全文获取类型
收费全文 | 554篇 |
免费 | 17篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 22篇 |
地球物理 | 132篇 |
地质学 | 179篇 |
海洋学 | 136篇 |
天文学 | 82篇 |
综合类 | 6篇 |
自然地理 | 22篇 |
出版年
2023年 | 5篇 |
2021年 | 9篇 |
2020年 | 6篇 |
2019年 | 25篇 |
2018年 | 9篇 |
2017年 | 10篇 |
2016年 | 15篇 |
2015年 | 3篇 |
2014年 | 23篇 |
2013年 | 25篇 |
2012年 | 13篇 |
2011年 | 17篇 |
2010年 | 22篇 |
2009年 | 24篇 |
2008年 | 28篇 |
2007年 | 35篇 |
2006年 | 26篇 |
2005年 | 30篇 |
2004年 | 13篇 |
2003年 | 15篇 |
2002年 | 8篇 |
2001年 | 15篇 |
2000年 | 10篇 |
1999年 | 22篇 |
1998年 | 15篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 7篇 |
1978年 | 10篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1974年 | 5篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1970年 | 5篇 |
排序方式: 共有581条查询结果,搜索用时 78 毫秒
41.
Hikari Hasegawa Takashi Mikouchi Akira Yamaguchi Masahiro Yasutake Richard C. Greenwood Ian A. Franchi 《Meteoritics & planetary science》2019,54(4):752-767
Northwest Africa (NWA) 6112, Miller Range (MIL) 090206 (plus its pairs: MIL 090340 and MIL 090405), and Divnoe are olivine‐rich ungrouped achondrites. We investigated and compared their petrography, mineralogy, and olivine fabrics. We additionally measured the oxygen isotopic compositions of NWA 6112. They show similar petrography, mineralogy, and oxygen isotopic compositions and we concluded that these five meteorites are brachinite clan meteorites. We found that NWA 6112 and Divnoe had a c axis concentration pattern of olivine fabrics using electron backscattered diffraction (EBSD). NWA 6112 and Divnoe are suggested to have been exposed to magmatic melt flows during their crystallization on their parent body. On the other hand, the three MIL meteorites have b axis concentration patterns of olivine fabrics. This indicates that the three MIL meteorites may be cumulates where compaction of olivine grains was dominant. Alternatively, they formed as residues and were exposed to olivine compaction. The presence of two different olivine fabric patterns implies that the parent body(s) of brachinite clan meteorites experienced diverse igneous processes. 相似文献
42.
Ariyoshi Keisuke Kuwano-Yoshida Akira Chi Wu-Cheng 《Marine Geophysical Researches》2019,40(4):451-451
Marine Geophysical Research - 相似文献
43.
Hasegawa Takuya Nagano Akira Matsumoto Hiroyuki Ariyoshi Keisuke Wakita Masahide 《Marine Geophysical Researches》2019,40(4):513-514
Marine Geophysical Research - In the original publication, the Fig. 2 was published incorrectly. The correct version (Fig. 2) is given in this correction. The original article has been... 相似文献
44.
Sachiko Oguma Tsuneo Ono Akira Kusaka Hiromi Kasai Yasuhiro Kawasaki Tomonori Azumaya 《Journal of Oceanography》2008,64(4):525-539
In this study we used two stable isotopes, δ13C and δ18O, for water mass classification in the coastal region off eastern Hokkaido. δ13C* values, which were corrected for the biological effect, and δ
18O values up to 300 m depth suggested that the isotopic character of the onshore and offshore water in the southern Okhotsk
Sea, the Nemuro Strait and the western North Pacific could be explained by the mixing of three source waters: the Oyashio
water (OYW), Soya Warm Current water (SWCW) and East Sakhalin Current water (ESCW). In summer, δ
13C*-δ
18O plots indicated mixing between SWCW from the southern Okhotsk Sea and OYW in the Pacific coast of southeastern Hokkaido,
while temperature-salinity plots of the onshore water showed minimal difference from the offshore OYW. In winter, on the other
hand, the mixed water of ESCW and OYW (or SWCW) appeared in the Pacific coastal region, distributed as cold, low salinity
onshore water. Finally, we estimated mixing ratios of OYW, SWCW and ESCW in the coastal region of western North Pacific using
their mean values of δ
13C* and δ
18O as endmembers. These results suggest seasonal and yearly changes of water mass combination en route from the southern Okhotsk
Sea to the western North Pacific. 相似文献
45.
