全文获取类型
收费全文 | 284篇 |
免费 | 7篇 |
国内免费 | 11篇 |
专业分类
大气科学 | 10篇 |
地球物理 | 53篇 |
地质学 | 37篇 |
海洋学 | 123篇 |
天文学 | 68篇 |
综合类 | 2篇 |
自然地理 | 9篇 |
出版年
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 11篇 |
2014年 | 7篇 |
2013年 | 8篇 |
2012年 | 3篇 |
2011年 | 10篇 |
2010年 | 11篇 |
2009年 | 10篇 |
2008年 | 10篇 |
2007年 | 11篇 |
2006年 | 6篇 |
2005年 | 19篇 |
2004年 | 14篇 |
2003年 | 12篇 |
2002年 | 6篇 |
2001年 | 9篇 |
2000年 | 11篇 |
1999年 | 11篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 7篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1971年 | 4篇 |
1970年 | 2篇 |
1968年 | 3篇 |
1963年 | 2篇 |
1958年 | 2篇 |
排序方式: 共有302条查询结果,搜索用时 15 毫秒
21.
Kazushi Aranami Shuichi Watanabe Shizuo Tsunogai Masato Hayashi Ken Furuya Toshi Nagata 《Journal of Oceanography》2001,57(3):315-322
Dimethylsulfide (DMS), chlorophyll a (Chl-a), accessory pigments (fucoxanthin, peridinin and 19-hexanoyloxyfucoxanthin), and bacterial production (BP) were measured in the surface layer (0–100 m) of the subarctic North Pacific, including the Bering Sea, during summer (14 July–5 September, 1997). In surface sewater, the concentrations of DMS and Chl-a varied widely from 1.3 to 13.2 nM (5.1 ± 3.0 nM, mean ± S.D., n = 48) and from 0.1 to 2.4 µg L–1 (0.6 ± 0.6 µg L–1, n = 24), respectively. In the subarctic North Pacific, DMS to Chl-a ratios (DMS/Chl-a) were higher on the eastern side than the western side (p < 0.0001). Below the euphotic zone, DMS/Chl-a ratios were law and the correlation between DMS and Chl-a was relatively strong (r
2 = 0.700, n = 27, p < 0.0001). In the euphotic zone, DMS/Chl-a ratios were higher and the correlation between DMS and Chl-a was weak (r
2 = 0.128, n = 50, p = 0.01). The wide variation in DMS/Chl-a ratios would be at least partially explained by the geographic variation in the taxonomic composition of phytoplankton, because of the negative correlation between DMS/Chl-a and fucoxanthin-to-Chl-a ratios (Fuc/Chl-a) (r
2 = 0.476, n = 26, p = 0.0001). Furthermore, there was a positive correlation between DMS and BP (r
2 = 0.380, n = 19, p = 0.005). This suggests that BP did not represent DMS and dimethylsulfoniopropionate (DMSP) removal by bacterial consumption but rather DMSP degradation to DMS by bacterial enzyme. 相似文献
22.
Molecular and isotopic characteristics of gas hydrate-bound hydrocarbons in southern and central Lake Baikal 总被引:4,自引:4,他引:0
Akihiro Hachikubo Oleg Khlystov Alexey Krylov Hirotoshi Sakagami Hirotsugu Minami Yutaka Nunokawa Satoshi Yamashita Nobuo Takahashi Hitoshi Shoji Shin’ya Nishio Masato Kida Takao Ebinuma Gennadiy Kalmychkov Jeffrey Poort 《Geo-Marine Letters》2010,30(3-4):321-329
We investigated the molecular composition (methane, ethane, and propane) and stable isotope composition (methane and ethane) of hydrate-bound gas in sediments of Lake Baikal. Hydrate-bearing sediment cores were retrieved from eight gas seep sites, located in the southern and central Baikal basins. Empirical classification of the methane stable isotopes (δ13C and δD) for all the seep sites indicated the dominant microbial origin of methane via methyl-type fermentation; however, a mixture of thermogenic and microbial gases resulted in relatively high methane δ13C signatures at two sites where ethane δ13C indicated a typical thermogenic origin. At one of the sites in the southern Baikal basin, we found gas hydrates of enclathrated microbial ethane in which 13C and deuterium were both highly depleted (mean δ13C and δD of –61.6‰ V-PDB and –285.4‰ V-SMOW, respectively). To the best of our knowledge, this is the first report of C2 δ13C–δD classification for hydrate-bound gas in either freshwater or marine environments. 相似文献
23.
