全文获取类型
收费全文 | 1643篇 |
免费 | 231篇 |
国内免费 | 144篇 |
专业分类
测绘学 | 492篇 |
大气科学 | 28篇 |
地球物理 | 348篇 |
地质学 | 518篇 |
海洋学 | 242篇 |
天文学 | 24篇 |
综合类 | 136篇 |
自然地理 | 230篇 |
出版年
2024年 | 5篇 |
2023年 | 10篇 |
2022年 | 45篇 |
2021年 | 43篇 |
2020年 | 39篇 |
2019年 | 61篇 |
2018年 | 34篇 |
2017年 | 87篇 |
2016年 | 55篇 |
2015年 | 61篇 |
2014年 | 62篇 |
2013年 | 86篇 |
2012年 | 137篇 |
2011年 | 107篇 |
2010年 | 61篇 |
2009年 | 90篇 |
2008年 | 106篇 |
2007年 | 114篇 |
2006年 | 112篇 |
2005年 | 85篇 |
2004年 | 101篇 |
2003年 | 74篇 |
2002年 | 59篇 |
2001年 | 34篇 |
2000年 | 41篇 |
1999年 | 37篇 |
1998年 | 40篇 |
1997年 | 49篇 |
1996年 | 36篇 |
1995年 | 20篇 |
1994年 | 31篇 |
1993年 | 13篇 |
1992年 | 16篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 13篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1981年 | 1篇 |
1979年 | 4篇 |
1954年 | 3篇 |
排序方式: 共有2018条查询结果,搜索用时 15 毫秒
21.
Contamination of seismic reflection records at early times by first-order water reverberations can be especially severe during survey operations over hard and flat sea floors on the continental shelf or in lake environments. A new dereverberation scheme based on two classical techniques — predictive deconvolution and velocity filtering — has been developed to address this problem. The techniques are combined spatially to take advantage of their complementary offset- and time-dependent properties. Stage I of the scheme consists of applying predictive deconvolution at short offset. The data are previously conditioned by a normal moveout correction with the water velocity which restores the periodicity of the reverberations in the offset-time plane and enhances the performance of deconvolution. Stage II of the scheme involves velocity filtering in the common-midpoint domain which is particularly effective at long offset where the moveout difference between primary reflections and reverberations is largest. The dereverberation scheme is well suited for the initial processing of large volumes of data due to the general availability of cost-effective deconvolution and velocity filtering algorithms in seismic processing software packages. Practical implementation issues are illustrated by a field example from the GLIMPCE survey in Lake Superior.Lithoprobe Publication No. 475. 相似文献
22.
In 1995, Suh and Park developed a numerical model that computes the reflection of regular waves from a fully perforated-wall caisson breakwater. This paper describes how to apply this model to a partially perforated-wall caisson and irregular waves. To examine the performance of the model, existing experimental data are used for regular waves, while a laboratory experiment is conducted in this study for irregular waves. The numerical model based on a linear wave theory tends to over-predict the reflection coefficient of regular waves as the wave nonlinearity increases, but such an over-prediction is not observed in the case of irregular waves. For both regular and irregular waves, the numerical model slightly over- and under-predicts the reflection coefficients at larger and smaller values, respectively, because the model neglects the evanescent waves near the breakwater. 相似文献
23.
Numerical analyses for the Bragg resonant reflection of carrier waves associated long waves due to sinusoidally varying seabeds are performed by using a set of coupled ordinary differential equations derived from the Boussinesq equations. The Boussinesq equations are firstly approximated with the Fourier decomposition. The coupled governing equations are then derived and used to simulate evolution of both short and long wave components. It is also found that wave groups are generated by two carrier waves with slightly different frequencies. The wave energy of the initial wave components is transferred to other harmonic components during propagation over a long distance. Evolution and reflection of both short and long waves were largely affected by nonlinearity. 相似文献
24.
In this paper, the theoretical analysis and experimental studies are employed to investigate the reflection characteris-tics of partial standing waves caused by wave overtopping and sloping top of structures. Based on the principle of conser-vation of wave energy flux, the third-order Stokes wave theory is used to formulate the reflection coefficient at wave overtopping; the calculation results are regressed into an applied expression. A series of experiments of wave reflection for a vertical-wall structure with chamfered and overhanging upper sections are carried out to investigate the influence of top slope on wave reflection. The regularity of variation of wave reflection in this case is analysed based on the experimental results. 相似文献
25.
The analytical method (AM) for separation of composite waves is presented based on the Hilbert transform. It is ap-plicable to both regular and irregular trains of waves. The wave data series measured with two wave gauges in the experi-ments are separated into two series of incident and reflected waves. Then, the reflection coefficient can be easily ob-tained. The arrival of reflected waves can also be detected for improveraent of the accuracy of the reflection coefficient. The reflection performance of the physical model can be estimated exactly without calculation of wave height and phase difference. Numerical samples developed to test the method are proved to be accurate. Physical experiments are conduct-ed and compared with Goda s method and satisfactory results are obtained. 相似文献
26.
27.
高校GIS专业课程设置的探索 总被引:8,自引:4,他引:4
通过对高校地理信息系统(简称GIS)专业基础理论、基本方法、应用技术、与学科最新发展前沿的深入分析,结合GIS专业学生的知识结构体系,提出了一种新的GIS专业基础课和专业课的设置,在对GIS人才的特点和能力培养途径提出了自己建议的同时,对课程内容及教学形式等相关问题进行了相应地探讨。 相似文献
28.
29.
酸溶——催化极谱法测定地质样品中的钨、钼 总被引:3,自引:0,他引:3
本文采用混合酸溶解样品,对影响催化体系稳定的酸度、温度和不同反应时间的因素分别进行了对比试验,确定催化体系相对稳定的最佳条件,经过大量样品的分析验证,分析方法可靠。 相似文献
30.