Masahiro Kayama Toshimori Sekine Naotaka Tomioka Hirotsugu Nishido Yukako Kato Kiyotaka Ninagawa Takamichi Kobayashi Akira Yamaguchi 《Meteoritics & planetary science》2018,53(7):1476-1488
Cathodoluminescence (CL) analyses were carried out on maskelynite and lingunite in L6 chondrites of Tenham and Yamato-790729. Under CL microscopy, bright blue emission was observed in Na-lingunite in the shock veins. Dull blue-emitting maskelynite is adjacent to the shock veins, and aqua blue luminescent plagioclase lies farther away. CL spectroscopy of the Na-lingunite showed emission bands centered at ~330, 360–380, and ~590 nm. CL spectra of maskelynite consisted of emission bands at ~330 and ~380 nm. Only an emission band at 420 nm was recognized in crystalline plagioclase. Deconvolution of CL spectra from maskelynite successfully separated the UV–blue emission bands into Gaussian components at 3.88, 3.26, and 2.95 eV. For comparison, we prepared K-lingunite and experimentally shock-recovered feldspars at the known shock pressures of 11.1–41.2 GPa to measure CL spectra. Synthetic K-lingunite has similar UV–blue and characteristic yellow bands at ~550, ~660, ~720, ~750, and ~770 nm. The UV–blue emissions of shock-recovered feldspars and the diaplectic feldspar glasses show a good correlation between intensity and shock pressure after deconvolution. They may be assigned to pressure-induced defects in Si and Al octahedra and tetrahedra. The components at 3.88 and 3.26 eV were detectable in the lingunite, both of which may be caused by the defects in Si and Al octahedra, the same as maskelynite. CL of maskelynite and lingunite may be applicable to estimate shock pressure for feldspar-bearing meteorites, impactites, and samples returned by spacecraft mission, although we need to develop more as a reliable shock barometer. 相似文献
46.
Secondary‐volatiles linked metallic iron in eucrites: The dual‐origin metals of Camel Donga 下载免费PDF全文
Paul H. Warren Junko Isa Mitsuru Ebihara Akira Yamaguchi Bastian Baecker 《Meteoritics & planetary science》2017,52(4):737-761
The unique occurrence of abundant (~1 vol%) near‐pure‐Fe metal in the Camel Donga eucrite is more complicated than previously believed. In addition to that component of groundmass metal, scattered within the meteorite are discrete nodules of much higher kamacite abundance. We have studied the petrology and composition of two of these nodules in the form of samples we call CD2 and CD3. The nodules are ovoids 11 (CD2) to 15 (CD3) mm across, with metal, or inferred preweathering metal, abundances of 12–17 vol% (CD2 is unfortunately quite weathered). The CD3 nodule also includes at its center a 5 mm ovoid clumping (6 vol%) of F‐apatite. Both nodules are fine‐grained, so the high Fe metal and apatite contents are clearly not flukes of inadequate sampling. The metals within the nodules are distinctly Ni‐rich (0.3–0.6 wt%) compared to the pure‐Fe (Ni generally 0.01 wt%) groundmass metals. Bulk analyses of three pieces of the CD2 nodule show that trace siderophile elements Ir, Os, and Co are commensurately enriched; Au is enriched to a lesser degree. The siderophile evidence shows the nodules did not form by in situ reduction of pyroxene FeO. Moreover, the nodules do not show features such as silica‐phase enrichment or pyroxene with reduced FeO (as constrained by FeO/MgO and especially FeO/MnO) predicted by the in situ reduction model. The oxide minerals, even in groundmass samples well away from the nodules, also show little evidence of reduction. Although the nodule boundaries are generally sharp, groundmass‐metal Ni content is anti‐correlated with distance from the CD3 nodule. We infer that the nodules represent materials that originated within impactors into the Camel Donga portion of the eucrite crust, but probably were profoundly altered during later metamorphism/metasomatism. Origin of the pure‐Fe groundmass metal remains enigmatic. In situ reduction probably played an important role, and association in the same meteorite of the Fe‐nodules is probably significant. But the fluid during alteration was probably not (as previously modeled) purely S and O, of simple heat‐driven internal derivation. We conjecture a two‐stage metasomatism, as fluids passed through Camel Donga after impact heating of volatile‐rich chondritic masses (survivors of gentle accretionary impacts) within the nearby crust. First, reduction to form troilite may have been triggered by fluids rich in S2 and CO (derived from the protonodules?), and then in a distinct later stage, fluids were (comparatively) H2O‐rich, and thus reacted with troilite to form pure‐Fe metal along with H2S and SO2. The early eucrite crust was in places a dynamic fluid‐bearing environment that hosted complex chemical processes, including some that engendered significant diversity among metal+sulfide alterations. 相似文献
47.
