全文获取类型
收费全文 | 15986篇 |
免费 | 1641篇 |
国内免费 | 1865篇 |
专业分类
测绘学 | 6025篇 |
大气科学 | 2052篇 |
地球物理 | 2175篇 |
地质学 | 3225篇 |
海洋学 | 1306篇 |
天文学 | 1229篇 |
综合类 | 1594篇 |
自然地理 | 1886篇 |
出版年
2024年 | 90篇 |
2023年 | 200篇 |
2022年 | 511篇 |
2021年 | 658篇 |
2020年 | 680篇 |
2019年 | 739篇 |
2018年 | 515篇 |
2017年 | 885篇 |
2016年 | 785篇 |
2015年 | 814篇 |
2014年 | 921篇 |
2013年 | 1163篇 |
2012年 | 1044篇 |
2011年 | 909篇 |
2010年 | 709篇 |
2009年 | 867篇 |
2008年 | 889篇 |
2007年 | 1054篇 |
2006年 | 974篇 |
2005年 | 809篇 |
2004年 | 771篇 |
2003年 | 581篇 |
2002年 | 509篇 |
2001年 | 411篇 |
2000年 | 325篇 |
1999年 | 295篇 |
1998年 | 254篇 |
1997年 | 172篇 |
1996年 | 167篇 |
1995年 | 146篇 |
1994年 | 131篇 |
1993年 | 113篇 |
1992年 | 75篇 |
1991年 | 69篇 |
1990年 | 42篇 |
1989年 | 44篇 |
1988年 | 37篇 |
1987年 | 19篇 |
1986年 | 22篇 |
1985年 | 14篇 |
1984年 | 13篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1977年 | 11篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1971年 | 5篇 |
1954年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 83 毫秒
961.
962.
本文通过对三种矢量数据动态存贮方法的分析比较,并通过实践,找到一种安全可靠并且比较实用的数据动态存贮方式。 相似文献
963.
地面移动测量技术的发展与现状 总被引:1,自引:0,他引:1
地面移动测量技术是当前倍受关注的测量前沿技术。本文论述了地面移动测量技术的基本原理和特点,回顾了该技术的发展历史,总结了国内外研究现状,展望了今后的发展趋势与应用前景,并对研究、发展和应用这一技术提出了建议。 相似文献
964.
DEM Compression Based on Integer Wavelet Transform 总被引:1,自引:0,他引:1
CHEN Renxi LI Xinhui 《地球空间信息科学学报》2007,10(2):133-136
DEM data is an important component of spatial database in GIS. The data volume is so huge that compression is necessary. Wavelet transform has many advantages and has become a trend in data compression. Considering the simplicity and high efficiency of the compression system, integer wavelet transform is applied to DEM and a simple coding algorithm with high efficiency is introduced. Experiments on a variety of DEM are carried out and some useful rules are presented at the end of this paper. 相似文献
965.
Comparison of Three Tropical Cyclone Intensity Datasets 总被引:3,自引:0,他引:3
Analyzed in this paper are the 16-yr (1988-2003) tropical cyclone (TC) intensity data from three major forecast centers of the western North Pacific, i.e., China Meteorological Administration (CMA), Regional Specialized Meteorological Center Tokyo (RSMC Tokyo), and Joint Typhoon Warning Center (JTWC) of the United States. Results show that there are significant discrepancies (at 1% significance level) in the intensity of TCs among the three centers, with a maximum difference for the same TC over 30 m s-1. The flight reconnaissance over TC can minish the discrepancy to some extent. A climatic and persistent prediction model is set up to study the impact of initial data from different forecast centers on the prediction of TC intensity. It is obtained that the root mean square error (RMSE) of a 4-yr independent test is the largest using data from JTWC, while the smallest using data from RSMC Tokyo. Average absolute deviation in 24-h intensity prediction is 2.5 m s-1 between CMA and RSMC Tokyo data, and 4.0 m s-1 between CMA and JTWC data, with a maximum deviation reaching 21 m s-1. Such a problem in the initial value increases the difficulty in intensity prediction of TCs over the western North Pacific. 相似文献
966.
新疆塔西河石门子水库大坝变形监测初步分析研究 总被引:1,自引:0,他引:1
本文对新疆玛纳斯石门子水库大坝变形监测网的设计进行了论述,介绍了该监测网的实施方法,并对变形监测成果进行了初步的分析研究。 相似文献
967.
无线GIS空间数据动态副本管理研究 总被引:2,自引:0,他引:2
针对GIS海量空间数据更新要求,研究了无线网络环境下空间数据传输和存储的副本动态复制与管理技术。通过分析空间数据移动复制服务策略,设计了基于无线网络的动态副本管理系统(DRMS)来实现空间数据的移动动态复制,并研究副本管理模型和副本更新算法,保证了无线网络传输的稳定性。 相似文献
968.
DO WE NEED TO MODEL PLATES AT ALL? 总被引:2,自引:0,他引:2
The historical method of obtaining equatorial coordinates for stars observed via astronomical photography has been to convert the measured coordinates to equatorial coordinates with the aid of a plate model which corrects for a variety of effects. However, we now have at our disposal novel smoothing techniques, of considerable generality, which in conjunction with modern star catalogues can reproduce the essence of the plate model while dramatically minimizing both the fortuitous and systematic errors of observation. In this paper we demonstrate that, with this technique and extant catalogues, one can obtain, with at least the same precision and better accuracy, the information necessary to transform the measured coordinates successfully into standard coordinates by a process that involves no sophisticated model for the plate. Using external checks we estimate the increase in accuracy to be of the order of 25 per cent. 相似文献
969.
Coryn A. L. Bailer-Jones Mike Irwin & Ted von Hippel 《Monthly notices of the Royal Astronomical Society》1998,298(2):361-377
We investigate the application of neural networks to the automation of MK spectral classification. The data set for this project consists of a set of over 5000 optical (3800–5200 Å) spectra obtained from objective prism plates from the Michigan Spectral Survey. These spectra, along with their two-dimensional MK classifications listed in the Michigan Henry Draper Catalogue, were used to develop supervised neural network classifiers. We show that neural networks can give accurate spectral type classifications (σ68 = 0.82 subtypes, σrms = 1.09 subtypes) across the full range of spectral types present in the data set (B2–M7). We show also that the networks yield correct luminosity classes for over 95 per cent of both dwarfs and giants with a high degree of confidence. Stellar spectra generally contain a large amount of redundant information. We investigate the application of principal components analysis (PCA) to the optimal compression of spectra. We show that PCA can compress the spectra by a factor of over 30 while retaining essentially all of the useful information in the data set. Furthermore, it is shown that this compression optimally removes noise and can be used to identify unusual spectra. This paper is a continuation of the work carried out by von Hippel et al. (Paper I). 相似文献
970.
对全球变化背景下构建生态地理区域系统的若干认识 总被引:3,自引:1,他引:2
研究复杂的人地系统,研究区域的可持续发展需要有一个比较适当的区域划分。全球变化问题研究的水平也取决于对地域差异认识的深度。因此,建立中国生态地理区域系统,探讨其在全球变化中的应用,可为区域发展与陆地生态系统关系的研究提供科学的区域框架。本文从理论基础、必要性、目的、意义、界线、指标和方法论等方面探讨了有关生态地理区划的若干问题。 相似文献