全文获取类型
| 收费全文 | 107篇 |
| 免费 | 22篇 |
| 国内免费 | 7篇 |
专业分类
| 测绘学 | 2篇 |
| 大气科学 | 3篇 |
| 地球物理 | 67篇 |
| 地质学 | 17篇 |
| 海洋学 | 18篇 |
| 天文学 | 29篇 |
出版年
| 2022年 | 3篇 |
| 2021年 | 1篇 |
| 2019年 | 2篇 |
| 2018年 | 2篇 |
| 2017年 | 6篇 |
| 2016年 | 4篇 |
| 2015年 | 4篇 |
| 2014年 | 4篇 |
| 2013年 | 6篇 |
| 2011年 | 6篇 |
| 2010年 | 1篇 |
| 2009年 | 13篇 |
| 2008年 | 11篇 |
| 2007年 | 12篇 |
| 2006年 | 4篇 |
| 2005年 | 5篇 |
| 2004年 | 6篇 |
| 2003年 | 5篇 |
| 2002年 | 2篇 |
| 2001年 | 4篇 |
| 2000年 | 7篇 |
| 1999年 | 7篇 |
| 1998年 | 2篇 |
| 1996年 | 3篇 |
| 1995年 | 2篇 |
| 1994年 | 2篇 |
| 1993年 | 3篇 |
| 1992年 | 2篇 |
| 1991年 | 2篇 |
| 1990年 | 2篇 |
| 1989年 | 1篇 |
| 1987年 | 1篇 |
| 1954年 | 1篇 |
排序方式： 共有136条查询结果，搜索用时 15 毫秒
91.
地面核磁共振方法(MRS)因具有对地下水探测定性、定量的特点而备受地球物理工作者关注.传统研究中,人们局限于一维探测方法,假设层状含水构造,导致复杂地质环境下难以确定井位、不均匀含水层小水体难以分辨的反演解释瓶颈.针对现有测量中的不足,本文提出了MRS二维分布式探测模式,依据激发场不均匀特性,定义了实际测量中的测线方位角α,推导了分布式接收线圈MRS响应核函数表达式,实现了二维正演计算,探索了α角与探测灵敏度之间的关系.在此基础上,首次将Occam方法用于MRS二维反演解释中,实现了磁共振断层成像MRT(magnetic resonance tomography).模型试算中,根据含水层位置以及环境噪声变化的磁共振响应,客观评价了分布式MRS探测适用范围.理论先行可推动仪器完善,本文通过分布式接收单元设计、接收线圈数量和匝数增加与调整、放大器参数自适应设置与矫正,成功研制了地面分布式磁共振探测系统,并进行了野外验证.本文的研究成果将为基岩裂隙水定位、堤坝渗漏灾害水源评价,喀斯特溶洞含水构造精确探测提供有力的科学支撑. 相似文献
92.
93.
本文给出了对共振现象出现概率的理论分析与实验数据间关系的思考。样品取自位于半空间的硬化粗质冻土地基,包括石质冻层。参考从三个场地14次地震记录的纵、横波速求得的土层相对频率特征,进行了对其共振频率的评估。纵、横波速在前贝加尔和后贝加尔地区的粗质冻土层中随湿度和温度而变化。将这些概括化的速度值与一个共振频率和纵、横波度之间的关系式结合起来,用于评估被调查土层的纵、横波速的概率值。结果显示,通过综合在实验室尺度获得的速度值和现场测量获得的速度值的数据,则利用地震记录波来确定在松散土层内传播速度的概率值是可能的。 相似文献
94.
利用特征函数展开方法，给出了基于扩散效应的核磁共振Bloch控制方程的弛豫模式解表达式, 在此基础上分别给出了水饱和与油水双相饱和孔隙模型的核磁共振特性模拟结果. 结果表明，孔隙流体的核磁弛豫与孔隙大小、孔隙表面弛豫率、孔隙流体的扩散能力以及含油饱和度等有密切的关系. 对于水饱和孔隙，弛豫时间主要由孔隙大小控制. 当孔隙较大时，即使均匀大小孔隙，孔隙流体的弛豫也会表现为多指数弛豫. 而且最小模式弛豫时间与孔隙大小为非线性关系. 对于油水双相饱和孔隙，在孔隙较小时，含油饱和度对弛豫的影响主要表现在弛豫时间随含油饱和度的增加而线性减小；但在孔隙较大时，含油饱和度的增加对弛豫影响表现在两个方面，其一，孔隙水弛豫由多个弛豫模式控制逐渐转变为由最小弛豫模式控制；其二，孔隙水弛豫时间与含油饱和度表现为非线性关系. 对由实际岩芯抽象出的孔隙模型，采用本文获得的理论公式，在油水双相饱和时进行了正反演模拟. 计算结果与已有的实验结果较为一致. 相似文献
95.
