全文获取类型
收费全文 | 33093篇 |
免费 | 2010篇 |
国内免费 | 3420篇 |
专业分类
测绘学 | 2289篇 |
大气科学 | 3396篇 |
地球物理 | 6561篇 |
地质学 | 16669篇 |
海洋学 | 2324篇 |
天文学 | 2077篇 |
综合类 | 2936篇 |
自然地理 | 2271篇 |
出版年
2024年 | 93篇 |
2023年 | 280篇 |
2022年 | 576篇 |
2021年 | 658篇 |
2020年 | 538篇 |
2019年 | 570篇 |
2018年 | 5275篇 |
2017年 | 4473篇 |
2016年 | 3136篇 |
2015年 | 818篇 |
2014年 | 725篇 |
2013年 | 668篇 |
2012年 | 1596篇 |
2011年 | 3301篇 |
2010年 | 2536篇 |
2009年 | 2811篇 |
2008年 | 2326篇 |
2007年 | 2737篇 |
2006年 | 477篇 |
2005年 | 520篇 |
2004年 | 637篇 |
2003年 | 625篇 |
2002年 | 435篇 |
2001年 | 253篇 |
2000年 | 274篇 |
1999年 | 336篇 |
1998年 | 250篇 |
1997年 | 253篇 |
1996年 | 206篇 |
1995年 | 171篇 |
1994年 | 182篇 |
1993年 | 152篇 |
1992年 | 112篇 |
1991年 | 74篇 |
1990年 | 85篇 |
1989年 | 65篇 |
1988年 | 48篇 |
1987年 | 34篇 |
1986年 | 39篇 |
1985年 | 34篇 |
1984年 | 14篇 |
1983年 | 15篇 |
1982年 | 21篇 |
1981年 | 30篇 |
1980年 | 30篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1976年 | 7篇 |
1965年 | 3篇 |
1958年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
281.
Mandyam B. Rajani Satadru Bhattacharya A. S. Rajawat 《Journal of the Indian Society of Remote Sensing》2011,39(4):519-527
Talakadu is a well known historic place situated on bank of the river Cauvery in Mysore district of Karnataka. The place is
close to concave side of a prominent meander where large amount of sand has accumulated. It is believed that after construction
of a reservoir upstream, sand was exposed to wind action burying the structures of Ganga dynasty and other later kingdoms.
A number of buried sites have been identified by archaeological excavations conducted so far. Presently the area forms sand
dunes with thick plantation cover. Analysis of RADAR data (fine beam RADARSAT and ENVISAT ASAR) led to identifying a hitherto
unknown buried channel through the Old Talakadu town adjoining the excavated archaeological sites. The study suggests that
RADAR penetration through the plantation canopy seems to have occurred as observed by comparing with corresponding optical
data of LISS-IV. Below the canopy, sand and shrubs on top of the channel (topographically low area) are acting as smooth surface
providing dark tone on radar imagery. During field validation GPS was extensively used to navigate through the forest canopy
and locate the buried channel, excavated archaeological sites as well as other anomalous patterns. Synergistic application
of optical (RESOURCESAT-1 LISS-IV and CARTOSAT-1 & 2) and radar (fine beam RADARSAT and ENVISAT ASAR) data led to identifying
remote sensing based guides for archaeological exploration. Integration of known archaeological sites with the identified
anomalous patterns was done in GIS environment. This study adds on to the knowledge base of the site and compliments already
known information and suggested new areas for further archaeological exploration. 相似文献
282.
Charles F. F. Karney 《Journal of Geodesy》2011,85(8):475-485
Implementations of two algorithms for the transverse Mercator projection are described; these achieve accuracies close to
machine precision. One is based on the exact equations of Thompson and Lee and the other uses an extension of Krüger’s series
for the mapping to higher order. The exact method provides an accuracy of 9 nm over the entire ellipsoid, while the errors
in the series method are less than 5 nm within 3900 km of the central meridian. In each case, the meridian convergence and
scale are also computed with similar accuracy. The speed of the series method is competitive with other less accurate algorithms
and the exact method is about five times slower. 相似文献
283.
