全文获取类型
收费全文 | 118篇 |
免费 | 7篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 9篇 |
地球物理 | 50篇 |
地质学 | 31篇 |
海洋学 | 20篇 |
天文学 | 11篇 |
自然地理 | 8篇 |
出版年
2022年 | 3篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 14篇 |
2017年 | 1篇 |
2016年 | 4篇 |
2015年 | 3篇 |
2014年 | 2篇 |
2013年 | 6篇 |
2012年 | 5篇 |
2011年 | 5篇 |
2010年 | 7篇 |
2009年 | 6篇 |
2008年 | 3篇 |
2007年 | 7篇 |
2006年 | 9篇 |
2005年 | 3篇 |
2004年 | 7篇 |
2003年 | 1篇 |
2002年 | 1篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有130条查询结果,搜索用时 171 毫秒
41.
Particle acceleration via Poynting vector with toroidal magnetic field is studied in 3D PIC simulation of electron-positron
plasma. We choose two different initial magnetic field configurations to compare how the particle acceleration is affected
by the expansion of electromagnetic wave. In the cylindrical case, the electromagnetic field strength decays as (ct)−2, and particles are accelerated in the radial direction as well as the axial direction. Rayleigh-Taylor instability is also
observed at the center of the cylinder. In the torus case, the field strength decays as (ct)−3, making the acceleration less efficient. Particles accelerated in the axial direction by E × B force creates strong charge separation. 相似文献
42.
Gatot E. Susilo Koichi Yamamoto Tsuyoshi Imai Yoshiyuki Ishii Hiroshi Fukami Masahiko Sekine 《水文科学杂志》2013,58(3):539-548
Abstract The effect of the El Niño Southern Oscillation (ENSO) on rainfall characteristics in the tropical peatland areas of Central Kalimantan, Indonesia, is demonstrated. This research used rainfall data collected between 1978 and 2008. The results suggest a relationship between ENSO events and the trend in rainfall observed in the study area. Further analyses show that El Niño events have a stronger effect on the rainfall compared to La Niña events. El Niño events were also correlated to the increase in the number of days with less than 1 mm of rainfall in the dry season. The analysis reveals that the impact of El Niño events on rainfall in dry seasons is intensifying annually. Furthermore, ENSO events are not the only factors affecting rainfall trends in the observed area. Other factors, such as deforestation, may also affect the trend. Editor Z.W. Kundzewicz Citation Susilo, G.E., Yamamoto, K., Imai, T., Ishii, Y., Fukami, H., and Sekine, M., 2013. The effect of ENSO on rainfall characteristics in the tropical peatland areas of Central Kalimantan, Indonesia. Hydrological Sciences Journal, 58 (3), 539–548. 相似文献
43.
Hideki Shimada Yanlong Chen Koichi Araki Takashi Sasaoka Kikuo Matsui 《Geotechnical and Geological Engineering》2012,30(2):289-297
Based on experimental and numerical investigations, the present paper focuses on under ground scope (UGS) chemical grouting
method that can actually improve the pipeline surrounding foundation to solve pipeline saggy damage. According to the experimental
results, a solution-type injection material could make lager soil deformation, using less total slurry amount than suspension-type
injection material. Therefore, a suspension-type injection material with shorter gel time is more suitable for the UGS method,
making it more effective to reinforce the pipeline foundation and restore pipelines. The results of some patterns of injection
tests revealed relationship between the behavior of the grouting material and the deformation of the soil. It is found that
the material can be injected into a foundation by fracture grouting if the permeation coefficient is lower than 1.00 × 10−3 mm/s. The situation was analyzed by using 2-D finite element method analysis software Phase2, and the analysis result proposes
that the real data and simulation data are nearly the same in impermeable soil. Furthermore, even if the construction object
is permeable soil, it can also be become impermeable soil by two phases grouting: soil improvement grouting and restoration
grouting. 相似文献
44.
Kenichiro Sugitani Kathleen Grey Tsutomu Nagaoka Koichi Mimura Malcolm R. Walter 《Precambrian Research》2009,173(1-4):50
Microstructures recently reported from an Archaean sedimentary succession (ca. 3.0 Ga) in the Mount Goldsworthy–Mount Grant area in the northeastern Pilbara Craton meet the criteria for compelling evidence of biogenicity [Sugitani, K., Grey, K., Allwood, A., Nagaoka, T., Mimura, K., Minami, M., Marshall, C.P., Van Kranendonk, M.J., Walter, M.R., 2007. Diverse microstructures from Archaean chert from the Mount Goldsworthy–Mount Grant area, Pilbara Craton, Western Australia: microfossils, dubiofossil, or pseudofossils. Precambrian Res. 158, 228–262]. The structures are morphologically diverse. Although they were tentatively classified into five major morphological types (thread-like, film-like, small (<15 μm) and large (>15 μm) spheroidal, and spindle-like), the possible taxonomic significance of these groups was not discussed. Building on our earlier analysis, we focus on the morphology of the larger spheroids, as well as presenting further evidence relating spindles and several bizarre forms, and attempt to group them taxonomically and adduce additional evidence for their biogenicity.Taphonomic features were identified in each of the various morphological groups, but the range of morphological diversity of the spheroids cannot be attributed solely to taphonomic alteration. Four subdivisions of spheroids are proposed: (1) simple single-walled spheroids, (2) thin-walled spheroids having a diffuse envelope, (3) thick-walled spheroids, and (4) spheroids having an extensively folded wall. Simple single-walled spheroids, 15–60 μm in diameter, with various wall textures but commonly lacking envelopes or appendages form the dominant subgroup. Other complex morphologies are present and include aligned or associated bodies of thin-walled spheroids with diffuse envelopes, and spindle-like structures containing inner spheroidal bodies. The degree of morphological complexity and associations between structures suggest the presence of reproductive phases. If correct, this implies that the early Earth (ca. 3.0 Ga) showed a higher level of biodiversity than is currently postulated. 相似文献
45.
