全文获取类型
收费全文 | 754篇 |
免费 | 18篇 |
国内免费 | 28篇 |
专业分类
测绘学 | 477篇 |
大气科学 | 18篇 |
地球物理 | 28篇 |
地质学 | 39篇 |
海洋学 | 47篇 |
天文学 | 149篇 |
综合类 | 30篇 |
自然地理 | 12篇 |
出版年
2022年 | 3篇 |
2021年 | 16篇 |
2020年 | 10篇 |
2019年 | 14篇 |
2018年 | 7篇 |
2017年 | 35篇 |
2016年 | 30篇 |
2015年 | 32篇 |
2014年 | 37篇 |
2013年 | 38篇 |
2012年 | 44篇 |
2011年 | 45篇 |
2010年 | 32篇 |
2009年 | 37篇 |
2008年 | 41篇 |
2007年 | 45篇 |
2006年 | 61篇 |
2005年 | 33篇 |
2004年 | 29篇 |
2003年 | 35篇 |
2002年 | 36篇 |
2001年 | 15篇 |
2000年 | 18篇 |
1999年 | 15篇 |
1998年 | 17篇 |
1997年 | 16篇 |
1996年 | 13篇 |
1995年 | 7篇 |
1994年 | 13篇 |
1993年 | 6篇 |
1992年 | 9篇 |
1991年 | 5篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有800条查询结果,搜索用时 31 毫秒
91.
利用被动微波可穿透云层的优势,基于GCOM-W1/AMSR2(Global Change Observation Mission-Water/ Advanced Microwave Scanning Radiometer 2)星载被动微波传感器的多通道亮度温度数据,反演了2016年1月下旬“超级寒潮”过程的广东省每日地表温度,分析了寒潮过程中广东省地表温度的时空变化特征。结果表明:在寒潮前后,广东省地表温度呈现出明显的先下降而后上升的趋势,寒潮过程带来的地表最低温度在广东北部大部分地区达到了277 K(4℃),西南大部分地区为280~282 K(7~9℃),其余大部分地区278~279 K(5~6℃);降温幅度在广东南部地区达到了8~12 K(8~12℃),北部大部分地区为5~7 K(5~7℃)。此外,利用归一化植被指数(NDVI)对植被生长的指示作用,基于HJ-1 A/B卫星的CCD传感器的多通道反射率数据,计算了近3年冬季广东省典型马铃薯种植区域马铃薯叶片的NDVI值,结果表明:马铃薯叶片的NDVI值在此次寒潮过程后出现了明显的下降,大部分地区(55.4%)马铃薯NDVI降低了0.1~0.2,部分地区(17.2%)马铃薯NDVI下降了0.2~0.3;进一步对比此次“超级寒潮”后同时段的前2年数据,发现寒潮后马铃薯叶片NDVI相对于正常年份也低了0.2,表明马铃薯叶片NDVI下降的主要原因是寒潮带来的低温,而不只是马铃薯的正常老化现象。NDVI的降低表明大部分地区马铃薯生长受到了抑制,马铃薯生长状况的这一变化也通过现场调查得到了证实。 相似文献
92.
ZHANG Chengcheng WANG Jun Justine Shanti ALEXANDER DOU Zhigang WU Liji DONG Wantao Dabuxilite YANG Jucai SHI Kun 《资源与生态学报(英文版)》2018,9(5):566-574
Camera traps serve as an important tool for monitoring species diversity. We used data from camera traps set for capturing snow leopards (Panthera uncia) in the Yanchiwan National Nature Reserve, Gansu Province, China, to assess species richness with respect to mammal and birds species. We also assessed survey efficiency for species detection, and conducted an initial analysis of species interactions. The survey effort of 10, 171 camera workdays yielded 2, 868 suitable animal image events involving 17 mammal and 20 bird species. Among these, the dhole (Cuon alpinus) is considered to be Endangered, the snow leopard and white-lipped deer (Cervus albirostris) Vulnerable, and the Pallas’s cat (Feli smanul), mountain weasel (Mustela altaica), Himalayan griffon (Gyps himalayensis) and cinereous vulture (Aegypius monachus) Near Threatened under the IUCN red list. Fourteen species were also listed as key protected wild animals according to China national standards. Both the rarefaction curves and richness estimators suggested our sampling for mammal and pheasant species is sufficient, while more survey efforts are still needed to detect other bird species. With a focus on the dominant species Eurasian lynx (Lynx lynx), occupancy models were used to estimate site use and detection probability for selected species, and to investigate predator-prey relationships between lynx on the one hand and woolly hare (Lepus oiostolus), pika (Ochotona spp.) and Tibetan partridge (Perdix hodgsoniae) on the other. We give recommendations on how to increase efficiency in camera-based species inventory and biodiversity monitoring. 相似文献
93.