The Above Ground Biomass(AGB) estimates of vegetation comprise both the bole biomass determined through a volumetric equation and litter biomass collected from the ground.For mature trees,the AGB estimated in phenologically different time periods is directly affected by the litter biomass since the Diameter at Breast Height(DBH) and height(H) of such trees that are used in the estimation of bole biomass would remain unchanged over a reasonable time period.In the present study,we have determined the AGB of Sal trees(Shorea robusta) in two contrasting seasons:the peak green period in October being devoid of lit-ter on the ground and the leaf shedding period in February with abundant amount of litter present on the ground.Estimation of AGB for the month of February included the litter biomass.In contrast,the AGB for October represented only the bole biomass.AGB was estimated for ten different plots selected in the study area.The AGB estimated from ten sampling plots for each time period was re-gressed with the individual tree parameters such as the average DBH and height of trees measured from the corresponding plots.The regression analysis exhibited a significantly stronger relationship between the AGB and DBH for the month of October as compared to February.Furthermore,the correlation between the remotely sensed derived data and AGB was also found to be significantly higher for the month of October than February.This observation indicates that inclusion of the litter biomass in AGB will tend to decrease the re-gression relationship between AGB and DBH and also between the remotely sensed data and AGB.Therefore,these conclusions invite careful consideration while estimating AGB from satellite data in phenologically different time periods. 相似文献
284.
Xavier Collilieux Laurent Métivier Zuheir Altamimi Tonie van Dam Jim Ray 《GPS Solutions》2011,15(3):219-231
The International GNSS Service (IGS) contributes to the construction of the International Terrestrial Reference Frame (ITRF)
by submitting time series of station positions and Earth Rotation Parameters (ERP). For the first time, its submission to
the ITRF2008 construction is based on a combination of entirely reprocessed GPS solutions delivered by 11 Analysis Centers
(ACs). We analyze the IGS submission and four of the individual AC contributions in terms of the GNSS frame origin and scale,
station position repeatability and time series seasonal variations. We show here that the GPS Terrestrial Reference Frame
(TRF) origin is consistent with Satellite laser Ranging (SLR) at the centimeter level with a drift lower than 1 mm/year. Although
the scale drift compared to Very Long baseline Interferometry (VLBI) and SLR mean scale is smaller than 0.4 mm/year, we think
that it would be premature to use that information in the ITRF scale definition due to its strong dependence on the GPS satellite
and ground antenna phase center variations. The new position time series also show a better repeatability compared to past
IGS combined products and their annual variations are shown to be more consistent with loading models. The comparison of GPS
station positions and velocities to those of VLBI via local ties in co-located sites demonstrates that the IGS reprocessed
solution submitted to the ITRF2008 is more reliable and precise than any of the past submissions. However, we show that some
of the remaining inconsistencies between GPS and VLBI positioning may be caused by uncalibrated GNSS radomes. 相似文献
285.
Sandip R. Oza R. K. K. Singh N. K. Vyas B. S. Gohil Abhijit Sarkar 《Journal of the Indian Society of Remote Sensing》2011,39(2):147-152
The identification of sea-ice has frequently been cited as one of the most important tasks for deriving the sea-ice parameters
and to avoid erroneous retrieval of wind vector over sea-ice infested oceans using space-borne scatterometer data. Discrimination
between sea-ice and ocean is ambiguous under the high wind and/or thin/scattered ice conditions. The pre-launch technique
developed for Oceansat-2, utilizes the dual-polarized QuikSCAT scatterometer data by using the spatio-temporal coherence properties
of sea ice in addition to backscatter coefficient and the Active Polarization Ratio. Results were compared with the operational
sea-ice products from National Snow and Ice Data Center. The threshold API value of −0.025 was found optimum for sea-ice and
ocean discrimination. The overall sea-ice identification accuracy achieved was of the order of 95 per cent, ranging from 92.5%
(during December in Southern Hemisphere) to 98% (during March in Northern Hemisphere). The applicability of the algorithm
for both the Arctic as well as Antarctic makes it suitable for its operational use with the Oceansat-2 scatterometer data. 相似文献
286.
