全文获取类型
收费全文 | 2325篇 |
免费 | 446篇 |
国内免费 | 607篇 |
专业分类
测绘学 | 107篇 |
大气科学 | 485篇 |
地球物理 | 572篇 |
地质学 | 1263篇 |
海洋学 | 248篇 |
天文学 | 154篇 |
综合类 | 239篇 |
自然地理 | 310篇 |
出版年
2024年 | 3篇 |
2023年 | 45篇 |
2022年 | 139篇 |
2021年 | 146篇 |
2020年 | 98篇 |
2019年 | 124篇 |
2018年 | 167篇 |
2017年 | 141篇 |
2016年 | 151篇 |
2015年 | 118篇 |
2014年 | 150篇 |
2013年 | 135篇 |
2012年 | 120篇 |
2011年 | 136篇 |
2010年 | 145篇 |
2009年 | 122篇 |
2008年 | 116篇 |
2007年 | 90篇 |
2006年 | 80篇 |
2005年 | 74篇 |
2004年 | 40篇 |
2003年 | 63篇 |
2002年 | 52篇 |
2001年 | 49篇 |
2000年 | 76篇 |
1999年 | 108篇 |
1998年 | 92篇 |
1997年 | 88篇 |
1996年 | 89篇 |
1995年 | 95篇 |
1994年 | 66篇 |
1993年 | 64篇 |
1992年 | 45篇 |
1991年 | 29篇 |
1990年 | 21篇 |
1989年 | 23篇 |
1988年 | 21篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1958年 | 2篇 |
排序方式: 共有3378条查询结果,搜索用时 15 毫秒
91.
XU QingHai CAO XianYong TIAN Fang ZHANG ShengRui LI YueCong LI ManYue LI Jie LIU YaoLiang LIANG Jian 《中国科学:地球科学(英文版)》2014,57(6):1254-1266
The Relative Pollen Productivities(RPPs)of common steppe species are estimated using Extended R-value(ERV)model based on pollen analysis and vegetation survey of 30 surface soil samples from typical steppe area of northern China.Artemisia,Chenopodiaceae,Poaceae,Cyperaceae,and Asteraceae are the dominant pollen types in pollen assemblages,reflecting the typical steppe communities well.The five dominant pollen types and six common types(Thalictrum,Iridaceae,Potentilla,Ephedra,Brassicaceae,and Ulmus)have strong wind transport abilities;the estimated Relevant Source Area of Pollen(RSAP)is ca.1000 m when the sediment basin radius is set at 0.5 m.Ulmus,Artemisia,Brassicaceae,Chenopodiaceae,and Thalictrum have relative high RPPs;Poaceae,Cyperaceae,Potentilla,and Ephedra pollen have moderate RPPs;Asteraceae and Iridaceae have low RPPs.The reliability test of RPPs revealed that most of the RPPs are reliable in past vegetation reconstruction.However,the RPPs of Asteraceae and Iridaceae are obviously underestimated,and those of Poaceae,Chenopodiaceae,and Ephedra are either slightly underestimated or slightly overestimated,suggesting that those RPPs should be considered with caution.These RPPs were applied to estimating plant abundances for two fossil pollen spectra(from the Lake Bayanchagan and Lake Haoluku)covering the Holocene in typical steppe area,using the"Regional Estimates of Vegetation Abundance from Large Sites"(REVEALS)model.The RPPs-based vegetation reconstruction revealed that meadow-steppe dominated by Poaceae,Cyperaceae,and Artemisia plants flourished in this area before 6500–5600 cal yr BP,and then was replaced by present typical steppe. 相似文献
92.
Two-dimensional tidal open boundary conditions of the M2 constituent in the Bohai and Yellow Seas(BYS) have been estimated by assimilating T/P altimeter data.During inversion,independent point(IP) strategy was used,in which several IPs on the open boundary is assumed,values at these IPs can be optimized with an adjoint method,and those at other grid points are determined by linearly interpolating the values at IPs.The reasonability and feasibility of the model are tested by ideal twin experiments.In the practical experiment(PE) after assimilation,the cost function may reach 1% or less of its initial value.Mean absolute errors in amplitude and phase can be less than 5 cm and 5°,respectively,and the obtained co-chart can show the character of the M2 constituent in the BYS.The results of the PE indicate that using only two IPs on the open boundary can yield better simulated results. 相似文献
93.
Wave breaking is an important process that controls turbulence properties and fluxes of heat and mass in the upper oceanic layer.A model is described for energy dissipation per unit area at the ocean surface attributed to wind-generated breaking waves,in terms of ratio of energy dissipation to energy input,windgenerated wave spectrum,and wave growth rate.Also advanced is a vertical distribution model of turbulent kinetic energy,based on an exponential distribution method.The result shows that energy dissipation rate depends heavily on wind speed and sea state.Our results agree well with predictions of previous works. 相似文献
94.
