全文获取类型
收费全文 | 2992篇 |
免费 | 277篇 |
国内免费 | 273篇 |
专业分类
测绘学 | 653篇 |
大气科学 | 132篇 |
地球物理 | 340篇 |
地质学 | 764篇 |
海洋学 | 133篇 |
天文学 | 200篇 |
综合类 | 246篇 |
自然地理 | 1074篇 |
出版年
2024年 | 28篇 |
2023年 | 52篇 |
2022年 | 165篇 |
2021年 | 170篇 |
2020年 | 139篇 |
2019年 | 179篇 |
2018年 | 105篇 |
2017年 | 161篇 |
2016年 | 163篇 |
2015年 | 132篇 |
2014年 | 125篇 |
2013年 | 179篇 |
2012年 | 154篇 |
2011年 | 132篇 |
2010年 | 118篇 |
2009年 | 137篇 |
2008年 | 138篇 |
2007年 | 148篇 |
2006年 | 126篇 |
2005年 | 116篇 |
2004年 | 139篇 |
2003年 | 115篇 |
2002年 | 99篇 |
2001年 | 81篇 |
2000年 | 84篇 |
1999年 | 56篇 |
1998年 | 54篇 |
1997年 | 44篇 |
1996年 | 32篇 |
1995年 | 29篇 |
1994年 | 32篇 |
1993年 | 20篇 |
1992年 | 15篇 |
1991年 | 22篇 |
1990年 | 10篇 |
1989年 | 16篇 |
1988年 | 9篇 |
1987年 | 9篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有3542条查询结果,搜索用时 0 毫秒
41.
F. Freistetter 《Celestial Mechanics and Dynamical Astronomy》2000,78(1-4):211-225
The correlation dimension D
2 is used to develop a method of classification for phase space orbits. D
2 depends only on the mutual distances of the orbits points, therefore the time development of the orbit is reflected in the time development of the correlation dimension approximants. It is shown, that this technique allows to investigate the dynamical properties of a phase space orbit, a classification of chaotic and regular orbits and a detection of sticky orbits. 相似文献
42.
Xue-Mei Deng 《天体物理学报》2012,(6):703-712
43.
David K. A. Barnes 《Marine Ecology》2001,22(3):189-200
Abstract. The reef‐dwelling oyster Dendrostrea frons occupied only a small proportion of space in coral reefs of the Quirimba Archipelago, Mozambique, but supported a disproportionately high variety of taxa. Assemblages on primary (substratum), secondary (dead coral heads) and ephemeral secondary space (D. frons shells) of similar area were compared across 5 depths (5, 10, 15, 20 and 25 m) and at four taxonomic levels (species, genus, class and phylum). Differences between the taxonomic richness of each type of space differed with both taxonomic level considered and depth. Of the three categories of space considered, ephemeral secondary space had the most taxa at all levels with the maximum at 10 – 15 m. Despite being small in space and time, animal externa, such as shells of D. frons, may provide important niches for particular organisms at many taxonomic levels. 相似文献
44.
在几年的工作实践中发现矿产勘查新规范存在一些问题,主要是量化度不够、操作性较差、关键词语多解或模糊,特别是在地质普查间距、储量估算方面不易理解掌握,造成地质工作的普遍简单化. 相似文献
45.
相位激发极化法应用研究 总被引:1,自引:0,他引:1
相位激发极化法是一种频率域激发极化方法,可直接测量电场电压与供电电流之间的绝对相位差。由于该方法对仪器精度要求较高,因而国内有关实际应用方面的资料相对较少。在金属矿产勘查中,目前国内大多采用时间域激发极化方法,测量岩矿石的极化率或充电率。虽然频率域激发极化法也有应用,但主要采用双频或多频测量,利用视频散率参数进行解释,野外测量工作量较大,测量精度相对较低。近几年,利用相位激发极化法在科研、生产中做了一些工作,这里介绍相位激发极化法模型试验及数据反演结果,岩矿石标本时间域(充电率)和频率域(相位)测试对比结果,以及实际应用实例及数据反演结果。应用结果表明,用相位激发极化法在矿产勘查中可以取得较好的勘察效果,并能在今后的工作中发挥更大的作用。 相似文献
46.
利用三维弹塑性模型研究了土钉基坑支护的空间效应,着重对深基坑工程中的阴角、阳角及分段分层开挖等问题进行了计算分析。结果表明,基坑的阴角能大大降低基坑位移和土钉轴力,其影响范围大于开挖深度,直立开挖面的阴角效应比放坡开挖面时的要大;阳角处的位移及土钉轴力明显增大,其影响范围延伸至3倍基坑开挖深度;分段分层开挖支护能充分利用土钉支护的空间效应,其影响范围接近于基坑开挖深度。 相似文献
47.
The damping‐solvent extraction method for the analysis of unbounded visco‐elastic media is evaluated numerically in the frequency domain in order to investigate the influence of the computational parameters—domain size, amount of artificial damping, and mesh density—on the accuracy of results. An analytical estimate of this influence is presented, and specific questions regarding the influence of the parameters on the results are answered using the analytical estimate and numerical results for two classical problems: the rigid strip and rigid disc footings on a visco‐elastic half‐space with constant hysteretic material damping. As the domain size is increased, the results become more accurate only at lower frequencies, but are essentially unaffected at higher frequencies. Choosing the domain size to ensure that the static stiffness is computed accurately leads to an unnecessarily large domain for analysis at higher frequencies. The results improve by increasing artificial damping but at a slower rate as the total (material plus artificial) damping ratio ζt gets closer to 0.866. However, the results do not deteriorate significantly for the larger amounts of artificial damping, suggesting that ζt≈0.6 is appropriate; a larger value is not likely to influence the accuracy of results. Presented results do not support the earlier suggestion that similar accuracy can be achieved by a large bounded domain with small damping or by a small domain with larger damping. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
48.
49.
A new method is proposed to inverse normalization data of hidden variables in a dynamical system by embedding a time series
in multidimensional spaces and applying a normalization analysis to the conditional probability density of points in the reconstructed
phase spaces. The method is robust in the application to Lorenz system and 4-dimensional R?ssler system by testing quantitatively
and qualitatively the correlation coefficient between inverse data and original data in time domain and in frequency domain,
respectively. By applying the method to analyzing the South China Sea data, the normalization data of wind speed is extracted
from the sea surface temperature time series. 相似文献
50.
In this paper, the response of a visco-elastic half-space subjected to moving loads with static and dynamic components is investigated. Four types of vehicle loads are considered, including the moving point load, uniformly distributed wheel load, elastically distributed wheel load, and a train load simulated as a sequence of elastically distributed wheel loads. In each case, the influence of the moving loads traveling in the subsonic, transonic and supersonic ranges on the dynamic responses of the half-space is studied. The parametric study conducted herein enables us to grasp insight into the mechanism of wave propagation for a visco-elastic half-space under moving loads. 相似文献