首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   22982篇
  免费   4329篇
  国内免费   6651篇
测绘学   1251篇
大气科学   4139篇
地球物理   6508篇
地质学   13387篇
海洋学   3118篇
天文学   927篇
综合类   2354篇
自然地理   2278篇
  2024年   99篇
  2023年   348篇
  2022年   805篇
  2021年   938篇
  2020年   762篇
  2019年   806篇
  2018年   943篇
  2017年   890篇
  2016年   1022篇
  2015年   863篇
  2014年   1020篇
  2013年   1129篇
  2012年   980篇
  2011年   1476篇
  2010年   1365篇
  2009年   1432篇
  2008年   970篇
  2007年   1181篇
  2006年   1159篇
  2005年   1232篇
  2004年   1589篇
  2003年   1227篇
  2002年   1001篇
  2001年   877篇
  2000年   871篇
  1999年   1136篇
  1998年   1042篇
  1997年   1006篇
  1996年   890篇
  1995年   773篇
  1994年   679篇
  1993年   771篇
  1992年   671篇
  1991年   404篇
  1990年   269篇
  1989年   251篇
  1988年   198篇
  1987年   154篇
  1986年   134篇
  1985年   70篇
  1984年   63篇
  1983年   60篇
  1982年   61篇
  1981年   41篇
  1980年   48篇
  1979年   41篇
  1978年   21篇
  1977年   24篇
  1976年   16篇
  1958年   17篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
In this study, a directional interpolation infinite element suited to a saturated porous medium is presented to account for dynamic problems with semi-infi  相似文献   
2.
3.
Sdsealbedoisdefinedasaratioofreflectivesolarradiationtototalacradiation,whichcanindicatetheaborptionandreflectivecapabilityofthe~hforsolarradiation.Itisan~tfactortoinfluencethes~radiationbalance,espeiallyfortheformationandvariationoflocalndcroclirnate.Generally,theactualdatafromo~tionalstationSforrebationareedintheanalysisofsolacealal.HOwever,therepresentativenessOfthedateisIratedduetothescarcityofobservationalstationandunevendistributionofs~condition.Afterthe1960s,theanalysisfors~ealbedoise…  相似文献   
4.
四川石棉大水沟独立碲矿床堪称世界首例,其矿体两侧的围岩蚀变较窄,且蚀变带与矿脉及未蚀变岩呈清楚而截然的接触关系。主要围岩蚀变为白云石化、白(绢)云母化、云英岩化及电气石化等。这些蚀变作用分别发生于177.7~165.1Ma和91.71~80.19Ma。蚀变作用过程中SiO2大量析出,Al2O3、TiO2、CaO、MgO、K2O、H2O、CO2、Fe2O3、MnO则有不同程度地带入。与此同时,REE在此过程中包集体迁出,Te、Bi、AS等元素的含量则决定于蚀变作用及其强度,而与原岩无关。  相似文献   
5.
Based on the CN and C2 comae isophotes for two comets (1961 IX and 1970 16) given by Rahe et al. and the relevant theory of physical chemistry, we have deduced the distributions of the CN and C2 modecules in the coma, their scale heights and mean lifetimes. The results favour the viewpoint that HCN is the parent of CN, and that C2H2 is the parent of C2.  相似文献   
6.
1 HYDROLOGIC FEATURES Lingdingyang Estuary, located at the middle south of Guangdong Province, is a bell-shaped estuary with a north-south direction. Its area is about 2100km2. The north of Qi′ao Island and Inner-Lingding Island, and the south of Humen are grouped as Neilingdingyang Estuary, having an area of 1041km2. Affected by topography, runoff and tide, its dynamic condition is very complicated. Different water areas have different hydrologic features. The topography under …  相似文献   
7.
8.
Northern Hemispheric“polar lows”,i.e.maritime,small,but fairly intense cyclonic systems have been studied formore than two decades.Recently researchers have turned their attention towards the occurrence of polar lows and othersmall-scale cyclonic disturbances on the Southern Hemisphere.In this paper a short account of our present knowledgeof Northern Hemispheric polar lows will be given,followed by some preliminary results of an investigation of the natureand occurrence of polar lows on the Southern Hemisphere.  相似文献   
9.
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   
10.
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   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号