全文获取类型
收费全文 | 51114篇 |
免费 | 500篇 |
国内免费 | 314篇 |
专业分类
测绘学 | 995篇 |
大气科学 | 2572篇 |
地球物理 | 9814篇 |
地质学 | 19546篇 |
海洋学 | 4855篇 |
天文学 | 12250篇 |
综合类 | 131篇 |
自然地理 | 1765篇 |
出版年
2022年 | 577篇 |
2021年 | 857篇 |
2020年 | 896篇 |
2019年 | 1005篇 |
2018年 | 2103篇 |
2017年 | 1914篇 |
2016年 | 2044篇 |
2015年 | 836篇 |
2014年 | 1827篇 |
2013年 | 2793篇 |
2012年 | 2078篇 |
2011年 | 2469篇 |
2010年 | 2318篇 |
2009年 | 2686篇 |
2008年 | 2358篇 |
2007年 | 2622篇 |
2006年 | 2301篇 |
2005年 | 1299篇 |
2004年 | 1214篇 |
2003年 | 1195篇 |
2002年 | 1159篇 |
2001年 | 1130篇 |
2000年 | 936篇 |
1999年 | 694篇 |
1998年 | 706篇 |
1997年 | 735篇 |
1996年 | 549篇 |
1995年 | 573篇 |
1994年 | 535篇 |
1993年 | 434篇 |
1992年 | 449篇 |
1991年 | 428篇 |
1990年 | 479篇 |
1989年 | 421篇 |
1988年 | 388篇 |
1987年 | 409篇 |
1986年 | 336篇 |
1985年 | 463篇 |
1984年 | 468篇 |
1983年 | 453篇 |
1982年 | 432篇 |
1981年 | 387篇 |
1980年 | 395篇 |
1979年 | 347篇 |
1978年 | 378篇 |
1977年 | 320篇 |
1976年 | 287篇 |
1975年 | 293篇 |
1974年 | 274篇 |
1973年 | 344篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
In connection with the celebration of the centennial of the Institute of Electrical and Electronics Engineers (UEEE) in 1984, the history of electrical engineering in relation to the world's oceans is traced, with emphasis on the 20-year period from the 1960's to the present. Note is taken of the breadth of the cross-disciplinary interests involved, as exemplified by the active participation of a score of IEEE Societies and Professional Groups, how they organized to cooperate, the periodic meetings and annual conferences they sponsored, the publications they undertook, the tokens of recognition they adopted, and how they adapted to changes in emphasis to reflect shifts in the areas of technology served. Finally, an assessment is made of the future of the recently organized IEEE Oceanic Engineering Society. 相似文献
12.
13.
Rostov State Pedagogical Institute; All-Union Scientific Research Institute Gradient. Translated from Astrofizika, Vol. 33, No. 3, pp. 379–393, November–December, 1990. 相似文献
14.
15.
V. G. Gorbatskii 《Astrophysics》1990,32(2):149-154
Leningrad State University. Translated from Astrofizika, Vol. 32, No. 2, pp. 267–275, March–April, 1990. 相似文献
16.
17.
18.
In the frame of 2D-static problems one approaches the problem of elastic-NRT (not-resisting tension) semi-plane loaded on its limit line. This problem is intended to model the stress situation induced in the soil by a foundation structure. The solution, in terms of activated stress field, is searched for in the class of stress fields satisfying equilibrium and admissibility conditions, by applying an energy approach. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
19.
J. V. WALTHER 《Journal of Metamorphic Geology》1996,14(3):351-360
ABSTRACT With increasing temperature during prograde metamorphism reactions will occur first at the lithological contacts of mixed pelite and calcsilicate terranes. At these interfaces, a fluid of lower chemical potential of H2O and CO2 than that required to produce a fluid in either layer can be produced whether reaction is caused by fluid infiltration or is initially fluid absent. If the interface region does not allow fluid transport then as temperature increases, a fluid pressure greater than lithostatic can develop. At some degree of over-pressure relative to rock pressure, the fluid hydraulically fractures the rock and a gradient in fluid composition away from the contact can be produced. These phenomena occur at the compositional interfaces whenever univariant reactions in the differing layers cross on a temperature vs. mole fraction of CO2 diagram with slopes of opposite sign. The first occurrence of these reaction products at lithological contacts delineates an isograd that defines temperature as well as the mole fraction of CO2 at constant pressure in systems open to fluid transport. These isograds can be contrasted with fluid-producing isograds in closed systems. As an illustration of possible effects, the reactions quartz + clinozoisite + muscovite = anorthite + K-feldspar + H2O and phlogopite + quartz + calcite = tremolite + K-feldspar + H2O + CO2 at 4 kbar are analysed and equations for fluid production and transport are developed. 相似文献
20.