全文获取类型
收费全文 | 511篇 |
免费 | 9篇 |
国内免费 | 16篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 30篇 |
地球物理 | 124篇 |
地质学 | 146篇 |
海洋学 | 88篇 |
天文学 | 109篇 |
综合类 | 6篇 |
自然地理 | 30篇 |
出版年
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 17篇 |
2018年 | 10篇 |
2017年 | 15篇 |
2016年 | 16篇 |
2015年 | 14篇 |
2014年 | 19篇 |
2013年 | 24篇 |
2012年 | 11篇 |
2011年 | 22篇 |
2010年 | 25篇 |
2009年 | 22篇 |
2008年 | 32篇 |
2007年 | 35篇 |
2006年 | 21篇 |
2005年 | 18篇 |
2004年 | 24篇 |
2003年 | 14篇 |
2002年 | 19篇 |
2001年 | 14篇 |
2000年 | 8篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 8篇 |
1996年 | 10篇 |
1995年 | 12篇 |
1994年 | 3篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1983年 | 9篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1973年 | 8篇 |
1972年 | 4篇 |
1971年 | 3篇 |
1969年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有536条查询结果,搜索用时 15 毫秒
531.
A Late Holocene geomagnetic secular variation record from Erhai Lake, southwest China 总被引:1,自引:0,他引:1
Masayuki Hyodo Arata Yoshihara Kenji Kashiwaya Takashi Okimura Toshiyuki Masuzawa Ryotaro Nomura Shingo Tanaka Tang Bang Xing Liu Su Qing & Liu Shi Jian 《Geophysical Journal International》1999,136(3):784-790
A secular variation record of the geomagnetic field direction for the last 6.5 kyr has been obtained from the magnetization of sediment cores from Erhai Lake, southwest China. In order to make a comparison with this record, secular variation in east-central China was investigated by combining available magnetic field data from historical records and archaeomagnetic measurements since about 350 bc . The secular variation in Erhai Lake shows features consistent with the combined record, except for the oldest three observed declination swings in Sian from 720 to 900 ad . Many features of declination and inclination in China also occur in Japan. From 500 to 1000 ad , declination was westerly ranging from about −20° to −5° in Erhai Lake, east-central China, and Japan. 相似文献
532.
A global data set describing the gridded mixed-layer depth (MLD) in 10-day intervals was produced using high-quality Argo
float data from 2001 to 2009. The characteristics and advantages provided by the new MLD data set are described here, including
a comparison based on two different thresholds and using data sets of different vertical and temporal resolution. The MLD
in the data set was estimated on the basis of a shallower depth of the iso-thermal layer (TLD) or iso-pycnal layer (PLD),
calculated using the finite difference method. The MLD data are incorporated into 2° × 2° grid in the global ocean, including
marginal seas. Also, two threshold values were used to examine differences in the MLD and its seasonal temporal variability.
The characteristics and advantages of using the Argo 10-day intervals to determine the MLD were then confirmed by comparing
those data with the station buoy daily means and the Argo monthly means. With respect to vertical and temporal resolutions,
the Argo 10-day data has two distinct advantages: (1) improved representation of the MLD vertical change due to high vertical
resolution, especially during periods of large MLD variability and (2) more detailed representation of the temporal change
in MLD than achieved with the Argo monthly mean data, especially from winter to spring in mid and high latitudes. These advantages
were maintained in the case of a larger threshold despite the fact that the MLD is rather deep and the detailed variation
in its distribution differs depending on the season and location. This study also investigated the relative influence of TLD
and PLD to the MLD calculation for each grid. Generally, the MLD is primarily determined based on the PLD at low and mid latitudes
(TLD > PLD), whereas the TLD is more important at high latitudes, especially in winter (TLD < PLD). In the case of a larger
threshold, the area of the larger PLD influence spreads polewards because of the greater effect of salinity in winter. Although
there are some differences in the effect of temperature and salinity in estimations of the MLD, both are indispensable factors
for the MLD estimations even at different thresholds. 相似文献
533.
