全文获取类型
收费全文 | 13963篇 |
免费 | 2802篇 |
国内免费 | 3638篇 |
专业分类
测绘学 | 1257篇 |
大气科学 | 2639篇 |
地球物理 | 3630篇 |
地质学 | 7226篇 |
海洋学 | 1721篇 |
天文学 | 684篇 |
综合类 | 1343篇 |
自然地理 | 1903篇 |
出版年
2024年 | 59篇 |
2023年 | 240篇 |
2022年 | 712篇 |
2021年 | 815篇 |
2020年 | 698篇 |
2019年 | 856篇 |
2018年 | 881篇 |
2017年 | 779篇 |
2016年 | 893篇 |
2015年 | 815篇 |
2014年 | 927篇 |
2013年 | 967篇 |
2012年 | 917篇 |
2011年 | 973篇 |
2010年 | 906篇 |
2009年 | 903篇 |
2008年 | 852篇 |
2007年 | 790篇 |
2006年 | 642篇 |
2005年 | 482篇 |
2004年 | 427篇 |
2003年 | 387篇 |
2002年 | 401篇 |
2001年 | 360篇 |
2000年 | 388篇 |
1999年 | 465篇 |
1998年 | 379篇 |
1997年 | 388篇 |
1996年 | 316篇 |
1995年 | 272篇 |
1994年 | 308篇 |
1993年 | 232篇 |
1992年 | 190篇 |
1991年 | 135篇 |
1990年 | 109篇 |
1989年 | 86篇 |
1988年 | 104篇 |
1987年 | 52篇 |
1986年 | 48篇 |
1985年 | 41篇 |
1984年 | 37篇 |
1983年 | 37篇 |
1982年 | 39篇 |
1981年 | 29篇 |
1980年 | 8篇 |
1979年 | 15篇 |
1978年 | 6篇 |
1958年 | 14篇 |
1957年 | 3篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
51.
52.
Effect of Cyclic Loading Frequency on Undrained Behaviors of Undisturbed Marine Clay 总被引:2,自引:0,他引:2
Based on a series of cyclic triaxial tests, the effect of cyclic frequency on the undrained behaviors of undisturbed marine clay is investigated. For a given dynamic stress ratio, the accumulated pore water pressure and dynamic strain increase with the number of cycles. There exists a threshold value for beth the accumulated pore water pressure and dynamic strain, below which the effect of cyclic frequency is very small, but above which the accumulated pore water pressure and dynamic strain increase intensely with the decrease of cyclic frequency for a given number of cycles. The dynamic strength increases with the increase of cyclic frequency, whereas the effect of cyclic frequency on it gradually diminishes to zero when the number of cycles is large enough, and the dynamic strengths at different frequencies tend to the same limiting minimum dynamic strength. The test results demonstrate that the reasons for the frequency effect on the undrained soil behaviors are beth the creep effect induced by the loading rate and the decrease of sample effective confining pressure caused by the accumulated pore water pressure. 相似文献
53.
54.
Fayun Liang Mingyi Zhao Chengrui Qin Yajie Jia Zhongwei Wang Guiping Yue 《Marine Georesources & Geotechnology》2020,38(1):114-121
AbstractThe construction of a 100-km road network is planned on a land reclamation area in the Oujiang Estuary in China. The embankment had a height of 4 m and a base width of 60 m. The reclamation area is newly filled by a 3-m dredger fill on a 48-m thick layer of marine clay. Estimation of the settlement of the future road network is difficult. To guide the construction of the road network, a 1/100-scale centrifuge model test was performed with a marine clay sample from the construction site to simulate the layered settlements and evaluate the drainage effect of prefabricated vertical drains in the dredger fill in the following 10 years. The results of the centrifuge modeling test are verified by 10-month in situ monitoring, which shows agreement between the centrifuge modeling test results and the in situ results. The test results indicate that additional time is needed to reinforce the newly added dredger fill by the surcharge preloading method to uplift the elevation of the reclamation area with dredger fill. 相似文献
55.
56.
Tetraploid induced by physical and chemical methods in Jinjiang oyster(Crassostrea rivularis) 总被引:1,自引:0,他引:1
Rong Shoubai Shi Shumei Mo Qirong Liu Shaeqiong Liang Ze Zhao Xiuzhu Tong Wangdong Li Shouwu Li Yimin 《海洋学报(英文版)》1994,13(2):275-283
TetraploidinducedbyphysicalandchemicalmethodsinJinjiangoyster(Crassostrearivularis)¥RongShoubai,ShiShumei,McQirong,LiuShaeqio... 相似文献
57.
登陆我国热带气旋活动的年代际变化分析 总被引:16,自引:1,他引:16
本文利用1950-1999年西北太平洋热带气旋资料,对50年来登陆我国热带气旋的月际、年际和年代际变化及异常情况进行了统计分析,指出了登陆我国的热带气旋频数存在明显的年代际差异,并对比分析了同期的副热带高压等海洋大气环流指数的统计特征。 相似文献
58.
59.
60.
Jennifer L. Mercer Meixun Zhao Steven M. Colman 《Estuarine, Coastal and Shelf Science》2005,63(4):675-682
Alkenone unsaturation indices (UK37 and UK′37) have long been used as proxies for surface water temperature in the open ocean. Recent studies have suggested that in other marine environments, variables other than temperature may affect both the production of alkenones and the values of the indices. Here, we present the results of a reconnaissance field study in which alkenones were extracted from particulate matter filtered from the water column in Chesapeake Bay during 2000 and 2001. A multivariate analysis shows a strong positive correlation between UK37 (and UK′37) values and temperature, and a significant negative correlation between UK37 (and UK′37) values and nitrate concentrations. However, temperature and nitrate concentrations also co-vary significantly. The temperature vs. UK37 relationships (UK37=0.018 (T)−0.162, R2=0.84, UK′37=0.013 (T)−0.04, R2=0.80) have lower slopes than the open-ocean equations of Prahl et al. [1988. Further evaluation of long-chain alkenones as indicators of paleoceanographic conditions. Geochimica et Cosmochimica Acta 52, 2303–2310] and Müller et al. [1998. Calibration of the alkenone paleotemperature index UK′37 based on core-tops from the eastern South Atlantic and the global ocean (60°N–60°S). Geochimica et Cosmochimica Acta 62, 1757–1772], but are similar to the relationships found in controlled studies with elevated nutrient levels and higher nitrate:phosphate (N:P) ratios. This implies that high nutrient levels in Chesapeake Bay have either lowered the UK37 vs. temperature slope, or nutrient levels are the main controller of the UK37 index. In addition, particularly high abundances (>5% of total C37 alkenones) of the tetra-unsaturated ketone, C37:4, were found when water temperatures reached 25 °C or higher, thus posing further questions about the controls on alkenone production as well as the biochemical roles of alkenones. 相似文献