Sushma Panigrahy Shibendu Shankar Ray K. R. Manjunath P. S. Pandey S. K. Sharma Anil Sood Manoj Yadav P. C. Gupta N. Kundu Jai Singh Parihar 《Journal of the Indian Society of Remote Sensing》2011,39(3):355-364
Cropping system study is not only useful to understand the overall sustainability of agricultural system, but also it helps
in generating many important parameters which are useful in climate change impact assessment. Considering its importance,
Space Applications Centre, took up a project for mapping and characterizing major cropping systems of Indo-Gangetic Plains
of India. The study area included the five states of Indo-Gangetic Plains (IGP) of India, i.e. Punjab, Haryana, Uttar Pradesh,
Bihar and West Bengal. There were two aspects of the study. The first aspect included state and district level cropping system
mapping using multi-date remote sensing (IRS-AWiFS and Radarsat ScanSAR) data. The second part was to characterize the cropping
system using moderate spatial resolution multi-date remote sensing data (SPOT VGT NDVI) and ground survey. The remote sensing
data was used to compute three cropping system performance indices (Multiple Cropping Index, Area Diversity Index and Cultivated
Land Utilization Index). Ground survey was conducted using questionnaires filled up by 1,000 farmers selected from 103 villages
based on the cropping systems map. Apart from ground survey, soil and water sampling and quality analysis were carried out
to understand the effect of different cropping systems and their management practices. The results showed that, rice-wheat
was the major cropping system of the IGP, followed by Rice-Fallow-Fallow and Maize-Wheat. Other major cropping systems of
IGP included Sugarcane based, Pearl millet-Wheat, Rice-Fallow-Rice, Cotton-Wheat. The ground survey could identify 77 cropping
systems, out of which 38 are rice-based systems. Out of these 77 cropping systems, there were 5 single crop systems, occupying
6.5% coverage (of all cropping system area), 56 double crop systems with 72.7% coverage, and 16 triple crop systems with 20.8%
coverage. The cropping system performance analysis showed that the crop diversity was found to be highest in Haryana, while
the cropping intensity was highest in Punjab state. 相似文献
287.
一个针对ASTER数据同时反演地表温度和比辐射率的四通道算法 总被引:14,自引:1,他引:14
本文利用对地观测卫星多传感器的特点,提出了针对ASTER数据同时反演地表温度和比辐射率的多通道算法。即利用ASTER数据的第11,12,13,14热红外波段建立热辐射传输方程,并通过对于地表比辐射率分析可知,ASTER4个热红外波段的比辐射率可以用近似线性方程表示,得到了6个方程6个未知数,从而形成了针对ASTER数据的同时反演地表温度和比辐射率的多通道算法。对于关键参数大气透过率,则是通过同一颗星的MODIS传感器的3个近红外波段反演大气水汽含量,然后用MODTRAN模拟大气水汽含量与ASTER热红外波段的统计关系,并进而根据这二关系来计算ASTER热红外波段的大气透过率。由于MODIS和ASTER是在同一颗星上。因此这种大气透过率估计方法保证了地表温度反演过程中所需大气参数的同步获取。 相似文献
288.
289.
290.
环境监测中无线传感器网络地面遥感新技术 总被引:11,自引:1,他引:11
最近国际上蓬勃发展起来一个新交叉科学领域——无线传感器网络技术。本文首先介绍了无线传感器网络(Wireless Sensor Network,WSN)技术,它是遥感技术的拓展而且两者互为支撑。然后介绍了无线传感器网络技术的潜在应用领域及其在地学应用中的国际发展趋势,提出了无线传感器网络技术应用到环境领域的基本问题,建议在地球观测领域发展无线传感器网络技术。最后介绍了无线传感器网络技术在环境监测中的几个设想。 相似文献