全文获取类型
收费全文 | 4870篇 |
免费 | 973篇 |
国内免费 | 1254篇 |
专业分类
测绘学 | 180篇 |
大气科学 | 1174篇 |
地球物理 | 1527篇 |
地质学 | 2244篇 |
海洋学 | 606篇 |
天文学 | 226篇 |
综合类 | 522篇 |
自然地理 | 618篇 |
出版年
2024年 | 19篇 |
2023年 | 87篇 |
2022年 | 207篇 |
2021年 | 272篇 |
2020年 | 174篇 |
2019年 | 257篇 |
2018年 | 287篇 |
2017年 | 246篇 |
2016年 | 293篇 |
2015年 | 239篇 |
2014年 | 330篇 |
2013年 | 260篇 |
2012年 | 292篇 |
2011年 | 295篇 |
2010年 | 297篇 |
2009年 | 272篇 |
2008年 | 274篇 |
2007年 | 251篇 |
2006年 | 222篇 |
2005年 | 185篇 |
2004年 | 143篇 |
2003年 | 178篇 |
2002年 | 150篇 |
2001年 | 130篇 |
2000年 | 161篇 |
1999年 | 191篇 |
1998年 | 193篇 |
1997年 | 171篇 |
1996年 | 152篇 |
1995年 | 168篇 |
1994年 | 134篇 |
1993年 | 135篇 |
1992年 | 95篇 |
1991年 | 56篇 |
1990年 | 51篇 |
1989年 | 51篇 |
1988年 | 44篇 |
1987年 | 42篇 |
1986年 | 26篇 |
1985年 | 14篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1958年 | 4篇 |
排序方式: 共有7097条查询结果,搜索用时 20 毫秒
991.
本文以汶川地震地表形变带的实地测量数据为基础,结合沿实测地震地表变形剖面建筑物破坏情况的调查与测量,分析了不同地震地表变形类型及其建筑物破坏特征,定量化地讨论了地表变形梯度与建筑物破坏程度间的关系。提出无论地震地表变形表现为何种类型的断层陡坎,地表破裂、强变形局部化在宽10~30m的地表破裂带内;建筑物受损情况最直接的影响是建筑物所处地点的地表变形梯度,地表变形梯度大于0.1的地段,建筑物均完全被摧毁;地表变形梯度在0.07~0.1间的地段,建筑物遭受严重损坏,产生倾斜及强烈变形等;地表变形梯度在0.03~0.07之间的地段,建筑物可能受到中度损坏,产生倾斜及变形等,具有抗震设防能力的构建筑物一般不会倒塌;地表变形梯度小于0.03的地段具有抗震设防能力的构建筑物一般只会受到轻的损坏或基本完好。 相似文献
992.
利用丹东地区1951—2009年4个测站逐日降水资料,对丹东地区暴雨变化进行了分析。结果表明:丹东地区年暴雨日数和暴雨量呈减少趋势,汛期洪涝贡献率趋势变化不明显;2001—2009年6月份暴雨日数明显增多,7月份暴雨日数偏少,暴雨初期和终期提前。 相似文献
993.
Characteristics of great geomagnetic storms during solar cycle 23 were statistically investigated. Firstly, we focused on the uniqueness of solar cycle 23 by analyzing both the great storm number and sunspot number from 1957 to 2008. It was found that the relationship between the sunspot number and great storm number weakened as the activity of the storms strengthened. There was no obvious relationship between the annual sunspot number and great storm number with Dstxi≤-300 nT. Secondly, we studied the relationship between the peak Dst and peak Bz in detail. It was found that the condition Bz≤-10 nT is not necessary for storms with Dst≤-100 nT, but seems necessary for storms with Dst≤-150 nT. The duration for Bz≤-10 nT has no direct relationship with the giant storm. The correlation coefficient between the Dst peak and Bz peak for the 89 storms studied is 0.81. After removing the effect of solar wind dynamic pressure on the Dst peak, we obtained a better correlation coefficient of 0.86. We also found the difference between the Dst peak and the corrected Dst peak was proportional to the Dst peak. 相似文献
994.
