全文获取类型
收费全文 | 5717篇 |
免费 | 1208篇 |
国内免费 | 1768篇 |
专业分类
测绘学 | 420篇 |
大气科学 | 2111篇 |
地球物理 | 1577篇 |
地质学 | 1555篇 |
海洋学 | 1467篇 |
天文学 | 64篇 |
综合类 | 545篇 |
自然地理 | 954篇 |
出版年
2024年 | 35篇 |
2023年 | 79篇 |
2022年 | 207篇 |
2021年 | 246篇 |
2020年 | 278篇 |
2019年 | 355篇 |
2018年 | 271篇 |
2017年 | 322篇 |
2016年 | 275篇 |
2015年 | 323篇 |
2014年 | 401篇 |
2013年 | 413篇 |
2012年 | 418篇 |
2011年 | 397篇 |
2010年 | 318篇 |
2009年 | 386篇 |
2008年 | 336篇 |
2007年 | 433篇 |
2006年 | 407篇 |
2005年 | 365篇 |
2004年 | 335篇 |
2003年 | 267篇 |
2002年 | 205篇 |
2001年 | 204篇 |
2000年 | 194篇 |
1999年 | 162篇 |
1998年 | 170篇 |
1997年 | 144篇 |
1996年 | 130篇 |
1995年 | 108篇 |
1994年 | 103篇 |
1993年 | 96篇 |
1992年 | 80篇 |
1991年 | 57篇 |
1990年 | 33篇 |
1989年 | 31篇 |
1988年 | 32篇 |
1987年 | 17篇 |
1986年 | 12篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1954年 | 3篇 |
排序方式: 共有8693条查询结果,搜索用时 328 毫秒
121.
重力异常垂向一阶导数的一种简便算法 总被引:1,自引:0,他引:1
利用拉格朗日插值导出了重力异常垂向一阶导数的计算公式,给出了地面以及地面之上不同高度的求导系数。该公式可以计算地面上的重力垂向一阶导数,还可以直接计算地面之上任意高度上的垂向一阶导数。鉴于该公式除系数不同外,与上延公式完全相同,因此,程序设计尤为简单。使用本公式对模型数据和实际资料进行了处理,证明了本算法的实用性。 相似文献
122.
对煤炭资源勘查资源量与客观物质量之间差值的误差理论探讨,提出误差由真值误差、系统误差和离差3个基本部分组成,其中真值误差是不可消除的观测误差、系统误差是控制网度所决定的准确度标准、而离差是由地质构造及矿床形态的多解性产生的资源量波动。在此基础上,构筑了一个关于误差的数学模型,最后应用误差理论对现行勘查工作中常见的错误进行分析,并就如何避免错误及减少误差提出了见解。 相似文献
123.
124.
125.
126.
127.
J. P. Putaud N. Mihalopoulos B. C. Nguyen J. M. Campin S. Belviso 《Journal of Atmospheric Chemistry》1992,15(2):117-131
Daily measurements of atmospheric sulfur dioxide (SO2) concentrations were performed from March 1989 to January 1991 at Amsterdam Island (37°50 S–77°30 E), a remote site located in the southern Indian Ocean. Long-range transport of continental air masses was studied using Radon (222Rn) as continental tracer. Average monthly SO2 concentrations range from less than 0.2 to 3.9 nmol m-3 (annual average = 0.7 nmol m-3) and present a seasonal cycle with a minimum in winter and a maximum in summer, similar to that described for atmospheric DMS concentrations measured during the same period. Clear diel correlation between atmospheric DMS and SO2 concentrations is also observed during summer. A photochemical box model using measured atmospheric DMS concentrations as input data reproduces the seasonal variations in the measured atmospheric SO2 concentrations within ±30%. Comparing between computed and measured SO2 concentrations allowed us to estimate a yield of SO2 from DMS oxidation of about 70%. 相似文献
128.
P. F. Biagi T. S. Gegechkory E. N. Its P. Manjgaladze V. Sgrigna D. Zilpimiani 《Pure and Applied Geophysics》1990,133(2):317-327
A three-dimensional ultrasonic modelling was used to study the Rayleigh waves reflected from a thin low velocity vertical layer and those transmitted through the same zone. The reflection and transmission coefficients of the Rayleigh waves have been calculated by an approximate method based on the Green function technique. Nonrigid contact boundary conditions were used for the low velocity layer modelling. A rather good correspondence between the theoretical and experimental absolute values of the reflection and the transmission coefficients was obtained. Some discrepancies between experimental and theoretical results, in particular with regard to phase shifts, may be explained by a certain inadequacy of the theoretical model to the low velocity layer investigated by the ultrasonic modelling. 相似文献
129.
Weiyang BAI Xinbin FENG Xuewu FU Tianrong HE Guangle QIU 《中国地球化学学报》2006,25(B08):154-154
In order to find out whether Aha Lake was polluted by the acid mining waste water or not, the concentration and distribution of different mercuryspecies in the water columns and sediment profile collected from Aha Lake were investigated. It was found that discernible seasonal variation of different mercury species in water body were obtained in the Aha Reservoir. With regards to the whole sampling periods, the concentrations of HgP in the Aha Reservoir water body were evidently correlated to the concentrations of total mercury, showing that total mercury was mostly associated with particle mercury. The concentrations of methylmercury in water body were also evidently correlated to the concentrations of dissolved mercury. The dissolved mercury evidently affects the distribution and transportation of methylmercury. However, there is no correlation between methylmercury and total mercury. The dissolved mercury, reactive mercury, dissolved methylmercury levels in the water body of high flow period were much higher than those in low flow period. The distribution, speciation and levels of mercury within the Aha Reservoir water body were governed by several factors, such as the output of river, the release of sediment . Discernible seasonal variation of total mercury and methylmercury in porewater was described during the sampling periods, with the concentrations in high flow period generally higher than those in low flow period. The methylmercury in pore water column was evidently correlated to that of the sediment. The results indicated that highly elevated MeHgD concentrations in the porewater were produced at the depths from 2 to 5 cm in the sediment profile, and decreased sharply with depth. A positive correlation has been found between MeHgD formation and sulfate reducing bacterial activity. These highly elevated concentrations of MeHgD at the intersurface between waters and sediments suggest a favorable methylation condition. Moreover, 相似文献
130.
Weihong WANG Min JI Yuwei XUE 《中国地球化学学报》2006,25(B08):167-168
In recent years, reclaimed wastewater as a water source for urban artificial landscape rivers is being rapidly developed in some coastal cities with limited water resource available in China. However, eutrophication occurs more often in the landscape waterbody with reclaimed wastewater than in natural rivers and lakes. The study of restoration and reconstruction of macrophytes, especially the submerged aquatic vegetation, is essential to inhibit eutrophication of reclaimed wastewater. This study investigated the seasonal variation of biomass of Ruppia maritima in the artificial landscape river using reclaimed wastewater as the only water source in Tianjin, China. It was found that there were two seasonal growth peaks of Ruppia maritima each year in the coastal reclaimedwastewater. The contents of nitrogen and phosphorus of Ruppia maritima varied with the season. 相似文献