This paper presents an investigation of the roughness effects in the turbulent boundary layer for asymmetric waves by using the baseline (BSL) k–ω model. This model is validated by a set of the experimental data with different wave non-linearity index, Ni (namely, Ni = 0.67, Ni = 0.60 and Ni = 0.58). It is further used to simulate asymmetric wave velocity flows with several values of the roughness parameter (am/ks) which increase gradually, namely from am/ks = 35 to am/ks = 963. The effect of the roughness tends to increase the turbulent kinetic energy and to decrease the mean velocity distribution in the inner boundary layer, whereas in the outer boundary layer, the roughness alters the turbulent kinetic energy and the mean velocity distribution is relatively unaffected. A new simple calculation method of bottom shear stress based on incorporating velocity and acceleration terms is proposed and applied into the calculation of the rate of bed-load transport induced by asymmetric waves. And further, the effect of bed roughness on the bottom shear stress and bed-load sediment transport under asymmetric waves is examined with the turbulent model, the newly proposed method, and the existing calculation method. It is found that the higher roughness elements increase the magnitude of bottom shear stress along a wave cycle and consequently, the potential net sediment transport rate. Moreover, the wave non-linearity also shows a big impact on the bottom shear stress and the net sediment transport. 相似文献
534.
Nakajima H. Shimada Y. Somekawa T. Fujita M. Tanaka K.A. 《Geoscience and Remote Sensing Letters, IEEE》2009,6(4):718-722
Conventional ground-penetrating radar (GPR) requires large-aperture antennas or long-span measurements to survey a remote location precisely. We propose a laser-driven GPR (LGPR) as a new detection method. LGPR uses microwaves from laser-produced plasmas as remote transmitters and can survey a remote location using a compact instrument. We performed numerical simulations to investigate the radiation mechanism of microwaves from laser plasmas and confirmed the pulsewidth of the laser suitable for LGPR. Experiments with subnanosecond pulse lasers clarified the feasibility and detection performance of LGPR. 相似文献
535.
Shigeyoshi Otosaka Takayuki Tanaka Orihiko Togawa Hikaru Amano Eugeny V. Karasev Masayuki Minakawa Shinichiro Noriki 《Journal of Oceanography》2008,64(6):911-923
Seasonal and spatial variations of particulate organic carbon (POC) flux were observed with sediment traps at three sites
in the Japan Sea (western and eastern Japan Basin and Yamato Basin). In order to investigate the transport processes of POC,
radiocarbon (14C) measurements were also carried out. Annual mean POC flux at 1 km depth was 30.7 mg m−2day−1 in the western Japan Basin, 12.0 mg m−2day−1 in the eastern Japan Basin and 23.8 mg m−2day−1 in the Yamato Basin. At all stations, notably higher POC flux was observed in spring (March–May), indicating biological production
and rapid sinking of POC in this season. Sinking POC in the high flux season showed modern Δ14C values (>0‰) and aged POC (Δ14C < −40‰) was observed in winter (December–January). The Δ14C values in sinking POC were negatively correlated with aluminum concentration, indicating that Δ14C is strongly related to the lateral supply of lithogenic materials. The Δ14C values also showed correlations with excess manganese (Mnxs) concentrations in sinking particles. The Δ14C-Mnxs relationship suggested that (1) the majority of the aged POC was advected by bottom currents and incorporated into sinking
particles, and (2) some of the aged POC might be supplied from the sea surface at the trap site as part of terrestrial POC.
From the difference in the Δ14C-Mnxs relationships between the Japan Basin and the Yamato Basin, we consider that basin-scale transport processes of POC occur
in the Japan Sea. 相似文献
536.
Yu Mizuno Jun Nishioka Takahiro Tanaka Yuya Tada Koji Suzuki Yuta Tsuzuki Atsuko Sugimoto Youhei Yamashita 《Journal of Oceanography》2018,74(5):509-521
Coastal Oyashio Water (COW), defined as a water mass with a temperature lower than 2 °C and a salinity lower than 33.0, is distributed in the North Pacific Ocean off southeastern Hokkaido, Japan, from winter to spring. COW is rich in macronutrients and dissolved iron and is thus considered to affect the spring phytoplankton blooms in the Oyashio region. Although river water and sea-ice melt water have been considered freshwater end-members of COW, the contributions of these freshwater sources to COW have not been well described. In this study, the humic-like components in dissolved organic matter were first applied as a parameter to evaluate the freshwater end-members of COW in March 2015. Linear regressions with negative slopes were determined between the humic-like components and the salinity of COW. The intercepts of the regressions against the humic-like components were within the ranges of those observed for the local rivers of Hokkaido but were very different from those of sea ice. These findings suggest that river water contributed to the COW observed here as a freshwater end-member, although the contribution of sea-ice melt water to COW could not be evaluated. This novel approach also highlighted two different less-saline water masses in COW. The first was characterized by a lower temperature and relatively high levels of humic-like components, while the second was higher in temperature and had higher levels of humic-like components. It is suggested that these different characteristics are due to the contributions of water from different rivers and/or different effects of sea-ice melt water. 相似文献