全文获取类型
收费全文 | 23021篇 |
免费 | 4983篇 |
国内免费 | 7717篇 |
专业分类
测绘学 | 2375篇 |
大气科学 | 3591篇 |
地球物理 | 5626篇 |
地质学 | 15177篇 |
海洋学 | 3027篇 |
天文学 | 683篇 |
综合类 | 2602篇 |
自然地理 | 2640篇 |
出版年
2024年 | 118篇 |
2023年 | 382篇 |
2022年 | 1022篇 |
2021年 | 1222篇 |
2020年 | 966篇 |
2019年 | 1107篇 |
2018年 | 1239篇 |
2017年 | 1082篇 |
2016年 | 1190篇 |
2015年 | 1281篇 |
2014年 | 1324篇 |
2013年 | 1422篇 |
2012年 | 1488篇 |
2011年 | 1921篇 |
2010年 | 1704篇 |
2009年 | 1729篇 |
2008年 | 1312篇 |
2007年 | 1345篇 |
2006年 | 1378篇 |
2005年 | 1293篇 |
2004年 | 1710篇 |
2003年 | 1262篇 |
2002年 | 1056篇 |
2001年 | 916篇 |
2000年 | 769篇 |
1999年 | 762篇 |
1998年 | 646篇 |
1997年 | 634篇 |
1996年 | 522篇 |
1995年 | 416篇 |
1994年 | 384篇 |
1993年 | 530篇 |
1992年 | 450篇 |
1991年 | 255篇 |
1990年 | 150篇 |
1989年 | 146篇 |
1988年 | 98篇 |
1987年 | 108篇 |
1986年 | 59篇 |
1985年 | 38篇 |
1984年 | 18篇 |
1983年 | 19篇 |
1982年 | 23篇 |
1981年 | 15篇 |
1979年 | 18篇 |
1977年 | 16篇 |
1976年 | 13篇 |
1958年 | 15篇 |
1937年 | 15篇 |
1933年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Late Cretaceous-Paleogene Palynostratigraphy from the Arkhara-Boguchan Brown Coal Mine of Zeya-Bureya Depression, Russia 总被引:1,自引:1,他引:0
Tatyana V. Kezina 《东北亚地学研究》2003,(2)
1IntroductionThe Arkhara-Boguchan brown coal mine is lo-cated in the western Arkhara depression,southeast-ern part of the Zea-Bureya Basin (Fig.1). Late Creta-ceous-Paleogene coal-bearing strata are well out-cropped at the Arkhara-Boguchan quarry. It contains four coal-bearing beds (in descending order): “Ve-likan”, “Promezhutochny”,“Dvoinoy”and “Nyzhny”, and composed of three sedimentary cycles (Fig.2). The lower cycle can be divided into two sub-cycles:the lowest sub-cycle is … 相似文献
62.
1StrongtideandastronomicalconditionsPartial solar eclipse occurred 4 times in 1964, 1982 and 2000 respectively. Time interval is about 3 Saros periods (one Saros period is 18 years and 10.33~11.33 days). Total lunar eclipse occurred 2 times in 1964 and 2000 respectively and 3 times in 1982. However, there was no lunar eclipse in 1966, 1984 and 2002. It seems that they had similar astro-nomical conditions and the best was in 1982. The studies about the effect of tide on the global climate… 相似文献
63.
1 IntroductionDiscontinuousDeformationAnalysis(DDA)developedbyShiin 1 980’s[1 ,2 ] maybeusedtocalculatethedeformationanddisplacementsinamulti blocksystemandtoanalyzetherelationbe tweenforcesanddisplacementsinthesystem .Ifthesurveydisplacementofeverypointordirectionisknown,alldisplacementsanddeformationsofblocks,eventheglide ,theclosureandthestretchoftheboundary planeofblocks ,canbecalculated .TheresultisoptimallyfittedaccordingtotheLeastSquarePrinciple.DDAismainlyusedinrockblockssystems… 相似文献
64.
