全文获取类型
收费全文 | 38168篇 |
免费 | 6812篇 |
国内免费 | 8899篇 |
专业分类
测绘学 | 2409篇 |
大气科学 | 7715篇 |
地球物理 | 9540篇 |
地质学 | 18832篇 |
海洋学 | 4647篇 |
天文学 | 1900篇 |
综合类 | 4069篇 |
自然地理 | 4767篇 |
出版年
2024年 | 106篇 |
2023年 | 488篇 |
2022年 | 1458篇 |
2021年 | 1731篇 |
2020年 | 1395篇 |
2019年 | 1699篇 |
2018年 | 1913篇 |
2017年 | 1761篇 |
2016年 | 2133篇 |
2015年 | 1708篇 |
2014年 | 2181篇 |
2013年 | 2229篇 |
2012年 | 2144篇 |
2011年 | 2230篇 |
2010年 | 2220篇 |
2009年 | 2125篇 |
2008年 | 1967篇 |
2007年 | 2006篇 |
2006年 | 1561篇 |
2005年 | 1618篇 |
2004年 | 1227篇 |
2003年 | 1171篇 |
2002年 | 1299篇 |
2001年 | 1260篇 |
2000年 | 1311篇 |
1999年 | 1847篇 |
1998年 | 1479篇 |
1997年 | 1508篇 |
1996年 | 1374篇 |
1995年 | 1204篇 |
1994年 | 1001篇 |
1993年 | 917篇 |
1992年 | 741篇 |
1991年 | 570篇 |
1990年 | 446篇 |
1989年 | 350篇 |
1988年 | 351篇 |
1987年 | 232篇 |
1986年 | 190篇 |
1985年 | 139篇 |
1984年 | 103篇 |
1983年 | 76篇 |
1982年 | 84篇 |
1981年 | 67篇 |
1980年 | 58篇 |
1979年 | 47篇 |
1978年 | 23篇 |
1976年 | 22篇 |
1975年 | 19篇 |
1958年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
71.
72.
73.
STUDY ON GIS FOR YIELD ESTIMATION BY REMOTE SENSING IN JILIN MAIZE BELTSTUDYONGISFORYIELDESTIMATIONBYREMOTESENSINGINJILINMAIZ... 相似文献
74.
75.
1 INTRODUCTIONCompact Symmetric Objects (CSOs) are powerful and compact sources (overall size <1 bpc) with lobe emission on both sides of the central engine. The small size of these sourcesis almost certainly to be attributed to the youth of the sources themselves (ages < 104 yr) andnot due to a dense coallning medium (Readhead 1996). The unification scenario assumes thatCSOs evolve into compact steep spectrum (CSS) sotirces and then into Fanaroff-Riley type 11objects (Fanti 1995). … 相似文献
76.
Summary. The elastodynamic fields of point forces and shear dislocations of finite source duration are analysed with the aim of establishing the frequency and time-domain characteristics of the field in the near-source region. Criteria are obtained for amplitude dominance in regions where the source–sensor distance is much smaller than the wavelength.
It is shown that in the frequency domain , the Green's tensor (and hence the displacement field of a single point force) attenuates like R−1 in the near-source region and there exists no region in which the 'near-field' term becomes dominant such that the 'far-field' term can be neglected. Hence, there is no real 'near-field' term for the elastodynamic Green's tensor. The near-field terms of the displacements, velocities and accelerations excited by a shear dislocation attenuate like R −2 , since the R −3 and R −4 terms tend to be eliminated due to mutual cancellation of P and S motions in the near-source region.
In the time domain , the corresponding near field of the displacement field is defined for the steady amplitude interval (away from transients) R /β < t < R /α+ T by the condition R ≤βT where β is the shear velocity and T is the source's duration. The relative strengths of all other arrivals will depend on the particular time window under consideration.
The particle motion patterns due to a single force in the near-source region are shown to be similar to rotating hyperbolas with an axis along the force direction, which are quite different from the 'smoke ring' motion patterns of the so-called 'near-field' term itself. 相似文献
It is shown that in the frequency domain , the Green's tensor (and hence the displacement field of a single point force) attenuates like R
In the time domain , the corresponding near field of the displacement field is defined for the steady amplitude interval (away from transients) R /β < t < R /α+ T by the condition R ≤βT where β is the shear velocity and T is the source's duration. The relative strengths of all other arrivals will depend on the particular time window under consideration.
The particle motion patterns due to a single force in the near-source region are shown to be similar to rotating hyperbolas with an axis along the force direction, which are quite different from the 'smoke ring' motion patterns of the so-called 'near-field' term itself. 相似文献
77.
CLIMATICTRENDINDICATEDBYVARIATIONSOFGLACIERSANDLAKESINTHETIANSHANMOUNTAINS¥HuRuji;YangChuande;MaHong;JiangFengqing(XinjiangIn... 相似文献
78.
79.
位于华南褶皱带南缘的右江盆地,其发展可分为两个不同的阶段。它的轮廓和结构,与NW向及NE向同沉积断裂关系密切。盆地内的沉积物,分别由特征不同的非补偿性和补偿性沉积相组成两个双层结构。盆地内火山活动发育,也明显的分为两个阶段。海西期,古特提斯洋的发展使哀牢山洋盆开裂,导致了右江地区在拉张应力条件下出现若干NW向裂陷带,这时的盆地具有大陆边缘裂谷特点。东吴运动后开始的印支期,区域应力条件发生变化。滨大平洋构造的发生,使盆地轮廓和结构发生明显变化,与此同时开始的哀牢山洋盆向NE方向的俯冲消减作用,使盆地在新的挤压条件下再次发生张裂和拗陷。进入了弧后盆地发展阶段。印支期末,盆地封闭。 相似文献
80.
通过对中、上鞍山群变质沉积岩中黑云母化学成分的对比,确认区内两层位黑云母化学组分存在一定差异,这种差异主要反映了其形成时变质条件的不同。随变质程度增加,区内黑云母的Si、AI~Ⅵ,Fe~(3 )、Mg和K含量增加,而Fe~(2 )、Al~Ⅳ和CH降低,Mg/Fe~(2 )比值从1.00增至2.18。中鞍山群黑云母变质温度为550—620℃,变质压力在5×10~8Pa左右;上鞍山群黑云母变质温度为450-500℃,变质压力低于5×10~8Pa。黑云母含铁系数(f)可作为鞍山地区寻找富铁矿的一种标志。 相似文献