全文获取类型
收费全文 | 1250篇 |
免费 | 141篇 |
国内免费 | 125篇 |
专业分类
测绘学 | 374篇 |
大气科学 | 75篇 |
地球物理 | 245篇 |
地质学 | 286篇 |
海洋学 | 91篇 |
天文学 | 133篇 |
综合类 | 117篇 |
自然地理 | 195篇 |
出版年
2023年 | 7篇 |
2022年 | 31篇 |
2021年 | 48篇 |
2020年 | 47篇 |
2019年 | 56篇 |
2018年 | 40篇 |
2017年 | 69篇 |
2016年 | 59篇 |
2015年 | 63篇 |
2014年 | 65篇 |
2013年 | 84篇 |
2012年 | 70篇 |
2011年 | 81篇 |
2010年 | 62篇 |
2009年 | 86篇 |
2008年 | 75篇 |
2007年 | 98篇 |
2006年 | 65篇 |
2005年 | 57篇 |
2004年 | 45篇 |
2003年 | 45篇 |
2002年 | 42篇 |
2001年 | 27篇 |
2000年 | 30篇 |
1999年 | 32篇 |
1998年 | 20篇 |
1997年 | 15篇 |
1996年 | 14篇 |
1995年 | 16篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 9篇 |
1991年 | 8篇 |
1990年 | 2篇 |
1989年 | 11篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有1516条查询结果,搜索用时 140 毫秒
941.
Natural Metrics in the Spaces of Elliptic Orbits 总被引:1,自引:1,他引:0
Konstantin V. Kholshevnikov Nikolay N. Vassiliev 《Celestial Mechanics and Dynamical Astronomy》2004,89(2):119-125
Different natural metrizations by Hölder type on the five dimensional space of Keplerian elliptic orbits are introduced. Certain applications of topological and metrical properties of the space of Keplerian elliptic orbits to several problems of Celestial Mechanics are discussed. 相似文献
942.
用边长变化结果计算地应变及块体划分 总被引:4,自引:4,他引:0
在均匀应变的假设下,给出了由边长变化求解地应变的新方法,通过统计检验相邻三角形的最大主应变,可判别相邻测点是否位于同一个均匀应变体上,采用弹性位错理论设计的模拟算例表明,该方法能成功地将位于断层两侧的测量点分辨开。 相似文献
943.
E. R. Siegel R. Guzmán Jorge P. Gallego M. Orduña López P. Rodríguez Hidalgo 《Monthly notices of the Royal Astronomical Society》2005,356(3):1117-1122
This work investigates the use of a well-known empirical correlation between the velocity dispersion, metallicity and luminosity in Hβ of nearby H ii galaxies to measure the distances to H ii -like starburst galaxies at high redshifts. This correlation is applied to a sample of 15 starburst galaxies with redshifts between z = 2.17 and z = 3.39 to constrain Ωm , using data available from the literature. A best-fitting value of Ωm = 0.21+0.30 −0.12 in a Λ-dominated universe and of Ωm = 0.11+0.37 −0.19 in an open universe is obtained. A detailed analysis of systematic errors, their causes and their effects on the values derived for the distance moduli and Ωm is carried out. A discussion of how future work will improve constraints on Ωm by reducing the errors is also presented. 相似文献
944.
945.
随着致密气田的深入开发,低产低效井逐年增加,已经成为制约气田开发的关键问题之一。以苏里格气田某区块30口气井为研究对象,引入产量贡献率作为动态分类指标,运用气井产量贡献率累计分布曲线的类分割点将气井划分为4类。以纵向合采砂体数、有效砂体厚度、孔隙度、渗透率和含气饱和度等参数作为静态评价指标,采用熵权-理想点法,对气井进行静态分类。基于动态和静态分类结果,引入自相关距离判断异常值点,进行低产低效气井优选。研究表明,Ⅰ、Ⅱ、Ⅲ、Ⅳ类气井的储层质量依次变差,累计产量依次减小;4口气井为低产低效井,优选结果符合生产实际。该研究成果可为气田进一步挖潜的选井、选层提供一种新的技术途径。 相似文献
946.
《地学前缘(英文版)》2022,13(3):101370
Air pollution has seriously endangered human health and the natural ecosystem during the last decades. Air quality monitoring stations (AQMS) have played a critical role in providing valuable data sets for recording regional air pollutants. The spatial representativeness of AQMS is a critical parameter when choosing the location of stations and assessing effects on the population to long-term exposure to air pollution. In this paper, we proposed a methodological framework for assessing the spatial representativeness of the regional air quality monitoring network and applied it to ground-based PM2.5 observation in the mainland of China. Weighted multidimensional Euclidean distance between each pixel and the stations was used to determine the representativeness of the existing monitoring network. In addition, the K-means clustering method was adopted to improve the spatial representativeness of the existing AQMS. The results showed that there were obvious differences among the representative area of 1820 stations in the mainland of China. The monitoring stations could well represent the PM2.5 spatial distribution of the entire region, and the effectively represented area (i.e. the area where the Euclidean distance between the pixels and the stations was lower than the average value) accounted for 67.32% of the total area and covered 93.12% of the population. Forty additional stations were identified in the Northwest, North China, and Northeast regions, which could improve the spatial representativeness by 14.31%. 相似文献
947.
基于密度的抽样和动态时间扭曲距离,提出了一种半监督高光谱模糊聚类方法。该方法首先应用基于密度的方法对样本进行抽样,然后采用动态时间扭曲距离计算样本之间的相似度,最后利用半监督模糊C均值算法进行聚类。为了验证所提出方法的有效性,在广泛使用的Indian Pines数据集和PaviaU数据集上进行试验。结果表明,本文提出的方法能够取得理想的分类结果。 相似文献
948.
949.
In the autumn of 1914, Austria-Hungary began to prepare for the possibility of an Italian offensive by building field fortifications, which formed the Tyrol Defense Line (TDL). Mountainous areas, such as the area of the TDL, present obstacles to trafficability in large part caused by terrain slope. On the eastern Tyrol front, steep slope obstructed trafficability when the Italians attacked the TDL and represented, in turn, an advantage for the Austro-Hungarian defense. This paper focuses on the assessment of the conditions of trafficability determined by slope in the eastern Tyrol front, using a GIS cost distance analysis. Key sources were the maps of Austrian and Italian official histories, parameters derived mainly from Marinelli’s slope classification, and from the interpretation of the particular historical circumstances. The advantages and disadvantages were considered from the perspective of the defensive and offensive and their significance for the history of this conflict. In particular, these were related to the perimeter to be defended by alternative Austro-Hungarian lines. 相似文献
950.
为实现无人机航拍图像的实时拼接,本文深入研究了无人机航拍图像拼接中的关键技术,提出了一种基于遗传算法优化的图像拼接算法。首先利用SIFT算法提取图像的特征点,在特征点粗匹配过程中,采用欧氏距离作为相似度测量,利用遗传算法的并行性优化特征点匹配性能;然后使用RANSAC算法去除误匹配点对并获得转换矩阵,从而完成图像拼接。试验结果表明,采用遗传算法进行特征匹配,可大大降低匹配时间,匹配时间与特征点数量成正比;同时提高了匹配精度,进而提高了图像拼接的实时性和稳健性。 相似文献