全文获取类型
收费全文 | 7764篇 |
免费 | 1606篇 |
国内免费 | 2423篇 |
专业分类
测绘学 | 1070篇 |
大气科学 | 1274篇 |
地球物理 | 1657篇 |
地质学 | 4770篇 |
海洋学 | 1074篇 |
天文学 | 269篇 |
综合类 | 740篇 |
自然地理 | 939篇 |
出版年
2024年 | 39篇 |
2023年 | 122篇 |
2022年 | 373篇 |
2021年 | 411篇 |
2020年 | 324篇 |
2019年 | 423篇 |
2018年 | 460篇 |
2017年 | 434篇 |
2016年 | 440篇 |
2015年 | 426篇 |
2014年 | 479篇 |
2013年 | 563篇 |
2012年 | 586篇 |
2011年 | 643篇 |
2010年 | 595篇 |
2009年 | 586篇 |
2008年 | 607篇 |
2007年 | 554篇 |
2006年 | 528篇 |
2005年 | 416篇 |
2004年 | 304篇 |
2003年 | 313篇 |
2002年 | 387篇 |
2001年 | 377篇 |
2000年 | 279篇 |
1999年 | 219篇 |
1998年 | 139篇 |
1997年 | 143篇 |
1996年 | 95篇 |
1995年 | 102篇 |
1994年 | 68篇 |
1993年 | 86篇 |
1992年 | 50篇 |
1991年 | 52篇 |
1990年 | 33篇 |
1989年 | 29篇 |
1988年 | 22篇 |
1987年 | 18篇 |
1986年 | 12篇 |
1985年 | 9篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1973年 | 2篇 |
1958年 | 3篇 |
1957年 | 3篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
871.
872.
Weiwei Song Wenting Yi Yidong Lou Chuang Shi Yibin Yao Yanyan Liu Yong Mao Yu Xiang 《GPS Solutions》2014,18(3):323-333
GLONASS carrier phase and pseudorange observations suffer from inter-channel biases (ICBs) because of frequency division multiple access (FDMA). Therefore, we analyze the effect of GLONASS pseudorange inter-channel biases on the GLONASS clock corrections. Different Analysis Centers (AC) eliminate the impact of GLONASS pseudorange ICBs in different ways. This leads to significant differences in the satellite and AC-specific offsets in the GLONASS clock corrections. Satellite and AC-specific offset differences are strongly correlated with frequency. Furthermore, the GLONASS pseudorange ICBs also leads to day-boundary jumps in the GLONASS clock corrections for the same analysis center between adjacent days. This in turn will influence the accuracy of the combined GPS/GLONASS precise point positioning (PPP) at the day-boundary. To solve these problems, a GNSS clock correction combination method based on the Kalman filter is proposed. During the combination, the AC-specific offsets and the satellite and AC-specific offsets can be estimated. The test results show the feasibility and effectiveness of the proposed clock combination method. The combined clock corrections can effectively weaken the influence of clock day-boundary jumps on combined GPS/GLONASS kinematic PPP. Furthermore, these combined clock corrections can improve the accuracy of the combined GPS/GLONASS static PPP single-day solutions when compared to the accuracy of each analysis center alone. 相似文献
873.
874.
Liang Mao 《Transactions in GIS》2014,18(5):704-717
The research community of Geographic Information Systems and Science (GIS) has been growing rapidly during the last two decades. Little attention has been paid to understanding its geography, structure and evolution. Taking a new organizational perspective, this article aims to fill the knowledge gap by analyzing collaboration and citation networks between GIS research organizations, including academic institutions, government agencies, businesses, and others. These two networks are analyzed in geographical and bibliographical spaces, respectively, to discover characteristic distributions and structures. The results show an uneven geographic distribution of GIS research organizations, and clustered spatial interactions between them. Both collaboration and citation networks exhibit typical “scale‐free” structures, which came into being around the year 2000 and have remained to the present. Further, the GIS research community is composed of 11 cohesive sub‐groups, with each having a clear hub‐spoke structure and a few highly connected organizations as leaders. These results shed light on the overall picture of the GIS research community, and offer a reference system that stimulates further exploration. 相似文献
875.
