全文获取类型
收费全文 | 9968篇 |
免费 | 3111篇 |
国内免费 | 5090篇 |
专业分类
测绘学 | 533篇 |
大气科学 | 725篇 |
地球物理 | 2118篇 |
地质学 | 11466篇 |
海洋学 | 1397篇 |
天文学 | 296篇 |
综合类 | 727篇 |
自然地理 | 907篇 |
出版年
2024年 | 165篇 |
2023年 | 600篇 |
2022年 | 653篇 |
2021年 | 707篇 |
2020年 | 620篇 |
2019年 | 766篇 |
2018年 | 541篇 |
2017年 | 563篇 |
2016年 | 622篇 |
2015年 | 703篇 |
2014年 | 862篇 |
2013年 | 759篇 |
2012年 | 860篇 |
2011年 | 880篇 |
2010年 | 827篇 |
2009年 | 792篇 |
2008年 | 800篇 |
2007年 | 922篇 |
2006年 | 869篇 |
2005年 | 742篇 |
2004年 | 709篇 |
2003年 | 437篇 |
2002年 | 296篇 |
2001年 | 307篇 |
2000年 | 243篇 |
1999年 | 269篇 |
1998年 | 283篇 |
1997年 | 179篇 |
1996年 | 123篇 |
1995年 | 90篇 |
1994年 | 97篇 |
1993年 | 140篇 |
1992年 | 173篇 |
1991年 | 125篇 |
1990年 | 121篇 |
1989年 | 90篇 |
1988年 | 41篇 |
1987年 | 56篇 |
1986年 | 29篇 |
1985年 | 21篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1973年 | 6篇 |
1948年 | 5篇 |
1945年 | 3篇 |
1942年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
11.
ASCA observations of the two Type Ⅱ AGNs,NGC7314 and NGC 7582,show clear variations in the broad X-ray band(0.4-10keV)on short timescales-10^4s.Spectral analysis indicates that they bot have an absorbed hard X-ray component and an unabsorbed soft“excess” component.To clarify the origin of the latter,we made a cross-correlation analysis of the two components.The results show that,for NGC7314,the soft X-ray variability is proportional to that of the hard X-ray component.This indicates that the active nucleus of NGC 7314 must be partially covered and so the soft emission is a “leaking” of the variable hard component.For NGC 7582,there is no detectable variability in the soft component, although there is a definite one in the hard component.This indicates that the variable nucleus of NGC 7582 must be fully blocked by absorbing matter,and the soft emission is most likely the scattered component predicted by the AGN unified model. 相似文献
12.
13.
从香蕉(Musa AAA)组织培养繁殖后代中,选育出特长果指香蕉新品系“93-1”,主要特点为植株表现中矮秆(216 cm),茎粗中等(67.1 cm),苗期叶色浓绿,叶形椭圆形,叶形比(长/宽)1.91,叶尖急尖,叶基凹陷呈耳垂状;果穗7~12梳,平均8.07梳/穗,穗长81.6 cm,单穗重22.8 kg,单果重213.5 g,果指数123.4条/穗,果指特长(25.8 cm);可溶性固形物含量21.8%;全生育期321d(春植)至368 d(夏植),约44片叶。“93-1”适宜在广东雷州半岛及海南岛栽培种植。 相似文献
14.
本文讨论了利用LAMOST作银河系研究的科学意义及可能性;并提出具体实施LAMOST/GAIAXY计划的初步方案。 相似文献
15.
长乐-南澳左行韧性剪切带位于东南沿海,是酉太平洋大陆边缘构造带的一个组成部分。本文基于野外观察及室内分析,并借助透射电镜对变形石英的内部结构进行了观察,利用变形石英显微构造参数估算剪切带中的应力差值,由此探讨了形成构造岩的机制。 相似文献
16.
17.
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
18.
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
19.
提出川滇地洼系“四层楼”铜矿床序列的形成与陆壳演化的成生联系,是与本区陆壳由前地槽—地槽—地台—地洼演化各阶段与之相匹配的成矿作用的产物.与此同时,并总结了本区“四层楼”铜矿床序列的成矿作用具有明显的继承性、新生性、旋回性及层控性四大特点和多因复成矿床的成矿模式. 相似文献
20.