全文获取类型
收费全文 | 517篇 |
免费 | 129篇 |
国内免费 | 70篇 |
专业分类
测绘学 | 89篇 |
大气科学 | 57篇 |
地球物理 | 210篇 |
地质学 | 183篇 |
海洋学 | 101篇 |
天文学 | 15篇 |
综合类 | 35篇 |
自然地理 | 26篇 |
出版年
2023年 | 2篇 |
2022年 | 8篇 |
2021年 | 7篇 |
2020年 | 21篇 |
2019年 | 24篇 |
2018年 | 22篇 |
2017年 | 24篇 |
2016年 | 23篇 |
2015年 | 24篇 |
2014年 | 19篇 |
2013年 | 28篇 |
2012年 | 25篇 |
2011年 | 32篇 |
2010年 | 31篇 |
2009年 | 36篇 |
2008年 | 22篇 |
2007年 | 33篇 |
2006年 | 45篇 |
2005年 | 26篇 |
2004年 | 28篇 |
2003年 | 29篇 |
2002年 | 26篇 |
2001年 | 22篇 |
2000年 | 18篇 |
1999年 | 12篇 |
1998年 | 15篇 |
1997年 | 10篇 |
1996年 | 21篇 |
1995年 | 11篇 |
1994年 | 17篇 |
1993年 | 16篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1976年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有716条查询结果,搜索用时 312 毫秒
61.
62.
63.
高分辨区域输送模式中不同输送格式的对比试验 总被引:3,自引:0,他引:3
本文对两种输送格式在理论试验的基础上,引入19层高分辨区域输送模式EM3,由中尺度模式(MM4)提供实例输送风场,积分至13、18、30、50、70小时,作分析和对比数值试验。采用的两种格式是:二阶动量矩守恒的Prather格式(以下简称为SOM)及通量订正的Smolar格式。数值试验结果表明,高精度的SOM格式使数值扩散减小一个量级, 使输送物质(SO#-[2])中心浓度比Smolar格式增大3~4倍, 采用SOM格式还明显改进了浓度中心水平平均运动轨迹的模拟精度,选择高精度的平流格式是改进模拟结果的重要途径。 相似文献
64.
本文提出了三度体重磁异常的人机联作校正-迭代反演方法。该方法用二度半组合多边形棱柱体来逼近三度体,从而把三度体重磁异常反演问题转化为二度半体的反演问题;为了消除组合体迭加场的影响,该方法采用了一种校正-迭代技术。理论模型反演计算表明,该方法实际可行。 相似文献
65.
66.
The three-dimensional (3-D) resection problem is usually solved by first obtaining the distances connecting the unknown point P{X,Y,Z} to the known points Pi{Xi,Yi,Zi}i=1,2,3 through the solution of the three nonlinear Grunert equations and then using the obtained distances to determine the position {X,Y,Z} and the 3-D orientation parameters {,, }. Starting from the work of the German J. A. Grunert (1841), the Grunert equations have been solved in several substitutional steps and the desire as evidenced by several publications has been to reduce these number of steps. Similarly, the 3-D ranging step for position determination which follows the distance determination step involves the solution of three nonlinear ranging (`Bogenschnitt') equations solved in several substitution steps. It is illustrated how the algebraic technique of Groebner basis solves explicitly the nonlinear Grunert distance equations and the nonlinear 3-D ranging (`Bogenschnitt') equations in a single step once the equations have been converted into algebraic (polynomial) form. In particular, the algebraic tool of the Groebner basis provides symbolic solutions to the problem of 3-D resection. The various forward and backward substitution steps inherent in the classical closed-form solutions of the problem are avoided. Similar to the Gauss elimination technique in linear systems of equations, the Groebner basis eliminates several variables in a multivariate system of nonlinear equations in such a manner that the end product normally consists of a univariate polynomial whose roots can be determined by existing programs e.g. by using the roots command in Matlab.Acknowledgments.The first author wishes to acknowledge the support of JSPS (Japan Society of Promotion of Science) for the financial support that enabled the completion of the write-up of the paper at Kyoto University, Japan. The author is further grateful for the warm welcome and the good working atmosphere provided by his hosts Professors S. Takemoto and Y. Fukuda of the Department of Geophysics, Graduate School of Science, Kyoto University, Japan. 相似文献
67.
A calibration method to solve the groundwater inverse problem under steady- and transient-state conditions is presented. The method compares kriged and numerical head field gradients to modify hydraulic conductivity without the use of non-linear optimization techniques. The process is repeated iteratively until a close match with piezometric data is reached. The approach includes a damping factor to avoid divergence and oscillation of the solution in areas of low hydraulic gradient and a weighting factor to account for temporal head variation in transient simulations. The efficiency of the method in terms of computing time and calibration results is demonstrated with a synthetic field. It is shown that the proposed method provides parameter fields that reproduce both hydraulic conductivity and piezometric data in few forward model solutions. Stochastic numerical experiments are conducted to evaluate the sensitivity of the method to the damping function and to the head field estimation errors. 相似文献
68.
地图数字化中基于点位坐标的统一平差模型 总被引:3,自引:0,他引:3
探讨了地图数字化过程中采用平差方法来建立坐标计算的统一模型。将测得的角度、边长等数据化为方向、距离观测值列立误差方程,通过调用统一的平差迭代计算程序来计算未知点坐标及精度。详细给出了基于平差的11种常用坐标计算方法,并通过实例进行了说明。 相似文献
69.
Salt is widespread in the Australian landscape – in soil, regolith and groundwater – leading to concerns that land management practices may be putting much agricultural land and important water resources at risk of salinisation. Defining the location and nature of salt stores is an important first step in understanding the processes leading to salinity of soils, streams and groundwater resources, and predicting areas that may be at risk. Airborne geophysics can define subsurface salt stores and mobilisation pathways. Airborne electromagnetics (AEM) can map the three-dimensional conductivity structure of the landscape but does not, intrinsically, quantify the amount of salt. Salinity, moisture content, porosity and mineralogy all contribute to the electromagnetic signal, and each can vary significantly throughout the landscape.In the Lower Balonne catchment, Queensland, the relationship between AEM and the amount of salt in the landscape was quantified using laboratory analyses of pore fluids from core samples. A general statistical relationship was established between AEM conductivity and salt load (defined as the product of pore fluid salinity, porosity and moisture content)—with a significant positive correlation although data were generally widely dispersed. Comparison of calculated salt load with borehole electromagnetic logs gives insight into the factors contributing to dispersion in the AEM data.The relationship transforms bulk conductivity to salt load in 5 m layers, allowing the generation of a three-dimensional map of the salt load. This is a powerful tool for identifying areas that may require monitoring and management interventions to reduce salinity risk. An example is given of salt loads beneath an established irrigation area in the Lower Balonne catchment, Queensland. 相似文献
70.
A. H. W. Kearsley R. Forsberg A. Olesen L. Bastos K. Hehl U. Meyer A. Gidskehaug 《Journal of Geodesy》1998,72(10):600-605
Two detailed geoids have been computed in the region of North Jutland. The first computation used marine data in the offshore
areas. For the second computation the marine data set was replaced by the sparser airborne gravity data resulting from the
AGMASCO campaign of September 1996. The results of comparisons of the geoid heights at on-shore geometric control showed that
the geoid heights computed from the airborne gravity data matched in precision those computed using the marine data, supporting
the view that airborne techniques have enormous potential for mapping those unsurveyed areas between the land-based data and
the off-shore marine or altimetrically derived data.
Received: 7 July 1997 / Accepted: 22 April 1998 相似文献