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91.
浅地表软弱覆盖层对地震动的影响具有强非线性,但因观测记录样本量过小,难以通过参考谱比法等直接方法予以可靠分析。本文基于日本KiK-net台网136个竖向钻井台阵获取的141881组加速度记录的统计分析,研究了地表/井下反应谱比值随地震动强度变化的非线性变化规律与主要影响因素。利用变窗口尺度的滑动窗口平均法加强数据线性度,并确定了与地震动强度相关的台站最小记录样本量,统计结果表明地表/井下反应谱比值平台值随地震动强度变化的非线性衰减指数为−0.24~−0.08。利用套索(Lasso)算法统计回归发现,本研究12个场地特性表征参数中,30 m平均剪切波速($ {V}_{\mathrm{s}30} $)、场地卓越频率与地表/井下反应谱比值非线性衰减指数具有较好的正相关性;较弱强度地震动作用下地表/井下傅里叶谱比值峰值、地表/井下反应谱比值峰值与地表/井下反应谱比值非线性衰减指数具有较好的负相关性。 相似文献
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Introduced to astronomy less than a decade ago, infrared detector arrays have radically and forever changed astronomer's observational techniques, instruments, and telescope designs. This paper first examines the array technology development that caused this change, with emphasis on the 1- to 5-m band. Technology trends and projections for further development within the infrared industry are analyzed to assist astronomers in planning future instruments. This technology development is predicted to result in arrays with lower noise, greater well depth, response to a wider band of wavelengths, and, above all, much larger formats than arrays currently in use. 相似文献
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Anton M. Dainty 《Pure and Applied Geophysics》1990,132(1-2):221-244
The application of standard array processing techniques to the study of coda presents difficulties due to the design criteria of these techniques. Typically the techniques are designed to analyze isolated, short arrivals with definite phase velocity and azimuth and have been useful in the frequency range around 1 Hz. Coda is long in time and may contain waves of different types, phase velocities and azimuths. Nonetheless, it has proved possible to use or adapt array methods to answer two questions: what types of waves are present in coda and where are they scattered? Most work has been carried out on teleseismicP coda; work on local coda has lagged due to lack of suitable data and the difficulties of dealing with high frequencies. The time domain methods of beamforming and Vespagram analysis have shown that there is coherent energy with a high phase velocity comparable toP orPP in teleseismicP coda. These methods can detect this “coherent” coda because it has a fairly definite phase velocity and the same, or close to, azimuth as firstP orPP. This component must consist ofP waves and is either scattered near the source, or reflected in the mantle path as apdpP or precursorPP reflection. The Fourier transform method of the frequency-wavenumber spectrum has been adapted by integrating around circles of constant phase velocity (constant total wavenumber) to produce the wavenumber spectrum, which shows power as a function of wavenumber, or phase velocity. For teleseismicP coda, wavenumber spectra demonstrate that there is a “diffuse” coda of shear,Lg or surface waves scattered from teleseismicP near the receiver. Wavenumber spectra also suggest that the coherent coda is produced by near-source scattering in the crust, not mantle reflection, since it is absent or weak for deep-focus events. Crustal earthquakes have a very strong coherent component of teleseismic coda, suggesting scattering from shear to teleseismicP near the source. Three-component analysis of single-station data has shown the presence of off-azimuth arrivals and may lead to the identification of waves scattered from a single scatterer. 相似文献
97.
针对收发分置的MIMO模式阵列天线物理设计时,一个等效阵列可由多种物理收发阵列实现的病态问题,从测绘角度切入,依据等效相位中心原理,分析了ARTINO系统不同收发组合的优缺点。引入测绘应用关心的波段、分辨率、高程精度及工作高度等要求,优化设计了真实测绘航空平台的MIMO下视阵列SAR线阵阵元的数目和位置矢量。根据该配置进行了仿真实验,通过三维成像结果和原始仿真场景的差分对比,高程重建误差均值和标准差,以及整个场景和单独建筑物区域误差在半分辨率之内的概率值,证明了优化阵列配置的合理性和有效性。 相似文献
98.
Marianna V. Ivashina Jan Simons Jan Geralt Bij De Vaate 《Experimental Astronomy》2004,17(1-3):149-162
In this paper we demonstrate the practical analysis of a dense Focal Plane Array (FPA) for a deep dish radio telescope. The analytical model is used to optimize efficiency and bandwidth of deep dish system by varying design parameters such as feed size and FPA aperture field. A prototype FPA was evaluated on the Westerbork Synthesis Radio Telescope (WSRT) and the resulting efficiency is discussed. 相似文献
99.
Jaap D. Bregman 《Experimental Astronomy》2004,17(1-3):407-416
Five out of six Square Kilometre Array (SKA) science programs need extensive surveys at frequencies below 1.4 GHz and only four need high-frequency observations. The latter ones drive to expensive high surface accuracy collecting area, while the former ask for multi-beam receiver systems and extensive post correlation processing. In this paper, we analyze the system cost of a SKA when the field-of-view (Fov) is extended from 1 deg2 at 1.4 GHz to 200 deg2 at 0.7 GHz for three different antenna concepts. We start our analysis by discussing the fundamental limitations and cost issues of wide-band focal plane arrays (FPA) in dishes and cylinders and of wide-band receptors in aperture arrays. We will show that a hybrid SKA in three different antenna technologies will give the highest effective sensitivity for all six key science programs. 相似文献
100.
Ian S. McLean 《Experimental Astronomy》2002,14(1):25-32
The advent of solid-state imaging devices transformed astronomy. Beginning with the introduction into astronomy of charge-coupled
devices in 1976, followed a decade later by infrared arrays, astronomers gained access to near-perfect imaging devices. The
consequences have been nothing short of revolutionary, perhaps especially so in the infrared. Witness, for example, the spectacular
pictures from the Hubble Space Telescope cameras, or the impressive infrared imagery from the 2MASS project. Within the last
decade CCD formats deployed or planned for use in ground-based cameras have become huge. Infrared mosaics, stimulated by the
Next Generation Space Telescope, are coming soon. In addition, new technologies such as CMOS (Complementary Metal Oxide Semiconductors)
and STJs (Superconductiong Tunnel Junctions) are being developed and the future of astronomical detectors looks very exciting,
especially in an era of giant telescopes performing at their diffraction-limit.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献