全文获取类型
收费全文 | 19550篇 |
免费 | 4852篇 |
国内免费 | 8850篇 |
专业分类
测绘学 | 928篇 |
大气科学 | 2608篇 |
地球物理 | 3175篇 |
地质学 | 21095篇 |
海洋学 | 2386篇 |
天文学 | 244篇 |
综合类 | 1431篇 |
自然地理 | 1385篇 |
出版年
2024年 | 254篇 |
2023年 | 942篇 |
2022年 | 995篇 |
2021年 | 1100篇 |
2020年 | 891篇 |
2019年 | 1135篇 |
2018年 | 821篇 |
2017年 | 852篇 |
2016年 | 846篇 |
2015年 | 1006篇 |
2014年 | 1420篇 |
2013年 | 1170篇 |
2012年 | 1356篇 |
2011年 | 1403篇 |
2010年 | 1292篇 |
2009年 | 1305篇 |
2008年 | 1344篇 |
2007年 | 1470篇 |
2006年 | 1409篇 |
2005年 | 1273篇 |
2004年 | 1167篇 |
2003年 | 985篇 |
2002年 | 916篇 |
2001年 | 1063篇 |
2000年 | 703篇 |
1999年 | 730篇 |
1998年 | 730篇 |
1997年 | 611篇 |
1996年 | 609篇 |
1995年 | 517篇 |
1994年 | 541篇 |
1993年 | 477篇 |
1992年 | 448篇 |
1991年 | 391篇 |
1990年 | 366篇 |
1989年 | 298篇 |
1988年 | 86篇 |
1987年 | 91篇 |
1986年 | 48篇 |
1985年 | 30篇 |
1984年 | 18篇 |
1983年 | 11篇 |
1982年 | 16篇 |
1981年 | 20篇 |
1980年 | 13篇 |
1979年 | 7篇 |
1976年 | 7篇 |
1973年 | 9篇 |
1972年 | 7篇 |
1954年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
31.
32.
33.
GiovanniB.Piccardo 《《幕》》2003,26(3):193-199
Mantle peridotites were early exposed at the sea-floor of the Jurassic Tethys derived from the subcontinental mantle of the Europe-Adria system. During continental rifting and oceanic spreading, these lithospheric peri-dotites were percolated via diffuse reactive porous flowby melt fractions produced by near-fractional melting of the upwelling asthenosphere. Ascending melts inter-acted with the lower lithosphere, dissolving pyroxenes and precipitating olivine, and crystallized at shallower levels in the mantle column causing melt impregnation.Subsequent focused porous flow formed replacive dunitechannels, cutting the impregnated oeridotites, which were conduits for upward migration of MORB-type liq-uids. Melt migration produced depletionlrefertilization and significant heating of the percolatedlimpregnated mantle, i.e the thermochemical erosion of the litho-sphere. Impregnated and thermally modified lithos-pheric mantle was cooled by conductive heat loss dur-ing progressive lithosphere thinning and was intrudeaby MORB magmas, which formed Mg-rich and Fe-richgabbroic dykes and bodies. Alpine-Apennine ophiolitic peridotites record the deep-seated migration of melts which changed their compositions and dynamics during the rift evolution. The thermochemical erosion of the lithospheric mantle by the ascending asthenospheric melts, which induces significant compositional and rhe-ological changes in the lower lithosphere, is a major process in the evolution of the continent-ocean transi-tion towards a slow spreading oceanic system. 相似文献
34.
本文叙述南天区 5GHzVLBI普查中新发现的视超光速射电源 ,0 4 2 0— 0 1 4,1 334—1 2 7和 2 345— 1 67,这些结果尚待进一步的观测加以证实 相似文献
35.
QinChengzhi ZhouChenghu PeiTao LiQuanlin 《中国地震研究》2004,18(2):178-187
The migration of strong earthquakes is an important research topic because the migration phenomena reflect partly the seismic mechanism and involve the prediction of tendency of seismic activity. Research on migration of strong earthquakes has mostly focused on finding the phenomena. Some attempts on getting regularity were comparatively subjective. This paper suggests that there should be indices of migration in earthquake dataset and the indexes should have statistical meaning if there is regularity in the migration of strong earthquakes. In this study, three derivative attributes of migration, i.e., migration orientation, migration distance and migration time interval, were statistically analyzed. Results in the North China region show that the migration of strong earthquakes has statistical meaning. There is a dominant migration orientation (W by S to E by N), a dominant distance ( ≤ 100kin and on the confines of 300 ~ 700km), and a dominant time interval ( ≤ la and on the confines of 3 - 4a). The results also show that the migration will differ slightly with different magnitude range or earthquake activity phase. 相似文献
36.
高从堦 《中国海洋湖沼学报》2003,21(1):40-45
Seawater desalination has been people‘s fond dream since ancient times,the dream is now becoming a reality.This paper presents a brief development history of reverse osmosis.Much attention was paid to innovative development in mebranes,modules.equipments and applied technology,including asymmetric and composite membranes,spiral-wound element and hollow fiber module,energy recovery equipments and different technological processes.The extension of reverse osmosis,such as desalination,pre-concentration,integrated processes and nanofiltration,is also briefly mentioned. 相似文献
37.
叙述密县—鹿邑断层、临汝—老城断层、凡城—沈丘断层、封丘—商丘断层、汤阴断层、青羊口断层的物理场特征,并结合煤田地质特征,说明它们对河南聚煤盆地后期的改造作用,从而为煤田预测指明了方向。 相似文献
38.
准噶尔盆地陆1井砂岩成岩作用及其对储层的影响 总被引:1,自引:1,他引:0
本文探讨了陆1井岩屑砂岩的成岩作用及其对砂岩储层的影响.研究表明,压实作用使岩屑砂岩的孔隙度随埋深迅速减小,成岩早期的胶结物使大部分原生孔隙被充填。水化作用在成岩早期及有机质半成熟和成熟期成岩作用过程中,制约着各个阶段的成岩作用特点。在水化作用和有机质热演化作用的共同影响下,使得方解石胶结物发生选择性溶蚀形成了深部(上乌尔禾组)次生孔隙发育带。 相似文献
39.
40.