全文获取类型
收费全文 | 34210篇 |
免费 | 6306篇 |
国内免费 | 8246篇 |
专业分类
测绘学 | 2819篇 |
大气科学 | 7027篇 |
地球物理 | 8400篇 |
地质学 | 16755篇 |
海洋学 | 4055篇 |
天文学 | 1413篇 |
综合类 | 3813篇 |
自然地理 | 4480篇 |
出版年
2024年 | 76篇 |
2023年 | 490篇 |
2022年 | 1526篇 |
2021年 | 1708篇 |
2020年 | 1415篇 |
2019年 | 1635篇 |
2018年 | 1862篇 |
2017年 | 1732篇 |
2016年 | 2030篇 |
2015年 | 1768篇 |
2014年 | 2116篇 |
2013年 | 2064篇 |
2012年 | 2024篇 |
2011年 | 2089篇 |
2010年 | 2203篇 |
2009年 | 2075篇 |
2008年 | 1905篇 |
2007年 | 1800篇 |
2006年 | 1410篇 |
2005年 | 1307篇 |
2004年 | 989篇 |
2003年 | 991篇 |
2002年 | 999篇 |
2001年 | 1039篇 |
2000年 | 1174篇 |
1999年 | 1557篇 |
1998年 | 1226篇 |
1997年 | 1161篇 |
1996年 | 1073篇 |
1995年 | 932篇 |
1994年 | 821篇 |
1993年 | 736篇 |
1992年 | 582篇 |
1991年 | 472篇 |
1990年 | 334篇 |
1989年 | 310篇 |
1988年 | 282篇 |
1987年 | 160篇 |
1986年 | 147篇 |
1985年 | 96篇 |
1984年 | 100篇 |
1983年 | 74篇 |
1982年 | 67篇 |
1981年 | 55篇 |
1980年 | 34篇 |
1979年 | 32篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1976年 | 8篇 |
1958年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 937 毫秒
91.
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
92.
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
93.
94.
LUO Kai-li LI Bao-sheng ZHU Yi-zhi JIN He-ling ZHANG David Dian YAN Man-cun LI Hou-xin YAO Chun-xia ZHANG Yu-hongf . Department of Geography South China Normal University Guangzhou P. R. China . State Key Labor 《中国地理科学(英文版)》2001,11(4):336-342
About 70years ago,Frenc卜卜alaeohdoglst回LL sc卜dars al卜ome and a卜road卜ave successively con-HARD de Chardin P.et al.Initiated the Quaternary ducted large amount ofwork on the Later Quaternarygeologlcal research In the >alawusu River Basin of strata(TEILHARD,1924; YUAN,1978; LI,1987;desert region of Northern China and established th,ZHENG,1989; SUN et al,1996; LI et al,1993),Salawusu Formation门EILHARD,1924).Sine,then,palaeobiology… 相似文献
95.
Profiles of spectral lines emitted from an accretion ring around an object with strong gravitational field should be affected by Doppler shift, gravitational redshift, and deflection of light. Taking these effects into account, precise line profile of a Keplerian ring around a Kerr black hole for a distant observer is obtained by solving the kinetic equation of photons. 相似文献
96.
We study the magnetic field evolution and topology of the active region NOAA 10486 before the 3B/X1.2 flare of October 26, 2003, using observational data from the French–Italian THEMIS telescope, the Michelson Doppler Imager (MDI) onboard Solar and Heliospheric Observatory (SOHO), the Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observation Station (HSOS), and the Transition Region and Coronal Explorer (TRACE). Three dimensional (3D) extrapolation of photospheric magnetic field, assuming a potential field configuration, reveals the existence of two magnetic null points in the corona above the active region. We look at their role in the triggering of the main flare, by using the bright patches observed in TRACE 1600 Å images as tracers at the solar surface of energy release associated with magnetic reconnection at the null points. All the bright patches observed before the flare correspond to the low-altitude null point. They have no direct relationship with the X1.2 flare because the related separatrix is located far from the eruptive site. No bright patch corresponds to the high-altitude null point before the flare. We conclude that eruptions can be triggered without pre-eruptive coronal null point reconnection, and the presence of null points is not a sufficient condition for the occurrence of flares. We propose that this eruptive flare results from the loss of equilibrium due to persistent flux emergence, continuous photospheric motion and strong shear along the magnetic neutral line. The opening of the coronal field lines above the active region should be a byproduct of the large 3B/X1.2 flare rather than its trigger. 相似文献
97.
介绍了车载流动型人卫激光测距仪光学系统(包括激光发射系统、接收系统及微光电视监视系统)的设计思想和方法,着重叙述了光学系统的结构设计、关键部件几何尺寸的确定及重要元器件的选取。设计基于流动型仪器应满足的防振、体积小、调校方便、抗环境干扰能力强等特点。多年的实测证明,这种光学系统不仅能满足流动型人卫激光测距仪总体设计要求,而且经济实用。 相似文献
98.
VPN技术在浙江省气象网络中的应用 总被引:2,自引:0,他引:2
随着浙江省气象业务的不断发展,网络数据交换日益增多,同时更多基于网络的气象业务的增加,如网络视频会商、自动站数据传输等,使目前浙江省气象系统专线网络运行已达到极限,所以需要建立VPN网以对现有的网络作链路上的备份,而VPN的建立同时还可以实现移动办公,领导能在远程调用内网的资料进行远程决策服务和汇报工作。主要介绍VPN技术并叙述VPN技术在浙江省气象系统网络中的具体应用。 相似文献
99.
100.
本文提出了激变变星0623十71的4个时间分辨光谱,覆盖轨道周期的73%.其中的3个谱清楚地显示了各种光谱特征随轨道运动的变化,在流量、能谱以及谱线轮廓方面的这种变化正是对一个倾角不太大的激变变星所期望的.然而另一个曝光对分钟的谱,流量和视向速度与预期的相比都太大,很难加以解释,可能它是一次象AEAqr中观测到的跃发事件. 相似文献