全文获取类型
收费全文 | 115篇 |
免费 | 4篇 |
国内免费 | 11篇 |
专业分类
大气科学 | 4篇 |
地球物理 | 31篇 |
地质学 | 66篇 |
海洋学 | 15篇 |
天文学 | 7篇 |
综合类 | 2篇 |
自然地理 | 5篇 |
出版年
2021年 | 3篇 |
2020年 | 1篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 6篇 |
2016年 | 6篇 |
2015年 | 6篇 |
2014年 | 5篇 |
2013年 | 8篇 |
2012年 | 2篇 |
2011年 | 8篇 |
2010年 | 10篇 |
2009年 | 1篇 |
2008年 | 13篇 |
2007年 | 7篇 |
2006年 | 3篇 |
2005年 | 5篇 |
2004年 | 4篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有130条查询结果,搜索用时 15 毫秒
91.
Yusuke Sawaki Manabu Nishizawa Takeshi Suo Tsuyoshi Komiya Takafumi Hirata Naoto Takahata Yuji Sano Jian Han Yoshiaki Kon Shigenori Maruyama 《Gondwana Research》2008,14(1-2):148
The Precambrian/Cambrian (PC/C) boundary is one of the most important intervals for the evolution of life, represented by prominent biological evolution from the first appearance of soft-bodied animals from the late Neoproterozoic to the sudden diversification of animals with mineralized skeletons in the Cambrian. In South China several areas contain many fossils and are well exposed, suitable for the investigation of PC/C boundary. However, geochronological relationships are still poorly known because of lack of combined detailed investigations of internal structures of zircons and in-situ U–Pb dating.We focus on the internal structure of zircons from a tuff layer within Bed 5 in the Meishucun section on which we undertook cathodoluminescence (CL) imaging and in-situ U–Pb dating with LA-ICP-MS and nano-SIMS. Over 600 zircons from the tuff layer were classified into three types based on their CL images: oscillatory rims, inherited cores and dull structures. U–Pb dating of the internal structure of the zircons by LA-ICP-MS clearly shows a distinct unimodal age population dependent on the structure: 531 ± 17 Ma for the oscillatory rims and 515 Ma for the dull structures. The clear oscillatory zonation, the prismatic morphology, and their occurrence indicate that the oscillatory rims were formed from felsic magmatism, and that the U–Pb nano-SIMS age of 536.5 ± 2.5 Ma records the depositional age of the tuff. Our results indicate that the PC/C boundary is situated below Bed 5, and therefore the bottom of Zone 1 (Marker A) is more appropriate for the PC/C boundary than is the top of Zone 1 (Marker B). The age of a positive anomaly (P2) in the early Cambrian is estimated to be ca. 536 Ma. 相似文献
92.
The Permian planktonic distribution is not well known, in contrast to other fossil distributions of nekton and benthos. Radiolaria are representative microfossils of plankton in the Permian palaeocean. This study compares both correlated radiolarian occurrences (Pseudotormentus De Wever et Caridroit and Quadriremis Nazarov et Ormiston) in literature data from the Pacific Rim and quantitative data from the Liuhuang and Gujingling sections in South China. Pseudotormentus distributions are concentrated in the Panthalassa, whereas Quadriremis occurrences are distributed over both the Panthalassa and the Palaeotethys. The uneven distribution of Pseudotormentus seems to have been controlled by a difference in the oceanic basins, indicating the presence of faunal differences in Permian planktonic microorganisms between the Panthalassa and the Palaeotethys. In other words, this study infers the provincialism of Permian planktonic microorganisms. The uneven distribution is explainable by a hypothesis that Pseudotormentus was strongly affected by a Panthalassan equatorial current. 相似文献
93.
Regional characteristics of the synoptic-scale wave disturbances in the tropical lower troposphere were examined by analyzing the FGGE level III-b data. Three tropical regions, western Pacific, eastern Pacific, and a region from the African Continent to the Atlantic, were selected for the present study. Spectrum analysis, trajectory analysis and composite analysis were used to obtain characteristics of the wave disturbances for each region.Main findings are as follows: 1.) The generation region of the western Pacific wave disturbances related to typhoon development are found around 5° N and 170° E. 2.) An interaction of the western Pacific wave disturbances with the upper Mid-Pacific trough was indicated statistically as an intensifying condition for typhoons. 3.) The wave disturbances in the eastern Pacific originate to the west of Panama and propagate west-north-westward with a period of 5.7 day and a wavelength of about 2700 km. 4.) The structure of the eastern Pacific wave disturbances is similar to that of the western Pacific disturbances. 5.) Two different paths of the African waves are found over the African Continent. The northern disturbance has a period of 4.4 days while the southern one has a period of 3.3–3.6 days. 6.) Disturbances along the northern path of the African waves are traced only to as far as 45° W, and those along the southern path are traced to the Caribbean Sea. 相似文献
94.
