全文获取类型
收费全文 | 314篇 |
免费 | 12篇 |
国内免费 | 7篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 10篇 |
地球物理 | 91篇 |
地质学 | 102篇 |
海洋学 | 53篇 |
天文学 | 56篇 |
自然地理 | 20篇 |
出版年
2024年 | 1篇 |
2021年 | 3篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 11篇 |
2017年 | 7篇 |
2016年 | 7篇 |
2015年 | 5篇 |
2014年 | 9篇 |
2013年 | 12篇 |
2012年 | 11篇 |
2011年 | 17篇 |
2010年 | 16篇 |
2009年 | 21篇 |
2008年 | 24篇 |
2007年 | 19篇 |
2006年 | 10篇 |
2005年 | 14篇 |
2004年 | 12篇 |
2003年 | 11篇 |
2002年 | 10篇 |
2001年 | 5篇 |
2000年 | 10篇 |
1999年 | 9篇 |
1998年 | 7篇 |
1997年 | 6篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 7篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 5篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有333条查询结果,搜索用时 62 毫秒
101.
Damping systems that are effective over a wide range of displacement amplitudes using metallic yielding component and viscoelastic damper in series 下载免费PDF全文
A damper system that absorbs energy over a wide range of displacement amplitudes during building vibration was proposed. This system uses a serial connection of a metallic yielding component and viscoelastic damper with a displacement limit mechanism. Three types of the system were developed and tested: a diagonal bracing type, inverted V bracing type, and wall type. The test results showed that all these systems have damping ratios higher than 8% at small vibration amplitudes on the order of 0.1 mm. For a large vibration, a displacement limit mechanism with two pins limited the displacement of the viscoelastic damper as designed. Analytical simulations established that the system reduced the acceleration and the story drift to 60–70% and 80%, respectively, during a small earthquake compared with a conventional metallic yielding damper system. Furthermore, it showed an equivalent control performance during a severe earthquake. The damper system requires that a clearance be maintained for the displacement limit mechanism. However, this may be lost through construction error, residual displacement after an earthquake, and temperature effects. The changes in the clearance due to these effects were discussed. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
102.
Kyunghoi Kim Tadashi Hibino Tamiji Yamamoto Shinjiro Hayakawa Yugo Mito Kenji Nakamoto In-Cheol Lee 《Marine pollution bulletin》2014
Field experiments were carried out to evaluate the effect of Granulated Coal Ash (GCA) on remediation of coastal sediments in terms of removing phosphates and hydrogen sulfide. Phosphate concentrations in the sediment were kept below 0.2 mg/l after the application of GCA, whereas those in the control sites increased up to 1.0 mg/l. The concentration of hydrogen sulfide in the sediment was maintained at almost zero in the experimental sites (GCA application sites) for over one year, whereas it ranged 0.1–2.4 mg S L−1 in control sites. Meanwhile, individual number of benthos increased in the experimental sites by several orders of magnitude compared to the control sites. The major process involved in hydrogen sulfide removal by GCA was thought to be the increase in pH, which suppresses hydrogen sulfide formation. From our findings, we concluded that GCA is an effective material for remediating organically enriched coastal sediment. 相似文献
103.
