全文获取类型
收费全文 | 606篇 |
免费 | 17篇 |
国内免费 | 13篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 20篇 |
地球物理 | 129篇 |
地质学 | 203篇 |
海洋学 | 136篇 |
天文学 | 117篇 |
综合类 | 5篇 |
自然地理 | 24篇 |
出版年
2023年 | 4篇 |
2021年 | 9篇 |
2020年 | 6篇 |
2019年 | 25篇 |
2018年 | 10篇 |
2017年 | 12篇 |
2016年 | 17篇 |
2015年 | 5篇 |
2014年 | 23篇 |
2013年 | 21篇 |
2012年 | 13篇 |
2011年 | 19篇 |
2010年 | 23篇 |
2009年 | 29篇 |
2008年 | 33篇 |
2007年 | 33篇 |
2006年 | 30篇 |
2005年 | 33篇 |
2004年 | 15篇 |
2003年 | 19篇 |
2002年 | 10篇 |
2001年 | 15篇 |
2000年 | 14篇 |
1999年 | 20篇 |
1998年 | 15篇 |
1997年 | 8篇 |
1996年 | 11篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 13篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 7篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 4篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1972年 | 4篇 |
1970年 | 4篇 |
排序方式: 共有636条查询结果,搜索用时 593 毫秒
341.
Kanako SAKAMOTO Tomoki NAKAMURA Takaaki NOGUCHI Akira TSUCHIYAMA 《Meteoritics & planetary science》2010,45(2):220-237
Abstract– Eight saponite‐rich micrometeorites with very similar mineralogy were found from the recent surface snow in Antarctica. They might have come to Earth as a larger meteoroid and broke up into pieces on Earth, because they were recovered from the same layer and the same location of the snow. Synchrotron X‐ray diffraction (XRD) analysis indicates that saponite, Mg‐Fe carbonate, and pyrrhotite are major phases and serpentine, magnetite, and pentlandite are minor phases. Anhydrous silicates are entirely absent from all micrometeorites, suggesting that their parental object has undergone heavy aqueous alteration. Saponite/serpentine ratios are higher than in the Orgueil CI chondrite and are similar to the Tagish Lake carbonaceous chondrite. Transmission electron microscope (TEM) observation indicates that serpentine occupies core regions of fine‐grained saponite, pyrrhotite has a low‐Ni concentration, and Mg‐Fe carbonate shows unique concentric ring structures and has a mean molar Mg/(Mg + Fe) ratio of 0.7. Comparison of the mineralogy to hydrated chondrites and interplanetary dust particles (IDPs) suggests that the micrometeorites are most similar to the carbonate‐poor lithology of the Tagish Lake carbonaceous chondrite and some hydrous IDPs, but they show a carbonate mineralogy dissimilar to any primitive chondritic materials. Therefore, they are a new variant of saponite‐rich micrometeorite extracted from a primitive hydrous asteroid and recently accreted to Antarctica. 相似文献
342.
Monthly variations of hydrographic structures and water mass distribution off the Doto area, Japan 总被引:2,自引:2,他引:0
Monthly variations of hydrographic structures and water mass distributions were investigated over a nearly 30-year period (January 1982–March 2011) off the Doto area, Japan, to examine temporal evolutions and devolutions of representative water masses in this area. In the continental shelf area, the Coastal Oyashio Water (COW) was distributed along the coast during January–May, when COW has been modified by relatively higher salinity water, which may have originated from the Oyashio Water (OW) off the Kuril Islands. On the other hand, the Surface COW (S-COW) may have formed with COW heated by solar radiation, simultaneously mixing with the Tokachi River freshwater and OW in the continental shelf area, and the area of this S-COW spread offshoreward during June and July, and stayed in the offshore area during June and October. Although coastal density current structures, probably due to the Modified Soya Warm Current Water (M-SWCW) inflows, were conspicuous in the continental shelf area during August–October, those structures were weak after November. These weakening structures may be due to developed surface mixed layer caused by surface cooling, and decay of volume transport of the Soya Warm Current in the Okhotsk Sea, and such weakening accordingly may lead to weakening of higher salinity water inflows from the upstream regions. M-SWCW was radically replaced by COW during December and January with rapid salinity decreases, which suggest extremely lower salinity water inflows, probably due to influences of the East Sakhalin Current Water. 相似文献
343.
