全文获取类型
收费全文 | 1489篇 |
免费 | 191篇 |
国内免费 | 166篇 |
专业分类
测绘学 | 449篇 |
大气科学 | 226篇 |
地球物理 | 478篇 |
地质学 | 255篇 |
海洋学 | 127篇 |
天文学 | 135篇 |
综合类 | 85篇 |
自然地理 | 91篇 |
出版年
2024年 | 7篇 |
2023年 | 3篇 |
2022年 | 13篇 |
2021年 | 28篇 |
2020年 | 58篇 |
2019年 | 53篇 |
2018年 | 51篇 |
2017年 | 40篇 |
2016年 | 65篇 |
2015年 | 53篇 |
2014年 | 86篇 |
2013年 | 118篇 |
2012年 | 54篇 |
2011年 | 84篇 |
2010年 | 72篇 |
2009年 | 100篇 |
2008年 | 87篇 |
2007年 | 118篇 |
2006年 | 107篇 |
2005年 | 82篇 |
2004年 | 73篇 |
2003年 | 68篇 |
2002年 | 66篇 |
2001年 | 51篇 |
2000年 | 47篇 |
1999年 | 39篇 |
1998年 | 36篇 |
1997年 | 30篇 |
1996年 | 35篇 |
1995年 | 26篇 |
1994年 | 22篇 |
1993年 | 15篇 |
1992年 | 21篇 |
1991年 | 4篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有1846条查询结果,搜索用时 46 毫秒
101.
全站仪三角高程测量具有效率高,实施灵活等优点,经研究并通过实践验证,在对观测结果进行相关改正的条件下,全站仪三角高程测量完全能达到三、四等水准测量的精度要求,同时可借助Excel所具备的强大数据处理能力,使观测数据的处理更为方便快捷。 相似文献
102.
Optimizing support vector machine learning for semi-arid vegetation mapping by using clustering analysis 总被引:1,自引:0,他引:1
In remote sensing communities, support vector machine (SVM) learning has recently received increasing attention. SVM learning usually requires large memory and enormous amounts of computation time on large training sets. According to SVM algorithms, the SVM classification decision function is fully determined by support vectors, which compose a subset of the training sets. In this regard, a solution to optimize SVM learning is to efficiently reduce training sets. In this paper, a data reduction method based on agglomerative hierarchical clustering is proposed to obtain smaller training sets for SVM learning. Using a multiple angle remote sensing dataset of a semi-arid region, the effectiveness of the proposed method is evaluated by classification experiments with a series of reduced training sets. The experiments show that there is no loss of SVM accuracy when the original training set is reduced to 34% using the proposed approach. Maximum likelihood classification (MLC) also is applied on the reduced training sets. The results show that MLC can also maintain the classification accuracy. This implies that the most informative data instances can be retained by this approach. 相似文献
103.
对嫦娥一号干涉成像光谱仪(IIM)数据的特点进行了分析,并就存在的一些问题提出了解决方案,制定了IIM数据应用处理流程,为该数据的正确使用提供方法参考。研究结果表明,在空间域传感器左侧响应偏低,右侧响应偏高;在波谱域长波段响应存在较大偏差。经过绝对定标和辐射畸变校正后的反射率与地基望远镜光谱匹配良好,可以用于应用研究。利用校正后的数据对Aristarchus地区岩石类型开展初步研究的结果表明,该地区在纵向和横向上都存在岩性的多样性。校正后的图像不仅提高了分类精度,还被识别出撞击坑可能存在的滑坡。嫦娥一号IIM能够在全球、区域和局部尺度上以较高的空间分辨率和光谱分辨率获取月表元素和矿物成分信息,有助于深化对月球形成和演化的认识。 相似文献
104.
105.
Solić M Krstulović N Vilibić I Kuspilić G Sestanović S Santić D Ordulj M 《Marine environmental research》2008,65(5):388-404
Month-to-month fluctuations in the abundance of bacteria and heterotrophic nanoflagellates (HNF) and bacterial production, as well as various chemical (nutrients, oxygen) and physical (salinity, temperature) parameters were analysed at a station located in the open middle Adriatic Sea during one decade (1997-2006). Being influenced by both coastal waters and open Adriatic circulation in the surface layer, and by the deep Adriatic water masses in the deep layers (100 m), this station is quite suitable for detecting the environmental changes occurring in the open Adriatic Sea with respect to the circulation of its water masses and their long-term changes and anomalies. Multivariate methods were used to identify seasonal and inter-annual changes of the investigated parameters, associating observed changes to the changes in Adriatic water masses and circulation regimes. The analyses showed that bacterial abundance and production were controlled by different water mass dynamics during 1997-2001 compared to 2002-2006 period, particularly noticeable in different seasonal patterns of biological parameters. The interplay between North Adriatic Dense Water (NAdDW) and Levantine Intermediate Water (LIW) resulted in a change in the available nutrients (NAdDW is poor in orthophosphates), and as a consequence different bacterial abundance and production. A few periods were examined in detail, such as 2004, when LIW inflow was particularly strong and was accompanied by an increase of bacterial and HNF abundances, as well as of bacterial production. 相似文献
106.
Data-based methods for forecasting beach volumes are tested using ground-measured bathymetry from Duck, North Carolina, comprising 26 profiles, 20 year duration and one-month resolution. Derived beach volume time series show weak seasonal and strong event signals. The forecasting methods used are: Holt–Winters (standard and modified), three types of linear regression, and a default forecast in which the latest measurement persists unchanged into the future. Improved forecast accuracies are obtained by two modifications to Holt–Winters, involving an autocorrelation correction and long-term trend-damping, and by smoothing the fitting data using running medians or wavelet approximations. Beach volume forecasts are tested mainly at monthly intervals up to 12 months ahead, with further tests at up to 36 months ahead. Overall, modified Holt–Winters performs best and the default forecast second-best. With an added artificial seasonal signal, modified Holt–Winters outperforms the other methods more substantially. 相似文献
107.
Nondimensionalization of variables enables us to treat experiment data much more simply and efficiently by decreasing the
number of variables. In some cases, trivial conclusions (which Kenney, 1982, called spurious self-correlation) result from
a formal application of dimensional analyses. In contrast, in some cases fully significant conclusions can be derived. We
first discuss how to construct nondimensional variables retaining the physical meanings of variables. We then propose simple
and efficient methods, especially the use of “spurious triangle (SpT)”, to discriminate between significant conclusions and
spurious self-correlations in the analysis of nondimensionalized variables. 相似文献
108.
109.
110.
采用GIS管理测量数据是提高城市勘测效率的重要基础。本文介绍了利用MapX组件开发广州市建设工程测量信息系统,实现了建设工程测量图形与属性数据之间的双向查询。侧重研究建设工程测量的数据组织形式,以及空间信息和属性信息之间的关联。实验证明,利用MapX组件能高效地建造建设工程测量信息系统;系统中的空间数据结构设计合理,能较好地实现建设工程测量数据的录入、查询以及综合管理等系统要求。 相似文献