全文获取类型
收费全文 | 2673篇 |
免费 | 448篇 |
国内免费 | 469篇 |
专业分类
测绘学 | 96篇 |
大气科学 | 519篇 |
地球物理 | 844篇 |
地质学 | 1029篇 |
海洋学 | 311篇 |
天文学 | 88篇 |
综合类 | 163篇 |
自然地理 | 540篇 |
出版年
2024年 | 20篇 |
2023年 | 60篇 |
2022年 | 75篇 |
2021年 | 122篇 |
2020年 | 112篇 |
2019年 | 113篇 |
2018年 | 79篇 |
2017年 | 98篇 |
2016年 | 85篇 |
2015年 | 121篇 |
2014年 | 145篇 |
2013年 | 201篇 |
2012年 | 165篇 |
2011年 | 144篇 |
2010年 | 113篇 |
2009年 | 155篇 |
2008年 | 125篇 |
2007年 | 172篇 |
2006年 | 144篇 |
2005年 | 125篇 |
2004年 | 168篇 |
2003年 | 105篇 |
2002年 | 111篇 |
2001年 | 93篇 |
2000年 | 84篇 |
1999年 | 75篇 |
1998年 | 95篇 |
1997年 | 73篇 |
1996年 | 78篇 |
1995年 | 60篇 |
1994年 | 54篇 |
1993年 | 62篇 |
1992年 | 37篇 |
1991年 | 34篇 |
1990年 | 20篇 |
1989年 | 15篇 |
1988年 | 15篇 |
1987年 | 12篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1979年 | 2篇 |
排序方式: 共有3590条查询结果,搜索用时 0 毫秒
1.
This research paper analyses the grain-size characteristics of the Quaternary deposits at Xingshan near Siping, Jilin province in China by employing graphic measures to study the grain size distribution and its mode of transport and deposition. The Quaternary deposits at Xingshan lie unconformable on Cretaceous rocks made of siltstone, mudstone and sandstone. The average grain size is between 8.06 to 8.55Φ (0.002 6 ~0.003 7 mm). The Quaternary deposits at Xingshan mainly compose of very fine silt to clay. The compositions of the grade are clay 63% and silt 37%. The clay size components are weathered debris transported and deposited by flowing water from the SE highlands or hills to the low lying NW Xingshan plains whereas the silty components accumulated by aoelian process. The Quaternary deposits at Xingshan accumulated in the middle and late Pleistocene interglacial periods from (459.12~39.03) ka to (88.92~7.56) ka. The standard deviation ranged from 0.96 to 1.36Φ, indicating that the sediments are moderately to poorly sorted, Coefficient of skewness ranged from 0.16~0.31 with an average skewness of 0.218, (Positively skewed towards fine). Kurtosis values (0.84~1.05) from the grain size distribution and visual inspection of the frequency curves indicate platykurtic to mesokurtic curves and unimodal to bimodal grain-size distribution. The type of deposit formation is sand dune and the source is at a distal from its provenance. 相似文献
2.
3.
Martin Groenewegen 《Astrophysics and Space Science》1995,224(1-2):321-324
The relation between mass loss rate and pulsation period in carbon Miras is discussed. The dust mass loss rate is very low (about 2 × 10–10 M/yr) up to aboutP = 380 days, where there is a sudden increase. ForP > 400 days there is a linear relation between logM andP. The change in the mass loss rate near 380 days may be related to radiation pressure on dust becoming effective in driving the outflow. 相似文献
4.
5.
The knowledge of past events is important for the assessment of debris-flow hazard. Amongst the sources of information, documents
from historical archives are particularly important in sites where the debris flows cause damage to urban areas and transportation
routes. The paper analyses the availability of historical documents on debris flows in Northeastern Italy and discusses factors
that can influence the building of time series from archive data both at regional and single basin scales. An increased number
of debris flows was observed in the studied region for the last decades. This could be due both to an increased frequency
of the events and to a larger availability of information: the analysis carried out indicates that the latter factor is probably
the most influencing. The importance of factors, which affect the collection of data, including the conservation of documents
and the presence and fragility of the elements at risk, is stressed in view of a wise use of historical data on debris flows. 相似文献
6.
根据对蓖麻发育期的观测,结合当地气象条件,分析了阿克苏种植蓖麻的适应性及栽培中应采取的趋利避害的技术措施。 相似文献
7.
8.
9.
According to archaeological data from about sixty samples the relative stability of physical and human geographical environment in the tropical zone of China is discussed in this paper. Because of the superior natural environment, sufficient food resources and a sparse population resulting in the absence of social requirement to transform the productive forces, the advancement of economy and society was stagnated during prehistorical period in China's tropics. Compared with northern China, the appearance of ground stone tool stagnated about 3,000 years, the beginning of Bronze Age, about 1,000 years, and the agriculture, 2,500-3,000 years. The no ceramics age continued till the early Neolithic Age and the appearance of colour or white ceramics was 2,000 years later than that in northern China. The life form of migration to gather and to hunt continued till the middle Neolithic Age, and the fixed settlement based on agriculture 1,000-2,000 years stagnated. The clan commune just appeared at the end of the Neolithic Age which was 2,000-3,000 years later than that in northern China. 相似文献
10.
丽江大研镇震灾分布和地脉动测量结果之间的相关性 总被引:4,自引:2,他引:4
丽江7.0级地震后,大研镇被毁建筑物的地理分布呈显4条条带,伤亡人员的地理分布和上述条带重合。91个短周期地脉动测点的观测资料表明,分布在上述条带内的大多数测点,其卓越周期大于0.3S;条带外的测点,其卓越周期一般在0.1S左右。作认为卓越周期和烈度异常之间良好的相关性,是因为地脉动卓越周期和地方震的频谱之间存在良好的相关性。 相似文献