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101.
Hikaru Iwamori Hitomi Nakamura Masaki Yoshida Takashi Nakagawa Kenta Ueki Atsushi Nakao Tatsuji Nishizawa Satoru Haraguchi 《Comptes Rendus Geoscience》2019,351(2-3):209-220
Recent statistical analyses on the isotopic compositions of oceanic, arc, and continental basalts have revealed that the Earth's mantle is broadly divided into eastern and western hemispheres. The present study aimed to characterize the isotopically defined east–west geochemical hemispheres using trace-element concentrations. Basalt data with Rb, Sr, Nd, Sm, Pb, Th, and U in addition to the isotopic ratios 87Sr/86Sr, 143Nd/144Nd, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb were selected mostly from the GEOROC and PetDB databases. A total of 4787 samples were used to investigate the global geochemical variations. The results show that the wide trace-element variations are broadly explained by the melting of melt-metasomatized and fluid-metasomatized mantle sources. The larger amount of the fluid component derived from subducted plates in the eastern hemisphere than that in the western hemisphere is inferred from the basalts. These characteristics support the hypothesis that focused subduction towards the supercontinent created the mantle geochemical hemispheres. 相似文献
102.
基于低温热年代学特征的构造重建(或解译)与浅部地表过程模型在诠释盆-山结构与演化过程中受到越来越广泛的重视与应用.青藏高原东缘米仓山-川北前陆盆山系统楔入冲断构造模型与浅部地貌建造(非)耦合的检验校正为米仓山造山带构造变形及其动力学模型研究提供了契机.基于稳态楔入冲断构造低温热年代学模型研究表明,米仓山-川北前陆盆-山结构带盆山地貌的建造和低温热年代学(磷灰石裂变径迹和(U-Th)/He)特征具有明显的耦合性,二者统一于(盆地向)具~4°古地貌斜坡的楔入冲断构造模型.现今米仓山地区低温热年代学不具有明显的海拔高程和年龄线性关系,但当古地貌具有~4°坡度时低温热年代学与古地貌具有明显的线性相关性,揭示晚白垩世米仓山东西段具有一致(或相似)的稳态抬升剥露特征,东西段剥露速率分别为0.05 mm/a 和0.03 mm/a.古地貌坡度与古地温梯度具有较好的相关性(R2=95%~98%),相关古地温梯度(25~35 ℃/km)符合米仓山稳态剥露地质结构特征.米仓山造山带楔入冲断构造模型的发育可能受控于多套滑脱层系(尤其是深部和浅部滑脱层系)和扬子板块能干性基底对造山带盆地向扩展变形过程的阻挡作用. 相似文献
103.
A numerical simulation was conducted to predict the change of pCO2 in the ocean caused by CO2 leaked from an underground aquifer, in which CO2 is purposefully stored. The target space of the present model was the ocean above the seafloor. The behavior of CO2 bubbles, their dissolution, and the advection-diffusion of dissolved CO2 were numerically simulated. Here, two cases for the leakage rate were studied: an extreme case, 94,600 t/y, which assumed that a large fault accidentally connects the CO2 reservoir and the seafloor; and a reasonable case, 3800 t/y, based on the seepage rate of an existing EOR site. In the extreme case, the calculated increase in ΔpCO2 experienced by floating organisms was less than 300 ppm, while that for immobile organisms directly over the fault surface periodically exceeded 1000 ppm, if momentarily. In the reasonable case, the calculated ΔpCO2 and pH were within the range of natural fluctuation. 相似文献
104.
Partitioning of the grain-size components of Dali Lake core sediments: evidence for lake-level changes during the Holocene 总被引:4,自引:0,他引:4
Jule Xiao Zhigang Chang Bin Si Xiaoguang Qin Shigeru Itoh Zaur Lomtatidze 《Journal of Paleolimnology》2009,42(2):249-260
We recovered a sediment core (DL04) from the depocenter of Dali Lake in central-eastern Inner Mongolia. The upper 8.5 m were
analyzed at 1-cm intervals for grain-size distribution to partition the grain-size components and provide a high-resolution
proxy record of Holocene lake level changes. Partitioning of three to six components, C1, C2, C3 through C6 from fine to coarse
modes within the individual polymodal distributions, into overlapping lognormal distributions, was accomplished utilizing
the method of lognormal distribution function fitting. Genetic analyses of the grain-size components suggest that two major
components, C2 and C3, interpreted as offshore-suspension fine and medium-to-coarse silt, can serve as sediment proxies for
past changes in the level of Dali Lake. Lower modal sizes of both C2 and C3 and greater C3 and lower C2 percentages reflect
higher lake stands. The proxy data from DL04 core sediments span the last 12,000 years and indicate that Dali Lake experienced
five stages during the Holocene. During the interval ca. 11,500–9,800 cal year BP, lake level was unstable, with drastic rises
and falls. Following that interval, the lake level was marked by high stands between ca. 9,800 and 7,100 cal year BP. During
the period from ca. 7,100 to 3,650 cal year BP, lake level maintained generally low stands, but displayed a slight tendency
to rise. Subsequently, the lake level continued rising, but exhibited high-frequency, high-amplitude fluctuations until ca.