Tsuyoshi Komiya Shinji Yamamoto Shogo Aoki Keiko Koshida Masanori Shimojo Yusuke Sawaki Kazumasa Aoki Shuhei Sakata Takaomi D. Yokoyama Kenshi Maki Akira Ishikawa Takafumi Hirata Kenneth D. Collerson 《地学前缘(英文版)》2017,8(2):355-385
The Archean continental crusts account for ca.20% of the present volume,but the thermal history of the Earths' mantle suggests much more continental crusts were formed in the early Archean.Because the Archean continental crust underwent severe metamorphism,it is important to avoid influence by the later thermal events.We carried out a comprehensive geochronological work of Cathodoluminescence(CL) observation and U-Pb dating of zircons from orthogneisses and supracrustal rocks over the Saglek Block to obtain their protolith ages.The zircons were classified into three domains of core,mantle and rims,and the cores were further classified into three groups of inherited,altered and zoned cores based on the zonation on the CL images.We estimated the protolith ages from Pb-Pb ages of the zoned-cores of zircons with low U contents.We made a detailed sketch of a small outcrop in St.John's Harbour South(SJHS) area,and classified the orthogneisses and mafic enclaves into seven generations based on the geologic occurrence.The first and second generations comprise mafic rocks and lack magmatic zircons.We conducted CL imaging and U-Pb dating of zircons from the third,sixth and seventh generation of the orthogneisses to estimate the protolith ages at 3902 L 25,3892 ± 33 and 3897 ± 33 Ma for each,supporting the presence of the over 3.9 Ca Iqaluk Gneiss.The geological occurrence that the mafic rocks occur as enclaves within the 3.9 Ga Iqaluk Gneiss indicates that they are the oldest supracrustal rocks in the world.Our geochronological and geological studies show the Uivak Gneiss is quite varied in lithology and age from 3.6 to 3.9 Ga,and tentatively classified into six groups based on their ages.The oldest Uivak Gneiss components including the Iqaluk Gneiss are present around the SJHS area,and the orthogneisses become young as it is away.The lines of evidence of overprinting of younger granitoid on older granitoid in small outcrops and geological-map scale as well as presence of inherited zircons even in the oldest suite suggests that crustal reworking played an important role on erasing the ancient crusts. 相似文献
104.
http://dx.doi.org/10.1016/j.gsf.2016.08.001 总被引:1,自引:1,他引:0
Geological observations indicate that there are only a few rocks of Archean Earth and no Hadean rocks on the surface of the present-day Earth. From these facts, many scientists believe that the primordial continents never existed during Hadean Earth, and the continental volume has kept increasing. On the other hand, recent studies reported the importance of the primordial continents on the origin of life, implying their existence. In this paper, we discussed the possible process that could explain the loss of the primordial continents with the assumption that they existed in the Hadean. Although depending on the timing of the initiation of plate tectonics and its convection style, subduction erosion, which is observed on the present-day Earth, might have carried the primordial continents into the deep mantle. 相似文献
105.
We propose that competent layers composed of silicified rocks in the Cretaceous Ryoke low-pressure/temperature (low- P/T ) metamorphic belt in the Iwakuni–Yanai area, Southwest Japan, may be an exhumed equivalent of a seismically-reflective bright-layer in the middle crust. Silicified rocks crop out as layers or long lenticular bodies several to fifteen meters in thickness, and they are restricted to the area of greenschist facies conditions within a structural thickness of about one kilometer. The silicified rock layers exhibit a sharp contact with subjacent biotite schist but a gradational contact with overlying pelitic schist. Silicified rock is mainly composed of fine-grained quartz and minor muscovite and biotite, and some colored minerals have been variably decolorized by alteration. This implies that silicification turned the color of pelitic schists to pale gray or milky white. Quartz veins cutting schistosity at high angles were preferentially developed in the silicified rocks, while schistosity-parallel quartz veins, which underwent viscous flow, were observed in the underlying biotite schists. En echelon quartz veins and fishnet-like quartz veins are characteristic of silicified rocks. The modes of occurrence of quartz veins indicate that silicified rocks were competent relative to underlying biotite schist. The combination of contact with high-competence contrast adjacent to low-permeability silicified rocks may be a good reflector of seismic waves. If the silicified rocks were distributed in the middle crust to a considerable extent, they may result in seismic bright-layer reflections. 相似文献
106.
