全文获取类型
收费全文 | 54882篇 |
免费 | 18000篇 |
国内免费 | 42346篇 |
专业分类
测绘学 | 3126篇 |
大气科学 | 22559篇 |
地球物理 | 16480篇 |
地质学 | 40969篇 |
海洋学 | 17890篇 |
天文学 | 7057篇 |
综合类 | 3997篇 |
自然地理 | 3150篇 |
出版年
2023年 | 240篇 |
2022年 | 384篇 |
2021年 | 735篇 |
2020年 | 2014篇 |
2019年 | 5524篇 |
2018年 | 6040篇 |
2017年 | 5744篇 |
2016年 | 5925篇 |
2015年 | 4981篇 |
2014年 | 4723篇 |
2013年 | 5889篇 |
2012年 | 5100篇 |
2011年 | 5069篇 |
2010年 | 4991篇 |
2009年 | 4630篇 |
2008年 | 3817篇 |
2007年 | 3816篇 |
2006年 | 3451篇 |
2005年 | 3111篇 |
2004年 | 3481篇 |
2003年 | 3158篇 |
2002年 | 2825篇 |
2001年 | 2504篇 |
2000年 | 2161篇 |
1999年 | 2099篇 |
1998年 | 2199篇 |
1997年 | 2236篇 |
1996年 | 1712篇 |
1995年 | 1670篇 |
1994年 | 1560篇 |
1993年 | 1437篇 |
1992年 | 1255篇 |
1991年 | 977篇 |
1990年 | 998篇 |
1989年 | 841篇 |
1988年 | 731篇 |
1987年 | 661篇 |
1986年 | 545篇 |
1985年 | 572篇 |
1984年 | 619篇 |
1983年 | 501篇 |
1982年 | 534篇 |
1981年 | 407篇 |
1980年 | 388篇 |
1979年 | 336篇 |
1978年 | 267篇 |
1977年 | 270篇 |
1976年 | 227篇 |
1975年 | 212篇 |
1974年 | 208篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
101.
IntroductionThe area of eastern Liaoning is an importantmetal and nonmetal metallogenetic district in China,and the Liaohe group is one of the most importantstrata that hosts Pb, Zn, Au, B and Mg etcstratabound deposits. Up to now many geo1ogistssuch as Z… 相似文献
102.
103.
104.
本文讨论了河西走廊东部地区早二叠世地层研究的有关问题,认为甘肃山丹青羊泉下二叠统剖面是北祁连山—河西走廊地区的重要代表剖面之一。以该剖面研究为依据,提出走廊东部地区下二叠统的进一步划分方案,分析该区早二叠世地层岩性特征差异的原因,并与走廊西部地区同期地层进行对比,进一步明确了大黄沟组的含意。 相似文献
105.
The restricted problem of 2 + 2 bodies when one of the infinitesimal masses is further acted upon by the light pressure of the two primaries, is considered. The stationary solutions of this problem are found out. A short discussion is devoted to the stability of these solutions. 相似文献
106.
Formation of saline groundwaters in the Baltic region through freezing of seawater during glacial periods 总被引:1,自引:0,他引:1
Typical Ca---Cl brines occur in crystalline and metamorphic rocks below freshwater horizons at various localities in Sweden and Finland. Total dissolved solids (TDS) range in concentration between 2 and 120 gl−1 and have long been thought to derive from water-rock interactions. The relationships between Na, Cl and Br in these brines suggest, however, that they were derived from freezing of seawater during glacial periods. The brines were subsequently diluted by meteoric waters and their Ca/Mg ratio was increased through water-rock interactions in the subsurface. The hydrogeological model for both the formation of freeze-derived marine brines and their lateral intrusion involves restricted inland marine basins in recent and subrecent polar climatic belts. Seawater in such basins gradually freezes in response to glaciation. The solutes which concentrate in the remaining water body are residual after precipitation of a sequence of minerals which include carbonates, mirabilite and hydrohalite. Hydraulic pressure of the growing ice sheet over the frozen seas is gradually added to the ambient hydrostatic pressure exerted on the brines. This, together with their increased density, increases the intrusional potential of the brines. As the land ice cannot exert hydraulic pressure on continental groundwater in the aquifers, the balance of pressure favours deep landward intrusion of brines. Post-glacial processes cause the subsurface dilution and replacement of the brines both by seawater and fresh waters. The presence of such brines also far from present-day coastal settings reflects the shifting of coastlines as a result of isostatic movements and eustatic sea-level changes associated with glaciation and deglaciation. 相似文献
107.
Swath bathymetric, gravity, and magnetic studies were carried out over a 55 km long segment of the Central Indian Ridge.
The ridge is characterized by 12 to 15 km wide rift valley bounded by steep walls and prominent volcanic constructional ridges
on either side of the central rift valley. A transform fault at 7°45′S displaces the ridge axis. A mantle Bouguer anomaly
low of −14 mGals and shallowing of rift valley over the middle of the ridge segment indicate along axis crustal thickness
variations. A poorly developed neovolcanic zone on the inner rift valley floor indicate dominance of tectonic extension. The
off-axis volcanic ridgs suggest enhanced magmatic activity during the recent past.
Received: 24 May 1996 / Rivision received: 13 January 1997 相似文献
108.
109.
110.
Shi Zhi-dong Li Zhong-yuanUniversity of Science Technology of China Hefei PRC Advanced Centre for Earth Science Astronomy Third World Academy of Science 《紫金山天文台台刊》1996,(2)
Areview about K-H instability related to comet tail is presented.The effect of dust graing on KHI is theoretically analysed and relations of critical shear to excit KHI with the properties of dust grains both for sheared ion flow and for sheared dust flow re put out.Their possible application in comet tail is suggested. 相似文献