全文获取类型
收费全文 | 20321篇 |
免费 | 3750篇 |
国内免费 | 3145篇 |
专业分类
测绘学 | 1549篇 |
大气科学 | 2707篇 |
地球物理 | 8878篇 |
地质学 | 7084篇 |
海洋学 | 2045篇 |
天文学 | 875篇 |
综合类 | 1186篇 |
自然地理 | 2892篇 |
出版年
2024年 | 86篇 |
2023年 | 219篇 |
2022年 | 512篇 |
2021年 | 660篇 |
2020年 | 612篇 |
2019年 | 819篇 |
2018年 | 615篇 |
2017年 | 755篇 |
2016年 | 735篇 |
2015年 | 828篇 |
2014年 | 1044篇 |
2013年 | 1153篇 |
2012年 | 1133篇 |
2011年 | 1159篇 |
2010年 | 1083篇 |
2009年 | 1261篇 |
2008年 | 1270篇 |
2007年 | 1340篇 |
2006年 | 1341篇 |
2005年 | 1168篇 |
2004年 | 1067篇 |
2003年 | 994篇 |
2002年 | 861篇 |
2001年 | 755篇 |
2000年 | 750篇 |
1999年 | 738篇 |
1998年 | 721篇 |
1997年 | 546篇 |
1996年 | 584篇 |
1995年 | 524篇 |
1994年 | 439篇 |
1993年 | 327篇 |
1992年 | 244篇 |
1991年 | 186篇 |
1990年 | 156篇 |
1989年 | 138篇 |
1988年 | 119篇 |
1987年 | 57篇 |
1986年 | 34篇 |
1985年 | 23篇 |
1984年 | 37篇 |
1983年 | 14篇 |
1982年 | 11篇 |
1981年 | 4篇 |
1980年 | 24篇 |
1979年 | 17篇 |
1978年 | 16篇 |
1977年 | 20篇 |
1954年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
为建立高精度的边坡位移预测模型,采用相空间重构(PSR)将边坡位移时间序列数据转换为多维数据,同时构造小波核函数改进的支持向量机模型,建立PSR-WSVM模型并应用于边坡位移预测。将PSR-WSVM模型预测结果与传统支持向量机(SVM)模型、小波支持向量机(WSVM)模型和基于相空间重构的支持向量机(PSR-SVM)模型预测结果进行对比,通过平均绝对误差(MAE)、平均绝对误差百分比(MAPE)和均方根误差(RMSE)3个精度评价指标验证PSR-WSVM模型的可行性。工程实例结果表明,PSR-WSVM模型预测结果的3个精度评价指标都优于另外3种模型,边坡位移预测的精度明显提升。 相似文献
2.
ABSTRACTThe purpose of this study is to examine local level spatiotemporal rainfall and temperature variability in drought-prone districts of rural Sidama, Central Rift Valley region of Ethiopia. The study used 129 gridded monthly rainfall and temperature data of 32 years (1983–2014). The gridded rainfall and temperature records were encoded into GIS software and evaluated through different statistical and geospatial techniques. Mann-Kendal rank test and F distribution tests were used to test temporal and spatial statistical significance, respectively, of the data. The analysis revealed that Belg and Kiremt are the main rainfall seasons, constituting 81% of the annual rainfall. Although annual, Kiremt, and Belg rainfall amounts appear to have decreased over time, the decreasing trend is statistically significant only for Belg rainfall records. On the other hand, rainfall standard anomaly results indicated seven droughts of different magnitudes: one extreme, two severe, and four moderate. The study also revealed increasing temperature trends over the years under consideration that are statistically significant. The findings of this study on rainfall contradict other findings obtained around the study area. Thus, climate change adaptations need to focus on location-specific climate data analysis so that the intended adaptive interventions can be successful. 相似文献
3.
4.
5.
1 IntroductionAccordingtogeologicalstructure ,theGansu Ningxia Qinghaiareabelongstothenortheastmar ginofQinghai Tibetblock .Thisareahasbeenpaidmuchattentionby geo specialistsinChinaandabroadbecauseofitssignificanttectonicmovement,itsintensiveseismicity ,anditsimportanceinearth quakehazardmitigation .IntheDevelopmentPro gramonNationalKeyBasicResearchesundertheProject“MechanismandPredictionofContinentalStrongEarthquakes”,themechanismsofcontinen talstrongearthquakesarestudied ,usinghypo… 相似文献
6.
FEASIBLE STUDY ON THE INTEGRATION SYSTEM FOR THE SPACE MONITORING OF MAJOR EARTHQUAKES AND VOLCANOES IN TERRESTRIAL LAND 总被引:1,自引:1,他引:0
BOLi-qun 《中国地理科学(英文版)》2002,12(4):350-353
With the rapid development of space technology, earth observation technology and sky observatory technolo-gy, they have played a more and more important part in monitoring and predicting of earthquakes and volcanoes in the terres-trial land. In recent years, the related agencies have done the experiments and researches on monitoring and predicting ofearthquakes and volcanoes in the forewarning period by means of many approaches, such as satellite thermal infrared re-mote sensing (TIRS), Global Positioning System (GPS), differential interferometric synthesis aperture radar (D-INSAR),astronomical time-latitude residual anomaly, and Geographic Information Systems (GIS), etc. A quite large number of re-search foundation has been built in the fundamental theories and application methods. The experiments and researcheshave shown that these technology is efficient methods for high frequency crust movement. If the existed separate scientificforces and results are possibly assembled together to form a more complete integration monitoring system with the combina-tion of space, sky observation, ground, deep geology and macro anomaly, it will come into a new stage of monitoring andpredicting of earthquakes and volcanic eruptions. 相似文献
7.
本文简要介绍了陆地系列地球资源卫星的轨道特征,并以陆地—5号资源卫星为例,根据南山站的座标计算出该站对陆地—5号资源卫星的可观测范围及以该站为中心的卫星的覆盖区域。 相似文献
8.
9.
10.