Yutaka Yoshikawa Akira Masuda Kenichi Marubayashi Michiyoshi Ishibashi 《Journal of Oceanography》2010,66(2):223-232
Seasonal variations of the surface currents in the Tsushima Strait were investigated by analyzing the monthly mean surface
currents measured with HF radar. Several new features of the surface currents have been found. One notable feature is the
large, complicated seasonal variation in the current structure in the eastern channel of the strait. For example, in the southeastern
and northwestern regions of the channel, southwestward countercurrents are found in summer while southeastward acrossshore
currents are found in autumn and winter. The wind-driven flow (Ekman flow) as well as surface geostrophic currents are responsible
for these complicated variations of the surface currents. To quantify each variation of the flow and current, the wind-driven
flow was calculated from the monthly wind (more precisely, the friction velocity) using the monthly speed factor and deflection
angle estimated in our previous study, and the surface geostrophic currents were then estimated by subtracting the wind-driven
flow from the measured surface currents. It was found that the acrossshore currents are the wind-driven flow, and that the
surface geostrophic currents flow almost in the along-shore direction, indicating the validity of the decomposition of the
surface velocity into the wind-driven flow and the geostrophic currents using the speed factor and deflection angle. A real-vector
empirical orthogonal function (EOF) analysis of the surface geostrophic currents shows a pair of eddies in the lee of Tsushima
and Iki Islands as the first mode, which indicates that the southwestward countercurrents in the eastern channel are formed
primarily by the incoming Tsushima Warm Current. 相似文献
24.
We describe a least-squares inversion approach to estimating the subsurface resistivity structure from cross-hole or borehole-to-surface electromagnetic data. It is assumed that the resistivity distribution is symmetric about the axis of a borehole and that vertical magnetic dipoles are located on the borehole axis. The receivers are placed either in another borehole or on the earth's surface. The inversion scheme uses the finite-element and smoothness-constrained least-squares methods. The computational effort required to obtain partial derivatives is reduced considerably by using the reciprocity principle. Numerical simulations show that the reconstructions are generally in good agreement with the true structures when the assumption of an axisymmetric earth structure holds. An example involving the breakdown of this assumption, which can be obtained by interchanging the source and receiver boreholes, suggests that the inversion result may also be useful for locating a general 3D anomaly although artifacts are present. 相似文献
25.
Naomi AOTA Yutaka MIYAMOTO Sakae KOSANDA Yasuji OURA Koh SAKAMOTO 《Geostandards and Geoanalytical Research》1994,18(1):65-84
Fifteen rock reference samples "Igneous rock series" issued by the Geological Survey of Japan were analysed for up to 31 elements by neutron activation analysis (NAA); 14 MeV-NAA for Si and Al, fission track method for U, radiochemical and instrumental NAA for rare-earth elements, and instrumental NAA for the remaining elements, with reactor neutrons for the latter three. The present results are compared with published values. 相似文献
26.
Yutaka Ishizaka Peter V. Hobbs Lawrence F. Radke 《Journal of Atmospheric Chemistry》1989,9(1-3):149-159
Airborne measurements made during August 1985 over Greenland and its environs show that both accumulation-mode (0.1 m D2.0 m) and giant (D2 m) particles were present in relatively high concentrations in arctic haze layers and that the accumulation-mode particles dominated light scattering. Particles with diameters (D) between 1 and 4 m consisted predominately of mixed materials, small and dense inclusions, and probably organic compounds containing sulfur. Many of the particles from 0.1 to 1 m in diameter were also of mixed composition, with sulfuric acid, ammonium sulfate and organics probably the dominant constituents. 相似文献
27.
