全文获取类型
收费全文 | 4381篇 |
免费 | 827篇 |
国内免费 | 1097篇 |
专业分类
测绘学 | 589篇 |
大气科学 | 636篇 |
地球物理 | 901篇 |
地质学 | 2333篇 |
海洋学 | 601篇 |
天文学 | 85篇 |
综合类 | 434篇 |
自然地理 | 726篇 |
出版年
2024年 | 11篇 |
2023年 | 63篇 |
2022年 | 274篇 |
2021年 | 289篇 |
2020年 | 236篇 |
2019年 | 280篇 |
2018年 | 279篇 |
2017年 | 228篇 |
2016年 | 282篇 |
2015年 | 275篇 |
2014年 | 275篇 |
2013年 | 335篇 |
2012年 | 333篇 |
2011年 | 328篇 |
2010年 | 317篇 |
2009年 | 269篇 |
2008年 | 271篇 |
2007年 | 251篇 |
2006年 | 249篇 |
2005年 | 179篇 |
2004年 | 143篇 |
2003年 | 145篇 |
2002年 | 184篇 |
2001年 | 143篇 |
2000年 | 115篇 |
1999年 | 103篇 |
1998年 | 76篇 |
1997年 | 57篇 |
1996年 | 66篇 |
1995年 | 57篇 |
1994年 | 39篇 |
1993年 | 27篇 |
1992年 | 29篇 |
1991年 | 19篇 |
1990年 | 19篇 |
1989年 | 13篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1957年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有6305条查询结果,搜索用时 843 毫秒
991.
Jinzhu Ma Feng Pan Jiahua He Lihua Chen Sujing Fu Bing Jia 《Environmental Earth Sciences》2012,66(7):1769-1782
The possible sources of water pollution and the evolution of water quality in the Malian River Basin of China’s Longdong Loess Plateau were studied based on chemical analysis. Concentrations of major chemicals in the river were related to the distance downstream from the source of the river and the surface water in the upstream had good quality, while the river from Southern Huanxian County to Qingcheng County was seriously polluted. Groundwater quality was generally good in the phreatic aquifer beneath the loess plateau, with bicarbonate and calcium dominant, but salinity was high and petroleum pollution was present in many parts of the study area. Both surface water and groundwater quality have declined rapidly during the past 20 years, leading to much of the water unsafe to drink and unsuitable for use in irrigation. The substances released into the water included industrial wastes, domestic sewage, organic and inorganic fertilizers, and pesticides, as well as a range of other substances that are harmful to humans. However, petroleum contamination caused by the oil industry in the Longdong oilfield is the largest source of pollution that infiltrates surface water and groundwater, leading to deterioration of water quality. It is recommended that oilfield management must be improved and the petroleum products and wastes must be disposed carefully to reduce the risk of further spills and pollution. 相似文献
992.
Distribution characteristics of Geo-hazards in Ganxi Valley after the Wenchuan earthquake 总被引:1,自引:1,他引:0
A devastating earthquake of Ms 8.0 struck the Wenchuan area on May 12, 2008. The quake triggered numerous landslides and avalanches
in Ganxi Valley. Aerial photo interpretation indicates that the landslides and avalanches, presently in a stable state, are
concentrated in 91 subregions of the valley, occupying 10.42 km2, about 29% of the valley area. Some laws have been found on the gradient, aspect, elevation, distance of rupture, and formation
lithology of geo-hazards in Ganxi Valley: (1) They are mainly situated on slopes between 30° and 50° and increase in number
with increasing slope; (2) Failures are mainly in a southerly direction; and most occurred between 1,000 and 1,600 m, especially
between 1,000 and 1,400 m; (3) Most are within 2,000 m of the Beichuan fault or within 1,000 m of other major faults; (4)
most failures occurred from the T1f + t formation in the study area. The geo-hazards status quo of Ganxi Valley provides foundation for the scheme of hazard
reducing in the future. 相似文献
993.
基于遥感技术的吉林省生态资产定量评估与动态监测 总被引:1,自引:0,他引:1
利用TM/ETM+卫星影像,在对生态参数测量的基础上,依据生态资产估算方法,对吉林省2000年和2008年的生态资产进行定量测量,得到生态资产空间分布图,并进行了动态变化分析。结果表明:2000~2008年,吉林省生态资产总价值由4 385.61亿元增加到6 751.31亿元,单位面积价值增加了24.17万元/(km2.a)。在不同生态系统类型中,有林地生态资产总价值的变化最大,8 a间增加了1 193.60亿元;而未利用地生态价值增加得最少,只有15.75亿元。从生态资产总价值的空间分布上来看,2000年和2008年的吉林省生态资产总价值分布都呈现由东向西逐渐降低的趋势。 相似文献
994.
995.
利用GRACE卫星高采样率精密轨道,进行了拉格朗日插值、牛顿插值和线性插值方法的研究,并对插值结果进行了比较和分析,探讨了插值方法的插值精度及其应用于低轨卫星轨道内插的适用性。 相似文献
996.
997.
998.
999.
1000.
Millimeter-wavelength radar has proved to be an effective instrument for cloud observation and research. In this study, 8-mm-wavelength cloud radar (MMCR) with Doppler and polarization capabilities was used to investigate cloud dynamics in China for the first time. Its design, system specifications, calibration, and application in measuring clouds associated with typhoon are discussed in this article. The cloud radar measurements of radar reflectivity (Z), Doppler velocity (Vr), velocity spectrum width (Sw) and the depolar-ization ratio (LDR) at vertical incidence were used to analyze the microphysical and dynamic processes of the cloud system and precipitation associated with Typhoon Nuri, which occurred in southern China in August 2008. The results show the reflectivity observed using MMCR to be consistent with the echo height and the melting-layer location data obtained by the nearby China S-band new-generation weather radar (SA), but the Ka-band MMCR provided more detailed structural information about clouds and weak precipitation data than did the SA radar. The variation of radar reflectivity and LDR in vertical structure reveals the transformation of particle phase from ice to water. The vertical velocity and velocity spectrum width of MMCR observations indicate an updraft and strong turbulence in the stratiform cloud layer. MMCR provides a valuable new technology for meteorological research in China. 相似文献