Reishi Takashima Hiroshi Nishi Toshiro Yamanaka Keiichi Hayashi Amane Waseda Akiko Obuse Takashige Tomosugi Naoki Deguchi Sunao Mochizuki 《Earth and Planetary Science Letters》2010,289(3-4):570-582
Making Upper Cretaceous biostratigraphic correlations between the Northwest Pacific and Tethyan–Atlantic sections have been difficult because of rare frequencies of age-diagnostic macro- and microfossils in the sequences in the Northwest Pacific region. In order to correlate these sections precisely, an integrated planktic foraminiferal and bulk wood carbon-isotope stratigraphy from the upper Cenomanian to the lower Campanian succession (the middle–upper part of the Yezo Group) of Hokkaido, northern Japan is established with an average resolution of 50 k.y. The δ13C curves from bulk wood of the Yezo Group and from bulk carbonate of English Chalk show remarkably similar patterns of isotopic fluctuation, allowing the correlation of 22 carbon isotopic events between these sections. This high-resolution correlation greatly improves the previous micro- and macrofossil biostratigraphic schemes in the Northwest Pacific region, and reveals that global events, such as the oxygen depletion at the OAE 2 horizon, the constant decrease in pCO2 during the Late Cretaceous, and the eustatic sea-level falls in the late middle Turonian, Santonian/Campanian Boundary and early Campanian, are recorded in the Upper Cretaceous sequence of the Northwest Pacific. 相似文献
46.
Linkage of deep sea rapid acidification process and extinction of benthic foraminifera in the deep sea at the Paleocene/Eocene transition
下载免费PDF全文
![点击此处可从《Island Arc》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ocean Drilling Program Leg 199 Site 1220 provides a continuous sedimentary section across the Paleocene/Eocene (P/E) transition in the carbonate‐bearing sediments on 56–57 Ma oceanic crust. The large negative δ13C shift in seawater is likely due to the disintegration of methane hydrate, which is expected to be rapidly changed to carbon dioxide in the atmosphere and well‐oxygenated seawater, leading to a reduction in deep‐sea pH. A pH decrease was very likely responsible for the emergence of agglutinated foraminiferal fauna as calcareous fauna was eliminated by acidification at the P/E transition at Site 1220. The absence of the more resistant calcareous benthic foraminifera and the presence of the planktonic foraminifera at Site 1220 is interesting and unique, which indicates that calcareous benthic foraminifera suffered greatly from living on the seafloor. Box model calculation demonstrates that, assuming the same mean alkalinity as today, pCO2 must increase from 280 ppm to about 410 ppm for the calcite undersaturation in the deep ocean and for the oversaturation in the surface ocean during the P/E transition. The calculated increased pCO2 coincides with paleo‐botanical evidence. The current global emission rate (~7.3 peta (1015) gC/y) of anthropogenic carbon input is approximately 30 times of the estimate at the P/E transition. The results at the P/E transition give an implication that the deep sea benthic fauna will be threatened in future in combination with ocean acidification, increased sea surface temperature and more stratified surface water. 相似文献
47.
