全文获取类型
收费全文 | 3087篇 |
免费 | 466篇 |
国内免费 | 484篇 |
专业分类
测绘学 | 978篇 |
大气科学 | 423篇 |
地球物理 | 845篇 |
地质学 | 752篇 |
海洋学 | 318篇 |
天文学 | 66篇 |
综合类 | 321篇 |
自然地理 | 334篇 |
出版年
2024年 | 22篇 |
2023年 | 35篇 |
2022年 | 99篇 |
2021年 | 123篇 |
2020年 | 153篇 |
2019年 | 150篇 |
2018年 | 125篇 |
2017年 | 168篇 |
2016年 | 189篇 |
2015年 | 213篇 |
2014年 | 218篇 |
2013年 | 219篇 |
2012年 | 194篇 |
2011年 | 207篇 |
2010年 | 163篇 |
2009年 | 180篇 |
2008年 | 204篇 |
2007年 | 192篇 |
2006年 | 172篇 |
2005年 | 145篇 |
2004年 | 115篇 |
2003年 | 109篇 |
2002年 | 83篇 |
2001年 | 89篇 |
2000年 | 64篇 |
1999年 | 48篇 |
1998年 | 63篇 |
1997年 | 43篇 |
1996年 | 43篇 |
1995年 | 26篇 |
1994年 | 28篇 |
1993年 | 20篇 |
1992年 | 16篇 |
1991年 | 27篇 |
1990年 | 26篇 |
1989年 | 14篇 |
1988年 | 16篇 |
1987年 | 11篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有4037条查询结果,搜索用时 0 毫秒
971.
基于小波包分解和模糊聚类的网格结构损伤诊断方法 总被引:4,自引:1,他引:3
本文针对网格结构的特点,利用其在快速正弦扫频激励下的动力响应,基于小波包分解频带能量分析和模糊聚类法,提出了一种适合于网格结构的损伤诊断方法。利用两个传感器损伤信息的联合诊断,有效地解决了使用一个传感器无法检测出对称损伤的难题。利用有限元模拟,应用上述方法对一单层球面网壳结构进行了损伤诊断。结果表明,对网壳杆件较小程度的损伤,子频带能量成分变化敏感,用其构造诊断向量和建立损伤样本库,并进行模糊聚类和目标识别,基本可以正确地识别出网壳杆件的损伤位置和程度。同时该方法测试时间短,使用设备少,有可靠的理论基础,具有一定的工程应用参考价值。 相似文献
972.
大型城市管网抗震可靠性分析与优化 总被引:3,自引:0,他引:3
本文提出了地震作用下供水系统的渗漏模型,发展了地震后带渗漏管网的流分析技术,结合一次二阶矩方法获得了地震后供水管网的功能可靠度。针对供燃气管网系统则提出了一类高效精确的大型网络抗震连通可靠度分析的概率解析算法———递推分解算法。以上述管网抗震可靠性分析理论为基础,分别发展了基于模拟退火算法的供水系统网络拓扑优化分析理论和基于遗传算法的供燃气网络系统拓扑优化理论。 相似文献
973.
Ocean vector acoustic measurement is feasible affected by the hydrodynamic interference caused by the flow fluctuations and structural vibrations, especially in the very-low-frequency monitoring. Hence, a novel horizontal floating platform including a horizontal floating cable, vertical mooring cable and floating main body is proposed and described in this paper. It has the advantages of good maneuverability along with the current and multi-stage vibration isolation. The main application of this platform is to measure the ocean ambient noise coming from the wave fluctuation and the deterministic acoustic signals such as aquatic organisms, underwater targets and sailing vehicles. The influence of the current fluctuation on the attitude angle and flow induced vibration of cables and main body are analyzed with some previous sea test data. Moreover, the comparison between the vertical type platform used before and the horizontal type platform is also discussed. It is concluded that there is obvious relevance between the attitude angle and ocean current variation. Meanwhile, the abnormal influence on the main body is caused by the vibration transmission from the fluctuation of cables. There will be the influence on the accuracy of the acoustic measurement above 100 Hz, and the inherent vibration characteristic of the main body is the primary reason. 相似文献
974.
975.
976.
977.
Margarita Menndez 《Estuarine, Coastal and Shelf Science》2009,82(4):608-614
The response of early Ruppia cirrhosa Petagna (Grande) litter decomposition to external nitrogen and phosphorus availability in La Tancada (Ebro River, NE Spain), a coastal lagoon that receives agricultural freshwater runoff from rice fields has been examined. Recently abscised dead R. cirrhosa stems were collected and 25 g of fresh weight was placed in litter bags with a mesh size of 100 μm and 1 mm. These bags were fertilised by adding nitrogen (N), a mixture of nitrogen plus phosphorus (N + P), or phosphorus (P), or were left untreated (CT). Macroinvertebrates were retrieved from the bags and the ash-free dry weight, and carbon, and N and P content of the remaining plant material were measured after 0, 3, 7, 14, 22 and 32 days. Litter decomposition rates, k (day−1), were estimated using a simple exponential model. Litter decay was clearly accelerated by the addition of P in the fine (100 μm) litter bags (0.042), but when N was added alone (0.0099) the decomposition rate was lower than in the CT treatments (0.022). No significant difference was observed between the N (0.0099–0.018) and N + P (0.0091–0.015) treatments in either the fine or the coarse (1 mm) litter bags. These results could be attributed to the relatively high availability of external (environmental) and internal (detritus contents) N. No significant effect of macro invertebrates was observed in the CT treatment or under N or P or N + P addition. The ratio between the decomposition rates in coarse and fine litter bags (kc/kf) was lower in disturbed Tancada lagoon (0.82) than in Cesine lagoon (2.11), a similar Mediterranean coastal water body with almost pristine conditions. These results indicate that, in addition to data on macroinvertebrate community structure, decomposition rates could also be used to assess water quality in coastal lagoons. 相似文献
978.
???t??????????????о????λ?????????????????????????????????????,???λ?????????????λ????????λ?????????????????????????????λ?????????????????????????Χ?????????????????? 相似文献
979.
980.