全文获取类型
收费全文 | 7526篇 |
免费 | 1153篇 |
国内免费 | 968篇 |
专业分类
测绘学 | 1118篇 |
大气科学 | 432篇 |
地球物理 | 1547篇 |
地质学 | 3110篇 |
海洋学 | 814篇 |
天文学 | 1511篇 |
综合类 | 442篇 |
自然地理 | 673篇 |
出版年
2024年 | 18篇 |
2023年 | 63篇 |
2022年 | 146篇 |
2021年 | 211篇 |
2020年 | 214篇 |
2019年 | 219篇 |
2018年 | 178篇 |
2017年 | 239篇 |
2016年 | 277篇 |
2015年 | 277篇 |
2014年 | 433篇 |
2013年 | 422篇 |
2012年 | 467篇 |
2011年 | 432篇 |
2010年 | 362篇 |
2009年 | 492篇 |
2008年 | 444篇 |
2007年 | 613篇 |
2006年 | 499篇 |
2005年 | 461篇 |
2004年 | 362篇 |
2003年 | 366篇 |
2002年 | 296篇 |
2001年 | 271篇 |
2000年 | 274篇 |
1999年 | 276篇 |
1998年 | 233篇 |
1997年 | 195篇 |
1996年 | 183篇 |
1995年 | 120篇 |
1994年 | 128篇 |
1993年 | 99篇 |
1992年 | 93篇 |
1991年 | 39篇 |
1990年 | 65篇 |
1989年 | 48篇 |
1988年 | 42篇 |
1987年 | 23篇 |
1986年 | 17篇 |
1985年 | 15篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 1篇 |
1954年 | 4篇 |
1928年 | 1篇 |
排序方式: 共有9647条查询结果,搜索用时 93 毫秒
61.
62.
由共聚法制得的铁铝复合交联剂交换钠基蒙脱石层间的水合钠离子,再经SO42-改性处理制备了铁铝复合层柱粘土固体超强酸催化剂.利用xRD、FT-IR和BET法对催化剂的结构进行了表征.以乙酸正丁酯的合成反应为探针反应对催化剂的活性进行了测试.通过正交实验确定了铁铝复合交联粘土SO42-改性最佳工艺条件.研究了催化剂对探针反应的选择性及重复使用情况.结果表明:在由实验确定的最佳改性工艺条件下,乙酸的转化率达92.2%,反应中无副产物产生,催化剂具有较好的重复使用性能. 相似文献
63.
INTRODUCTIONTheOkinawaTrough (OT) ,locatednorthwestoftheRyukyuTrenchandtheRyukyugunto ,eastoftheEastChinaSeashelf,isaback arcbasinbulgedtotheRyukyuTrench .TheOTextendsfromKyushuinthesouthwestofJapantotheIlanPlaininthenortheasternTaiwan ,Chinainthesouthwest… 相似文献
64.
65.
66.
Lodolo Emanuele Coren Franco Schreider Anatoly A. Ceccone Giulio 《Marine Geophysical Researches》1997,19(5):439-450
The southwestern part of the Scotia Sea, at the corner of the Shackleton Fracture Zone with the South Scotia Ridge has been investigated, combining marine magnetic profiles, multichannel seismic reflection data, and satellite-derived gravity anomaly data. From the integrated analysis of data, we identified the presence of the oldest part of the crust in this sector, which tentative age is older than anomaly C10 (28.7 Ma). The area is surrounded by structural features clearly imaged by seismic data, which correspond to gravity lows in the satellite-derived map, and presents a rhomboid-shaped geometry. Along its southern boundary, structural features related to convergence and possible incipient subduction beneath the continental South Scotia Ridge have been evidenced from the seismic profile. We interpret this area, now located at the edge of the south-western Scotia Sea, as a relict of ocean-like crust formed during an earlier, possibly diffuse and disorganized episode of spreading at the first onset of the Drake Passage opening. The successive episode of organized seafloor spreading responsible for the opening of the Drake Passage that definitively separated southern South America from the Antarctic Peninsula, instigated ridge-push forces that can account for the subduction-related structures found along the western part of the South Scotia Ridge. This seafloor accretion phase occurred from 27 to about 10 Ma, when spreading stopped in the western Scotia Sea Ridge, as resulted from the identification of the marine magnetic anomalies. 相似文献
67.
Riccardo?Geletti Emanuele?LodoloEmail author Anatoly?A.?Schreider Alina?Polonia 《Marine Geophysical Researches》2005,26(1):17-28
The structural framework of the southern part of the Shackleton Fracture Zone has been investigated through the analysis of
a 130-km-long multichannel seismic reflection profile acquired orthogonally to the fracture zone near 60° S. The Shackleton
Fracture Zone is a 800-km-long, mostly rectilinear and pronounced bathymetric lineation joining the westernmost South Scotia
Ridge to southern South America south of Cape Horn, separating the western Scotia Sea plate from the Antarctic plate. Conventional
processing applied to the seismic data outlines the main structures of the Shackleton Fracture Zone, but only the use of enhanced
techniques, such as accurate velocity analyses and pre-stack depth migration, provides a good definition of the acoustic basement
and the architecture of the sedimentary sequences. In particular, a strong and mostly continuous reflector found at about
8.0 s two-way traveltime is very clear across the entire section and is interpreted as the Moho discontinuity. Data show a
complex system of troughs developed along the eastern flank of the crustal ridge, containing tilted and rotated blocks, and
the presence of a prominent listric normal fault developed within the oceanic crust. Positive flower structures developed
within the oceanic basement indicate strike-slip tectonism and partial reactivation of pre-existing faults. Present-day tectonic
activity is found mostly in correspondence to the relief, whereas fault-induced deformation is negligible across the entire
trough system. This indicates that the E–W-directed stress regime present in the Drake Passage region is mainly dissipated
along a narrow zone within the Shackleton Ridge axis. A reappraisal of all available magnetic anomaly identifications in the
western Scotia Sea and in the former Phoenix plate, in conjunction with new magnetic profiles acquired to the east of the
Shackleton Fracture Zone off the Tierra del Fuego continental margin, has allowed us to propose a simple reconstruction of
Shackleton Fracture Zone development in the general context of the Drake Passage opening. 相似文献
68.
Fishing, selection, and phenotypic evolution 总被引:10,自引:9,他引:10
69.