全文获取类型
收费全文 | 1389篇 |
免费 | 195篇 |
国内免费 | 292篇 |
专业分类
测绘学 | 53篇 |
大气科学 | 261篇 |
地球物理 | 193篇 |
地质学 | 569篇 |
海洋学 | 62篇 |
天文学 | 564篇 |
综合类 | 86篇 |
自然地理 | 88篇 |
出版年
2024年 | 5篇 |
2023年 | 13篇 |
2022年 | 41篇 |
2021年 | 46篇 |
2020年 | 44篇 |
2019年 | 45篇 |
2018年 | 37篇 |
2017年 | 35篇 |
2016年 | 35篇 |
2015年 | 51篇 |
2014年 | 55篇 |
2013年 | 63篇 |
2012年 | 63篇 |
2011年 | 54篇 |
2010年 | 55篇 |
2009年 | 96篇 |
2008年 | 92篇 |
2007年 | 138篇 |
2006年 | 152篇 |
2005年 | 101篇 |
2004年 | 112篇 |
2003年 | 94篇 |
2002年 | 81篇 |
2001年 | 64篇 |
2000年 | 52篇 |
1999年 | 58篇 |
1998年 | 48篇 |
1997年 | 22篇 |
1996年 | 25篇 |
1995年 | 20篇 |
1994年 | 26篇 |
1993年 | 13篇 |
1992年 | 5篇 |
1991年 | 8篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1985年 | 1篇 |
1984年 | 3篇 |
排序方式: 共有1876条查询结果,搜索用时 318 毫秒
951.
952.
953.
954.
955.
从模型研究的角度出发,分别讨论了全球和区域尺度的构造节律问题。以地球的圈层结构和质量分布为前提,可推出固态内核不能稳定平衡于球心位置的结论。以此为基础,可以建立一个简约和自洽的全球运动模型。按照相应的热-机械能耦合模式,地球的运动可以划分出4个不同性质的阶段,从而构成地球演化的最高一级运动节律。区域构造节律在这一背景下存在,且可由更为简单的机械运动产生。 相似文献
956.
刘成明 《地震地磁观测与研究》2005,26(5):24-32
通过对宜宾北4.7级地震震中及附近地区地震地质、地震活动背景、区域地震活动性、水位资料的分析,表明宜宾北4.7级地震震前经历了区域地震活跃至平静、再发震的过程,其部分地震学参数存在异常,川12井水位也出现较大异常,并对宜宾北所处的华蓥山断裂带上的中强震与川滇交界附近地区南北地震带上的强震存在较高的对应关系成因进行了分析,认为华蓥山断裂带上中强地震活动对川滇交界地区南北地震带上强震的发生存在中短期预报意义。 相似文献
957.
YANG Dongzhen XU Xiangde LIU Xiaoduan XU Qing DING Guoan CHENG Xinghong CHEN Huailiang ZHOU Huaigang WANG Zhenfa WANG Wenyan 《中国科学D辑(英文版)》2005,48(Z2)
The comprehensive impact of atmospheric dry deposition and wet deposition and the pollution sources of farmlands, mining areas, and towns along the Baihe River on the water quality of Miyun reservoir is investigated from the angle of the complex sources of air-soil-water pollution processes, in the context of the 1990-2001 precipitation chemical data at Shangdianzi station--a WMO regional background air pollution monitoring station 15 km far from the Miyun reservoir, in conjunction with the atmospheric dry deposition and wet deposition data of the 2002-2003 Beijing City Air Pollution Observation Field Experiment (BECAPEX). Analysis results suggest that the major ions in precipitation in the Miyun reservoir region in this period were SO, NO, NH and Ca2+; wet acid deposition quantity of Miyun reservoir in the summer half year (April to September) was greater than the quantity in the winter half year (October to March), and the annual wet acid deposition in the reservoir exhibited a rising trend with the mean 1038.45 t, the maximum 1766.31 t occurred in 1996, and the minimum 604.02 t in 1994; the long-term averaged pH of atmospheric precipitation in the Miyun reservoir region was 5.20, i.e. weakly acidic, and the interannual variation of pH values displayed a falling trend. pH values of water body at various depths in the Miyun reservoir were all greater than 7.0, but they exhibited vertical and horizontal nonhomogeneity, and at the same region pH decreased vertically with depth; the 2002 and 2003 annual dustfalls in the Miyun reservoir were 13513.08 t and 3577.64 t, respectively, and the spring dustfall was the number one in a year, accounting for the 61.91% and 44.56% of the annual totals of 2002 and 2003, respectively. Because the atmospheric dry deposition and wet depositions contain multiple types heavy metal elements and harmful elements, they to some extent exacerbated the eutrophication, acidification and potential heavy metal pollution of the reservoir water. The above comprehensive analysis results reveal the complex source characters of the air-soil-water pollution process and the multi-sphere interaction effect. Besides, summer (rainy season) is a season when local soil pollutants enter the water system of reservoir after being washed out by torrential rain or heavy precipitation, which starts the air-soil- water chaining pollution processes, and results in the water pollution of rivers and reservoirs. It is found from the statistical analysis in this paper that the water pollution of Miyun reservoir was correlated with the rain wash-out and confluent flow in the peripheral and upstream local region of the reservoir, and the pollutant concentration of the reservoir water was significantly correlated with the upstream local region precipitation. Those correlation characters reveal the effect of the air-soil-water multi-spheric interaction of reservoir water pollution process. This paper presents the point of view of the complex source analysis of reservoir water pollution and a technical approach for tracing the spatial distribution of the upstream pollution source of the water systems of reservoir. 相似文献
958.
