全文获取类型
收费全文 | 6452篇 |
免费 | 1484篇 |
国内免费 | 2057篇 |
专业分类
测绘学 | 920篇 |
大气科学 | 929篇 |
地球物理 | 1309篇 |
地质学 | 4133篇 |
海洋学 | 1114篇 |
天文学 | 200篇 |
综合类 | 542篇 |
自然地理 | 846篇 |
出版年
2024年 | 60篇 |
2023年 | 160篇 |
2022年 | 412篇 |
2021年 | 456篇 |
2020年 | 397篇 |
2019年 | 491篇 |
2018年 | 444篇 |
2017年 | 380篇 |
2016年 | 405篇 |
2015年 | 462篇 |
2014年 | 421篇 |
2013年 | 515篇 |
2012年 | 512篇 |
2011年 | 516篇 |
2010年 | 497篇 |
2009年 | 481篇 |
2008年 | 433篇 |
2007年 | 417篇 |
2006年 | 362篇 |
2005年 | 290篇 |
2004年 | 227篇 |
2003年 | 175篇 |
2002年 | 194篇 |
2001年 | 186篇 |
2000年 | 167篇 |
1999年 | 146篇 |
1998年 | 119篇 |
1997年 | 95篇 |
1996年 | 90篇 |
1995年 | 75篇 |
1994年 | 57篇 |
1993年 | 57篇 |
1992年 | 64篇 |
1991年 | 40篇 |
1990年 | 40篇 |
1989年 | 29篇 |
1988年 | 19篇 |
1987年 | 15篇 |
1986年 | 12篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 13篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1977年 | 8篇 |
1976年 | 3篇 |
1957年 | 2篇 |
1954年 | 5篇 |
排序方式: 共有9993条查询结果,搜索用时 78 毫秒
341.
Ocean surface waves are strongly forced by high wind conditions associated with winter storms in the Sea of Japan. They are also modulated by tides and storm surges. The effects of the variability in surface wind forcing, tides and storm surges on the waves are investigated using a wave model, a high-resolution atmospheric mesoscale model and a hydrodynamic ocean circulation model. Five month-long wave model simulations are inducted to examine the sensitivity of ocean waves to various wind forcing fields, tides and storm surges during January 1997. Compared with observed mean wave parameters, results indicate that the high frequency variability in the surface wind filed has very great effect on wave simulation. Tides and storm surges have a significant impact on the waves in nearshores of the Tsushima-kaihyō, but not for other regions in the Sea of Japan. High spatial and temporal resolution and good quality surface wind products will be crucial for the prediction of surface waves in the JES and other marginal seas, especially near the coastal regions. 相似文献
342.
343.
TOPEX/POSEIDON altimeter data from October 1992 to June 2002 are used to calculate the global barotropic M2 tidal currents using long-term tidal harmonic analysis. The tides calculated agree well with ADCP data obtained from the South China Sea (SCS). The maximum tide velocities along the semi-major axis and semi-minor axis can be computed from the tidal ellipse. The global distribution of M2 internal tide vertical energy flux from the sea bottom is calculated based on a linear internal wave generation model. The global vertical energy flux of M2 internal tide is 0.96 TW, with 0.36 TW in the Pacific, 0.31 TW in the Atlantic and 0.29 TW in the Indian Ocean, obtained in this study. The total horizontal energy flux of M2 internal tide radiating into the open ocean from the lateral boundaries is 0.13 TW, with 0.06 TW in the Pacific, 0.04TW in the Atlantic, and 0.03 TW in the Indian Ocean. The result shows that the principal lunar semi-diurnal tide M2 provides enough energy to maintain the large-scale thermohaline circulation of the ocean. 相似文献
344.
Twenty-four compounds including eight steroids (1-8), nine triterpenoids (9-16, 24), three flavonoids (20-22), and four benzenecarboxylic derivatives (17-19, 23) were isolated and identified from stems and twigs of medicinal mangrove plant Sonneratia caseolaris. The structures of the isolated compounds were determined by extensive analysis of their spectroscopic data. Among these metabolites, compounds 1, 4-20 and 22-24 were isolated and identified for the f'urst time from S. caseolaris. In the in vitro cytotoxic assay against SMMC-7721 human hepatoma cells, compound 21 (3',4',5,7-tetrahydroxyflavone)exhibited significant activity with IC50 2.8 μg/mL, while oleanolic acid (14), 3,3'-di-O-methyl ether ellagic acid (18), and 3,3',4-O-tri-O-methyl ether ellagic acid (19) showed weak activity. None of these compounds displayed significant antibacterial activites. 相似文献
345.
Early Cretaceous precious fossil-bearing beds in Weijialing-Yaolugou of Jianchang Basin , western Liaoning 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《世界地质(英文版)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The Jianchang Basin is one of the main localities of the precious fossils of Jehol Biota in western Liaoning. The fossil-bearing horizons are mainly in the Yixian- and J iufotang formations. In the Weijialing-Yaolugou of southwest Jianchang Basin, many precious fossils have been found at Luojiagou Bed of the 2nd Member of the Yixian Formation and at Xidian Bed of the 1st member of the Jiufotang Formation. The geologic setting, sedimentary environment and paleogeography of the precious fossil-bearing beds were also studied. 相似文献
346.
台风作用下淤泥质海岸动力地貌响应 总被引:6,自引:0,他引:6
基于200509号麦莎台风(近似百年一遇)作用前后杭州湾北岸龙泉-南竹港实测的海岸地形和水文资料,利用分形技术、冲刷深度和闭合水深等相关概念分析淤泥质海岸的剖面变化、岸线进退以及地形冲淤,进而探讨海岸响应台风作用的动力地貌行为.结果表明:1)台风作用前后的海岸动力地貌过程表现为水下类似沙坝的堆积体削平、凹处填洼,水下平台发育锯齿或较小的坝--槽,海岸剖面的分维数降低,剖面坡度处于平缓;2)麦莎台风对海床的整体冲淤幅度不大,这可能是由于研究区大潮讯的增水致使波浪对海床的塑造能力减弱以及码头的遮蔽作用造成;3)台风作用对海岸的冲刷深度约为0.8 m,闭合水深为9.5 m,近岸-1 m邻近区成为海岸响应台风作用最敏感的地带;泥沙主要在0 m到闭合水深区间的海床发生纵、横向运移. 相似文献
347.
348.
349.
基于GIS的公路自然灾害的预警预报系统研究 总被引:2,自引:1,他引:1
自然灾害发生后,首先考虑的问题之一是如何尽快赶赴灾区实施救助,而自然灾害的一个直接结果往往是对道路交通产生毁灭性的破坏即所谓的公路自然灾害。因此,研究公路自然灾害及其应急预警预报方法具有重要的意义。本文立足于建立基于GIS的公路自然灾害预警预报系统,分析了自然灾害的类型和公路自然灾害的成因,讨论了公路自然灾害GIS的空间数据和属性数据的类型和数据组织技术,针对地质、暴风雪天气、地震等不同成因的公路自然灾害,提出了基于GIS的公路自然灾害预警预报系统的解决方案。并已经运用于为用户开发的公路自然灾害应急预警预报系统中。 相似文献
350.