全文获取类型
收费全文 | 106993篇 |
免费 | 18512篇 |
国内免费 | 42657篇 |
专业分类
测绘学 | 4159篇 |
大气科学 | 26194篇 |
地球物理 | 27057篇 |
地质学 | 59228篇 |
海洋学 | 22639篇 |
天文学 | 17861篇 |
综合类 | 4117篇 |
自然地理 | 6907篇 |
出版年
2022年 | 686篇 |
2021年 | 1321篇 |
2020年 | 2638篇 |
2019年 | 6179篇 |
2018年 | 7282篇 |
2017年 | 6891篇 |
2016年 | 7273篇 |
2015年 | 5798篇 |
2014年 | 6036篇 |
2013年 | 8477篇 |
2012年 | 6601篇 |
2011年 | 7099篇 |
2010年 | 6835篇 |
2009年 | 7006篇 |
2008年 | 5862篇 |
2007年 | 5854篇 |
2006年 | 5239篇 |
2005年 | 4579篇 |
2004年 | 4928篇 |
2003年 | 4663篇 |
2002年 | 4255篇 |
2001年 | 3720篇 |
2000年 | 3245篇 |
1999年 | 2984篇 |
1998年 | 3074篇 |
1997年 | 3169篇 |
1996年 | 2561篇 |
1995年 | 2444篇 |
1994年 | 2222篇 |
1993年 | 2104篇 |
1992年 | 1851篇 |
1991年 | 1606篇 |
1990年 | 1577篇 |
1989年 | 1430篇 |
1988年 | 1298篇 |
1987年 | 1306篇 |
1986年 | 1180篇 |
1985年 | 1319篇 |
1984年 | 1453篇 |
1983年 | 1286篇 |
1982年 | 1226篇 |
1981年 | 1169篇 |
1980年 | 1011篇 |
1979年 | 978篇 |
1978年 | 831篇 |
1977年 | 850篇 |
1976年 | 771篇 |
1975年 | 731篇 |
1974年 | 734篇 |
1973年 | 763篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
河口表层悬浮泥沙气象卫星遥感定量模式研究 总被引:1,自引:0,他引:1
分析了HRIS光谱图像帧序列的相关性 ,并针对这一特性 ,提出了利用D2 PCM方法 ,降低光谱图像序列的谱相关和空间相关 ,减少图像中的冗余 ,从而实现光谱图像的压缩。该方法提高了压缩比和压缩效率 ,算法运算量小 ,快速。 相似文献
952.
B C Sarkar B S Deota P L N Raju D K Jugran 《Journal of the Indian Society of Remote Sensing》2001,29(3):151-164
GIS. a potential tool for facilitating the generation and use of thematic information, has been applied to groundwater potentiality of the Shamri micro-watershed in Shimla Taluk. The role of various parameters, namely, drainage. lineament. lithology . slope and landuse have been emphasised for delineation of groundwater potential iones. IRS-I C IAN and LISS Ill FCC merged satellite images on 1:25000 scale and Topographic map no. 53L/4 SI together with field traverses have been used as the data source. A multi-criteria evaluation following probability weighted approach has been applied for overlay analysis that allows a linear combination of weights of each thematic map with the individual capability value. 1 he resultant map indicates a high groundwater potentiality in the flood plains, river terraces and river channels in the vicinity of the Shamri nala. Other sites of high potentiality include places showing break in slopes and criss-crossing of lineaments. 相似文献
953.
Derek D. Lichti 《GPS Solutions》2000,4(2):54-62
Kinematic differential Global Positioning System (DGPS) positioning is routinely used in industry for directly observing an
aircraft's position at each instant of photographic exposure during a photogammetric survey. A critical aspect of the subsequent
data processing is estimation of the aircraft position at the exact time of exposure. GPS measurements are acquired at a uniform
sampling rate, typically 1 Hz. The exposure times, however, do not generally coincide with these times. As a result, the exposure
station positions must be interpolated from the adjacent GPS positions. This is typically done using a low-order polynomial,
expressed as a function of time, for each coordinate dimension. However, trajectory perturbations induced by atmospheric turbulence
can render such interpolation methods ineffective.
This article will convey the results of an investigation into the use of several different interpolation models with airborne
GPS data during straight, level flight. The fundamental task of time series reconstruction will first be addressed, in which
several possible interpolation models are described. Two 10-Hz, airborne GPS data sets were collected to test the accuracy
of each model. The error properties resulting from the application of each model to these data will be presented and analyzed
in terms of time-domain statistics and frequency-domain characteristids. It will be demonstrated that interpolation error
can be significantly reduced, especially in the height dimension, through judicious choice of an interpolator. ? 2000 John
Wiley & Sons, Inc. 相似文献
954.