Tsuyoshi Tanaka 《Contributions to Mineralogy and Petrology》1975,52(4):233-246
Rare earth elements (REE), Ba, Sr as well as major elements in 47 pre-Cenozoic geosynclinal volcanics in Japan have been determined. The types of chondrite-normalized REE patterns can be classified into two large groups viz. log-linear REE pattern group and convex REE pattern group. Each group thus classified is also closely related to major element features. Although the REE pattern of the latter group is observed in the island arc tholeiite as well as abyssal tholeiite, the relative content of Ba to La indicates that the Japanese geosynclinal volcanics of this group are more akin to those of abyssal tholeiites than are the island arc ones. Two distinct types of REE fractionation are found in the volcanics of the Japanese geosyncline. The geographical distribution of two groups of the geosynclinal volcanics is different from that of the Cenozoic volcanics in Japan, and the petrochemical features of volcanics from northeast Japan can be distinguished from those of southwest Japan. By analogy with the current knowledge concerning a close relation between the tectonic settings and the geochemical features of the present-day volcanics, the geosynclinal basalts in question are inferred to have been formed during a tensional tectonic movement and have erupted along a local rift zone like the marginal seas and inter-arc basins in the Western Pacific Ocean or along part of a global rift system such as the Red Sea Trough. 相似文献
95.
Tsuyoshi Ishida 《Computers and Geotechnics》1990,9(4):341-353
To examine the accuracy and the chracteristics of the Distinct Element Method (DEM) which has non-deformable elements, the results simulated by the DEM were compared to the results of experiments and/or theories for three simple block models of a pillar, a mass and a toppling model. Consequently, it was elucidated that the DEM is a good numerical method which can be effectively applied to toppling failure of real fissured rock slopes. 相似文献
96.
97.
Tsuyoshi Komiya Shigenori Maruyama Takafumi Hirata Hisayoshi Yurimoto Susumu Nohda 《Island Arc》2004,13(1):47-72
Abstract Recent geological investigations of the Isua Supracrustal Belt (3.8 Ga), southern West Greenland, have suggested that it is the oldest accretionary complex on earth, defined by an oceanic plate‐type stratigraphy and a duplex structure. Plate history from mid‐oceanic ridge through plume magmatism to subduction zone has been postulated from analysis of the reconstructed oceanic plate stratigraphy in the accretionary complex. Comparison between field occurrence of greenstones in modern and ancient accretionary complexes reveals that two types of tholeiitic basalt from different tectonic settings, mid‐oceanic ridge basalt (MORB) and oceanic island basalt (OIB), occur. This work presents major, trace and rare earth element (REE) compositions of greenstones derived from Isua MORB and OIB, and of extremely rare relict igneous clinopyroxene in Isua MORB. The Isua clinopyroxenes (Cpx) have compositional variations equivalent to those of Cpx in modern MORB; in particular, low TiO2 and Na2O contents. The Isua Cpx show slightly light (L)REE‐depleted REE patterns, and the calculated REE pattern of the host magma is in agreement with that of Isua MORB. Analyses of 49 least‐altered greenstones carefully selected from approximately 1200 samples indicate that Isua MORB are enriched in Al2O3, and depleted in TiO2, FeO*, Y and Zr at the given MgO content, compared with Isua OIB. In addition, Isua MORB show an LREE‐depleted pattern, whereas Isua OIB forms a flat REE pattern. Such differences suggest that the Early Archean mantle had already become heterogeneous, depending on the tectonic environment. Isua MORB are enriched in FeO compared with modern MORB. Comparison of Isua MORB with recent melting experiments shows that the source mantle had 85–87 in Mg? and was enriched in FeO. Potential mantle temperature is estimated to be approximately 1480°C, indicating that the Early Archean mantle was hotter by at most approximately 150°C than the modern mantle. 相似文献
98.