We estimated the long-term vertical velocity profile across the northeastern Japan forearc by using the height distribution of late Quaternary marine and fluvial terraces, and we correlated the ages of the two marine terraces with marine isotope stages (MIS) 5.5 and 5.3 or 5.1 by cryptotephra stratigraphy. The uplift rate, estimated as 0.11-0.19 m ka− 1 from the relative heights between the terrace surfaces and eustatic sea levels, was nearly equal to, or slightly slower than, the uplift rate farther inland (0.15-0.19 m ka− 1), as determined from the relative heights of fill terrace surfaces. In contrast, the short-term vertical velocity profile, obtained from GPS observations, showed that the forearc is currently subsiding at a maximum rate of 5.4 ± 0.4 mm yr− 1. Thus, the current short-term (geodetic) subsidence does not reflect long-term (geological) tectonic movement. Short-term vertical deformation is probably driven by subduction erosion or elastic deformation caused by interplate coupling, or both. However, long-term uplift is probably due not to moment release on the mega-thrust but to crustal thickening. 相似文献
344.
Groundwater vulnerability assessment in shallow aquifer of Kathmandu Valley using GIS-based DRASTIC model 总被引:1,自引:0,他引:1
Dhundi Raj Pathak Akira Hiratsuka Isao Awata Luonan Chen 《Environmental Geology》2009,57(7):1569-1578
In this paper, groundwater aquifer vulnerability map has been developed by incorporating the major geological and hydro-geological
factors that affect and control the groundwater contamination using GIS based DRASTIC model. This work demonstrates the potential
of GIS to derive a map by overlying various spatially referenced digital data layers that portrays cumulative aquifer sensitivity
ratings across the Kathmandu Valley, Nepal, providing a relative indication of groundwater vulnerability to contamination.
In fact, the groundwater is the major natural resources in Kathmandu for drinking purpose. The decline in groundwater levels
due to the over exploitation and thus extracted water from shallow aquifer has been contaminated by the infiltration of pollutants
from polluted river and land surface is continuous and serious. As the demand for water for human and industrial use has escalated
and at the same time, the engineering and environmental costs are much higher for new water supplies than maintaining the
existing sources already in use. Management of groundwater source and protecting its quality is therefore essential to increase
efficient use of existing water supplies. Aquifer vulnerability maps developed in this study are valuable tools for environmental
planning and predictive groundwater management. Further, a sensitivity analysis has been performed to evaluate the influence
of single parameters on aquifer vulnerability assessment such that some subjectivity can be reduced to some extent and then
new weights have been computed for each DRASTIC parameters. 相似文献
345.
Jonny Rutqvist Ann Bäckström Masakazu Chijimatsu Xia-Ting Feng Peng-Zhi Pan John Hudson Lanru Jing Akira Kobayashi Tomofumi Koyama Hee-Suk Lee Xiao-Hua Huang Mikael Rinne Baotang Shen 《Environmental Geology》2009,57(6):1313-1324
This simulation study shows how widely different model approaches can be adapted to model the evolution of the excavation
disturbed zone (EDZ) around a heated nuclear waste emplacement drift in fractured rock. The study includes modeling of coupled
thermal-hydrological-mechanical (THM) processes, with simplified consideration of chemical coupling in terms of time-dependent
strength degradation or subcritical crack growth. The different model approaches applied in this study include boundary element,
finite element, finite difference, particle mechanics, and elasto-plastic cellular automata methods. The simulation results
indicate that thermally induced differential stresses near the top of the emplacement drift may cause progressive failure
and permeability changes during the first 100 years (i.e., after emplacement and drift closure). Moreover, the results indicate
that time-dependent mechanical changes may play only a small role during the first 100 years of increasing temperature and
thermal stress, whereas such time-dependency is insignificant after peak temperature, because of decreasing thermal stress. 相似文献
346.
Junichi Nakajima Yusuke Tsuji Akira Hasegawa Saeko Kita Tomomi Okada Toru Matsuzawa 《Gondwana Research》2009,16(3-4):470-481
We estimate detailed three-dimensional seismic velocity structures in the subducting Pacific slab beneath Hokkaido, Japan, using a large number of arrival-time data from 6902 local earthquakes. A remarkable low-velocity layer with a thickness of ~ 10 km is imaged at the uppermost part of the slab and is interpreted as hydrated oceanic crust. The layer gradually disappears at depths of 70–80 km, suggesting the breakdown of hydrous minerals there. We find prominent low-velocity anomalies along the lower plane of the double seismic zone and above the aftershock area of the 1993 Kushiro-oki earthquake (M7.8). Since seismic velocities of unmetamorphosed peridotite are much higher than the observations, hydrous minerals are expected to exist in the lower plane as well as the hypocentral area of the 1993 earthquake. On the other hand, regions between the upper and lower planes, where seismic activity is not so high compared to the both planes, show relatively high velocities comparable to those of unmetamorphosed peridotite. Our observations suggest that intermediate-depth earthquakes occur mainly in regions with hydrous minerals, which support dehydration embrittlement hypothesis as a cause of earthquake in the subducting slab. 相似文献
347.
