全文获取类型
收费全文 | 59049篇 |
免费 | 10357篇 |
国内免费 | 14385篇 |
专业分类
测绘学 | 5241篇 |
大气科学 | 8241篇 |
地球物理 | 11162篇 |
地质学 | 34203篇 |
海洋学 | 8209篇 |
天文学 | 2431篇 |
综合类 | 4255篇 |
自然地理 | 10049篇 |
出版年
2024年 | 212篇 |
2023年 | 579篇 |
2022年 | 1625篇 |
2021年 | 1972篇 |
2020年 | 2012篇 |
2019年 | 2477篇 |
2018年 | 1999篇 |
2017年 | 2213篇 |
2016年 | 2383篇 |
2015年 | 2621篇 |
2014年 | 3238篇 |
2013年 | 3219篇 |
2012年 | 3583篇 |
2011年 | 3790篇 |
2010年 | 3230篇 |
2009年 | 3885篇 |
2008年 | 3826篇 |
2007年 | 4295篇 |
2006年 | 4183篇 |
2005年 | 3707篇 |
2004年 | 3512篇 |
2003年 | 3331篇 |
2002年 | 2897篇 |
2001年 | 2569篇 |
2000年 | 2305篇 |
1999年 | 2124篇 |
1998年 | 1836篇 |
1997年 | 1644篇 |
1996年 | 1505篇 |
1995年 | 1238篇 |
1994年 | 1254篇 |
1993年 | 1072篇 |
1992年 | 832篇 |
1991年 | 616篇 |
1990年 | 506篇 |
1989年 | 457篇 |
1988年 | 309篇 |
1987年 | 207篇 |
1986年 | 140篇 |
1985年 | 93篇 |
1984年 | 36篇 |
1983年 | 35篇 |
1982年 | 36篇 |
1981年 | 22篇 |
1980年 | 26篇 |
1979年 | 33篇 |
1978年 | 41篇 |
1977年 | 27篇 |
1973年 | 4篇 |
1954年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
PROPAGATION OF 30—60 DAY LOW FREQUENCY OSCILLATIONS AND THEIR INFLUENCE UPON THE SUBTROPICAL WESTERLIES JET STREAM DURING NORTHERN HEMISPHERE WINTER 下载免费PDF全文
Based on daily ECMWF gridpoint data of two winters during 1981—1983 including an ENSOyear,propagation of low frequency oscillations(LFO)during Northern Hemisphere winters andtheir influences upon 30—60 day oscillations of the subtropical jet stream are studied with the sta-tistical methods as complex empirical orthogonal function(CEOF)and so on.Results show that inthe winter of a normal year(1981—1982),30—60 day oscillations in the subtropical zone aremainly in the northern and southern flanks of exit region of jet stream.In the ENSO year(1982—1983),they are mainly in the vicinity of entrance and exit regions of jet stream.Intraseasonalchanges of subtropical jet stream manifested themselves as latitudinal fluctuation or longitudinalprogression or regression of about 40 day period.There are marked differences between propagat-ing passages of low frequency modes responsible for changes of subtropical jet stream in the normalyear(1981—1982)and in the ENSO year(1982—1983).Changes of oscillation amplitude showobvious phases.In general,the one in late winter is stronger than that in early winter,strongestone occurs in February. 相似文献
82.
A recently developed near infrared high speed photometer intended for lunar oc-cultation studies is described. The primary scientific objective is to reach milli arc second levels of angular resolution so that circumstellar structure of the occulted sources can be resolved. Near infrared sky brightness close to the lunar limb is also studied. Angular diameter derived from the observed occultation of IRC +20169 is presented and system performance discussed. 相似文献
83.
矿床谱系是对成矿多样性的理论概括,而成矿多样性又是由不同级别、不同性质的致矿地质异常决定的.本文论述了山东省内生金矿矿床谱系及其致矿地质异常. 相似文献
84.
本文分析了国外用于测定度盘分划改正的几种方法,并分析了固定角距法的优点和不足之处;详细叙述了组合固定角距法测定对径改正的原理和计算公式;并且讨论了两对显微镜之间夹角变化以及显微镜比例尺变化对对径改正的影响,给出了相应的修正方法。用固定角距法所测的对径改正精度可达±0″.009。 相似文献
85.
In recent years,scholars at home and abroad have method,and that vanous disasters would be analyzed assynthetically studied natural dlsaste‘theoretically and an Integral.SHI Peilun(1991)putforwad a scientificmethodologlcally,as well as its cases analys。s(CND,term—regional disaster system,which Indicates that1987; MA et al,1990; MARBLE,1990; NE et al,the situation of a disaster(calamity loss)results from1999; PATAK et al,1982; SHI,1991;VAN et al,h… 相似文献
86.
87.
We have analysed short-exposure high-resolution images obtained on the William Herschel Telescope (WHT), Big Telescope Azimuthal (BTA) and CanadaFranceHawaii Telescope (CFHT) in order to investigate mechanical vibrations that are capable of reducing the high angular resolution allowed by speckle-interferometric methods. After filtering the photon noise we have computed power spectra of the image centres of gravity. In these spectra we have found vibration features that differ from one telescope to another and that vary in particular with the zenith angle. In the case of the WHT we discuss these results in terms of possible causes and in terms of degradation of the transfer function. We present some means to improve the data. 相似文献
88.
89.
G. M. Karataeva V. A. Yakovleva V. A. Hagen-Thorn O. V. Mikolaichuk 《Astronomy Letters》2001,27(2):74-80
We analyze our BVR c photometry for UGC 5600, a candidate polar ring galaxy, obtained with the 6-m telescope. We have confirmed the existence of an inner polar ring and show that the outer ring-shaped structure represents spiral arms; i.e., UGC 5600 belongs to the rare class of gas-rich spiral galaxies with inner polar rings. 相似文献
90.
基于可靠度理论的黄土高边坡优化设计 总被引:11,自引:2,他引:9
对黄土高边坡进行可靠性分析,应用数学原理和优化原理,建立了黄土高边坡的优化模型,对铜黄一级公路黄土高边坡进行分析验证。结果表明,该方法计算的结果与实际较接近.应用中易操作。 相似文献