全文获取类型
收费全文 | 515篇 |
免费 | 160篇 |
国内免费 | 113篇 |
专业分类
测绘学 | 34篇 |
大气科学 | 100篇 |
地球物理 | 309篇 |
地质学 | 186篇 |
海洋学 | 39篇 |
天文学 | 6篇 |
综合类 | 21篇 |
自然地理 | 93篇 |
出版年
2024年 | 3篇 |
2023年 | 8篇 |
2022年 | 12篇 |
2021年 | 8篇 |
2020年 | 23篇 |
2019年 | 26篇 |
2018年 | 18篇 |
2017年 | 10篇 |
2016年 | 22篇 |
2015年 | 28篇 |
2014年 | 33篇 |
2013年 | 26篇 |
2012年 | 26篇 |
2011年 | 35篇 |
2010年 | 26篇 |
2009年 | 39篇 |
2008年 | 33篇 |
2007年 | 42篇 |
2006年 | 48篇 |
2005年 | 34篇 |
2004年 | 37篇 |
2003年 | 30篇 |
2002年 | 35篇 |
2001年 | 21篇 |
2000年 | 22篇 |
1999年 | 22篇 |
1998年 | 13篇 |
1997年 | 14篇 |
1996年 | 20篇 |
1995年 | 13篇 |
1994年 | 3篇 |
1993年 | 11篇 |
1992年 | 11篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1980年 | 6篇 |
1978年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有788条查询结果,搜索用时 31 毫秒
71.
Introduction The effect of local site conditions on wave propagation is one of the most attractive topics in engineering seismology. It may be resolved by either a numerical method or an analytical method. Numerical methods include the finite difference, finite element, boundary element method, etc. The analytical method is the wave function expansion method. The advantage of these numerical methods is that they can be applied to local inhomogeneity of arbitrary shapes, but analytical method … 相似文献
72.
文章介绍了瞬态瑞雷面波勘探技术的理论基础和勘探原理、工作方法、资料的整理与解释,并结合工程实例说明瞬态面波勘探技术的应用效果。 相似文献
73.
介绍了太空垃圾监测及清除工作现状,分析了现有监测太空垃圾的雷达技术、激光技术及激光雷达技术的可行性,以STK软件模拟分析太空垃圾运动轨迹,得出了太空垃圾实时监测系统的可实现方法和建议。 相似文献
74.
Fabien Gibert Juan Cuesta Jun-Ichi Yano Nicolas Arnault Pierre H. Flamant 《Boundary-Layer Meteorology》2007,125(3):553-573
We question the correlation between vertical velocity (w) on the one hand and the occurrence of convective plumes in lidar reflectivity (i.e. range corrected backscatter signal Pz
2) and depolarization ratio (Δ) on the other hand in the convective boundary layer (CBL). Thermal vertical motion is directly
investigated using vertical velocities measured by a ground-based Doppler lidar operating at 2 μm. This lidar provides also
simultaneous measurements of lidar reflectivity. In addition, a second lidar 200 m away provides reflectivities at 0.53 and
1 μm and depolarization ratio at 0.53 μm. The time series from the two lidars are analyzed in terms of linear correlation
coefficient (ρ). The main result is that the plume-like structures provided by lidar reflectivity within the CBL as well as the CBL height
are not a clear signature of updrafts. It is shown that the lidar reflectivity within the CBL is frequently anti-correlated
(ρ (w, Pz
2 )) with the vertical velocity. On the contrary, the correlation coefficient between the depolarization ratio and the vertical
velocity ρ (w, Δ ) is always positive, showing that the depolarization ratio is a fair tracer of updrafts. The importance of relative humidity
on the correlation coefficient is discussed.
An erratum to this article can be found at 相似文献
75.
76.
提出多分量瑞利波勘探的技术思想和方法,研制成功专用的防爆型多分量瑞利波勘探仪器,建立了在用极化分析对瑞利波勘探记录的多分量信号分析的基础上,用极化滤波提取有效瑞利波信号的方法。在煤矿井下及地面实际应用表明,多分量瑞利波勘探与单分量法比较,信号的信噪比、勘探深度和可靠性均有一定的提高。 相似文献
77.
Phase velocities of Rayleigh waves for the Adriatic Sea area are obtained in the period range 25–190 sec along the path (l'Aquila-Trieste) AQU-TRI and 20–167 sec along the path (Trieste-Bari) TRI-BAI.The phase velocities are systematically higher than the known values for the surrounding regions. The data inversion indicates the presence of a lithosphere typical of stable continental areas with clear high-velocity lid (V
s
4.6 km/sec) overlying a well developed low velocity zone (V
s
4.2 km/sec).P. F. Geodinamica C.N.R., Roma Pubbl. N. 189. 相似文献
78.
A row of rigid piles is addressed as the countermeasures for isolating Rayleigh waves in a poroelastic half‐space. The complex characteristic equations for Rayleigh waves are derived via Biot's theory and their existence conditions are given. The piles are modeled as Euler–Bernoulli beams with longitudinal displacements and the diffracted field by each pile is constructed only with Rayleigh waves. Six infinite linear systems of algebraic equations are obtained in terms of the equilibrium of forces and continuity of displacements at the pile–soil interfaces. The systems are subsequently solved in the complex least‐squares sense. The influence of certain pile and soil characteristics such as the permeability of poroelastic soil, spacing between the piles and length of the piles on the isolating performance of a pile barrier is investigated. Computed results show that the permeability of poroelastic soil displays a significant effect on the vertical amplitude reduction of Rayleigh waves. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
79.
Lidar methods for observing mineral dust aerosols are reviewed.These methods include Mie scattering lidars,polarization lidars,Raman scattering lidars,high-spectral-resolution lidars,and fluorescence lidars.Some of the lidar systems developed by the authors and the results of the observations and applications are introduced.The largest advantage of the lidar methods is that they can observe vertical distribution of aerosols continuously with high temporal and spatial resolutions.Networks of ground-based lidars provide useful data for understanding the distribution and movement of mineral dust and other aerosols.The lidar network data are actually used for validation and assimilation of dust transport models,which can evaluate emission,transport,and deposition of mineral dust.The lidar methods are also useful for measuring the optical characteristics of aerosols that are essential to assess the radiative effects of aerosols.Evolution of the lidar data analysis methods for aerosol characterization is also reviewed.Observations from space and ground-based networks are two important approaches with the lidar methods in the studies of the effects of mineral dust and other aerosols on climate and the environment.Directions of the researches with lidar methods in the near future are discussed. 相似文献
80.