Eduard Hanslík Eva Kalinov Martina Brtvov Diana Ivanovov Barbora Sedlov Jitka Svobodov Vra Jedinkov-Kíov Mark Rieder Jií Medek Karel Forejt Ladislav Vondrk Karel Jahn Jií Jusko 《Limnologica》2005,35(3):177-184
In the Czech Republic, river bottom sediments have been systematically monitored since 1999. In the paper, their radioactive contamination due to uranium mining and milling is assessed. The sediments samples were analyzed by gamma spectrometry. Especially the radium-226 and radium-228 activities were further evaluated.The highest values of the radium-226 activities were found at river profiles where the uranium industry impact was obvious. It turned out that the radium-226 and radium-228 activities ratio is more convenient to assess the level of radium-226 contamination than only the radium-226 activity itself. Based on this hypothesis, the sediment classification scheme for uranium industry contamination was suggested. The natural background activities of radium-226 and radium-228 in the Czech Republic were also evaluated. The case of radium-226 contamination due to the uranium industry was studied in details at the Ploučnice River. 相似文献
959.
960.
Guidelines for a low-density geochemical survey were described in 1990 by the Western European Geological Surveys. A low-density geochemical survey of Hungary was carried out in 1991–1995. The results are useful for future surveys and for the IGCP 360 project ‘Global Geochemical Baseline’. In regions with well-developed drainage systems in Hungary, 196 catchment basins of approx. 400 km2 were delineated and flood-plain deposits sampled at their outlets. The samples were taken from 0 to 10 cm and from 50 to 60 cm depths. Samples were analysed by ICP-AES and AAS techniques in two laboratories. A Geochemical Atlas of Hungary is in preparation that will show the distribution of 25 elements in the two sampled layers. Maps for the lower layer represent regional geochemical baseline values and a geochemical subdivision of the country (maps showing the distribution of element associations) was made on the basis of factor variables. Maps constructed from the data of the upper sampling level show us the present state of contamination of the surface. The results of this survey have contributed to the establishment of guidance values for soils prepared by the Hungarian Ministry of the Environment in 1995. Safe levels were established for As, Cd, Cr, Cu, Hg, Pb and Zn and regional environmental loads plotted. Differences between the median values of the two levels are generally small. However, the concentrations of certain elements like P, Pb and S are significantly greater in the upper layer reflecting contamination from agriculture. In certain regions, the rate of sedimentation was fairly fast such that the environmental effects of ore mining in Transylvania and southern Slovakia as well as those of heavy industry in northern Hungary can be observed in samples from the lower level. The main factor controlling the geochemical pattern in Hungary is the predominance of young (Pleistocene or Miocene) clastic sediments at the surface. Approx. 90% of the surface is covered by these young sediments. This kind of survey has the disadvantage of not providing enough contrast to differentiate geologically dissimilar areas but it has the advantage to provide regional surface background geochemical data and it helps to outline areas of possible surface contamination. Based on the results of this survey we conclude that it would be much better to sample smaller, but geologically homogeneous areas in mountainous terrain to obtain data characteristic of the geochemical background of lithologic units. This approach would mean a sampling density of a few tens of km2/sample for hilly areas, and a few hundred km2/sample for lowland areas. 相似文献