全文获取类型
收费全文 | 12111篇 |
免费 | 2154篇 |
国内免费 | 3325篇 |
专业分类
测绘学 | 1170篇 |
大气科学 | 2734篇 |
地球物理 | 2733篇 |
地质学 | 5955篇 |
海洋学 | 1844篇 |
天文学 | 508篇 |
综合类 | 1175篇 |
自然地理 | 1471篇 |
出版年
2024年 | 62篇 |
2023年 | 242篇 |
2022年 | 675篇 |
2021年 | 763篇 |
2020年 | 598篇 |
2019年 | 697篇 |
2018年 | 689篇 |
2017年 | 647篇 |
2016年 | 763篇 |
2015年 | 689篇 |
2014年 | 718篇 |
2013年 | 847篇 |
2012年 | 750篇 |
2011年 | 740篇 |
2010年 | 717篇 |
2009年 | 700篇 |
2008年 | 642篇 |
2007年 | 566篇 |
2006年 | 484篇 |
2005年 | 436篇 |
2004年 | 343篇 |
2003年 | 360篇 |
2002年 | 377篇 |
2001年 | 379篇 |
2000年 | 386篇 |
1999年 | 495篇 |
1998年 | 361篇 |
1997年 | 357篇 |
1996年 | 340篇 |
1995年 | 282篇 |
1994年 | 245篇 |
1993年 | 223篇 |
1992年 | 177篇 |
1991年 | 137篇 |
1990年 | 126篇 |
1989年 | 124篇 |
1988年 | 109篇 |
1987年 | 59篇 |
1986年 | 60篇 |
1985年 | 43篇 |
1984年 | 40篇 |
1983年 | 18篇 |
1982年 | 20篇 |
1981年 | 25篇 |
1980年 | 16篇 |
1979年 | 13篇 |
1978年 | 8篇 |
1976年 | 6篇 |
1973年 | 7篇 |
1958年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
During the period August 1985 to May 1986, phytoplankton in the southern Taiwan Strait was collected and studied for distributional variability in relation to hydrography. The results indicated that maximum standing crops of phytoplankton occurred in October and May due to the outgrowth of certain species of diatoms and blue-green algae. The majority of phytoplankton appeared in the water in the top 25 m and occurred in distinct clusters under the influence of water movement. Multivariate analysis indicated that hydrographic parameters, which accounted for the variability of phytoplankton distribution, varied seasonally. Vertical, spatial and temporal variabilities were also apparent. The close relationship between hydrography and algal distribution justifies the use of variations in the phytoplankton population as a useful tracer of water movement. 相似文献
75.
The impact of several chemical poisons on the Arca granosa absorbing 45Ca was studied. The results showed that the absorption of 45Ca in the blood and the soft tissue by Arca granosa was inhibited by the inorganic compounds of Cu, Zn, Pd, Cd, Hg and so on, among which the inhibition of Cd was the strongest, next was that of Cu and Hg. But the inhibition of the absorption of 45Ca in the shell of Arca granosa was little. The impact of three kinds of energy metabolism inhibitory substances on the absorption of 45Ca by the Area granosa showed that the absorption was an active transfer process. 相似文献
76.
河口只是河流与海洋之间的一小部分水域,但对人类社会的发展和生物的进化起着重要的作用。它不仅是生物种群繁殖、育幼和栖息的场所,而且是溯河和降海鱼类洄游的必经之路,因此,河口对生物种群的繁衍延续和资源补充,以及保持生态平衡具有十分重要的意义。
然而,河口又是生态环境十分脆弱和敏感的水域,同时也是受人类干扰最为严重的区域。因此,河口的生态环境问题愈来愈引起人们的关注,其中包括长江三峡水库的兴建对长江口及其附近海域生态、环境的影响,特别是对位于河口两侧的我国著名两大渔场——舟山渔场和吕四渔场的影响问题。影响渔业资源的因子是多方面而且错综复杂的。本文主要通过长江径流的变化与环境因子变量的相关分析,并根据三峡水库不同蓄水方案,对河口近海渔业的影响问题进行初步探讨。 相似文献
77.
Mark R. Jury Bohua Huang 《Deep Sea Research Part I: Oceanographic Research Papers》2004,51(12):2123-2136
We analyze the time-longitude structure of composite cases from model-assimilated ocean data in the period 1958–1998, following on from earlier work by Huang and Kinter (J. Geophys. Res. 107(C11) (2002) 3199) that studied east–west thermocline variability in the Indian Ocean. Our analysis focuses on the Rossby wave signal along the thermocline ridge in the tropical SW Indian Ocean (10°S, 60–80°E), where wind stress curl is important. Anomalous winds in the equatorial east Indian Ocean force successive Rossby waves westward at speeds of 0.1 m s−1±30%. With a wavelength of 7000 km, the period of oscillation is in the range 1.9–5.2 years. The Indian Ocean Rossby wave is partially resonant with the global influence of the El Nino–Southern Oscillation, except during quasi-biennial rhythm. The presence of the Rossby wave offers potential predictability for east–west atmospheric circulation systems and climate that affect resources in countries surrounding the Indian Ocean. 相似文献
78.
Practical implementation of Hilbert-Huang Transform algorithm 总被引:12,自引:0,他引:12
Hilbert-Huang Transform (HHT) is a newly developed powerful method for nonlinear and non-stationary time series analysis. The empirical mode decomposition is the key part of HHT, while its algorithm was protected by NASA as a US patent, which limits the wide application among the scientific community. Two approaches, mirror periodic and extrema extending methods, have been developed for handling the end effects of empirical mode decomposition. The implementation of the HHT is realized in detail to widen the application. The detailed comparison of the results from two methods with that from Huang et al. (1998, 1999), and the comparison between two methods are presented. Generally, both methods reproduce faithful results as those of Huang et al. For mirror periodic method (MPM), the data are extended once forever. Ideally, it is a way for handling the end effects of the HHT, especially for the signal that has symmetric waveform. The extrema extending method (EEM) behaves as good as MPM, and it is better t 相似文献
79.
该文对目前工业上生产纳米碳酸钙的方法作了较为详细的综述。对一步碳化法、两步碳化法、多段喷雾碳化法、旋转填充床碳化反应器碳化技术制备链形、纺锤形、球形、立方形等不同形状的纳米碳酸钙材料的方法进行了比较和总结 相似文献
80.
There is a low nutrient level in the Aoshan Bay. In June 1999, the chemical adjustmentand control experiment was made in the Aoshan Bay. Following tracts investigation was carried out before the experiment and on the 1st, 2nd, 4th, 5th, 6th and 45th day/after the experiment. While the variance of amount of phytoplankton, the replacement of superior species and the species composition of phytoplankton were researched. The results show that the amount of phytoplankton in the Aoshan Bay rises gradually after the experiment. Ceratium macroceros Cleve of pyrophyta was the dominant species before the experiment, its dominant index was 37.7%. Six days after the experiment, its dominant index dropped to 17.6% . Meanwhile the dominant index of Asterionella japanics Cleve rose from 7.1% to 39.2% , it became the first dominant species. Forty-five days after the experiment, the amount of phytoplankton in the Aoshan Bay was 5.15 to 137.32 times more than that in 1997. 相似文献