全文获取类型
收费全文 | 40028篇 |
免费 | 34931篇 |
国内免费 | 34402篇 |
专业分类
测绘学 | 5132篇 |
大气科学 | 22303篇 |
地球物理 | 14049篇 |
地质学 | 40582篇 |
海洋学 | 17453篇 |
天文学 | 863篇 |
综合类 | 4949篇 |
自然地理 | 4030篇 |
出版年
2025年 | 53篇 |
2024年 | 835篇 |
2023年 | 931篇 |
2022年 | 1334篇 |
2021年 | 1775篇 |
2020年 | 2675篇 |
2019年 | 6008篇 |
2018年 | 5992篇 |
2017年 | 5696篇 |
2016年 | 5748篇 |
2015年 | 5344篇 |
2014年 | 4769篇 |
2013年 | 5487篇 |
2012年 | 5346篇 |
2011年 | 5167篇 |
2010年 | 5108篇 |
2009年 | 4403篇 |
2008年 | 3811篇 |
2007年 | 3740篇 |
2006年 | 3346篇 |
2005年 | 3093篇 |
2004年 | 3159篇 |
2003年 | 2780篇 |
2002年 | 2556篇 |
2001年 | 2239篇 |
2000年 | 1849篇 |
1999年 | 1664篇 |
1998年 | 1692篇 |
1997年 | 1751篇 |
1996年 | 1356篇 |
1995年 | 1304篇 |
1994年 | 1167篇 |
1993年 | 1146篇 |
1992年 | 969篇 |
1991年 | 731篇 |
1990年 | 701篇 |
1989年 | 581篇 |
1988年 | 508篇 |
1987年 | 391篇 |
1986年 | 313篇 |
1985年 | 253篇 |
1984年 | 274篇 |
1983年 | 169篇 |
1982年 | 207篇 |
1981年 | 146篇 |
1980年 | 108篇 |
1979年 | 112篇 |
1978年 | 48篇 |
1971年 | 53篇 |
1970年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
In this work, enhanced poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) bulk-heterojunction photovoltaic devices are achieved via slow-solvent-vapour treatment. The correlations between the morphology of the active layer and the photovoltaic performance of polymer-based solar cell are investigated. The active layers are characterized by atomic force microscopy and optical absorption. The results show that slow-solvent-vapour treatment can induce P3HT self-organization into an ordered structure, leading to the enhanced absorption and efficient charge transport. 相似文献
102.
103.
对于大规模地形而言,地形网格的实时动态绘制速度和质量一直是人们关注的重点。地形漫游在仿真、模拟、虚拟现实、游戏等领域都有广泛的应用。该文在研究多种层次算法的基础上,采用一种地形瓦片重组数据结构的方法实现实时高帧率的绘制大规模地形。分析了地形场景数据管理与实时调度,视相关多层次细节模型与可见性判断以及分层数据组织和瓦片数据绘制等关键问题,并给出了相应的解决方法,改进了视景体裁切重组地形数据的方法。实验结果表明该方法在保持地形逼真的前提下,有很好的绘制网格帧率和实时动态交互效果。 相似文献
104.
The radon transport test, which is a widely used test case for atmospheric transport models, is carried out to evaluate the tracer advection schemes in the Grid-Point Atmospheric Model of IAP-LASG (GAMIL). Two of the three available schemes in the model are found to be associated with significant biases in the polar regions and in the upper part of the atmosphere, which implies potentially large errors in the simulation of ozone-like tracers. Theoretical analyses show that inconsistency exists between the advection schemes and the discrete continuity equation in the dynamical core of GAMIL and consequently leads to spurious sources and sinks in the tracer transport equation. The impact of this type of inconsistency is demonstrated by idealized tests and identified as the cause of the aforementioned biases. Other potential effects of this inconsistency are also discussed. Results of this study provide some hints for choosing suitable advection schemes in the GAMIL model. At least for the polax-region-concentrated atmospheric components and the closely correlated chemical species, the Flux-Form Semi-Lagrangian advection scheme produces more reasonable simulations of the large-scale transport processes without significantly increasing the computational expense. 相似文献
105.
Geostatistical Simulation of Regionalized Pore-Size Distributions Using Min/Max Autocorrelation Factors 总被引:1,自引:0,他引:1
In many fields of the Earth Sciences, one is interested in the distribution of particle or void sizes within samples. Like many other geological attributes, size distributions exhibit spatial variability, and it is convenient to view them within a geostatistical framework, as regionalized functions or curves. Since they rarely conform to simple parametric models, size distributions are best characterized using their raw spectrum as determined experimentally in the form of a series of abundance measures corresponding to a series of discrete size classes. However, the number of classes may be large and the class abundances may be highly cross-correlated. In order to model the spatial variations of discretized size distributions using current geostatistical simulation methods, it is necessary to reduce the number of variables considered and to render them uncorrelated among one another. This is achieved using a principal components-based approach known as Min/Max Autocorrelation Factors (MAF). For a two-structure linear model of coregionalization, the approach has the attractive feature of producing orthogonal factors ranked in order of increasing spatial correlation. Factors consisting largely of noise and exhibiting pure nugget–effect correlation structures are isolated in the lower rankings, and these need not be simulated. The factors to be simulated are those capturing most of the spatial correlation in the data, and they are isolated in the highest rankings. Following a review of MAF theory, the approach is applied to the modeling of pore-size distributions in partially welded tuff. Results of the case study confirm the usefulness of the MAF approach for the simulation of large numbers of coregionalized variables. 相似文献
106.
Annual and interannual variations of large-scale circulation over the tropics as revealed from OLR data 总被引:1,自引:0,他引:1
In this study, the outgoing longwave radiation (OLR) data of eight years have been used to investigate the annual and interannual variations of large-scale circulation over the tropics. The results of EOF analysis indicate that the first three eigenvectors reflect the essential features in OLR annual variation. However, they contribute little to the interannual change. In comparison, the fourth to the sixth components have very large year-to-year variations. The pronounced anomalies are located over the tropics with east-west dipole pattern. It implies that ENSO events are related closely to the variation of the Walker circulation. 相似文献
107.
108.
109.
南海东北部海底沉积物波的形态、粒度特征及物源、成因分析 总被引:4,自引:1,他引:4
在南海东北部广泛发育沉积物波。通过高分辨率多波束数据、地震剖面以及重力柱状样,对沉积物波的形态特征、粒度特征、物源以及形成机制进行了分析。研究表明大致以台湾浅滩南海底峡谷为界,北侧为近北东向展布,南侧为近南北向展布。对其分布规律、地貌和形态特征及重力柱状样粒度分析表明这些沉积物波为浊流成因。沉积物波的发育与新生代晚期研究区的构造活动密切相关,自距今6.5 Ma以来台湾造山运动使台湾岛强烈抬升剥蚀,这些剥蚀物为研究区提供了大量的陆源物质,而在南海东北部陆坡区大量发育的峡谷-冲沟系统为陆缘物质向下陆坡的输送提供了良好的通道。研究区西侧的东沙隆起长期处于抬升剥蚀状态,这种抬升剥蚀也为研究区沉积物波的发育提供了部分物源。随着坡度的减缓,浊流沉积物开始堆积,在台湾浅滩南海底峡谷的北侧形成了展布方向与冲沟垂直的沉积物波,而在南侧由于台湾浅滩南海底峡谷发生转向,浊流从水道中漫溢出来,沉积物堆积下来,形成了与原先水道近于垂直的近南北向的沉积物波。 相似文献
110.