Izu-Bonin arc subduction under the Honshu island, Japan: Evidence from geological and seismological aspect 总被引:1,自引:1,他引:0
Shinji Yamamoto Junichi Nakajima Akira Hasegawa Shigenori Maruyama 《Gondwana Research》2009,16(3-4):572-580
The Izu-Bonin intra-oceanic arc with 20–35 km thick continental crust is being subducted under the Honshu, presumably since 17 Ma. Tomographic image clearly demonstrates that the whole Izu-Bonin arc is subducting under the Honshu arc. Geologic cross section and the thickness of continental crust do not support the accretion of thick crust in spite of the continued subduction over 17 Ma. 相似文献
348.
Naoki Uchida Satoshi Yui Satoshi Miura Toru Matsuzawa Akira Hasegawa Yoshinobu Motoya Minoru Kasahara 《Gondwana Research》2009,16(3-4):527-533
We analyzed small repeating earthquakes recorded over a 13-year period and GPS data recorded over an 8-month period to estimate interplate quasi-static slip associated with the 2003 Tokachi-oki earthquake (M8.0) and the 2004 off-Kushiro earthquake (M7.1). The repeating-earthquake analysis revealed that the slip rate near the source region of the Tokachi-oki earthquake was relatively low (< 5 cm/year) prior to the earthquake; however, in the last 3 years leading up to the event, a minor acceleration in slip occurred upon the deeper extension of the coseismic slip area of the earthquake. Repeating-earthquake and GPS data indicate that large amounts of afterslip occurred around the rupture area following the earthquake; the afterslip mainly propagated to the east of the coseismic slip area. We also infer that the occurrence of the 2004 off-Kushiro earthquake, located about 100 km northeast of the epicenter of the Tokachi-oki earthquake, was advanced by the afterslip associated with the Tokachi-oki earthquake. 相似文献
349.
Nyein N. Sint Kotaro Yonezu Thomas Tindell May T. Aye Htay Win Akira Imai Koichiro Watanabe 《Resource Geology》2019,69(1):85-106
The Shwe Min Bon Cu–Au skarn deposit lies within one of the largest Au–Cu belts in Myanmar. The deposit is situated along the Shan scarp zone, which marks the boundary between the Myanmar central basin to the west and the Shan plateau to the east. The Shwe Min Bon deposit comprises skarn‐type metasomatic alteration, and the Cu–Au mineralization occurs along the contact face between the Nwabangyi Dolomite and Shweminbon Formation and the Cretaceous dioritic rocks. The metasomatic process resulted in pro‐ and retrograde mineral assemblages in exoskarn. Hydrothermal activities in the Shwe Min Bon deposit are classified into prograde, retrograde stage I, and retrograde stage II. The prograde skarn is classified into a proximal garnet skarn with minor clinopyroxene and a distal wollastonite skarn. Chlorite, epidote, and tremolite–actinolite were formed during the retrograde stage I. Cu–Au mineralization mainly occurred in retrograde stage I, which was characterized by moderate temperatures (260–320 °C) and fluid with a moderate salinity (5.0–6.0% NaCl equiv.). Low temperature (180–200 °C) and low salinity (2.0–3.0% NaCl equiv.) were responsible for retrograde stage II. Au mineralization is mainly associated with chalcopyrite and tennantite in retrograde stage I and with tellurobismuthite in retrograde stage II. 相似文献
350.
Nao Nakanishi Tetsuya Yokoyama Akira Ishikawa 《Geostandards and Geoanalytical Research》2019,43(2):231-243
In recent years, the 187Re–187Os isotope system has been increasingly used to study samples containing very small quantities of Os. For such samples, optimisation of measurement procedures is essential to minimise the loss of Os before mass spectrometric measurements. Micro‐distillation is a necessary purification step that is applied after the main Os chemical separation procedure, prior to Os isotope ratio measurements by negative‐thermal ionisation mass spectrometry (N‐TIMS). However, unlike the other separation steps, this procedure has not yet been optimised for small samples. In this study, we present a refined micro‐distillation method that achieved higher yields and allowed high‐precision R(187Os/188Os) expressed as 187Os/188Os measurements for small‐sized geological samples that contain only a few pg Os. The Os recovery in the micro‐distillation step was tested by changing the operating conditions including heating time and temperature, and amounts of oxidant and reductant. Recoveries were measured by the isotope dilution ICP‐MS method after the addition of 190Os‐enriched spike solution. We found that the most critical factor controlling the chemical yield of Os during micro‐distillation is the extent of dilution of the reductant (HBr) by H2O evaporated from the oxidant. A refined micro‐distillation method, in which the amount of oxidant solution is reduced from the conventional method, achieved an improved chemical yield of Os (~ 90%). This refined method was applied to the measurement of 187Os/188Os by N‐TIMS of varying test portions of the geological reference material BIR‐1a. The resulting 187Os/188Os ratios of BIR‐1a matched the literature data, with propagated uncertainties of 0.2, 1.1 and 11% digested sample quantities containing 150, 10 and 1 pg of Os, respectively. 相似文献