Ryoshi Ishiwatari Koichi Negishi Hiroyasu Yoshikawa Shuichi Yamamoto 《Organic Geochemistry》2009,40(4):520-530
Temporal changes in paleoproductivity of Lake Biwa (Japan) over the past 32 kyr have been studied by analyzing bulk organic carbon and photosynthetic pigments (chlorins) in the BIW95-5 core. Primary productivity was estimated on the assumption of C/Norg values of 8 for autochthonous organic matter (OM) and 25 for allochthonous OM and using an equation developed for the marine environment. The estimate indicates that primary productivity ranges from 50 to 90 g C m?2 yr?1 in the Holocene, while it is ~60 g C m?2 yr?1 on average in the last glacial. Pheophytin a and pheophorbide a are the major chlorins. A downcore profile of chlorin concentration normalized to autochthonous organic carbon (OC) shows a decreasing trend. Chlorin productivity was corrected by removal of the effect of post-burial chlorin degradation. The temporal profile of chlorin productivity thereby obtained resembles that from autochthonous OC.The difference in primary productivity between the Holocene and the glacial for the lake is markedly smaller than that for Lake Baikal situated in the boreal zone. This difference between the two lakes is probably caused by the difference in their climatic conditions, such as temperature and precipitation. Precipitation at Lake Biwa is relatively large during the glacial and the Holocene because of the continuous influence of the East Asian monsoon. Lake Baikal precipitation is generally small as a result of control by the continental (Siberia) climate regime. In addition, a significant difference in productivity between the glacial and the Holocene for Lake Baikal may be essentially controlled by the hydrodynamic systems in the lake.Lake Biwa terrigenous OM input events occurred at least five times over the period 11–32 kyr BP, suggesting enhanced monsoon activity. Molecular examination of the layer with a large input of terrigenous OM during the Younger Dryas indicates that concentrations of terrigenous biomarkers such as n-C27–C31 alkanes, lignin phenols, cutin acids, ω-hydroxy acids and C29 sterols are high, suggesting that soil OM with peat-like material entered the lake as a result of flooding. An enhanced sedimentation rate in the last 3000 years might have been partially caused by agricultural activity around the lake. 相似文献
48.
The effect of a tidal cycle on the dynamics of nutrients in a tidal estuary in the Seto Inland Sea, Japan 总被引:4,自引:0,他引:4
Shigeru Montani Paolo Magni Megumi Shimamoto Nao Abe Koichi Okutani 《Journal of Oceanography》1998,54(1):65-76
A 24 hour time series survey was carried out during a spring tide (tidal range ca.2 m) of May 1995 on a tidal estuary in the
Seto Inland Sea, Japan, in the context of an integrated program planned to quantify the dynamics of biophilic elements (carbon,
nitrogen and phosphorus) and the roles played by the macrobenthos on the processes. Three stations were set along a transect
line of about 1.4 km, which linked the river to the rear to the innermost part of the subtidal zone. Every hour, at each station,
measurements were made of surface water temperature, salinity and dissolved oxygen concentration, and surface water was collected
for the determination of nutrients [NH4
+−N, (NO3
−+NO2
−)−N, PO4
3−−P and Si (OH)4−Si]. During the ebb flow, riverine input of silicate and nitrate+nitrite significantly increased the concentrations of both
the intertidal and the subtidal stations. Conversely, during the high tide, river nutrient concentrations were lowered by
the mixing of fresh water with sea water. As a result, best (inverse) correlations were found at the river station for salinity
against silicate (y=-2.9 Sal.+110.7,r
2=0.879) and nitrate+nitrite (y=-1.3 Sal.+48.4,r
2=0.796). In contrast, ammonium nitrogen concentrations were higher at intermediate salinities. Indeed, no significant correlation
was found between salinity and ammonium. The effect of the macrobenthos, which is abundant on the intertidal flat, is discussed
as a biological component that influences the processes of nutrient regeneration within the estuary. The effect of the tidal
amplitude is an important one in determining the extent of the variations in nutrient concentrations at all three stations,
which were stronger between the lower low tide and the higher high tide. 相似文献
49.
Yoshifumi Nogi Kumiko Nishi Nobukazu Seama Yoichi Fukuda 《Marine Geophysical Researches》2004,25(3-4):221-231
The seafloor spreading evolution in the Southern Indian Ocean is key to understanding the initial breakup of Gondwana. We
summarize the structural lineaments deduced from the GEOSAT 10 Hz sampled raw altimetry data as well as satellite derived
gravity anomaly map and the magnetic anomaly lineation trends from vector magnetic anomalies in the West Enderby Basin, the
Southern Indian Ocean. The gravity anomaly maps by both Sandwell and Smith 1997, J. Geophys. Res. 102, 10039–10054 and 10 Hz raw altimeter data show almost the same general trends. However, curved structural trends, which turn
from NNW–SSE in the south to NNE–SSW in the north, are detected only from gravity anomaly maps by 10 Hz raw altimeter data
just to the east of Gunnerus Ridge. NNE–SSW structural trends and magnetic anomaly lineation trends that are perpendicular
to them are observed between the Gunnerus Ridge and the Conrad Rise. To the west of Gunnerus Ridge, structural elements trend
NNE–SSW and magnetic polarity changes are normal to them. In contrast, almost NNW–SSE structural trends and ENE–WSW magnetic
polarity reversal strikes are dominant to the east of Gunnerus Ridge. Curved structural trends, which turn from WNW–ESE direction
in the south to NNE–SSW direction in the west, and magnetic polarity reversal strikes that are almost perpendicular to them
are observed just south of Conrad Rise. The magnetic polarity reversals may be parts of the Mesozoic magnetic anomaly sequence
that formed along side of the structural lineaments before the long Cretaceous normal polarity superchron. Curved structural
trends, detected only from gravity anomaly maps by 10 Hz raw altimeter data, most likely indicate slight changes in spreading
direction from an initial NNW–SSE direction to NNE–SSW. Our results also suggest that these curved structural trends are fracture
zones that formed during initial breakup of Gondwana. 相似文献
50.