Total suspended sediment (TSS) data concentrations are retrieved from two sets of satellite ocean color data (the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Aqua and the Korean Geostationary Ocean Color Imager (GOCI)) using an existing regional model to characterize spatial and temporal variation of TSS in the Yellow and East China Seas. MODIS-derived TSS maps show that TSS concentrations are, in general, high along the Korean and Chinese coasts including the Bohai Sea and the Yangtz River estuary, and lower in the middle of the Yellow Sea and the southeastern area of the East China Sea. The monthly average of 10-year MODIS data reveals that TSS values are highest during winter (January to February) and lowest in summer (July to August). Short-term TSS concentrations retrieved from GOCI data showed the dominant influence of semi-diurnal tidal changes on sediment dynamics through temporal (hourly) and spatial distribution in coastal zones of the Yellow sea. The results presented here demonstrate that the satellite-derived TSS products can be utilized as an application tool for future studies on long- and short-term sediment dynamics of turbid coastal waters. In particular, GOCI observations provide unique important capabilities to characterize and quantify the water properties at high temporal (hourly) and spatial (0.5 km) resolutions in the turbid coastal waters of the Yellow Sea and its vicinities. 相似文献
876.
�й���½GPS����Ĺ��켰����ѧ��������Ԫ���� 总被引:2,自引:1,他引:2
????????й?????????????????????????????????????????????????????????????????????????μ??й?????α? ?????GPS???????????????????????????????:??????????????????10???????й????????????????????????10??GPS?????????????????????;?????????????????????:??????????????????????????,??????????????????????????????????????,??????????????????????黡???????????????????????????,?????????????????????????????????????????????:1)?й?????????????????????????????????????????????????????????????????????????????;2)?Щ????????????????????????????????????й?????????????????? 相似文献
877.
利用CMONOC提供的GNSS连续观测数据分析天顶对流层延迟(ZTD)代替水汽的可行性,并利用快速傅里叶变换(FFT)和小波变换(WT)开展GNSS ZTD对超强东部型厄尔尼诺事件的响应分析。结果表明,超强东部型厄尔尼诺事件会增加中国大陆地区水汽含量,在热带及亚热带地区响应更为显著;同时该事件会影响GNSS ZTD 的显著变化周期,使9个月的变化周期减弱,0.8~3个月内的变化周期增强。 相似文献
878.
土地是实现可持续发展的基础性资源和重要资产保障。扎实推进经营性土地使用权招标拍卖挂牌出让制度,通过市场机制形成土地价格,可以提高土地资源利用率,有效遏制土地资产的流失,最大限度地获取经济效益、社会效益和环境效益,促进可持续发展,并可以抑制权力进入市场,从源头上预防和治理腐败。近两年来,莱芜市土地市场与土地资源管理工作虽然取得了一定成绩,但仍存在土地市场不够规范的问题,全市土地资产经营的机制有待进一步健全完善。同时,个别单位、部门和同志对经营性土地使用权以招标拍卖挂牌出让的方式取得的严肃性还认识不足,以言代法… 相似文献
879.
根据实际应用研制制冷控制系统,该系统采用温度测量、PID控制及PWM脉宽调制等技术实现了对目标对象的制冷处理,具有一定的应用价值。 相似文献
880.
宏观生态环境遥感监测系统总体设计与关键技术 总被引:1,自引:0,他引:1
宏观生态环境遥感监测系统是基于环境遥感监测应用技术的软件实现.本文重点介绍了宏观生态环境遥感监测系统的总体结构设计、业务流程设计和核心功能设计,以及模型转换与实现技术、实时投影转换技术与以文件和数据库相结合的数据管理技术、基于XML的数据实时交换技术、产品自动化生产技术等关键技术,并给出了系统的应用实例.系统应用结果表... 相似文献