Lawrence E. Band Christina L. Tague Soren E. Brun David E. Tenenbaum & Richard A. Fernandes 《Transactions in GIS》2000,4(3):181-196
The generation, transport and fate of non-point source pollutants in surface water systems is recognized as a major threat to water supplies, aquatic and coastal ecosystems. The transformation and movement of water, carbon and nutrients through watersheds integrates a set of ecosystem processes along hydrologic flowpaths. Human individual and institutional interactions with these processes involve direct addition or abstraction of these substances, or the alteration of land cover and drainage systems. In natural and developed catchments, these processes often vary at granularities ranging from below the level of a hillslope, up through regional watersheds. This suggests the need for the development of hierarchical analysis tools that can address the integration of a set of biophysical, biogeochemical and socioeconomic processes over a spectrum of scales. We describe and illustrate the use of a watershed model implemented as a spatial object hierarchy, representing successively contained landform classes associated with class specific processes as member functions. The model has been linked in a range of looser and tighter couplings with GRASS and ArcView, supplemented by specific terrain analytical functions. We illustrate the data and model system for an instrumented catchment monitored as part of the Baltimore Ecosystem Study (BES), a Long Term Ecological Research (LTER) site centering on integrated carbon, water and nutrient cycling. 相似文献
955.
Evaluation of Information Loss in Digital Elevation Models With Digital Photogrammetric Systems 总被引:3,自引:0,他引:3
Y. D. Huang 《The Photogrammetric Record》2000,16(95):781-791
Information loss is caused when a surface is sampled with a finite interval, such as in the production of a digital elevation model (DEM). This information loss can become the dominant part of the error in a DEM. The ability to quantify information loss enables guidance to be provided for an appropriate choice of grid interval and better accuracy assessment for the DEM. With the use of digital photogrammetric systems, evaluation of information loss has become much easier. This paper describes three methods of evaluating information loss. An example is given of the method which is most appropriate for use with a digital photogrammetric system, based on rock cliff surface data and the VirtuoZo system. 相似文献
956.
957.
S Jayakumar D I Arockiasamy S John Britto 《Journal of the Indian Society of Remote Sensing》2000,28(2-3):141-151
The vegetation of Kolli Hill, has been classified for its forest cover types using landsat TM FCCs of two season namely summer (March) and winter (November). The FCCs of two seasons were interpreted visually based on the standard interpretation elements. Extensive field checks were done and corrections were made in both the maps wherever found necessary’. Finally the forest cover type map of Kolli Hill on 1:50,000 scale was drawn by overlaying the interpreted maps of the two seasons The different types of forest were named following Champion and Seth’s classification scheme and the areas of different forest types estimated. 相似文献
958.
It is well known that terrain may vary markedly over small areas and that statistics used to characterise spatial variation in terrain may be valid only over small areas. In geostatistical terminology, a non-stationary approach may be considered more appropriate than a stationary approach. In many applications, local variation is not accounted for sufficiently. This paper assesses potential benefits in using non-stationary geostatistical approaches for interpolation and for the assessment of uncertainty in predictions with implications for sampling design. Two main non-stationary approaches are employed in this paper dealing with (1) change in the mean and (2) change in the variogram across the region of interest. The relevant approaches are (1) kriging with a trend model (KT) using the variogram of residuals from local drift and (2) locally-adaptive variogram KT, both applied to a sampled photogrammetrically derived digital terrain model (DTM). The fractal dimension estimated locally from the double-log variogram is also mapped to illustrate how spatial variation changes across the data set. It is demonstrated that estimation of the variogram of residuals from local drift is worthwhile in this case for the characterisation of spatial variation. In addition, KT is shown to be useful for the assessment of uncertainty in predictions. This is shown to be true even when the sample grid is dense as is usually the case for remotely-sensed data. In addition, both ordinary kriging (OK) and KT are shown to provide more accurate predictions than inverse distance weighted (IDW) interpolation, used for comparative purposes. 相似文献
959.
本文继续文献 [10 ]的工作 ,进一步讨论了测量平差 Gauss- Markov模型参数岭型广义逆估计的若干性质 ,如允许性、优效性、相对效率、抗干扰性等等 ,得到了许多重要结论。计算结果表明 ,在设计阵呈病态时 ,岭型广义逆估计确能明显改善 L S估计 相似文献
960.
空间数据仓库研究综述 总被引:7,自引:0,他引:7
论述了空间数据仓库的定义、基本特征;着重叙述了目前国内外空间数据仓库在学术研究、产品研制和实际应用方面的发展现状;设计出了空间数据仓库的体系结构,说明了空间数据仓库和应用系统的区别与联系;最后得出结论,为支持我国空间数据基础设施建设,研制空间数据仓库十分必要。 相似文献