1,800 cal years ago. Since ca. 1,800 cal year BP, the lake has displayed a gradual lowering trend with frequent fluctuations. 相似文献
105.
Mitsuhiro Nagata Kazuhiro Miyazaki Hideki Iwano Tohru Danhara Hideyuki Obayashi Takafumi Hirata Koshi Yagi Yoshikazu Kouchi Koshi Yamamoto Shigeru Otoh 《Island Arc》2019,28(4)
We have estimated the timescale of material circulation in the Sanbagawa subduction zone based on U–Pb zircon and K–Ar phengite dating in the Ikeda district, central Shikoku. The Minawa and Koboke units are major constituents of the high‐P Sanbagawa metamorphic complex in Shikoku, southwest Japan. For the Minawa unit, ages of 92–81 Ma for the trench‐fill sediments, are indicated, whereas the age of ductile deformation and metamorphism of garnet and chlorite zones are 74–72 Ma and 65 Ma, respectively. Our results and occurrence of c. 150 Ma Besshi‐type deposits formed at mid‐ocean ridge suggest that the 60‐Myr‐old Izanagi Plate was subducted beneath the Eurasian Plate at c. 90 Ma, and this observation is consistent with recent plate reconstructions. For the Koboke unit, the depositional ages of the trench‐fill sediments and the dates for the termination of ductile deformation and metamorphism are estimated at c. 76–74 and 64–62 Ma, respectively. In the Ikeda district, the depositional ages generally become younger towards lower structural levels in the Sanbagawa metamorphic complex. Our results of U–Pb and K–Ar dating show that the circulation of material from the deposition of the Minawa and Koboke units at the trench through an active high‐P metamorphic domain to the final exhumation from the domain occurred continuously throughout c. 30 Myr (from c. 90 to 60 Ma). 相似文献
106.
Spatial distribution of the apatite fission‐track ages in the Toki granite,central Japan: Exhumation rate of a Cretaceous pluton emplaced in the East Asian continental margin 下载免费PDF全文
Takashi Yuguchi Shigeru Sueoka Hideki Iwano Tohru Danhara Masayuki Ishibashi Eiji Sasao Tadao Nishiyama 《Island Arc》2017,26(6)
The Cretaceous Toki granitic pluton of the Tono district, central Japan was emplaced in the East Asian continental margin at about 70 Ma. The Toki granite has apatite fission‐track (AFT) ages ranging from 52.1 ±2.8 Ma to 37.1 ±3.6 Ma (number of measurements, n = 33); this indicates the three‐dimensional thermal evolution during the pluton's low‐temperature history (temperature in the AFT partial annealing zone: 60–120 °C). The majority of the Toki granite has a spatial distribution of older ages in the shallower parts and younger ages in the deeper parts, representing that the shallower regions arrived (were exhumed) at the AFT closure depth earlier than the deeper regions. Such a cooling pattern was predominantly constrained by the exhumation of the Toki granitic pluton and was related to the regional denudation of the Tono district. The age–elevation relationships (AERs) of the Toki granite indicate a fast exhumation rate of about 0.16 ±0.04 mm/year between 50 Ma and 40 Ma. The AFT inverse calculation using HeFTy program gives time‐temperature paths (t–T paths), suggesting that the pluton experienced continuous slow cooling without massive reheating since about 40 Ma until the present day. A combination of the AERs and AFT inverse calculations represents the following exhumation history of the Toki granite: (i) the fast exhumation at a rate of 0.16 ±0.04 mm/year between 50 Ma and 40 Ma; (ii) slow exhumation at less than 0.16 ±0.04 mm/year after 40 Ma; and (iii) exposure at the surface prior to 30–20 Ma. The Tono district, which contains the Toki granite, underwent slow denudation at a rate of less than 0.16 ±0.04 mm/year within the East Asian continental margin before the Japan Sea opening at 25–15 Ma and then within the Southwest Japan Arc after the Japan Sea opening, which is in good agreement with representative denudation rates obtained in low‐relief hill and plain fields. 相似文献
107.