REE abundances in ten chondrites (nine falls and one find) were determined very accurately by mass-spectrometric stable isotope dilution techniques. All of the chondrites have different relative and absolute REE patterns. Except for Eu and, rarely, for Ce, the REE abundances in chondrites are smoothly fractionated from sample to sample. Notwithstanding differences in the abundances of common REE, four of five L6 chondrites have very similar absolute Eu abundances; their mutually-normalized REE patterns are not curved, but are composed of two rectilinear segments.The Leedey-normalized REE pattern for St. Séverin (LL6) is composed of two concave curves. Yonozu's (H4,5) pattern shows negligibly concave curvature on both sides of Eu. Kesen's (H4) pattern is unusual in its overall pattern but also in irregularities for particular elements. The irregularity may be connected with the unusually high vapor pressure of metallic Yb. The REE pattern for the Allende bulk sample shows a discontinuity, presumably reflecting its considerable heterogeneity of composition and structure. It is evident that any pattern of ordinary chondrites cannot be produced from the Allende bulk pattern. A comparison is also made with the results on the chondrite composites previously investigated. 相似文献
99.
Chemostratigraphy of the Ediacaran basinal setting on the Yangtze platform,South China: Oceanographic and diagenetic aspects of the carbon isotopic depth gradient 下载免费PDF全文
Seishiro Furuyama Akihiro Kano Yoko Kunimitsu Tsuyoshi Ishikawa Wei Wang Xin‐chun Liu 《Island Arc》2017,26(5)
The Ediacaran Yangtze platform in South China, which represents depositional settings ranging from coastal to basinal, provides valuable information for understanding climate changes and animal evolution during the Ediacaran Period. Although the shallower settings have been investigated, research on the basinal sections has been limited. This has hampered efforts to establish stratigraphic correlations and understand the oceanographic setting of the Yangtze platform. In this paper, the chemostratigraphy of a basinal section at Fengtan, Hunan Province, is reported based on analyses of stable carbon isotope profiles in carbonates (δ13Ccarb), organic matter (δ13Corg), total organic carbon, 87Sr/86Sr ratios, and Mn, Rb, and Sr concentrations. The basinal section of the Doushantuo Formation, which is represented at Fengtan, provides data supporting regional correlations and oceanography. Three intervals in the Doushantuo Formation are correlated with the Three Gorges: (i) a negative δ13Ccarb anomaly with stable δ13Corg values and altered 87Sr/86Sr ratios in the lower section can be correlated to the boundary between Doushantuo Members 2 and 3 (Interval A); (ii) a relatively high δ13Ccarb anomaly with unaltered 87Sr/86Sr ratios (up to 0.7086) in the middle section corresponding to the lower part of Doushantuo Member 3 (Interval B); and (iii) a negative δ13Ccarb anomaly with lowered δ values in the upper section can be correlated to the long interval of negative δ13Ccarb (Interval C). The Gaskiers glaciation is likely represented in Interval A, and Interval C corresponds to the Shuram excursion reported for other Ediacaran localities. Our correlations confirm the depth gradient of δ13Ccarb in the Yangtze platform and imply that reductive conditions prevailed in the basinal section from the Early to Middle Ediacaran. Under such conditions, anaerobic degradation of organic carbon or methane perturbed the inorganic carbon isotopic compositions and was at least partly responsible for the depth gradient of δ13Ccarb. 相似文献
100.
Yuichi Miyake Qinting Jiang Wang Yuan Nobuyasu Hanari Tsuyoshi Okazawa Barbara Wyrzykowska Man Ka So Paul K.S. Lam Nobuyoshi Yamashita 《Marine pollution bulletin》2008,57(6-12):357
Dietary intake is one of the important routes of human exposure to brominated flame retardants (BFRs) such as polybrominated diphenyl ethers (PBDEs). The use of PBDEs may also result in exposure to polybrominated dibenzo-p-dioxins and dibenzofurans (PBDDs/DFs), as these compounds are impurities in technical mixtures of BFRs and can also be formed unintentionally by the same processes that generate chlorinated dioxins. This study determined the concentrations of polybrominated compounds in common seafood in Guangzhou and Zhoushan, and assessed the health risks of these chemicals via consumption of contaminated seafood. Seafood samples (fish, bivalves, shrimp, crab, and cephalopods) purchased from local markets in 2003 and 2004 were analyzed for PBDEs and PBDDs/DFs. The highest concentration of total PBDEs (46.3 ng g−1 lipid wt.) was detected in fish from Guangzhou, in which BDEs 47 and 209 were the two predominant congeners. The total daily intakes of PBDEs, PBDDs, and PBDFs were, 946, 6.39, and 6.54 pg kg−1 body weight (bw) in Guangzhou, and 489, 4.99, and 7.65 pg kg−1 bw in Zhoushan, respectively. The hazard ratios for PBDDs and PBDFs were both greater than unity, indicating that these compounds may pose some health risks to the local population. 相似文献