全文获取类型
收费全文 | 8217篇 |
免费 | 2020篇 |
国内免费 | 3208篇 |
专业分类
测绘学 | 1641篇 |
大气科学 | 1145篇 |
地球物理 | 1632篇 |
地质学 | 5657篇 |
海洋学 | 1428篇 |
天文学 | 124篇 |
综合类 | 743篇 |
自然地理 | 1075篇 |
出版年
2024年 | 106篇 |
2023年 | 308篇 |
2022年 | 662篇 |
2021年 | 768篇 |
2020年 | 660篇 |
2019年 | 727篇 |
2018年 | 666篇 |
2017年 | 624篇 |
2016年 | 666篇 |
2015年 | 675篇 |
2014年 | 662篇 |
2013年 | 701篇 |
2012年 | 826篇 |
2011年 | 745篇 |
2010年 | 674篇 |
2009年 | 575篇 |
2008年 | 518篇 |
2007年 | 501篇 |
2006年 | 456篇 |
2005年 | 333篇 |
2004年 | 243篇 |
2003年 | 208篇 |
2002年 | 216篇 |
2001年 | 222篇 |
2000年 | 159篇 |
1999年 | 91篇 |
1998年 | 50篇 |
1997年 | 44篇 |
1996年 | 50篇 |
1995年 | 38篇 |
1994年 | 43篇 |
1993年 | 24篇 |
1992年 | 28篇 |
1991年 | 25篇 |
1990年 | 15篇 |
1989年 | 13篇 |
1988年 | 16篇 |
1987年 | 12篇 |
1986年 | 13篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1978年 | 4篇 |
1976年 | 4篇 |
1973年 | 4篇 |
1958年 | 4篇 |
1957年 | 3篇 |
1954年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Kunde Yang Yuanliang Ma Chao Sun Miller J.H. Potty G.R. 《Oceanic Engineering, IEEE Journal of》2004,29(4):964-972
This paper discusses the results of geoacoustic inversion carried out using explosive charge data from the Asian Seas International Acoustic Experiment (ASIAEX) East China Sea (ECS) Experiment. A multifrequency incoherent matched-field inversion processor and a genetic algorithm (GA) are used for the inversion. A multistep matched field inversion approach is presented, which makes use of the varying sensitivities of wave fields at various frequencies to reduce the inversion problem into a sequence of smaller inversions with fewer unknowns to estimate at each stage. Different parameters are estimated using data at different frequencies according to their sensitivities. Inversion results for different areas in the ECS region are summarized and compared with core data. 相似文献
2.
The properties of salinity in the South China Sea (SCS), a significant marginal sea connecting the Pacific andIndian Oceans, are greatly influenced by the transport of fresh water flux between the two oceans. However, the long-termchanges in the intermediate water in the SCS have not been thoroughly studied due to limited data, particularly in relationto its thermodynamic variations. This study utilized reanalysis data products to identify a 60-year trend of freshening in theintermediate waters of the northern South China Sea (NSCS), accompanied by an expansion of low-salinity water. Thestudy also constructed salinity budget terms, including advection and entrainment processes, and conducted an analysis ofthe salinity budget to understand the impacts of external and internal dynamic processes on the freshening trend of theintermediate water in the NSCS. The analysis revealed that the freshening in the northwest Pacific Ocean and theintensification of intrusion through the Luzon Strait at intermediate levels are the primary drivers of the salinity changes inthe NSCS. Additionally, a weakened trend in the intensity of vertical entrainment also contributes to the freshening in theNSCS. This study offers new insights into the understanding of regional deep sea changes in response to variations in boththermodynamics and oceanic dynamic processes. 相似文献
3.
支持向量机(SVM)是近年来发展起来的机器学习的新方法,它较好地解决小样本、非线性、高维数、局部极小点等实际问题.文中研究支持向量机的拓展算法--最小二乘支持向量机(LSSVM),并将其应用于确定大面积复杂似大地水准面.通过工程实例并与神经网络模型和二次曲面多项式拟合模型相比较,验证确定区域似大地水准面的LSSVM方法的有效性. 相似文献
4.
5.
A one-dimensional model for thinning of the plasma sheet is developed on the basis of launching a fast mode MHD rarefaction wave propagating in the tailward direction along the plasma sheet. Behind the rarefaction wave the pressure is reduced, leading to thinning of the plasma sheet and also to an Earthward plasma flow with a speed on the order of the sound speed a0. The plasma sheet thickness is reduced by a factor of 2 if an Earthward plasma flow speed of 0.8a0 is induced. The predictions of the model are in reasonable agreement with observations. 相似文献
6.
Debris flows have caused serious loss of human lives and a lot of damage to properties in Taiwan over the past decades. Moreover, debris flows have brought massive mud causing water pollution in reservoirs and resulted in water shortage for daily life locally and affected agricultural irrigation and industrial usages seriously. A number of methods for prediction of debris flows have been studied. However, the successful prediction ratio of debris flows cannot always maintain a stable and reliable level. The objective of this study is to present a stable and reliable analytical model for occurrence predictions of debris flows. This study proposes an Artificial Neural Networks (ANN) model that was constructed by seven significant factors using back-propagation (BP) algorithm. These seven factors include (1) length of creek, (2) average slope, (3) effective watershed area, (4) shape coefficient, (5) median size of soil grain, (6) effective cumulative rainfall, and (7) effective rainfall intensity. A total of 178 potential cases of debris flows collected in eastern Taiwan were fed into the ANN model for training and testing. The average ratio of successful prediction reaching 93.82% demonstrates that the presented ANN model with seven significant factors can provide a stable and reliable result for the prediction of debris flows in hazard mitigation and guarding systems. 相似文献
7.
8.
云南省防洪空间信息系统构建 总被引:4,自引:1,他引:4
通过讨论应用地理信息系统(GIS)技术,立足现实对相关空间数据进行集成和整合处理,实现防洪空间信息的数字化、标准化,为优化防汛指挥工作手段提供基础。系统数据库饭知不同比例尺精度的空间基础数据以满足不同目的的需求,对相关水文、防洪设施、全省洪涝风险和重点区风险图、土地利用等图件进行系统整合。系统有较强的管理功能和分析功能,可提高云南省防洪空间信息的共享度和系统有效管理,为政府统一组织和指挥抗洪救灾提供重要的辅助决策支持手段。 相似文献
9.
10.