全文获取类型
收费全文 | 32305篇 |
免费 | 4884篇 |
国内免费 | 6342篇 |
专业分类
测绘学 | 3980篇 |
大气科学 | 4434篇 |
地球物理 | 8608篇 |
地质学 | 14575篇 |
海洋学 | 3935篇 |
天文学 | 1370篇 |
综合类 | 2285篇 |
自然地理 | 4344篇 |
出版年
2024年 | 159篇 |
2023年 | 507篇 |
2022年 | 913篇 |
2021年 | 1230篇 |
2020年 | 1397篇 |
2019年 | 1605篇 |
2018年 | 1155篇 |
2017年 | 1509篇 |
2016年 | 1548篇 |
2015年 | 1582篇 |
2014年 | 1969篇 |
2013年 | 2299篇 |
2012年 | 1987篇 |
2011年 | 2093篇 |
2010年 | 1695篇 |
2009年 | 2092篇 |
2008年 | 2097篇 |
2007年 | 2173篇 |
2006年 | 2090篇 |
2005年 | 1714篇 |
2004年 | 1554篇 |
2003年 | 1343篇 |
2002年 | 1111篇 |
2001年 | 974篇 |
2000年 | 908篇 |
1999年 | 850篇 |
1998年 | 826篇 |
1997年 | 740篇 |
1996年 | 639篇 |
1995年 | 527篇 |
1994年 | 445篇 |
1993年 | 396篇 |
1992年 | 282篇 |
1991年 | 221篇 |
1990年 | 166篇 |
1989年 | 155篇 |
1988年 | 125篇 |
1987年 | 81篇 |
1986年 | 59篇 |
1985年 | 60篇 |
1984年 | 34篇 |
1983年 | 16篇 |
1982年 | 27篇 |
1981年 | 24篇 |
1980年 | 23篇 |
1978年 | 14篇 |
1977年 | 19篇 |
1976年 | 25篇 |
1973年 | 17篇 |
1971年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Instability analysis of three-dimensional ocean shear waves 总被引:1,自引:0,他引:1
Qiao Fangli 《海洋学报(英文版)》1996,15(1):1-8
Instabilityanalysisofthree-dimensionaloceanshearwaves¥QiaoFangli(ReceivedNovember6,1995,acceptedNovember30.1995)Abstract:Base... 相似文献
22.
董胜 《中国海洋大学学报(自然科学版)》1997,(2)
针对海上矿石运输,介绍了一种完成定量任务并能使投资费用最少为目标的最优船队组建方法,同时对易变参数进行了灵敏度分析,使决策更加科学化 相似文献
23.
24.
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
25.
26.
全站仪似水准法和对向法高程测量的比较研究 总被引:1,自引:0,他引:1
通过对似水准法和对向法高程测量原理、误差来源及精度的比较分析,我们发现随着距离和竖直角度的增大,对向法高程测量中误差的变化大于似水准法高程测量中误差的变化;当两观测点间的水平距离小于等于1km时,对向法高程测量精度一般高于似水准法高程测量精度,但是当两观测点间的水平距离大于1km时,似水准法高程测量精度一般高于对向法高程测量精度。 相似文献
27.
基于GIS的区域经济统计分析系统的设计与实现 总被引:1,自引:0,他引:1
随着经济的发展,区域间经济相互作用和影响的关系越来越密切,忽略空间相互作用的传统区域经济分析手段和方法开始显现出一些明显的不足。而GIS在处理和分析区域地理数据上具有强大的空间分析能力,为此我们引入GIS工具对区域经济进行分析,相较于传统的分析手法有了很大改善。本文以江西省区域经济数据为例,设计了一个基于GIS的区域经济统计分析系统,并利用Arcob-jects二次开发控件结合VB可视化编程语言,实现了大部分区域经济统计分析功能,最后并将结果进行网络发布。研究结果表明将GIS引入到区域经济统计分析中,更能正确、有效的揭示区域经济发展在空间上的联系,为区域经济研究决策提供服务。 相似文献
28.
R.P. Gupta D.P. Kanungo M.K. Arora S. Sarkar 《International Journal of Applied Earth Observation and Geoinformation》2008
Evaluation of maps generated from different conceptual models or data processing approaches at spatial level has importance in many geoenvironmental applications. This paper addresses the spatial comparison of different landslide susceptibility zonation (LSZ) raster maps of the same area derived from various procedures. 相似文献
29.
Yanming Feng 《Journal of Geodesy》2008,82(12):847-862
This paper presents a general modeling strategy for ambiguity resolution (AR) and position estimation (PE) using three or
more phase-based ranging signals from a global navigation satellite system (GNSS). The proposed strategy will identify three
best “virtual” signals to allow for more reliable AR under certain observational conditions characterized by ionospheric and
tropospheric delay variability, level of phase noise and orbit accuracy. The selected virtual signals suffer from minimal
or relatively low ionospheric effects, and thus are known as ionosphere-reduced virtual signals. As a result, the ionospheric parameters in the geometry-based observational models can be eliminated for
long baselines, typically those of length tens to hundreds of kilometres. The proposed modeling comprises three major steps.
Step 1 is the geometry-free determination of the extra-widelane (EWL) formed between the two closest L-band carrier measurements,
directly from the two corresponding code measurements. Step 2 forms the second EWL signal and resolves the integer ambiguity
with a geometry-based estimator alone or together with the first EWL. This is followed by a procedure to correct for the first-order
ionospheric delay using the two ambiguity-fixed widelane (WL) signals derived from the integer-fixed EWL signals. Step 3 finds
an independent narrow-lane (NL) signal, which is used together with a refined WL to resolve NL ambiguity with geometry-based
integer estimation and search algorithms. As a result, the above two AR processes performed with WL/NL and EWL/WL signals
respectively, either in sequence or in parallel, can support real time kinematic (RTK) positioning over baselines of tens
to hundreds of kilometres, thus enabling centimetre-to-decimentre positioning at the local, regional and even global scales
in the future. 相似文献
30.