ-irradiated samples. According to the spectra of optical absorption of Ni-doped chrysoberyl, two types of Ni centres have been established: Ni3+ and Ni2+ ions in octahedral Al3+ sites. From the EPR spectra of the X-ray irradiated crystals BeAl2O4: Ni, it follows that 68% of Ni+ ions occupy octahedral Al3+ sites with mirror symmetry and 32% are in Al3+ sites with inversion symmetry. In the approximation of trigonal field with regard to Trees correction, the energy levels of Ni3+ and Ni2+ have been calculated in octahedral and tetrahedral coordination. There is good agreement between the obtained experimental and calculated data. The polarization dependence of the optical absorption bands is well explained in terms of the spin–orbit interaction. 相似文献
149.
Ionospheric conductivity is not very easily measured directly. Incoherent scatter radars perhaps offer the best method but can only measure at one point in the sky at any one time and are limited in their time resolution. Statistical models of average conductivity are available but these may not be applied to individual case studies such as substorms. There are many instances where a real-time estimate of ionospheric conductivity over a large field-of-view is highly desirable at a high temporal and spatial resolution. We show that it is possible to make a reasonable estimate of the noctural height-integrated Pedersen conductivity, or conductance, with a single all-sky TV camera operating at 557.7 nm. This is not so in the case of the Hall conductance where at least two auroral wavelengths should be imaged in order to estimate additionally the energy of the precipitating particles. 相似文献
150.
The MEMO (MEsure Multicomposante des Ondes) experiment is a part of theINTERBALL 2 wave consortium. It is connected to a total of six electric and nine magnetic independent sensors. It provides waveforms associated with the measurement of two to five components in three frequency bands: ELF (5–1000 Hz), VLF (1–20 kHz), LF (20–250 kHz). Preliminary analyses of low and high resolution data are presented. The emphasis is put on the estimation of the propagation characteristics of the observed waves. VLF hiss emissions are shown to be mainly whistler mode emissions, but other modes are present. An accurate estimation of the local plasma frequency is proposed when the low L = 0 cutoff frequency is identified. AKR emissions observed just above source regions are studied. R-X and L-O modes are found: the first at the lowest frequencies and the second at the highest. Both propagate with wave normal directions weakly oblique or quasi-parallel to the Earths magnetic field direction. Propagation characteristics are also determined for a (non-drifting) fine structure of AKR. There is no fundamental difference with structurless events. Night-side and dayside bursts of ELF electromagnetic emissions are presented. It is not clear whether the two emissions belong to the lion roar emissions or not. 相似文献