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461.
462.
陈晓勇 《武汉大学学报(信息科学版)》1987,(3)
本文论述了利用IBM—PC/XT微型机和CdBASE-Ⅲ关系型DBMS,建立微机汉字大地测量数据库MC-GDB(Micro-computer Chinese Geodetic Data Base)系统的方法。系统采用了分块存贮和有效的数据压缩方法,实现了大规模数据的微机管理。最后,简述了检索、统计、报表等使用方式。针对大地测量数据的特点,还讨论了有关平差和绘图方面的功能。 相似文献
463.
Since 1979 the repeated observations and experiments of geomagnetic total intensity and vertical component have been carried out for ten years in the geomagetic network which is located in Jiangsu Province, China. Three earthquakes aboveM s 5.0 occurred during the decade, and some seismomagnetic effects were observed. The observation results show that the anomalies of the vertical geomagnetic component can’t be observed untill some months before the earthquake (M s>5.0) in this area. In this paper it is suggested that a densely distributed network for continuous observation of geomagnetic vertical component may catch seismomagnetic anomalies and thus improve earthquake prediction in the light of the geomagnetic measurements of the mid — or — low latitude locations. 相似文献
464.
本文利用灰色系统理论GM(1,1)模型研究了地震活跃幕的预测,建立了中国大陆及邻区地震活跃幕的灰色预测模型,通过实例计算证明该模型精密度较高,可以用来预测中国大陆及邻区下一地震活跃幕的大致开始时间以及持续时间。 相似文献
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Detailed studies on U-Pb ages and Hf isotope have been carried out in zircons from a carbonatite dyke associated with the Bayan Obo giant REE-Nb-Fe deposit, northern margin of the North China Craton(NCC), which provide insights into the plate tectonic in Paleoproterozoic. Analyses of small amounts of zircons extracted from a large sample of the Wu carbonatite dyke have yielded two ages of late Archaean and late Paleoproterozoic(with mean 207 Pb/206 Pb ages of 2521±25 Ma and 1921±14 Ma, respectively). Mineral inclusions in the zircon identified by Raman spectroscopy are all silicate minerals, and none of the zircon grains has the extremely high Th/U characteristic of carbonatite, which are consistent with crystallization of the zircon from silicate, and the zircon is suggested to be derived from trapped basement complex. Hf isotopes in the zircon from the studied carbonatite are different from grain to grain, suggesting the zircons were not all formed in one single process. Majority of εHf(t) values are compatible with ancient crustal sources with limited juvenile component. The Hf data and their TDM2 values also suggest a juvenile continental growth in Paleoproterozoic during the period of 1940–1957 Ma. Our data demonstrate the major crustal growth during the Paleoproterozoic in the northern margin of the NCC, coeval with the assembly of the supercontinent Columbia, and provide insights into the plate tectonic of the NCC in Paleoproterozoic. 相似文献
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WANG Lixia GUO Zhaohui XIAO Xiyuan CHEN Tongbin LIAO Xiaoyong SONG Jie WU Bin 《地理学报》2008,18(3):353-362
A total of 219 agricultural soil and 48 vegetable samples were collected from the midstream and downstream of the Xiangjiang River (the Hengyang–Changsha section) in Hunan Province. The accumulation characteristics, spatial distribution and potential risk of heavy metals in the agricultural soils and vegetables were depicted. There are higher accu-mulations of heavy metals such as As, Cd, Cu, Ni, Pb and Zn in agricultural soils, and the contents of Cd (2.44 mg kg-1), Pb (65.00 mg kg-1) and Zn (144.13 mg kg-1) are 7.97, 3.69 and 1.63 times the corresponding background contents in soils of Hunan Province, respectively. 13.2% of As, 68.5% of Cd, 2.7% of Cu, 2.7% of Ni, 8.7% of Pb and 15.1% of Zn in soil sam-ples from the investigated sites exceeded the maximum allowable heavy metal contents in the China Environmental Quality Standard for Soils (GB15618-1995, Grade II). The pollution characteristics of multi-metals in soils are mainly due to Cd. The contents of As, Cd, Cu, Pb and Zn in vegetable soils are significantly higher than the contents in paddy soils. 95.8%, 68.8%, 10.4% and 95.8% of vegetable samples exceeded the Maximum Levels of Contami-nants in Foods (GB2762-2005) for As, Cd, Ni and Pb concentrations, respectively. There are significantly positive correlations between the concentrations of Cd, Pb and Zn in vegetables and the concentrations in the corresponding vegetable soils (p<0.01). It is very necessary to focus on the potential risk of heavy metals for food safety and human health in agricultural soils and vegetables in the midstream and downstream of the Xiangjiang River, Hunan Province of China. 相似文献
470.
Incubation experiments are carried out to study the exchange rates of dissolved inorganic nutrients including silicate, phosphate, ammonium, nitrite, and nitrate (^vSiO3-Si,^vPO4-P, ^vNH4-N, ^vNO2-N and ^vNO3-N) at the sediment-water interface in the Jiaozhou Bay. Major factors influencing the exchange rates are discussed in detail, which include the dissolved inorganic nutrient concentrations in porewater (Cpw), water and clay contents, and grain size of the sediments (CH2O, Cclay and GSsed). The results may provide insight into the dynamics of nutrient transport and the environmental capacity of nutrients in Jiaozhou Bay, and should be beneficial to solving the problems caused by excessive nutrient input this area. 相似文献