The aim of this study is to assess the impact of sensor size and resolution of different digital camera sensors upon the accuracy and precision of three dimensional data derived by photogrammetry. Kodak DC40, DCS420 and DCS460 digital cameras were used to produce digital images of retroreflective targets in a 4 m three dimensional test field. The image locations of the targeted points were automatically measured using an off the shelf image processing software package. Two different sub-pixel measurement approaches were examined: centre of gravity and weighted mean. From the automated sub-pixel measurement of the targeted points, results indicate that the high resolution DCS460 camera produces optimum results using either the weighted mean or centre of gravity approaches. Although this was perhaps expected, the far lower resolution DC40 camera performed better than was originally anticipated, suggesting potential for the cheaper DC40 for many applications. 相似文献
94.
Cusp formation was continuously monitored on a manually flattened, plane section of a coarse clastic, microtidal, pocket beach on the Pacific coast of Japan using a CCD camera suspended in the air. Vertical video pictures enabled the examination of the temporal change in foreshore morphologies and swash pattern. Boulders on the beach face appeared to have triggered the formation of beach cusps, which gradually and successively grew up alongshore. In 2·5 h, two well defined beach cusps had developed with a spacing of 2·2 and 2·5 m, respectively. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
95.
The HY-1A satellite is the first oceanic satellite of China. During the winter of 2002~2003, the data of the HY-1A were applied to the sea ice monitoring and forecasting for the Bohai Sea of China for the first time. The sea ice retrieval system of the HY-1A has been constructed. It receives 1B data from the satellite, outputs sea ice images and provides digital products of ice concentration, ice thickness and ice edge, which can be used as important information for sea ice monitoring and the initial fields of the numeric sea ice forecast and as one of the reference data for the sea ice forecasting verification. The sea ice retrieval system of the satellite is described, including its processes, methods and parameters. The retrieving results and their application to the sea ice monitoring and forecasting for the Bohai Sea are also discussed. 相似文献
96.
97.
环境星CCD数据大气校正研究 总被引:1,自引:0,他引:1
利用6S模型和同步气象资料,对国产环境与灾害监测预报小卫星HJ-1 A的CCD1传感器数据进行了大气校正和反射率反演。同时对CCD1传感器1~4波段大气校正前后的反射率变化进行了对比研究,发现大气校正后的1~3波段的地面反射率明显降低,4波段的地面反射率升高;利用同步野外实测地面数据对大气校正后的反射率数据进行了检验,两者结果基本一致;此外,还进行了定量化误差分析,以同步野外实测地面数据作为标准,将大气校正后的反射率数据与之对比,分析了可能带来误差的原因。结果表明,利用6S大气校正方法能够有效去除HJ-1 A星CCD图像的大气影响,获取地物绝对反射率。 相似文献
98.
基于6S模型的环境星CCD数据大气校正 总被引:5,自引:0,他引:5
应用6S辐射传输模型建立查找表,对环境与减灾小卫星CCD数据进行大气校正。结果表明:校正后的图像更加清晰,对比度增强;与实测光谱对比,处理后的环境星数据可以更真实地反映地物反射特征,消除了NDVI信号在大气传输过程中的衰减效应,更好地复原了地表植被覆盖的真实状况。通过讨论,提出对于HJ-1-A的CCD数据,可以考虑通过同星搭载的高光谱传感器进行气溶胶光学厚度反演;对于HJ-1-B的CCD数据,可以采用对比方法反演气溶胶光学厚度,进而作为模型的输入来提高大气校正精度,以及考虑地表二向性反射现象来提高大气校正精度。 相似文献
99.
L. Kaml 《Astronomische Nachrichten》1998,319(3):183-185
CCD photometry of possible standard stars, in Cousins B, V, R and I, in a field in the region of NGC 188 is presented. 相似文献
100.