Hiroshi Yamamoto Natsumi Nakamori Masaru Terabayashi Hafiz Ur Rehman Masahiro Ishikawa Yoshiyuki Kaneko Takashi Matsui 《Island Arc》2010,19(3):458-469
Geological observations in the Horoman area, south‐central Hokkaido, show that the Horoman peridotite complex of the Hidaka metamorphic belt is a tectonic slice about 1200 m thick. The peridotite slab is intercalated into a gently east‐dipping structure. The underlying unit is a Cretaceous–Paleogene accretionary complex. Riedel shear planes in the sedimentary layers of the accretionary complex near the structural bottom of the peridotite slab indicate top‐to‐the‐west (thrust) displacement. The overlying unit is composed of felsic–pelitic gneisses and mafic–felsic intrusive rocks (the Hidaka metamorphic rocks). The boundary surface between the peridotite complex and metamorphic rocks forms a domal structure. Microstructures of sheared metamorphic rocks near the structural top of the peridotite slab indicate top‐to‐the‐east (normal) displacement. The results combined with previous studies suggest that the Horoman peridotite complex was emplaced onto the Asian margin (Northeast Japan) during the collision between the Asian margin and the Hidaka crustal block. 相似文献
107.
Ships carry ballast water for better stability and to control trim. However, the discharge of ballast water near ports is known to transport invasive species from one coastal area to another. The exchange of ballast water on the high seas is supposed to reduce such invasions of exotic species. In this study, we used denaturing gradient gel electrophoresis (DGGE) to analyze the composition of the bacterial community in ballast water before and after such a mid-ocean exchange, and we also measured total bacterial counts. Our findings confirmed that the ballast water was replaced by the mid-ocean exchange, as indicated by the marked change in the composition of the bacterial community. There was also a significant decrease in bacterial abundance after the mid-ocean exchange. Finally, our findings support the incubation hypothesis, because the composition of the bacterial communities changed over time within the same ballast water. 相似文献
108.
Maya P. Bhatt Toshiyuki Masuzawa Mineko Yamamoto Kevin H. Gardner 《Environmental Geology》2009,57(3):557-569
Surface water samples were collected from Langtang Lirung glacier outlet point to the Narayani river system in central Nepal
in order to investigate the role of elevation in the variation of chemistry along the drainage networks. The chemistry of
Langtang–Narayani river system was dominated by sulfide oxidation coupled with carbonate dissolution and weathering of silicate
minerals. Calcium and magnesium concentrations were relatively higher than other cations and the sum of both species strongly
correlated with alkalinity, supporting the dissolution of carbonate and dolomite as the dominant source for these ions. Aluminosilicate
minerals primarily as albite and anorthite appeared as dominant silicate minerals within the drainage basin. Bisiallitization
was the dominant type of weathering within the entire drainage system. Hydrogen ion concentration was lower in the low elevation
sites than in high elevation sites reflecting the more consumption of carbon dioxide in the low elevation sites due to enhanced
chemical weathering rates. Furthermore, major solutes like sum of base cations, silicon as well as alkalinity increased in
concentration in the lower elevation sites. All regulating factors appeared to be directly related to elevation and hence
elevation appeared to be the prime factor for the variation in chemical species along the Langtang–Narayani river system.
Toshiyuki Masuzawa: deceased. 相似文献
109.
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
110.
In a disk with a low optical depth, dust particles drift radially inward by the Poynting-Robertson (P-R) drag rather than are blown out by stellar radiation pressure following destructive collisions. We investigate the radial distribution of icy dust composed of pure ice and refractory materials in dust-debris disks taking into account the P-R drag and ice sublimation. We find that icy dust particles form a dust ring by their pile-ups at the edge of their sublimation zone, where they sublime substantially at the temperature 100-110 K. The distance of the dust ring is 20-35 AU from the central star with its luminosity L??30L⊙ and 65(L?/100L⊙)1/2 AU for L??30L⊙, where L⊙ is the solar luminosity. The effective optical depth is enhanced by a factor of 2 for L??100L⊙ and more than 10 for L??100L⊙. The optical depth of the outer icy dust disk exceeds that of the inner disk filled with refractory particles, namely, the residue of ice sublimation, which are further subjected to the P-R effect. As a result, an inner hole is formed inside the sublimation zone together with a dust ring along the outer edge of the hole. 相似文献