全文获取类型
收费全文 | 43674篇 |
免费 | 715篇 |
国内免费 | 272篇 |
专业分类
测绘学 | 920篇 |
大气科学 | 3115篇 |
地球物理 | 8917篇 |
地质学 | 16120篇 |
海洋学 | 3733篇 |
天文学 | 9218篇 |
综合类 | 181篇 |
自然地理 | 2457篇 |
出版年
2022年 | 311篇 |
2021年 | 535篇 |
2020年 | 620篇 |
2019年 | 660篇 |
2018年 | 1169篇 |
2017年 | 1168篇 |
2016年 | 1305篇 |
2015年 | 742篇 |
2014年 | 1279篇 |
2013年 | 2132篇 |
2012年 | 1427篇 |
2011年 | 1796篇 |
2010年 | 1652篇 |
2009年 | 2013篇 |
2008年 | 1793篇 |
2007年 | 1816篇 |
2006年 | 1665篇 |
2005年 | 1167篇 |
2004年 | 1150篇 |
2003年 | 1178篇 |
2002年 | 1066篇 |
2001年 | 946篇 |
2000年 | 865篇 |
1999年 | 791篇 |
1998年 | 797篇 |
1997年 | 773篇 |
1996年 | 658篇 |
1995年 | 625篇 |
1994年 | 562篇 |
1993年 | 500篇 |
1992年 | 439篇 |
1991年 | 456篇 |
1990年 | 471篇 |
1989年 | 427篇 |
1988年 | 396篇 |
1987年 | 437篇 |
1986年 | 443篇 |
1985年 | 542篇 |
1984年 | 586篇 |
1983年 | 591篇 |
1982年 | 537篇 |
1981年 | 489篇 |
1980年 | 462篇 |
1979年 | 439篇 |
1978年 | 414篇 |
1977年 | 416篇 |
1976年 | 368篇 |
1975年 | 386篇 |
1974年 | 375篇 |
1973年 | 404篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
本实验以可能是黔中铝土矿的成矿母岩的两种伊利石粘土岩为主要试样,并选择了与成矿过程有关的高岭石粘土岩和铝铁岩为实验对象,实验研究了碳酸水体系腐殖酸存在的不同条件下,上述岩样中铝、硅、铁的溶解作用;阐明了在碳酸水体系中,腐殖在成矿母岩和风化母岩脱硅、脱铁和富集铝过程中的重要作用;初步分析了腐殖酸在铝质迁移中的护胶作用;指出了腐殖酸在铝土矿形成中的重要意义。 相似文献
992.
993.
Solar System Research - This article describes the results of the Phobos 2 interplanetary mission, launched in 1988, and presents some prospective scenarios for studying near-Mars space, including... 相似文献
994.
995.
996.
997.
Dr. E. K. Walton 《International Journal of Earth Sciences》1960,50(1):63-77
Lower Palaeozoic successions in the Southern Uplands are much thicker than previously supposed and sedimentation may have lasted well into Ludlow times. Volcanic rocks are Arenig and Glenkiln in age and are often interbedded with greywackes and shales. Lapworth's concept of the structure as an anticlinorium and a synclinorium is rejected and it is suggested that the rocks have been folded into a series of compound monoclines which face north-westwards. These are probably cut by strike faults which bring up the older beds to the north.
Zusammenfassung Die altpaläozoischen Schichtfolgen in den Südlichen Hochlanden sind viel mächtiger, als bisher angenommen wurde, und die Ablagerung kann bis ins Ludlow gereicht haben. Vulkanite haben Arenig- und Glenkiln-Alter; sie wechsellagern oft mit Grauwacken und Tonschiefern.Lapworths Vorstellung, der tektonische Bau sei ein Antiklinorium und ein Synklinorium, wird bestritten. Es wird angenommen, daß die Gesteine zu zusammengesetzten Monoklinen gefaltet wurden, deren steile Flügel nordwestwärts weisen. Sie werden wahrscheinlich durch streichende Verwerfungen zerschnitten, die die älteren Schichten im Norden herausheben.相似文献
998.
N. Brice Orange Hakeem M. Oluseyi David L. Chesny Maulik Patel Katie Hesterly Lauren Preuss Chantale Neira Niescja E. Turner 《Solar physics》2014,289(5):1557-1584
Since their discovery 20 year ago, transition region bright points have never been observed spectroscopically. Bright point properties have not been compared with similar transition region and coronal structures. In this work we have investigated three transient quiet Sun brightenings including a transition region bright point (TR BP), a coronal bright point (CBP) and a blinker. We use time-series observations of the extreme-ultraviolet emission lines of a wide range of temperature T (logT=5.3?–?6.4) from the EUV Imaging Spectrometer (EIS) onboard the Hinode satellite. We present the EIS temperature maps and Doppler maps, which are compared with magnetograms from the Michelson Doppler Imager (MDI) onboard the SOHO satellite. Doppler velocities of the TR BP and blinker are ≤?25 km?s?1, which is typical of transient TR phenomena. The Doppler velocities of the CBP were found to be ≤?20 km?s?1 with exception of those measured at logT=6.2 where a distinct bi-directional jet is observed. From an EM loci analysis we find evidence of single and double isothermal components in the TR BP and CBP, respectively. TR BP and CBP loci curves are characterized by broad distributions suggesting the existence of unresolved structure. By comparing and contrasting the physical characteristics of the events we find that the BP phenomena are an indication of multi-scaled self-similarity, given the similarities in both their underlying magnetic field configuration and evolution in relation to EUV flux changes. In contrast, the blinker phenomena and the TR BP are sufficiently dissimilar in their observed properties as to constitute different event classes. Our work is an indication that the measurement of similar characteristics across multiple event types holds class-predictive power, and is a significant step towards automated solar atmospheric multi-class classification of unresolved transient EUV sources. Finally, the analysis performed here establishes a connection between solar quiet region CBPs and jets. 相似文献
999.
On 11 September 1973 a peculiar prominence was observed. The prominence displayed strong ( 50km s–1) systematic motions toward and away from the observer. The unusual spectrographic appearance of the prominence might have been due to downflowing material lifted into the corona during an earlier coronal transient.The National Center for Atmospheric Research is sponsored by the National Science Foundation.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. 相似文献
1000.
In this work, the history of the development of the Turali area (the Dagestan coast of the Caspian Sea) in the Late Holocene
is under consideration. The analysis of the geological structure of the bay bar that separates the Bolshoy Turali lagoon from
the sea, the granulometric analysis of the coastal deposits, and the data of geo-radar profiles make it possible to assert
that the large eolian relief forms were formed during the New Caspian (Novokaspiyskoe) transgression of the Caspian Sea. 相似文献