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131.
132.
Astronomical-topographic levelling using high-precision astrogeodetic vertical deflections and digital terrain model data 总被引:2,自引:1,他引:1
At the beginning of the twenty-first century, a technological change took place in geodetic astronomy by the development of
Digital Zenith Camera Systems (DZCS). Such instruments provide vertical deflection data at an angular accuracy level of 0.̋1
and better. Recently, DZCS have been employed for the collection of dense sets of astrogeodetic vertical deflection data in
several test areas in Germany with high-resolution digital terrain model (DTM) data (10–50 m resolution) available. These
considerable advancements motivate a new analysis of the method of astronomical-topographic levelling, which uses DTM data
for the interpolation between the astrogeodetic stations. We present and analyse a least-squares collocation technique that
uses DTM data for the accurate interpolation of vertical deflection data. The combination of both data sets allows a precise
determination of the gravity field along profiles, even in regions with a rugged topography. The accuracy of the method is
studied with particular attention on the density of astrogeodetic stations. The error propagation rule of astronomical levelling
is empirically derived. It accounts for the signal omission that increases with the station spacing. In a test area located
in the German Alps, the method was successfully applied to the determination of a quasigeoid profile of 23 km length. For
a station spacing from a few 100 m to about 2 km, the accuracy of the quasigeoid was found to be about 1–2 mm, which corresponds
to a relative accuracy of about 0.05−0.1 ppm. Application examples are given, such as the local and regional validation of
gravity field models computed from gravimetric data and the economic gravity field determination in geodetically less covered
regions. 相似文献
133.
Accuracy analysis of vertical deflection data observed with the Hannover Digital Zenith Camera System TZK2-D 总被引:4,自引:1,他引:3
This paper analyses the accuracy of vertical deflection measurements carried out with the Digital Zenith Camera System TZK2-D,
an astrogeodetic state-of-the-art instrumentation developed at the University of Hannover. During 107 nights over a period
of 3.5 years, the system was used for repeated vertical deflection observations at a selected station in Hannover. The acquired
data set consists of about 27,300 single measurements and covers 276 h of observation time, respectively. For the data collected
at an earlier stage of development (2003 to 2004), the accuracy of the nightly mean values has been found to be about 0′′.10−0′′.12.
Due to applying a refined observation strategy since 2005, the accuracy of the vertical deflection measurements was enhanced
into the unprecedented range of 0′′.05 − 0′′.08. Accessing the accuracy level of 0′′.05 requires usually 1 h of observational
data, while the 0′′.08 accuracy level is attained after 20 min measurement time. In comparison to the analogue era of geodetic
astronomy, the accuracy of vertical deflection observations is significantly improved by about one order of magnitude. 相似文献
134.
An experimental research was conducted to determine the corrosion and bearing capacity of a reinforced concrete (RC) slab at different ages in a marine environment. Results show that the development of corrosion-induced cracks on a slab in a marine environment can be divided into three stages according to crack morphology at the bottom of the slab. In the first stage, cracks appear. In the second stage, cracks develop from the edges to the middle of the slab. In the third stage, longitudinal and transverse corrosion-induced cracks coexist. The corrosion ratio of reinforcements nonlinearly increases with the age, and the relationship between the corrosion ratio of the reinforcements and the corrosion-induced crack width of the concrete is established. The flexural capacity of the corroded RC slab nonlinearly decreases with the age, and the model for the bearing capacity factor of the corroded RC slab is established. The mid-span deflection of the corroded RC slab that corresponds to the yield of the reinforcements linearly increases with the increase in corrosion ratio. Finally, the mechanisms of corrosion morphology and the degradation of the mechanical properties of an RC slab in a marine environment are discussed on the basis of the basic theories of steel corrosion in concrete and concrete structure design. 相似文献
135.
Structures subjected to large inelastic deformations during violent ground shaking do not always return to their initial ‘at-rest’ position but may have residual displacements. Even if collapse does not occur, large residual displacements may render them unusable or irreparable. In order to investigate the likely magnitude of residual displacement many bilinear single-degree-of-freedom oscillators with specified ductilities of 2·0, 4·0 and 6·0, stiffness ratios ranging from −0·25 to 1·0 and fundamental periods from 0 to 3·0s were subjected to 11 earthquake records from various ground types. It is shown that bilinear oscillators with positive stiffness ratios generally have small residual displacements, while those with negative stiffness ratios tend to undergo little inelastic reversal of deformation and have larger residual displacements. Reasons for this behaviour were able to be explained by means of a ‘hysteresis centre curve’. A design example for structures able to be modelled as single-degree-of-freedom oscillators is provided. © 1997 John Wiley & Sons, Ltd. 相似文献
136.
建立了一种Timoshenko裂纹梁的分析模型并且获得了闭合形式的挠度解析解。首先,在一致梁的理论框架下,通过引入δ函数模拟裂纹导致的局部柔度,建立用广义函数表示的Timoshenko裂纹梁的微分控制方程,进而得到挠度的闭合形式的解答;其次,根据线弹性断裂力学理论,利用转角及挠度突变与局部柔度系数的关系,建立Timoshenko裂纹梁的模型参数与裂纹深度的显式表示;最后,通过对裂纹深度与挠度、转角和曲率间关系的分析,总结了结构响应的损伤敏感性及其特征,并且通过与引入裂纹奇异单元的有限元结果进行比较,验证了本文所建分析模型及求解方法的正确性。研究结果表明,本文所建立的Timoshenko裂纹梁的分析模型,具有较高的计算精度和效率,在结构模型修正和损伤识别中具有良好的应用前景。 相似文献
137.
138.
139.
举力效应是指方向性切变气流经过地形激发的重力波能够使平均气流发生水平旋转.本文首先根据日本气象厅台风数据集统计了2006—2015年登陆台湾的台风个例,分析台风路径的偏转情况.然后利用二维傅里叶变换对欧洲中间尺度天气预报中心的再分析数据进行滤波,得到台风的环境大气层结和水平风场.最后根据台风环境风场以及台湾地形计算地形重力波举力,分析举力对台风路径偏转的可能贡献.结果表明,近十年共有20个台风登陆台湾,其中2006—2008年有10个.除去5个路径较为复杂的台风,本文对15个台风的地形重力波举力进行分析,发现有14个台风的路径偏转方向与举力方向一致.对于路径偏转最为明显的6个台风(偏转角度大于30°),地形重力波举力对台风路径偏转的贡献可达10%,部分解释了台风经过台湾地形时发生的路径偏转. 相似文献
140.
船舶监控系统中实现了船只航迹线的动态绘制,发过程中涉及到偏转角度算法和距离插值两个核心算法,视化表现方面取得了良好的效果。系统能够根据船只航行方向动态显示航行轨迹,程序开系统开发实践表明,这两个算法的合理应用在航迹线可 相似文献