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
48.
H. Kit Miyamoto Amir S. J. Gilani Akira Wada Christopher Ariyaratana 《地震工程与结构动力学》2010,39(11):1279-1297
Fluid viscous dampers are used to control story drifts and member forces in structures during earthquake events. These elements provide satisfactory performance at the design‐level or maximum considered earthquake. However, buildings using fluid viscous dampers have not been subjected to very large earthquakes with intensities greater than the design and maximum considered events. Furthermore, an extensive database of viscous damper performance during large seismic events does not exist. To address these issues, a comprehensive analytical and experimental investigation was conducted to determine the performance of damped structures subjected to large earthquakes. A critical component of this research was the development and verification of a detailed viscous damper mathematical model that incorporates limit states. The development of this model and the laboratory and simulation results conclude good correlation with the new model and the damper limit states and provide superior results compared with the typical damper model when considering near collapse evaluation of structures. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
49.
Akira Takada 《Bulletin of Volcanology》1989,52(2):118-126
A system of propagating cracks may explain magma transport and the evolution of a volcano. This paper considers only a basaltic magma. The system is controlled by two boundary conditions: the stress field, and the production rate of the magma-filled cracks in the mantle. Numerical solutions of crack propagation for various stress conditions, with a constant production rate high enough to coalesce isolated cracks, were performed, and the results applied to different tectonic conditions. For the hydrostatic stress conditions, most magma-filled cracks beneath a polygenetic volcano become trapped either in the lower crust, because there the density difference between magma and the host rocks () becomes suddenly small, compared with that in the mantle, or trapped in the upper crust, because there is near to zero. Magma traps composed of such cracks may grow into magma reservoirs if the production rate of cracks in the mantle is large. If horizontal stress with a vertical gradient is superimposed on the hydrostatic condition in the crust, that is, tensile stress which increases upward or compressional stress which increases downward, magmafilled cracks, even if the density of magma is higher than that of the crust, may ascend directly without trapping. When the crust undergoes relative tension, magma-filled cracks may become trapped. Then, the lower part of the trap may grow into a magma reservoir, while the upper part may become filled with dikes. When the production rate of cracks is small, an initial magma-filled crack can rise directly to the surface only when the stress with a gradient is superimposed as mentioned above, or when the average density in a crack decreases, owing to, for example, vesiculation of volatile components. 相似文献
50.
Akira Tsuchiyama 《Contributions to Mineralogy and Petrology》1985,91(1):12-23
Partial melting experiments on plagioclase (An60) and diopside have been carried out using pairs of large crystals to investigate textures and kinetics of melting. The experiments were done at one atmosphere pressure as a function of temperature (1,190–1,307° C) and time (1.5–192 h). Melting took place mainly at the plagioclase-diopside contact planes. Reaction zones composed of fine mixtures of calcic plagioclase and melt were developed from the surface of the plagioclase crystal inward. There exists a critical temperature, below which only a few % melting can occur over the duration of the experiments. This sluggish melting is caused by slow NaSi-CaAl diffusion in plagioclase, because the plagioclase crystal must change its composition to produce albite-rich cotectic melts. Diffusion in the solid also affects the chemical composition of the melts. During initial melting, potassium is preferentially extracted from plagioclase because K-Na diffusion in plagioclase is faster than that of NaSi-CaAl. This also causes a shift in the cotectic compositions. Above the critical temperature, on the other hand, melting is promoted by a metastable reaction in which the plagioclase composition does not change, and which produces melts with compositional gradients along the original An60-diopside tie line. The critical temperature is determined by the intersection of the cotectic and the An60-diopside tie line. Interdiffusion coefficients of plagioclase-diopside components in the melt are estimated from melting rates above the critical temperature by using a simplified steady-state diffusion model (e.g., 10–8 cm2/sec at 1,300° C).Many examples of reaction zones due to partial melting have been described as spongy or fingerprint-like textures in xenoliths. Metastable melting above the critical temperature is considered to take place in natural melting where there is a high degree of melting. However, we cannot exclude the possibility of disequilibrium created by sluggish melting controlled by diffusion in the minerals. If melting occurs close to the solidus, this process can be important even for partial melting in the upper mantle. 相似文献