As responses to metropolitan suburbanization and rural urbanization,the formation and evolution of urban fringes should be understood against the background of overall economic development and spatial reconstruction of entire metropolises.At the same time,however,endogenous interactions between industrial structure and spatial patterns of non-agricultural activities are also worthy of scholarly attention.Since the 1980s,studies on urban fringes in China have been restricted by the lack of micro-level data.This paper investigates the spatial expansion and structural evolution of the urban fringe by taking the case of Beijing and uses systematic firm-level data in 1996 and 2001 from the National Census of Basic Units.The diversity of distribution patterns across industrial sectors brings about two interrelated results.On the one hand,structural adjustment of non-agricultural industries promotes the expansion and spatial evolution of the urban fringe.On the other hand,the stability and dynamics of industrial structure coexist in the moving urban fringe.This study also reveals that the outward-moving urban fringe is the optimal location for manufacturing,especially heavy manufacturing,as well as traditional producer and consumer services.However,industries with spatial stickiness such as tourism and sports have not moved with the fringe.Most advanced services remain concentrated in the city center.The authors argue that it is essential for understanding and managing urban fringes to take into account spatial evolution and industrial structural adjustment together with their interaction with each other. 相似文献
95.
南昌地震台钻孔应变同震响应分析 总被引:2,自引:1,他引:1
通过总结2007年5月以来南昌地震台TJ-2钻孔应变仪的同震效应,并与同期中国地震台网(CSN)提供的全球大震目录中的数据进行对比分析,绘出了震级与震中距的对数关系图,得出南昌地震台体应变仪的映震能力的表达式近似为Ms=1.381gD+ 1.1. 相似文献
96.
隐伏金属矿床上升气流微粒特征、形成及迁移 总被引:3,自引:0,他引:3
结合地球化学和纳米科学技术的理论和研究方法,研究隐伏金属矿床有关微粒的形成、迁移和特征。对十多个金属矿床的研究表明,隐伏金属矿体地表沉积物中上升气流微粒样品有单个微粒和微粒聚合体,单个微粒形态有球状、近球状、不规则状、规则多边形、长柱状,微粒有晶质、非晶质和部分晶质。聚合体形态一般是不规则状、球状和近球状。它们的矿物成分主要有自然Au、自然Cu、氯化物、氧化物、硫酸盐、氢氧化物等。成矿元素Au、Cu可以自然金属或自然合金形式存在,Cu、Pb、Zn等成矿元素可以氧化物或硫酸盐等形式存在,也可以存在于氧化物、氢氧化物、氯化物、硫酸盐等微粒中作为杂质元素,这些是隐伏金属矿体的指示微粒。成矿期后,与隐伏金属矿体有关微粒主要形成于断层作用、氧化作用和生物作用。在上升气流中,微粒呈“布朗运动”。 相似文献
97.
基于广义回归神经网络的GPS高程转换 总被引:1,自引:1,他引:0
为提高GPS高程转换的精度,采用广义回归神经网络(GRNN)进行拟合。将控制点的X、Y坐标作为网络输入,高程异常作为网络输出,采用实验数据训练网络,训练完成的网络作为模型进行高程异常预测。结果表明,GRNN方法具有较高的GPS转换精度。 相似文献
98.
简要介绍"地电场数据实时监视波形软件"的作用和功能,详细说明了该软件主要功能的实现技巧,以及在嘉山地震台地电场观测中所发挥的作用. 相似文献
99.
100.
V. Mishin Z. Pu L. Sapronova A. Bazarzhapov Yu. Kuz’minykh X. Cao H. Zhang 《Geomagnetism and Aeronomy》2009,49(8):1193-1198
The maps of the field-aligned current (FAC) density distribution in the ionosphere obtained by the TIM-2 magnetogram inversion
technique are used to investigate the August 27, 2001 substorm. The open magnetic flux Ψ and intensity J of the substorm current wedge (SCW) have been determined with a step of 1–5 min. The substorm onsets are divided into two
types, PSR (plasma sheet reconnection) and TLR (tail lobe reconnection). The fast expansion tailward of the PSR region is
described as the transition from PSR to PSR+TLR. Assuming that the SCW FACs flow down into the ionosphere from the edges of
the disruption region of the cross-tail dawn-dusk current, several parameters of the disruption region have been estimated.
The disrupted magnetic field has been found to be ∼5% of the undisrupted one for PSR and ∼95% for PSR+TLR. The disturbance
power Q for PSR is an order of magnitude lower than that for PSR+TLR. The abrupt growth of Q during the transition from PSR to PSR+TLR is observed over the entire SCW area from its near-Earth part to the midtail and
distant tail. 相似文献