全文获取类型
收费全文 | 36669篇 |
免费 | 4930篇 |
国内免费 | 7061篇 |
专业分类
测绘学 | 5602篇 |
大气科学 | 6668篇 |
地球物理 | 7810篇 |
地质学 | 12465篇 |
海洋学 | 4006篇 |
天文学 | 1112篇 |
综合类 | 2563篇 |
自然地理 | 8434篇 |
出版年
2024年 | 193篇 |
2023年 | 581篇 |
2022年 | 1301篇 |
2021年 | 1591篇 |
2020年 | 1718篇 |
2019年 | 2019篇 |
2018年 | 1460篇 |
2017年 | 1896篇 |
2016年 | 1860篇 |
2015年 | 1951篇 |
2014年 | 2288篇 |
2013年 | 2943篇 |
2012年 | 2350篇 |
2011年 | 2378篇 |
2010年 | 1860篇 |
2009年 | 2308篇 |
2008年 | 2242篇 |
2007年 | 2415篇 |
2006年 | 2334篇 |
2005年 | 1856篇 |
2004年 | 1704篇 |
2003年 | 1394篇 |
2002年 | 1129篇 |
2001年 | 936篇 |
2000年 | 834篇 |
1999年 | 741篇 |
1998年 | 722篇 |
1997年 | 620篇 |
1996年 | 515篇 |
1995年 | 451篇 |
1994年 | 384篇 |
1993年 | 354篇 |
1992年 | 262篇 |
1991年 | 195篇 |
1990年 | 158篇 |
1989年 | 142篇 |
1988年 | 122篇 |
1987年 | 66篇 |
1986年 | 60篇 |
1985年 | 71篇 |
1984年 | 39篇 |
1983年 | 19篇 |
1982年 | 25篇 |
1981年 | 23篇 |
1980年 | 22篇 |
1978年 | 13篇 |
1977年 | 20篇 |
1976年 | 25篇 |
1973年 | 17篇 |
1971年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
概述了应用子波分析对悬浮物测量中的声散射信号进行特征提取的方法 ,并对声散射信号识别的研究进行了探讨。对实测数据的实验取得了较好的结果 相似文献
72.
工程风险分析中的风险当量及其评价标准 总被引:7,自引:2,他引:7
目前,量化、半量化风险分析是工程风险分析的主流。在对工程进行量化和半量化风险分析时,无论采用什么方法,风险评价指标和评价标准都是关键的重要问题。只有在建立了统一的评价指标和评价标准体系的基础上,对工程进行的风险分析能够得出正确和一致的结论。文章通过对国内外风险分析理论和实践的研究和总结,提出了在工程风险分析中确定风险评价指标和评价标准的原则和方法。 相似文献
73.
提出了海上浮动软管的三维静态分析模型。在四级海情下,对输送柴油的软管求得了解析解,得出了软管在侧向和垂直方向的偏移及其所受的拉力,认为此时的软管是不安全的。 相似文献
74.
信息时代的召唤,地球信息科学应运而生.经过10a左右的发展,地理信息科学已见雏形.总结了10a来地球信息科学的研究结果,并介绍了地球信息科学的研究内容和发展前景. 相似文献
75.
76.
77.
78.
In order to accurately design a sand compaction pile (SCP) with low replacement area ratio, it is important to understand the mechanical interaction between the sand pile and clay ground and its mechanism during consolidation process in composite ground. In this article, therefore, a series of numerical analyses on composite ground improved by SCP with low replacement area ratio were carried out. The applicability of numerical analyses, in which an elasto-viscoplastic consolidation finite element method was applied, were confirmed by comparing the results obtained from a series of laboratory model tests with the composite ground improved by SCP. Through the results of the numerical analyses, mechanical behavior of the sand pile and clay in composite ground during consolidation is elucidated, together with a stress sharing mechanism between sand pile and clay. 相似文献
79.
Christopher T. Mills Robert F. Dias Dennis Graham Kevin W. Mandernack 《Marine Chemistry》2006,98(2-4):197-209
Sediment samples ranging from 0.05 to 278 m below sea floor (mbsf) at a Northwest Pacific deep-water (5564 mbsl) site (ODP Leg 191, Site 1179) were analyzed for phospholipid fatty acids (PLFAs). Total PLFA concentrations decreased by a factor of three over the first meter of sediment and then decreased at a slower rate to approximately 30 mbsf. The sharp decrease over the first meter corresponds to the depth of nitrate and Mn(IV) reduction as indicated by pore water chemistry. PLFA-based cell numbers at site 1179 had a similar depth profile as that for Acridine orange direct cell counts previously made on ODP site 1149 sediments which have a similar water depth and lithology. The mole percentage of straight chain saturated PLFAs increases with depth, with a large shift between the 0.95 and 3.95 mbsf samples. PLFA stable carbon isotope ratios were determined for sediments from 0.05 to 4.53 mbsf and showed a general trend toward more depleted δ13C values with depth. Both of these observations may indicate a shift in the bacterial community with depth across the different redox zones inferred from pore water chemistry data. The PLFA 10me16:0, which has been attributed to the bacterial genera Desulfobacter in many marine sediments, showed the greatest isotopic depletion, decreasing from − 20 to − 35‰ over the first meter of sediment. Pore water chemistry suggested that sulfate reduction was absent or minimal over this same sediment interval. However, 10me16:0 has been shown to be produced by recently discovered anaerobic ammonium oxidizing (anammox) bacteria which are known chemoautotrophs. The increasing depletion in δ13C of 10me16:0 with the unusually lower concentration of ammonium and linear decrease of nitrate concentration is consistent with a scenario of anammox bacteria mediating the oxidation of ammonium via nitrite, an intermediate of nitrate reduction. 相似文献
80.
High-resolution underway temperature and conductivity measurements collected by R/V Knorr during winter and spring 2003 are used to characterize errors associated with spatial aliasing in the northern and central Adriatic Sea. During winter, 99th percentile temperature, salinity and density errors were 0.62 °C, 0.25 and 0.12 kg/m3 (0.25 °C, 0.10 and 0.05 kg/m3) for sampling at 10 km (5 km) horizontal resolution, respectively. The corresponding values in spring were 1.31 °C, 0.50 and 0.40 kg/m3 (0.93 °C, 0.25 and 0.22 kg/m3) for the 10 km (5 km) sample spacing, respectively. The largest errors were associated with energetic regions over the shallow, western Adriatic, in front of the Po River mouth and off the tip of the Istrian peninsula. The deeper eastern basin exhibited smaller errors. The variability of errors in time and space reflected the variability of small-scale density features, characterized by wavelengths as small as 2 km in winter and 1 km in spring and being more pronounced in the western and northern parts of the Adriatic. As these results indicate that errors associated with undersampling can be considerable, they should be taken into account while planning future CTD measurements in the region. 相似文献