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311.
Noriyuki Kawasaki Daiki Yamamoto Sohei Wada Changkun Park Hwayoung Kim Naoya Sakamoto Hisayoshi Yurimoto 《Meteoritics & planetary science》2024,59(4):630-639
Al–Mg mineral isochron studies using secondary ion mass spectrometry (SIMS) have revealed the initial 26Al/27Al ratios, (26Al/27Al)0, for individual Ca-Al-rich inclusions (CAIs) in meteorites. We find that the relative sensitivity factors of 27Al/24Mg ratio for SIMS analysis of hibonite, one of the major constituent minerals of CAIs, exhibit variations based on their chemical compositions. This underscores the critical need for using appropriate hibonite standards to obtain accurate Al−Mg data. We measured the Al−Mg mineral isochron for hibonite in a fine-grained CAI (FGI) from the Northwest Africa 8613 reduced CV chondrite by SIMS using synthesized hibonite standards with 27Al/24Mg of ~30, ~100, and ~400. The obtained mineral isochron of hibonite in the FGI yields (26Al/27Al)0 of (4.73 ± 0.09) × 10−5, which is identical to that previously obtained from the mineral isochron of spinel and melilite in the same FGI (Kawasaki et al., 2020). The uncertainties of (26Al/27Al)0 indicate that the constituent minerals in the FGI formed within ~0.02 Myr in the earliest solar system. The disequilibrium O-isotope distributions of the minerals in the FGI suggest that the O-isotope compositions of the nebular gas from which they condensed underwent a transitional change from 16O-rich to 16O-poor within ~0.02 Myr in the earliest solar system. Once formed, the FGI may have been removed from the forming region within ~0.02 Myr and transported to the accretion region of the parent body. 相似文献
312.
The L1-SAIF (L1 Submeter-class Augmentation with Integrity Function) signal is one of the Quasi-Zenith Satellite System (QZSS)
navigation signals, which provides an augmentation function for mobile users in Japan. The tropospheric delay correction in
the L1-SAIF augmentation is discussed in detail. Because the topographical features in Japan are complicated, the correction
information is generated from GPS observation data collected at 200 GPS stations which are densely distributed over Japan.
A total of 210 Tropospheric Grid Points (TGPs) are arranged to fully cover Japan. The TGPs that provide the correction information
are selected adaptively to achieve the expected correction accuracy. This selection of TGPs is provided by the TGP mask message.
Mobile users acquire the zenith tropospheric delay (ZTD) value at neighboring TGPs from the correction messages, and can estimate
the local ZTD value accurately by using a suitable ZTD model. Only up to seven L1-SAIF messages are sufficient to provide
the full correction information. Accuracy evaluations have proven that it is possible to achieve a correction accuracy of
13.4 mm RMS. The strategy presented here has been implemented into the augmentation system using the L1-SAIF signal, and its
application guidance is presented in the QZSS interface specification. 相似文献
313.
Microalgal-based indicators were used to assess terrestrial influence on Shiraho coral reef of Ishigaki Island (Okinawa, Japan). A typhoon occurred on 4-5 August 2005 and sampling were made on three occasions thereafter (6, 8, and 11 August). Pre-typhoon sampling was conducted on 26 July. The typhoon-enhanced terrestrial discharges increased reef nutrient levels (e.g. average NO(3)(-)-N: 0.088mg/L pre-typhoon to 0.817mg/L post-typhoon). This elevated chlorophyll-a concentrations by four times and shifted phytoplankton composition (spectral class-based) from an initial dominance of diatoms and green microalgae to the dominance of bluegreen microalgae (cyanobacteria) and cryptophytes. Cyanobacteria later increased by more than 200% and accounted for as much as 80% of total chl-a ( approximately 0.29microg/L), possibly assisted by favorable nutrient availability. In outer reef waters, diatoms and green microalgae predominated whereas cyanobacteria and cryptophytes were nearly undetectable. Due to detrital decomposition and river discharge, the CDOM was much higher in the inner reef than in the outer reef. Benthic bluegreen microalgae were relatively more abundant in areas close to the river mouth and coastal agricultural fields. At these locations, nutrient concentrations were much higher due to river discharge and potentially significant groundwater discharge. Thus, phytoplankton and benthic microalgae can serve as indicators of terrestrial influence on coral reefs. 相似文献
314.
Mutsuo Inoue Yusuke Nakano Yoko Kiyomoto Hisaki Kofuji Yasunori Hamajima Masayoshi Yamamoto 《Journal of Oceanography》2010,66(3):425-428
A total of 21 surface water samples were collected on the east side of the East China Sea (ECS) (3 sites) and at the Tsushima
Strait (1 site), and 226Ra and 228Ra activities were measured using low-background γ-spectrometry. The 228Ra/226Ra ratios among the samples exhibited notable seasonal variation (228Ra/226Ra = 0.2–2.6) accompanying changes of salinity (31.7–34.7). Seasonal water circulation within the ECS is hypothesized to cause
the change by altering the mixing ratio of 228Ra-rich continental shelf water and 228Ra-poor Kuroshio water. 相似文献
315.
Biomass and primary productivity of benthic microalgae (BMA) and planktonic algae in Suo Nada, the western part of the Seto
Inland Sea, Japan were compared in terms of unit area with regard to their seasonal and spatial distribution in 2002. Judging
from light compensation depth and water depth, the southwestern part of Suo Nada was considered to be a potential habitat
for BMA. Whereas the contribution of sedimented planktonic algae was high in biomass at the sediment surface, BMA was obviously
significant both in biomass and primary production in the shallow southwestern part. However, the contribution of BMA to the
total biomass in the entire water column was 7% in winter and 2% in summer. The primary production of BMA varied between 4.0
and 74.0 mg C m−2 d−1 in the southwestern part, accounting for 2–12% of the whole water column primary production. The ecological roles of BMA
in the Suo Nada ecosystem are discussed, such as reduction of benthic nutrient flux, oxidation of surface sediments and feed
for higher animals. 相似文献