全文获取类型
收费全文 | 2141篇 |
免费 | 570篇 |
国内免费 | 1110篇 |
专业分类
测绘学 | 35篇 |
大气科学 | 97篇 |
地球物理 | 358篇 |
地质学 | 2537篇 |
海洋学 | 289篇 |
天文学 | 402篇 |
综合类 | 63篇 |
自然地理 | 40篇 |
出版年
2024年 | 3篇 |
2023年 | 17篇 |
2022年 | 33篇 |
2021年 | 62篇 |
2020年 | 85篇 |
2019年 | 102篇 |
2018年 | 90篇 |
2017年 | 82篇 |
2016年 | 101篇 |
2015年 | 147篇 |
2014年 | 151篇 |
2013年 | 149篇 |
2012年 | 169篇 |
2011年 | 165篇 |
2010年 | 154篇 |
2009年 | 245篇 |
2008年 | 194篇 |
2007年 | 226篇 |
2006年 | 255篇 |
2005年 | 205篇 |
2004年 | 206篇 |
2003年 | 165篇 |
2002年 | 132篇 |
2001年 | 118篇 |
2000年 | 134篇 |
1999年 | 111篇 |
1998年 | 97篇 |
1997年 | 64篇 |
1996年 | 43篇 |
1995年 | 20篇 |
1994年 | 26篇 |
1993年 | 20篇 |
1992年 | 13篇 |
1991年 | 10篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有3821条查询结果,搜索用时 15 毫秒
61.
The chemical composition of fogwater has been studied in the city of Strasbourg (France) from 1990 to 1999. During these years, fogwater samples have been collected and analysed for major ions and trace metals. This paper reports on the analysis of the collected dataset. The analysis revealed a significant decrease in acidity of approximately one pH unit over the course of the study. This decrease in acidity appears to be linked to a decrease in SO2(g) and the resulting SO42−. Trace metal concentrations have also strongly decreased over the 10-year period. Pb concentrations, following the elimination of leaded gasoline, decreased by more than one order of magnitude. 相似文献
62.
63.
粉喷桩技术加固软土地基 总被引:3,自引:0,他引:3
简介了水泥粉体喷射搅拌加固软土地基的工作机理,结合沪蓉高速公路(沪宁段)地基处理实践,论述了粉喷桩加固软土地基的计算方法.采用粉喷桩加固软基,可加快路堤填土速率,铺筑路面后的工后沉降量能得到有效地控制,保证了工程质量. 相似文献
64.
本文以桥目标成本管理等现代化管理方法,系统地指出了降低灌注桩工程成本的途径.对于桥梁灌注桩以外的企业的经营活动同样具有重要的指导意义. 相似文献
65.
66.
67.
68.
螺旋CT三维重建在骨盆骨折中的应用 总被引:2,自引:0,他引:2
目的:探讨用螺旋CT三维重建评价骨盆骨折的临床应用价值。方法:收集骨盆骨折17例,采用螺旋CT三维重建检查。结果:17例检查均取得清晰立体图像,且可消除某一骨性结构,单独观察骨盆某一组成骨的骨折情况。结论:螺旋CT三维重建在骨盆骨折的诊断、手术方案的设计及教学等有较高价值。 相似文献
69.
液化场地桩-土-桥梁结构动力相互作用振动台试验研究进展 总被引:20,自引:3,他引:20
本文在全面归纳与总结液化场地桩-土-桥梁结构动力相互作用振动台试验及与之相关领域的国内外研究进展基础上,直接针对我国桥梁工程中的主要震害问题,提出在我国开展液化场地桩-土-桥梁结构动力相互作用振动台试验研究的必要性,并阐述作者对液化场地桩-土-张桥梁结构动力相互作用振动台试验中若干问题的认识。 相似文献
70.
Abstract. A simple, fast, moment-tensor inversion method using bandpass-filtered P-amplitudes was used to study the moment-tensor statistics of Long Valley caldera microearthquakes. The events were recorded in the summer of 1997, during a swarm in the caldera. The swarm was associated with geodetic extension, uplift, and subsequent moderate earthquake activity. The moment tensor solutions for 1,993 events were calculated using the new method. The majority of the resulting focal mechanisms appear to be explained in terms of double couple mechanisms. Since some events did exhibit considerable deviation from double-couples, the moment data were studied for their statistical significance. The moments of the actual data were compared to the moments of synthetic data with varying degrees of random noise in their spectra. The results of this study suggested that unless data from more than 20 stations are used and the earthquake epicenter is located inside or very close to the network area, moment-tensor inversion does not correctly resolve the non-double-couple components of microearthquakes. Analysis of the inversion residuals shows that the average noise in the P-wave spectra was close to 20%. The fluctuations of the volumetric components of the moment-tensor are in good agreement with those of the synthetic pure double-couples with 20% of added noise. Thus the moment-tensor statistics suggests that little if any volume change is required to explain the observed seismic energy release in the swarm. However, the statistics do show that a significant compensated-linear-vector-dipole component maybe present in the bulk of the seismicity. Given the network used in this study, such a component could not be precisely resolved for individual earthquakes. This possibility deserves further investigation because of its bearing on the nature of fluid-fault-earthquake processes in swarms. 相似文献