全文获取类型
收费全文 | 247篇 |
免费 | 6篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 12篇 |
地球物理 | 63篇 |
地质学 | 99篇 |
海洋学 | 26篇 |
天文学 | 21篇 |
自然地理 | 30篇 |
出版年
2021年 | 1篇 |
2020年 | 4篇 |
2019年 | 3篇 |
2018年 | 2篇 |
2017年 | 5篇 |
2016年 | 7篇 |
2015年 | 7篇 |
2014年 | 8篇 |
2013年 | 6篇 |
2012年 | 7篇 |
2011年 | 12篇 |
2010年 | 12篇 |
2009年 | 13篇 |
2008年 | 11篇 |
2007年 | 9篇 |
2006年 | 11篇 |
2005年 | 8篇 |
2004年 | 13篇 |
2003年 | 8篇 |
2002年 | 10篇 |
2001年 | 12篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1995年 | 1篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 1篇 |
1968年 | 1篇 |
1965年 | 1篇 |
1961年 | 1篇 |
排序方式: 共有255条查询结果,搜索用时 0 毫秒
61.
Masato Naruse Tetsuya Ito Yutaro Sekimoto Hiroyuki Toba Naohisa Satou Masahiro Sugimoto Wenlei Shan Yoshizou Iizuka Toshiaki Kamba Mamoru Kamikura Yasutaka Serizawa 《Experimental Astronomy》2009,24(1-3):89-107
We have developed a near-field vector beam measurement system covering the range of frequencies from 385 to 500 GHz. The measurement set-up is capable of measurements with dynamic range exceeding 50 dB and amplitude and phase stability respectively of 0.1 dB/h and 1 degree/5 min at room temperature. Beam patterns of the ALMA band 8 corrugated horns and receiver optics block were measured at room temperature and lately compared with physical optics calculations obtained in the far-field. Both co-polar and cross-polar beam patterns of a qualification model of the ALMA band 8 cartridge cooled in a cartridge-test-cryostat have also been measured in the near-field as a detector of a submillimeter vector network analyzer. The measurements presented in this work refer to the lowest, middle and upper frequencies of band 8. The comparisons between software model and experimental measurements at these frequencies show good agreement down to ?30 dB for the main polarization component. The cross-polarization level of the beam propagating through the receiver optics block was also characterized. We found that a cross-polarization level better than ?28 dB can be achieved at all measured frequencies. The measured beam pattern of this receiver corresponds to efficiency of greater than 92% at the sub reflector (diameter of 750 mm) of the ALMA 12 m optics. 相似文献
62.
Shin Ozawa Eiji Ohtani Masaaki Miyahara Akio Suzuki Makoto Kimura Yoshinori Ito 《Meteoritics & planetary science》2009,44(11):1771-1786
Abstract— The high‐pressure polymorphs of olivine, pyroxene, and plagioclase in or adjacent to shock melt veins (SMVs) in two L6 chondrites (Sahara 98222 and Yamato 74445) were investigated to clarify the related transformation mechanisms and to estimate the pressure‐temperature conditions of the shock events. Wadsleyite and jadeite were identified in Sahara 98222. Wadsleyite, ringwoodite, majorite, akimotoite, jadeite, and lingunite (NaAlSi3O8‐hollandite) were identified in Yamato 74445. Wadsleyite nucleated along the grain boundaries and fractures of original olivine. The nucleation and growth of ringwoodite occurred along the grain boundaries of original olivine, and as intracrystalline ringwoodite lamellae within original olivine. The nucleation and growth of majorite took place along the grain boundaries or fractures in original enstatite. Jadeite‐containing assemblages have complicated textures containing “particle‐like,” “stringer‐like,” and “polycrystalline‐like” phases. Coexistence of lingunite and jadeite‐containing assemblages shows a vein‐like texture. We discuss these transformation mechanisms based on our textural observations and chemical composition analyses. The shock pressure and temperature conditions in the SMVs of these meteorites were also estimated based on the mineral assemblages in the SMVs and in comparison with static high‐pressure experimental results as follows: 13–16 GPa, >1900 °C for Sahara 98222 and 17–24 GPa, >2100 °C for Yamato 74445. 相似文献
63.