CORROSION AND ADHERENCE AT SEA OIL-PLATFORM 总被引:1,自引:0,他引:1
Measurements of the adhesive corrosion and protective potentials of 3 Bohai Sea oilplatforms under different cathodic protection showed corrosion still occurred on these platforms undertheir designed protective potentials. Preliminary conclusions from indoor experiments on the relation betweenadhesive corrosion and cathodic protection showed adhering organisms caused the corrosion onthese platforms. 相似文献
65.
A THREE-DIMENSIONAL ELASTIC NESTED-GRID MESO-(β-γ)SCALE ATMOSPHERIC MODEL——PARTI:MODEL DESCRIPTION 下载免费PDF全文
A three-dimensional elastic nonhydrostatic mesoscale(β-γ)model with nested-grid is presented.It uses a set of fullequations in terrain-following coordinates as its basic dynamic frame,which is solved with a time-splitting algorithmfor acoustic and gravity waves.The model physical parameterization includes a K-theory subgrid eddy mixing for cloudand free atmosphere,a bulk planetary boundary layer parameterization,and three types of sofisticated cloudmicrophysics schemes with double-parameters for hail-bearing clouds,warm clouds and snowing clouds respectively.The model is designed to be used flexibly for simulations of a variety of meso-and small-scale atmospheric processes,and can be improved as a regional and local operational NWP system in future. 相似文献
66.
Four bromophenols were isolated from the extract of marine red alga,Rhodomela confervoides by column chromatography and HPLC methods. By means of spectroscopic methods inclding IR, MS, 1D, and 2D-NMR techniques,
their structures were elucidated as (1) 3-bromo-4,5-dihydroxy benzoic acid methyl ester; (2) bis (2,3-dibromo-4,5-dihydroxybenzyl)
ether; (3) 3,4-dibromo-5-(methoxymethyl)-1,2-benzenediol and (4) 3-bromo-4,5-dihydroxy-benzaldehyde. Compound 1 was first
isolated from the algae in nature, and 1, 4 were found to have selective cytotoxic activities against KB, Bel 7402 and A549
cells, 2 showed powerful antibacterial activities againstStaphylococcus aurens andPseudomonas aeruginosa.
Supported by National “863” Program (No. 2004AA625030, 2001AA620503), Quingdao marine sciences project (No. 04-2-NN-26) and
Key Knowledge Innovative Project of the Chinese Academy of Sciences (KZCX3-SW-215). 相似文献
67.
提出一种基于负反馈权值的动态网络负载调度算法。算法主要用在多出口路由器上,其执行效率高,开销小。基于算法的多出口路由器不仅能够很好的保持出口间的负载均衡。还具有良好的出口容错性能。 相似文献
68.
田斌 《紫金山天文台台刊》2003,(2)
在本文中我们对两种不同的 βCephei变星的理论脉动不稳定带作了比较。它们具有明显的不同之处。为了确定这种变星的脉动不稳定带的轮廓 ,我们根据 4 9颗 βCephei变星的观测资料作了统计研究。在从样本星的色指数 (B -V) ,(U -B)和视差得到它们的有效温度和光度之后 ,我们发现在赫罗图上它们大多数是位于主序带内的。而且这些样本星的质量都位于 7M⊙ 到 30M⊙ 之间。和理论模型的比较表明我们提出的具有光度上边界和红蓝边界的 βCephei变星的理论脉动不稳定带跟观测吻合得更好 相似文献
69.
利用三维有限元模拟两层地球模型(包括弹性层和粘弹性层)介质的横向不均匀和断层错动的复杂性对震后地表位移场的影响,其数值结果包括弹性解和粘弹性解。结果表明,震后位移场的分布特征不仅与粘弹性层的流变特性有关,还与弹性层介质的剪切模量以及断层的同震错动有关。 相似文献
70.
1IntroductionOne of the key factors related to basin geody-namics is deep process controlling formation and evolution of sedimentary basin. Depth and tempera-ture of asthenosphere,existence of mantle plume,occurrence of mantle melting,and amounts of melts under depressurization during thinning of lithosphere are controlling factors influenced formation and characteristics of extensional basin directly (Li,1994). Rifting is probably governed by frictional forces exerted on the base of litho… 相似文献