全文获取类型
收费全文 | 10476篇 |
免费 | 2299篇 |
国内免费 | 3137篇 |
专业分类
测绘学 | 1344篇 |
大气科学 | 1751篇 |
地球物理 | 2509篇 |
地质学 | 6113篇 |
海洋学 | 1609篇 |
天文学 | 200篇 |
综合类 | 983篇 |
自然地理 | 1403篇 |
出版年
2024年 | 85篇 |
2023年 | 266篇 |
2022年 | 595篇 |
2021年 | 724篇 |
2020年 | 577篇 |
2019年 | 667篇 |
2018年 | 673篇 |
2017年 | 604篇 |
2016年 | 653篇 |
2015年 | 656篇 |
2014年 | 644篇 |
2013年 | 760篇 |
2012年 | 740篇 |
2011年 | 712篇 |
2010年 | 746篇 |
2009年 | 684篇 |
2008年 | 612篇 |
2007年 | 607篇 |
2006年 | 524篇 |
2005年 | 484篇 |
2004年 | 393篇 |
2003年 | 322篇 |
2002年 | 408篇 |
2001年 | 410篇 |
2000年 | 363篇 |
1999年 | 312篇 |
1998年 | 254篇 |
1997年 | 210篇 |
1996年 | 187篇 |
1995年 | 165篇 |
1994年 | 161篇 |
1993年 | 130篇 |
1992年 | 118篇 |
1991年 | 86篇 |
1990年 | 67篇 |
1989年 | 59篇 |
1988年 | 48篇 |
1987年 | 40篇 |
1986年 | 22篇 |
1985年 | 24篇 |
1984年 | 19篇 |
1983年 | 21篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 11篇 |
1958年 | 8篇 |
1957年 | 3篇 |
1954年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
A new in-situ seabed acoustic measurement system is developed for direct in-situ measurement of sediment geoacoustic properties (compressional wave velocity and attenuation). The new in-situ system consists of two parts: the deck control unit and the underwater measurement unit. The underwater measurement unit emits sonic waves that propagate through the seafloor sediment, receives the returning signals, and transmits them to the deck control unit for waveform display and analysis. The entire operation is controlled and monitored in real time by the deck control unit on the research vessel and can provide recording of full waveforms to determine the sound velocity and attenuation. This paper outlines the design of the system, the measurement process, and demonstrates its application in tests carded out on seabed sediment off the Qingdao coast, China. The test results show that the system performed well and rapidly provided accurate in-situ acoustic velocity and attenuation estimates of the seafloor sediment. 相似文献
22.
Designing a spatial pattern to rebalance the orientation of development and protection in Wuhan 总被引:1,自引:5,他引:1
Patterns of spatial development and protection form a basic category of geoscience,and redesigning them is a popular subject of research in regional sustainable development that is important for ecological civilization construction.The authors here report a case study of Wuhan city using the circuit theory model and minimum cumulative resistance(MCR)model to rebalance its spatial protection and development.The results show the following:(1)Using the density of the gross domestic product(GDP),density of population,rate of urbanization,and access to transportation as evaluation indicators,seven core areas of development in Wuhan were identified,accounting for 59%of the total number of streets,that exhibited a “circular-satellite”spatial structure.(2)According to the importance of ecosystem services,ecological sensitivity,land use type,and slope of the terrain,the resistance surface of spatial development in Wuhan had a stereoscopic spatial form of an“inverted pyramid,”with high surroundings and a low center.The area of low resistance accounted for 6.64%of the total area of Wuhan.(3)Based on coupling analysis using the MCR and spatial morphological characteristics of current,nine axes of spatial development with a total area of 427.27 km2 and eight key strategic points with a total area of 40.02 km2 were identified.Streets that were prioritized for development accounted for 9.63%of Wuhan's total area.(4)By combining the characterization of the development axis with the structure of the three-level core area,we extracted the structure of spatial development of "one heart,two wings,and three belts" in Wuhan.The research framework and empirical results can provide scientific guidance for the urban spatial layout,the development of regional linkages,and ecological environmental protection in China. 相似文献
23.
Yan Huang Xiang-Ping Wu Quan Guo Qian Zheng Bi-Ying Li Huan-Yuan Shan Ke-Jia Lee Hai-Guang Xu 《天文和天体物理学研究(英文版)》2021,(10):17-26
We present a conceptual design study of external calibrators in the 21 cm experiment towards detecting the globally averaged radiation of the epoch of reionization(EoR). Employment of external calibrator instead of internal calibrator commonly used in current EoR experiments allows removing instrumental effects such as beam pattern, receiver gain and instability of the system if the conventional three-position switch measurements are implemented in a short time interval. Furthermore, in the new design the antenna system is placed in an underground anechoic chamber with an open/closing ceiling to maximally reduce the environmental effect such as RFI and ground radiation/reflection. It appears that three of the four external calibrators proposed in this paper, including two indoor artificial transmitters and one outdoor celestial radiation(the Galactic polarization), fail to meet our purpose. Diurnal motion of the Galactic diffuse emission turns out to be the most probable source as an external calibrator, for which we have discussed the observational strategy and the algorithm of extracting the EoR signal. 相似文献
24.
????????????????д????????ò???????????????????????????ε??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????硢??????????????????Ч??????????????????????????????????????????С?? 相似文献
25.
本文通过对铁炉坪银、铅矿床围岩蚀变的研究,划分出6种基本蚀变类型,3种蚀变带。各蚀变带以矿体为中心对称分布,各带之间呈渐变过渡关系。并指出由蚀变作用引起围岩化学成分及微量元素含量的变化,岩石化学成分与矿物成分变化相一致,成矿与围岩蚀变相辅相成。还指出了围岩蚀变的找矿意义。 相似文献
26.
郭遂红 《广东海洋大学学报》2002,22(2):78-81
随着我国改革开放的进展 ,跨国度、跨文化之间的交往越来越频繁。由于文化因素上的差异 ,交际行为在不同的文化中往往产生不同的意义 ,语用迁移难免会造成理解失误或交际失败。因而外语教学在培养学生整体语言技能的同时 ,应注意文化因素的渗透 ,提高学生的跨文化交际能力 相似文献
27.
28.
长江沿岸港口体系的形成过程与机制 总被引:4,自引:0,他引:4
长江沿岸港口体系是长江经济带的重要支撑。本文首先对自古以来长江沿岸港口体系的形成发展过程进行了科学实证,发现港口体系经历了“港口的起源与产生—港口体系萌芽—港口体系雏形—港口体系形成—港口体系升级”5个阶段。依据实证分析,对长江沿岸港口体系的形成机制进行了归纳演绎,认为相关港口对水水中转和陆水中转腹地的长期相互竞争是导致港口体系形成的主要机制,其中对水水中转腹地的竞争尤为关键,而港口对中转腹地的竞争随时间推移不断向更深层次更广领域推进。最后从政策层面,对长江沿岸港口体系和长江经济带综合运输体系建设的若干问题进行了讨伦。 相似文献
29.
?????????????????????????ο??????????????????????????????????????????????????????????NGA?????????????????????????飬??????????????????????о?????????????????????????????????????????2012?????4.7??????????е?????????????????????????????????????PGA??????S??a??T???????б????о?????????????????????????????????????????????????????????????????????????????????????????????? 相似文献
30.
介绍了气候生态监测服务系统建设的必要性、当前发展的状况和未来趋势.并就存在的问题、今后改进气候生态监测网络建设和加强相关部门间合作、奠定合作基础等问题进行了探讨. 相似文献