Simple monitoring method for precaution of landslides watching tilting and water contents on slopes surface 总被引:2,自引:2,他引:0
Taro Uchimura Ikuo Towhata Trinh Thi Lan Anh Jou Fukuda Carlos J. B. Bautista Lin Wang Ichiro Seko Taro Uchida Akira Matsuoka Yosuke Ito Yuichi Onda Sho Iwagami Min-Seok Kim Naoki Sakai 《Landslides》2010,7(3):351-357
A low-cost and simple monitoring method for early warning of landslides is proposed. To detect abnormal deformation of a slope, this method employs a tilt sensor in place of an extensometer on the slope surface. In order to examine the relevance of measuring rotation angle on a slope surface by tilt sensor, model tests were conducted, and rotation on the slope surface was observed together with slide displacement along the surface. The rotation data responded 30 min before failure in a model test, which could be useful as a signal for early warning. However, the behavior of rotation before failure varies from case to case, and thus, criteria to issue warning should be defined more carefully. For a model slope made of uniform loose sand, measurement of slide displacement along the slope surface is sensitive to failure at the toe, while the measurement of rotation on the slope surface is useful to detect the development of progressive failure upward along the slope. Wireless sensor units with microelectromechanical systems (MEMS) tilt sensor and volumetric water content sensor were also examined on a real slope in Kobe City, and a long-term monitoring was attempted. A simple but possible way to define the criteria of judgment to issue warning can be proposed based on combination of data obtained by the tilt sensors and volumetric water content sensors. 相似文献
64.
Strong γ-ray emission from cocoons of young radio galaxies is predicted for the first time. Considering the process of adiabatic injection of the shock dissipation energy and mass of the relativistic jet in active nuclei into the cocoon, while assuming thermalizing electron plasma interactions, we find that the thermal electron temperature of the cocoon is typically predicted to be of the order of ∼ MeV, and is determined only by the bulk Lorentz factor of the relativistic jet. Together with the time-dependent dynamics of the cocoon expansion, we find that young cocoons can yield thermal bremsstrahlung emissions at energies ∼MeV. 相似文献
65.
Glonass Laser Ranging Accuracy With Satellite Signature Effect 总被引:1,自引:0,他引:1
GLONASS satellites have been tracked by the worldwide laser ranging networkas well as by the GLONASS-borne microwave-based technique. Owing to thelarge size of their corner cube reflector arrays, the amount of ranging data is enough to determine their orbits from laser ranging data alone. We found, however, that the large size of the array affected the accuracy of measurement to an extent that is dependent on the characteristics of the ranging systems. An azimuthal variation of the reflector array response was also detected in observations from single-photon laser ranging. Orbital analysis reveals that the effect makes the measured range on average 22 mm shorter than expected in the absence of the large array, which explains more than half of the offset of 39 mm previously discovered between microwave and laser orbits. 相似文献
66.
Ikeda M Maezawa H Ito T Saito G Sekimoto Y Yamamoto S Tatematsu K Arikawa Y Aso Y Noguchi T Shi SC Miyazawa K Saito S Ozeki H Fujiwara H Ohishi M Inatani J 《The Astrophysical journal》1999,527(1):L59-L62
Large-scale mapping observations of the 3P1-3P0 fine-structure transition of atomic carbon (C i, 492 GHz) and the J=3-2 transition of CO (346 GHz) toward the Orion A molecular cloud have been carried out with the Mount Fuji submillimeter-wave telescope. The observations cover 9 deg2 and include the Orion Nebula M42 and the L1641 dark cloud complex. The C i emission extends over almost the entire region of the Orion A cloud and is surprisingly similar to that of 13CO (J=1-0). The CO (J=3-2) emission shows a more featureless and extended distribution than C i. The C i/CO (J=3-2) integrated intensity ratio shows a spatial gradient running from the north (0.10) to the south (1.2) of the Orion A cloud, which we interpret as a consequence of the temperature gradient. On the other hand, the C i/13CO (J=1-0) intensity ratio shows no systematic gradient. We have found a good correlation between the C i and 13CO (J=1-0) intensities over the Orion A cloud. This result is discussed on the basis of photodissociation region models. 相似文献
67.