Tomonori Naya Yoshihiro Tanimura Yutaka Kanai Fujio Kumon Kazuo Amano 《Journal of Paleolimnology》2007,37(4):547-563
In order to assess the recent anthropogenic environmental changes in Lake Kitaura, central Japan, changes during the past
few centuries were reconstructed from results of radiometric and tephrochlonological age determination, magnetic susceptibility
measurements, total organic carbon analyses, total nitrogen analyses and fossil diatom analyses on a sediment core from the
lake. A total of six major and sub-zones are recognized according to the diatom fossil assemblages, and we discuss aquatic
environmental change in Lake Kitaura mainly based on these diatom assemblage change. Zone Ia and Zone Ib (older than AD 1707)
are marine to brackish. In Zone IIa (AD␣1707–AD 1836), most of the brackish diatoms disappeared, and were replaced by freshwater
species indicating a decrease in salinity. We interpret the salinity decrease in Zone I–IIa as a sea-level fall during the
Little Ice Age. The salinity of the lake decreased to near freshwater conditions in Zone IIb (AD 1836–AD 1970), which could
arise from alteration in River Tone or development of a sandspit in the mouth of River Tone in addition to sea-level change.
In Zone IIIa (AD 1970–AD 1987), the diatom assemblage indicates a freshwater environment, and sedimentation rates increase
rapidly. These changes reflect sedimentary environment change and an ecosystem transition due to the construction of the tide
gate. In Zone IIIb (AD 1987–AD 2002), the diatom flux (valves cm−2 y−1) increased and species composition changed. The changes in Zone IIIb show a good agreement with limnological monitoring data
gathered from the lake. These paleolimnological data suggest that the recent human-induced changes of the aquatic environment
of the lake after the 1970s exceed rates during the period concerned in this study. 相似文献
28.
The CQC rule for modal combination is extended to include the quasi-static contribution of truncated modes and the effects of input narrow-bandedness and cut-off frequency. A simple measure of the error in approximating a high-frequency modal response by its quasi-static contribution is derived. The extended rule is applicable to structures with high-frequency modes and to seismic inputs which may not be regarded as wide band. Numerical examples demonstrate the significance of input bandwidth and cut-off frequency on modal cross-correlation coefficients, and on the error resulting from truncation of high-freqeuncy modes. 相似文献
29.
Prof. Dr. T. Nagata 《Pure and Applied Geophysics》1958,39(1):96-101
Summary Disturbances in the critical frequency of theF2-region of the ionosphere at Watheroo on international magnetically disturbed days are analyzed together with simultaneous geomagnetic data at the same station. The results show that the daily average disturbanceDm (foF2) becomes negative or positive according as the maximum of the disturbance daily variationSD (foF2) takes place in night time or in daytime respectively. This fact may show that bothDm (foF2) andSD (foF2) are due to the condition that the daytime increase in the daily variation of theF2-region is reduced or enhanced owing to vertical drift of the ionosphere caused by electric currents responsible for geomagneticSD. 相似文献
30.
Toshifumi Yanagisawa Yasushi Muraki Yutaka Matsubara Fumio Abe Kimiaki Masuda Sachiyo Noda Takahiro Sumi Yuji Kato Mitsuaki Fujimoto Shuji Sato Ian Bond Nicholas Rattenbury Philip Yock Pam Kilmartin John Hearnshaw Micheal Reid Denis Sullivan Brian Carter Richard Dodd Garry Nankivell Noiman Rumsey Morihiro Honda Maki Sekiguchi Masanori Yoshizawa Takashi Nakamura Humitaka Sato Seiji Kabe Makoto Kobayashi Yoshiyuki Watase Jun Jugaku Toshiharu Saito Barbel Koribalsky 《Experimental Astronomy》2000,10(4):519-535
We have constructed a large, mosaic CCD camera called MOA-cam2 which has 4096 × 6144-pixelsto search for gravitational microlensing events. MOA-cam2 has three4096 × 2048-pixel SITe CCD chips, which have a very high quantum efficiency (nearly 80% in the wave region 500 to 800 nm),and three buttable sides. We have placed the threechips side by side with 100 m dead space. MOA-cam2 has been installed on the 61 cm Boller and Chivens telescope of the MOA collaboration at the Mt. John University Observatory (MJUO) in NewZealand since July 1998. The field coverage is 0.92° × 1.38° per exposure. The technical details of MOA-cam2 and the first images obtained with the Boller and Chivens telescope are presented. MOA-cam2 introduces a second phase of research on gravitational microlensing by the MOA collaboration. 相似文献