全文获取类型
收费全文 | 40763篇 |
免费 | 6057篇 |
国内免费 | 8443篇 |
专业分类
测绘学 | 2395篇 |
大气科学 | 7717篇 |
地球物理 | 9695篇 |
地质学 | 19458篇 |
海洋学 | 5481篇 |
天文学 | 2879篇 |
综合类 | 3320篇 |
自然地理 | 4318篇 |
出版年
2024年 | 127篇 |
2023年 | 551篇 |
2022年 | 1612篇 |
2021年 | 1908篇 |
2020年 | 1666篇 |
2019年 | 1808篇 |
2018年 | 2250篇 |
2017年 | 2087篇 |
2016年 | 2250篇 |
2015年 | 1829篇 |
2014年 | 2223篇 |
2013年 | 2465篇 |
2012年 | 2214篇 |
2011年 | 2352篇 |
2010年 | 2311篇 |
2009年 | 2269篇 |
2008年 | 2002篇 |
2007年 | 2052篇 |
2006年 | 1730篇 |
2005年 | 1329篇 |
2004年 | 1029篇 |
2003年 | 1165篇 |
2002年 | 1172篇 |
2001年 | 1158篇 |
2000年 | 1219篇 |
1999年 | 1659篇 |
1998年 | 1341篇 |
1997年 | 1359篇 |
1996年 | 1273篇 |
1995年 | 1125篇 |
1994年 | 991篇 |
1993年 | 864篇 |
1992年 | 724篇 |
1991年 | 524篇 |
1990年 | 424篇 |
1989年 | 406篇 |
1988年 | 353篇 |
1987年 | 214篇 |
1986年 | 218篇 |
1985年 | 147篇 |
1984年 | 133篇 |
1983年 | 113篇 |
1982年 | 109篇 |
1981年 | 85篇 |
1980年 | 74篇 |
1979年 | 70篇 |
1978年 | 38篇 |
1977年 | 29篇 |
1976年 | 28篇 |
1975年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
41.
红阳煤田含煤地层太原组与山西组,是一套典型的“海陆交互相”沉积。依据剖面上沉积相序列变化特点,可划分为14个沉积旋回,每个沉积旋回均含有一层煤。有二种聚煤环境:一是海水退出潮坪后形成的泥炭沼泽聚积的煤层;二是扇三角洲平原形成的泥炭沼泽聚积的煤层。 相似文献
42.
Mercury (Hg) was investigated in bone tissues of skua ( Catharacta maccormick) and penguin (Pygoscelis adeliae) collected in the maritime Antarctic using atomic fluorescence spectrometry (AFS) and synchrotron radiation X-ray fluorescence (SR-XRF) method. The total levels of mercury in bone tissues of penguin and skua are much lower than those in other organs (e. g. , kidney, liver). The toxic effects of mercury in bone tissues of seabirds in polar region are not known. We have used SR- XRF method to map the distribution of trace levels of mercury in bones. The levels of mercury are found to be enriched somewhere near the periosteal surface and/or endosteal surface. The distribution of mercury shows strongly correlation with that of some essential elements and probably poses negative effect on the bone metabolism inferring from the relationship of mercury with the other elements. These studies represent a first step toward understanding the toxic effects of mercury on bone of polar animals by suggesting the possible microscopic investigation. 相似文献
43.
Xue-Fei Chen Zhan-Wen HanNational Astronomical Observatories Yunnan Observatory Chinese Academy of Sciences. Kunming Graduate School of the Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2005,5(1):65-76
We have studied the influence of different choices of core-envelope transition point on the final merger of contact binaries with two main-sequence components. A binary of 1.00 + 0.90M⊙ with an initial orbital period of 0.35d is examined. The mass fraction of the primary mixed with the matter of the secondary, qmix, determined by the chosen core-envelope transition point, ranges from 0.04 to 1.00 in our analysis. If as qmix< 0.8, none of the 相似文献
44.
ENVIRONMENTAL SUSTAINABILITY AND SCENARIOS OF URBANIZATION IN ARID AREA——A Case Study in Wuwei City of Gansu Province 总被引:1,自引:0,他引:1
YOUFei LIYu DONGSuo-cheng 《中国地理科学(英文版)》2005,15(2):120-130
1IN T R O D U C T IO N The western China isfacinggrowing problems of eco- logicaland economic development. The disparitiebse- tween the socio-economy of the western and eastern China were enlarging, and the major ecologicalprob- lems stilelvolve as past(H… 相似文献
45.
1 IntroductionBacteriaandtheiractivitiesplayanimportantroleintheelementalbiogeochemicalcyclesandenergytransformingintheocean (Zhenetal.1 997) .DortchandPackard(1 989) proposedthatfoodwebsintheeutrophicwatersaredominatedbythebiomassofprimaryproducerswhilefoodwebsintheoligotrophicwatersaredominatedbythebiomassofmicrobes.Heterotrophicbacteriahadbeenshowntoplayanimportantroleinthedecompositionoflarge ,rapidlysinkingorganicparticleswithinandbelowtheeuphot iczone ,andfurthertoaffecttheelementaldyn… 相似文献
46.
本文论述了珠穆朗玛峯地区土壤中稀土元素的含量,以及它们在土壤中的分布模式,并发现土壤中稀土元素的含量水平在很大程度上受土壤母质的制约。 相似文献
47.
48.
Maarten A. Prins Hongbo Zheng Kay Beets Simon Troelstra Patrick Bacon Ilse Kamerling Wouter Wester Martin Konert Xiangtong Huang Wang Ke Jef Vandenberghe 《第四纪科学杂志》2009,24(1):75-84
The Mangshan Plateau is located on the south bank of the Huang He (Yellow River) just west of the city of Zhengzhou, well outside the Loess Plateau in central China. Mixing models of the grain‐size data indicate that the loess deposits are mixtures of three loess components. Comparison of the mixing model with existing models established for a series of loess–palaeosol sequences from the Loess Plateau indicates that the Mangshan loess has been supplied from a proximal dust source, the Huang He floodplain, during major dust outbreaks. The high accumulation rates, the composition of the loess components, and especially the high proportions of a sandy loess component support this. Owing to the exceptionally high accumulation rates, the Mangshan grain size, magnetic susceptibility and carbonate records provide a high‐resolution archive of environmental and climate change. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
49.
Methyl-galactosides were oxidized at room temperature by galactose oxidase in a one-step reaction and afforded methyl-galactoaldehyde
in excellent yield and high purity. The resulting galactoaldehyde as a useful intermediate can be directly used in glycopeptide
synthesis. 相似文献
50.
从太湖流域旱涝史料看历史气候信息处理 总被引:15,自引:1,他引:14
历史气候信息处理建立在信息提取的基础上,目的在于建立一套方法,将定性的历史气候信息转化为气候变化参数,并消除各种不均—性,从而建立历史气候序列。本文着重介绍建立太湖流域历史旱涝等级序列的方法与步骤: 1)确立信息源,建立信息网络;2)站点等级的确定与订正;3)弱信息处理;4)信息的综合。 相似文献