W.-J. Wang 《Journal of Geodesy》2002,76(4):209-215
The 7 month-period (sub-Chandler) wobble is considered with respect to the nonlinear dynamical equation of polar motion.
Starting with the frequency modulation of Chandler wobble (CW) in the model developed by introduction of damping from perturbed
visco-elastic deformation, the rotation equation of the CW becomes a resonance model with a time-dependent parameter. According
to evolution calculation, the parameter resonance model is essentially identical to the reality of CW observations. If the
frequency of CW is modulated about 3 by visco-elastic deformation, then the amplitude of CW will be modulated by greater than 70. On the other hand, bifurcation may occur according to the nonlinear dynamical system of the parameter resonance model, i.e.
a pair of solutions splitting from the main CW. One is the 7-month-period wobble and the other is a motion with a period of
about 28 months. Although the latter is very weak, the 7-month-period wobble will be observed as the stability condition is
satisfied. The maximum amplitude is about 22.89 mas and the average 12.65 mas. This is identical to what is observed in reality.
Received: 7 April 2000 / Accepted: 5 March 2001 相似文献
96.
The dynamical evolution of dust particles forming a circumstellar disk around Pictoris is followed by numerical simulations on a Connection Machine. The disk appears to be cleared inside a radius of about 20 AU. We integrate simultaneously the orbits of 8,000 dust particles subjected to Poynting-Robertson drag and perturbed by one alleged planet. The simulations show that a planet revolving about Pictoris at a mean distance of 20 AU with a mass of at least 2 * 10–5 central stellar mass can confine the disk by outer resonance trapping. The azimuthal density distribution of particles which shows very strong variations. appears to be stationary in a frame rotating with the planet. 相似文献
97.
A short cut numerical method for evaluation of the modes of free oscillations of the basins which have irregular geometry and bathymetry is presented in this paper. In the method, a single wave is inputted to the basin as an initial impulse. The respective agitation in the basin is computed by using the numerical method solving the nonlinear form of long wave equations. The time histories of water surface fluctuations at different locations due to propagation of the waves in relation to the initial impulse are stored and analyzed by the fast Fourier transform technique (FFT) and energy spectrum curves for each location are obtained. The frequencies of each mode of free oscillations are determined from the peaks of the spectrum curves. The method is tested by using regular shaped flat bottom basins with different depths. The computed periods of free oscillations are compared with the theoretical values. The accuracy and performance of the method are discussed. As a case study for the application to the basins of irregular shape and bathymetry, the periods of free oscillations of the sea of Marmara is determined and discussed. 相似文献
98.
高质量的图像是ＭＲ诊断的基础。ＭＲ有多参数成像的特点，操作者必须发利用机器的技术指标，掌握人体组织固有的参数及与成像参数之间的关系优化组合，以达到提高图像质量之目的。本文着重讨论了影响ＭＲ图像质量的主要因素，提高信噪比，对比分辩率和空间分辩率等技术措施以合理的选择成像参数。 相似文献
99.
Quasi-electrostatic Z-mode waves created by the transmitting part of the OEDIPUS-C payload were measured on the receiving part at 1200 m distance. Solutions of the complete electromagnetic dispersion relation for a hot magnetoplasma reveal, however, that there is no solution that provides direct ray paths along the transmitter-receiver separation direction with the observed signal group delays. An interpretive model is therefore proposed in which sounder-accelerated electrons (SAE) radiate incoherently as they spiral along the magnetic field direction in the general direction of the receiving subpayload. Test-particle theory combined with the hot-plasma dispersion solution is used to predict the total electric field for previously reported SAE flux levels. It is found that voltage levels measured on the receiving dipoles have about the same order of magnitude as the predicted ones. 相似文献
100.
由于沉积有机质都存在有自由基，使其具有顺磁性。因此，它可以用于电子顺磁共振的分析和研究。近年来，电子顺磁共振应用于沉积有机质的研究无论在理论方面还是应用方面都有很大的进展。本文主要概述沉积有机质中自由基形成与演化机理及电子顺磁共振在研究有机质成熟度、油气源岩评价和古地温方面的研究现状和主要进展。 相似文献