全文获取类型
收费全文 | 673篇 |
免费 | 135篇 |
国内免费 | 217篇 |
专业分类
测绘学 | 136篇 |
大气科学 | 87篇 |
地球物理 | 154篇 |
地质学 | 445篇 |
海洋学 | 77篇 |
天文学 | 25篇 |
综合类 | 56篇 |
自然地理 | 45篇 |
出版年
2024年 | 5篇 |
2023年 | 11篇 |
2022年 | 27篇 |
2021年 | 38篇 |
2020年 | 40篇 |
2019年 | 38篇 |
2018年 | 25篇 |
2017年 | 49篇 |
2016年 | 37篇 |
2015年 | 51篇 |
2014年 | 42篇 |
2013年 | 41篇 |
2012年 | 68篇 |
2011年 | 44篇 |
2010年 | 46篇 |
2009年 | 42篇 |
2008年 | 26篇 |
2007年 | 43篇 |
2006年 | 58篇 |
2005年 | 39篇 |
2004年 | 41篇 |
2003年 | 34篇 |
2002年 | 31篇 |
2001年 | 28篇 |
2000年 | 28篇 |
1999年 | 15篇 |
1998年 | 10篇 |
1997年 | 8篇 |
1996年 | 10篇 |
1995年 | 8篇 |
1994年 | 10篇 |
1993年 | 12篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有1025条查询结果,搜索用时 15 毫秒
11.
惯性/双星组合导航系统的滤波与仿真 总被引:2,自引:0,他引:2
介绍了惯性导航系统和双星导航系统各自的运行方式和优缺点;详细推导了组合导航系统的误差方程和量测方程;介绍了Kalman滤波的整个过程并最后进行了仿真计算。仿真结果显示,惯性导航系统和双星导航系统的组合弥补了各自的不足,具有较好的精度和可靠性。 相似文献
12.
13.
14.
指出了共线条件方程式教学中应注意的一些问题:共线条件方程式是联立的两个平面方程式,存在双主距(fx,fy)时的几何概念,以及它的变换式与直接线性变换关系式的异同点。 相似文献
15.
Use of Geomorphological Information in Indirect Landslide Susceptibility Assessment 总被引:31,自引:6,他引:31
The objective of this paper is to evaluate the importance of geomorphological expert knowledge in the generation of landslide susceptibility maps, using GIS supported indirect bivariate statistical analysis. For a test area in the Alpago region in Italy a dataset was generated at scale 1:5,000. Detailed geomorphological maps were generated, with legends at different levels of complexity. Other factor maps, that were considered relevant for the assessment of landslide susceptibility, were also collected, such as lithology, structural geology, surficial materials, slope classes, land use, distance from streams, roads and houses. The weights of evidence method was used to generate statistically derived weights for all classes of the factor maps. On the basis of these weights, the most relevant maps were selected for the combination into landslide susceptibility maps. Six different combinations of factor maps were evaluated, with varying geomorphological input. Success rates were used to classify the weight maps into three qualitative landslide susceptibility classes. The resulting six maps were compared with a direct susceptibility map, which was made by direct assignment of susceptibility classes in the field. The analysis indicated that the use of detailed geomorphological information in the bivariate statistical analysis raised the overall accuracy of the final susceptibility map considerably. However, even with the use of a detailed geomorphological factor map, the difference with the separately prepared direct susceptibility map is still significant, due to the generalisations that are inherent to the bivariate statistical analysis technique. 相似文献
16.
Application of Weights of Evidence to Mineral Potential Mapping of Yujiacun Ore Field in Northwest Yunnan Province, China 总被引:1,自引:0,他引:1
ZHAO Pengda 《中国地质大学学报(英文版)》2003,14(3):269-273
The multivariate information conprehensive processing technique is especially important at present to the digital mineral prospecting. However, the GIS-based weights of evidence have provided us with powerful tool for the quantitative assessment of mineral resource potential. In this paper, the mineralization model is established, based on the achievements made by previous researchers, to mend such deficiencies ad few references on ore fields in Yujiacun, Yunnan Province and the shortage of quantitative prediction and assessment of mineral resources. In addition, the weights of evidence are used to make a systematic quantitative prediction and assessment of mineral resources there, so that 2 mineral prospecting target areas of grade Ⅰ and 8 mineral prospecting target areas of grade Ⅱ are delineated, providing the further mineral resource exploration with the basis for the selection of mineral deposits. 相似文献
17.
付载波频偏测量对于保证调频系统传输质量具有重要的意义。本文介绍了我们设计制作的付载波频编测量仪。该仪器便于携带、使用方便、精度送±10^-3*f0+1赫该精度满足模拟传输台网的需要。 相似文献
18.
19.
20.
用GPS秒信号锁定高频振荡器的方法研究 总被引:1,自引:0,他引:1
对用远距离传输的GPS秒信号锁定本地高频晶体振荡器的方法进行了探讨。介绍了高精度的时间数字转换器TDC(Time to Digital Converter)和对滤波的方法进行了探讨。为了降低成本又能够满足设计要求的精度,还考虑了双D/A转换的方法。有关的硬件系统已经通过了调试和一系列的测试和实验,在测量和控制精度方面,能达到设计的要求。此外,提出了这个系统有待解决的问题,如双D/A转换的非线性问题,Kalman滤波抗野值及继续提高精度的问题。 相似文献