Keisuke Ito 《Earth and Planetary Science Letters》1976,30(1):65-70
Existing thermal models of the oceanic lithosphere predict too sharp an increase of heat flow towards the ridge axis. A new mathematical model of a thickening lithosphere is presented. The temperature distribution is computed by the use of observed surface heat flow as a boundary condition. If observed heat flow values represent flow of heat from the mantle, the model predicts a rather rapid growth of the lithosphere within the first 30 m.y. and a nearly steady state after 100 m.y. Heat flow from the asthenosphere to the lithosphere shows a minimum near the ridge axis, suggesting a down-going convective flow in the asthenosphere at both sides of a spreading center. 相似文献
68.
High-pressure phase transformations were investigated for two silicates, MgSiO3 and ZnSiO3; six germanates, MGeO3 and six titanates, MTiO3 (M=Ni, Mg, Co, Zn, Fe, and Mn) at about 1,000°C and pressures up to ca. 30 GPa. CoGeO3 was found to assume the ilmenite form. The ilmenite phases were confirmed to transform in the following schemes: to perovskite in MgSiO3 and MnGeO3, to corundum in MgGeO3 and ZnGeO3, to rocksalt plus rutile in ZnSiO3 and CoGeO3 and to rocksalt plus TiO2 (possibly of some denser structure) in NiTiO3, MgTiO3, CoTiO3, ZnTiO3 and FeTiO3. In the case of FeTiO3, the corundum form appeared as an intermediate phase. The possibility that the corundum type MnTiO3 might transform to some denser modification could not be excluded. The compound NiGeO3 was nonexistent throughout the pressure range studied. High-pressure phases of ABO3 (A=Ni, Mg, Co, Zn, Fe, and Mn; B=Si, Ge and Ti) are summarized, and those stabilized at pressures higher than 20 GPa are discussed. 相似文献
69.
Eiji Ito 《Physics of the Earth and Planetary Interiors》1975,10(1):88-93
High-pressure stability relations in cobalt and nickel silicates have been studied over the pressure range 130–330 kbar employing a double-staged split-sphere-type high-pressure apparatus.γ-Co2SiO4 and γ-Ni2SiO4 decompose directly into their constituent oxide mixtures (rocksalt plus stishovite) 175 kbar and 280 kbar, respectively. The result that γ-Ni2SiO4 has a wider stability field in pressure than γ-Co2SiO4, is consistent with simple crystal-field theory.The experimental precision is high enough to show that the decomposition boundary of γ-Co2SiO4 has a positive slope (dP/dT > 0) and a preliminary determination of the boundary curve is P(kbar) = 0.065 T (°C) + 110.No positive evidence for the existence of high-pressure forms of CoSiO3 and NiSiO3 has been obtained in these quenching experiments, and they finally decompose into constituent oxide mixtures as in the cases of orthosilicates. 相似文献
70.
We delineate shallow structures of the Mozumi–Sukenobu fault, central Japan, using fault zone waves generated by near-surface explosions and detected by a seismometer array. Two explosive sources, S1 and S2, were placed at a distance of about 2 km from the array, and the other two, S3 and S4, were at a distance of about 4 km. Fault zone head waves and fault zone trapped waves following direct P wave arrivals were clearly identified in the seismograms recorded by a linear seismometer array deployed across the fault in a research tunnel at a depth of 300 m. Synthetic waveforms generated by a 3-D finite-difference (3-D FD) method were compared with observed fault zone waves up to 25 Hz. The best fitting model indicates a 200-m-wide low-velocity zone extending at least to shot site S1 located 2 km east of the seismic array with a 20% decrease in the P wave velocity relative to the wall rock. The width of the low-velocity zone is consistent with the fault zone defined by direct geological observation in the research tunnel. However, the low-velocity zone should disappear just to the east of the site S1 to explain the observed fault zone waves for shot S3 and S4 located 4 km east of the seismometer array. Yet the observation and the simulation show notable trapped wave excitation even though shots S3 and S4 are outside the fault zone. These results indicate that (1) the effective waveguide for seismic waves along the fault does not exist east of source site S1 although the surface traces of the fault are observed in this region, and (2) considerable trapped waves can be excited by sources well outside the fault zone. These results highlight the along-strike variability in fault zone structure. 相似文献