Yoshiaki Ishihara Masaki Kanao Masa-yuki Yamamoto Shigeru Toda Takeshi Matsushima Takahiko Murayama 《地学前缘(英文版)》2015,6(2)
Characteristic infrasound waves observed at Antarctic stations demonstrate physical interaction involving environmental changes in the Antarctic continent and the surrounding oceans.A Chaparraltype infrasound sensor was installed at Syowa Station(SYO;39°E,69°S),East Antarctica,as one of the projects of the International Polar Year(IPY2007—2008).Data continuously recorded during the three seasons in 2008—2010 clearly indicate a contamination of the background oceanic signals(microbaroms)with peaks between 4 and 10 s observed during a whole season.The peak amplitudes of the microbaroms have relatively lower values during austral winters,caused by a larger amount of sea-ice extending around the L(u|")tzow-Holm Bay near SYO,with decreasing ocean wave loading effects.Microbaroms measurements are useful tool for characterizing ocean wave climate,complementing other oceanographic and geophysical data.A continuous monitoring by infrasound sensors in the Antarctic firmly contributes to the Comprehensive Nuclear-Test-Ban Treaty(CTBT) in the southern high latitude,together with the Pan-Antarctic Observations System(PAntOS) under the Scientific Committee on Antarctic Research(SCAR).Detailed measurements of the infrasound waves in Antarctica,consequently,could be a new proxy for monitoring regional environmental change as well as the temporal climate variations in the polar regions. 相似文献
108.
A mathematical model of spit growth and barrier elongation adjacent to an inlet (of arbitrary width), supplied by sediment coming from longshore sediment transport, was developed based on the spit growth model proposed by Kraus (1999). The fundamental governing equation is the conservation equation for sand, where the width of the spit is assumed constant during growth. The portion of the longshore sediment transport feeding the spit has been estimated based on the ratio between the depth of the inlet channel and the depth of active longshore transport. Sediment transport from the channel due to the inlet flow, as well as other sinks of sand (e.g., dredging), are taken into account. Measured data on spit elongation at Fire Island Inlet, United States, and at Badreveln Spit, Sweden, were used to validate the model. The simulated results agree well with the measured data at both study sites, where spit growth at Fire Island was restricted by the inlet flow and the growth at Badreveln Spit was unrestricted. The model calculation for Fire Island Inlet indicates that the dredging to maintain channel navigation is the major reason for the stable period observed from 1954 to 1994 at the Fire Island barrier. The average annual net longshore transport rate at the eastern side of the Fire Island inlet obtained in this study was about 220,000 m3/yr, of which approximately 165,000 m3/yr (75% of the net longshore transport) is deposited in the inlet feeding the spit growth, whereas the remaining portion (25%) is bypassed downdrift through the ebb shoal complex. 相似文献
109.
110.
Michael E. Jones Alastair C. Edge Keith Grainge William F. Grainger Rüdiger Kneissl G. G. Pooley Richard Saunders Shigeru J. Miyoshi Taisuke Tsuruta Koujun Yamashita Yuzuru Tawara Akihiro Furuzawa Akihiro Harada Isamu Hatsukade 《Monthly notices of the Royal Astronomical Society》2005,357(2):518-526
We have observed the Sunyaev–Zel'dovich (SZ) effect in a sample of five moderate-redshift clusters with the Ryle Telescope, and used them in conjunction with X-ray imaging and spectral data from ROSAT and ASCA to measure the Hubble constant. This sample was chosen with a strict X-ray flux limit using both the Bright Cluster Sample and the Northern ROSAT All-Sky Survey (RASS) cluster catalogues to be well above the surface brightness limit of the RASS, and hence to be unbiased with respect to the orientation of the cluster. This controls a major potential systematic effect in the SZ/X-ray method of measuring H 0 . Taking the weighted geometric mean of the results and including the main sources of error, namely the noise in the SZ measurement, the uncertainty in the X-ray temperatures and the unknown ellipticity and substructure of the clusters, we find H 0 = 59+10 −9 (random)+8 −7 (systematic) km s−1 Mpc−1 assuming a standard cold dark matter model with ΩM = 1.0, ΩΛ = 0.0 or H 0 = 66+11 −10 +9 −8 km s−1 Mpc−1 if ΩM = 0.3, ΩΛ = 0.7 . 相似文献