全文获取类型
收费全文 | 30291篇 |
免费 | 384篇 |
国内免费 | 265篇 |
专业分类
测绘学 | 637篇 |
大气科学 | 2833篇 |
地球物理 | 6556篇 |
地质学 | 11737篇 |
海洋学 | 2054篇 |
天文学 | 5381篇 |
综合类 | 41篇 |
自然地理 | 1701篇 |
出版年
2018年 | 291篇 |
2017年 | 267篇 |
2016年 | 414篇 |
2015年 | 301篇 |
2014年 | 423篇 |
2013年 | 1227篇 |
2012年 | 515篇 |
2011年 | 787篇 |
2010年 | 645篇 |
2009年 | 919篇 |
2008年 | 837篇 |
2007年 | 801篇 |
2006年 | 842篇 |
2005年 | 730篇 |
2004年 | 759篇 |
2003年 | 716篇 |
2002年 | 722篇 |
2001年 | 592篇 |
2000年 | 611篇 |
1999年 | 581篇 |
1998年 | 570篇 |
1997年 | 591篇 |
1996年 | 529篇 |
1995年 | 503篇 |
1994年 | 478篇 |
1993年 | 465篇 |
1992年 | 516篇 |
1991年 | 472篇 |
1990年 | 512篇 |
1989年 | 427篇 |
1988年 | 467篇 |
1987年 | 542篇 |
1986年 | 447篇 |
1985年 | 586篇 |
1984年 | 665篇 |
1983年 | 682篇 |
1982年 | 597篇 |
1981年 | 587篇 |
1980年 | 580篇 |
1979年 | 553篇 |
1978年 | 544篇 |
1977年 | 497篇 |
1976年 | 478篇 |
1975年 | 467篇 |
1974年 | 493篇 |
1973年 | 500篇 |
1972年 | 350篇 |
1971年 | 316篇 |
1970年 | 249篇 |
1968年 | 230篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
53.
54.
A generalized database of global palaeomagnetic data from 3719 lava flows and thin dykes of age 0–5 Ma has been constructed for use with a relational database management system. The database includes all data whose virtual geomagnetic poles (VGP) lie within 45 of the spin axis and can be used for studies of palaeosecular variation and for geomagnetic field modelling. Because many of these data were collected and processed more than 15–20 years ago, each result has been characterized according to the demagnetization procedures carried out. Analysis of these data in terms of the latitude variation of the angular dispersion of VGPs (palaeosecular variation from lavas) strongly suggests that careful data selection is required and that many of the older studies may need to be redone using more modern methods. Differences between the angular dispersions for separate normal- and reverse-polarity data sets confirm that many older studies have not been adequately cleaned magnetically. Therefore, the use of the database for geomagnetic field modelling should be carried out with some caution. Using a VGP cut-off angle that varies with latitude, the best data set consists of 2636 results that show a smooth increase of VGP angular dispersion with latitude. Model G for palaeosecular variation, which is based on modelling of the antisymmetric (dipole) and symmetric (quadrupole) dynamo families, provides a good fit to these results. 相似文献
55.
56.
Rainfall thresholds for landsliding in the Himalayas of Nepal 总被引:5,自引:0,他引:5
Emmanuel J. Gabet Douglas W. Burbank Jaakko K. Putkonen Beth A. Pratt-Sitaula Tank Ojha 《Geomorphology》2004,63(3-4):131-143
Landsliding of the hillslope regolith is an important source of sediment to the fluvial network in the unglaciated portions of the Himalayas of Nepal. These landslides can produce abrupt increases of up to three orders of magnitude in the fluvial sediment load in less than a day. An analysis of 3 years of daily sediment load and daily rainfall data defines a relationship between monsoonal rainfall and the triggering of landslides in the Annapurna region of Nepal. Two distinct rainfall thresholds, a seasonal accumulation and a daily total, must be overcome before landslides are initiated. To explore the geomorphological controls on these thresholds, we develop a slope stability model, driven by daily rainfall data, which accounts for changes in regolith moisture. The pattern of rainfall thresholds predicted by the model is similar to the field data, including the decrease in the daily rainfall threshold as the seasonal rainfall accumulation increases. Results from the model suggest that, for a given hillslope, regolith thickness determines the seasonal rainfall necessary for failure, whereas slope angle controls the daily rainfall required for failure. 相似文献
57.
René Rutten, Director of the Isaac Newton Group of Telescopes, sets the scene for future developments in international astronomy on La Palma. 相似文献
58.
59.
60.
W. Lohmann 《Astronomische Nachrichten》1972,294(4):187-189
This cluster consists of ≈ 130 members up to the photographic limiting magnitude ≈ 19m·0, its radius amounts to ≈ 1.0 Mpc (according to the distance of 90 Mpc), and it is built up according to the generalized SCHUSTER density law with n = 2.45. The mean velocity of its stars may be of the order of 250 km/s. 相似文献