针对卫星激光数据处理算法这一难题,分析了COMPASS系统GEO卫星激光观测数据的质量,讨论了反求工程和计算机视觉中的曲线识别与激光观测数据预处理的异同,提出了基于点云曲线辨识的卫星激光数据预处理算法。该算法将卫星激光观测数据预处理视为有序带噪声的空间曲线重建问题,利用COMPASS系统多圈GEO卫星实测数据进行验证。结果表明:该方法与常用算法一致率在85%以上,能够实现激光观测数据的自动处理与满足导航系统的需要。 相似文献
995.
天津市地震前兆台网的运行监控与维护管理 总被引:8,自引:0,他引:8
介绍天津市地震前兆台网的基本概况以及前兆台网部的职责任务;阐述仪器设备运行监控、观测数据质量监控的方式与方法;总结在仪器设备、技术系统维护过程中解决的一些关键技术问题;最后提出了关于仪器和软件系统的一些问题与建议。 相似文献
996.
临汾台摆式倾斜仪平行观测的差异性特征及其观测布局建议 总被引:1,自引:1,他引:0
根据临汾地震台石英摆、垂直摆、宽带垂直摆3套摆式倾斜仪器的观测资料,对山西中南部几次中等地震进行分析,发现在地震前各仪器同测向曲线有一定的异常反映,但异常并非呈相关一致性变化,有的还表现出明显的差异性特征;在同一台址条件下,异常的差异性与仪器的工作周期、动态响应范围、记录频段等有关;河津地震前后宽带垂直摆倾斜仪记录到的连续阶跃扰动(错位掉格)可能是慢地震现象,由此说明了宽频段仪器的优越性及发展性;建议在形变台网观测中,同一台站应建立宽频或多种同类型的形变观测仪器,组成尽量具有低、中、高频段的全面观测系统,这可能对于扑捉近震的短临前兆异常有实效意义. 相似文献
997.
???????????????????????VTEC????????????????????????????????????????????????????е?GPS??????????3С???????????????????????????????????????Ч??С???????? 相似文献
998.
????????????д?????????????????????????ζ?????????(UPF)?????????????????????????μ???????????ζ?????????(AR??UPF)???÷??????÷???????????????????????????????UKF??????????????????????Э????????????????????????????????·????????Ч?????????????????????????????? 相似文献
999.
The wave crest is an important factor for the design of both fixed and floating marine structures. Wave crest height is a
dominant parameter in assessing the likelihood of wave-in-deck impact and resultant severe damage. Many empirical and theoretical
distribution functions for wave crest heights have been proposed, but there is a lack of agreement between them. It is of
significance to develop a better new nonlinear wave crest height distribution model. The progress in the research of wave
crest heights is reviewed in this paper. Based on Stokes’ wave theory, an approximate nonlinear wave crest-height distribution
formula with simple parameters is derived. Two sets of measured data are presented and compared with various theoretical distributions
of wave crests obtained from nonlinear wave models and analysis of the comparison is given in detail. The new crest-height
distribution model agrees well with observations. Also, the new theoretical distribution is more accurate than the other methods
cited in this paper and has a greater range of applications. 相似文献
1000.
Community structure and seasonal variation of soil arthropods in the forest-steppe ecotone of the mountainous region in Northern Hebei,China 总被引:1,自引:0,他引:1
Soil fauna have been receiving more and more attention because they play an important role in nutrient cycling. However, there
is a lack of information on soil arthropods in the forest-steppe ecotone in the mountainous region of northern Hebei, which
makes it difficult to meet the need of protecting biodiversity in this area. Soil arthropod communities were investigated
in the forest-steppe ecotone in northern Hebei province to provide basic information on changes in mountain soil fertility,
which could promote the development of soil arthropod communities in mountain ecotones. From the preliminary identification,
a total of 7994 individual soil arthropods were collected, which belonged to 25 groups, 6 classes and 24 orders. Acarina, Hymenoptera and Collembola were the dominant groups in the ecotone. The number of Acarina was higher than Collembola, and this phenomenon was obviously different from other areas in the same climate zone. The increased abundance of rare groups
in the Forest zone with the richer vegetation, higher arthropod abundance and more substantial litter depth, could be interpreted
as a reaction to the suitable soil environment and food supply. And these rare groups were sensitive to environmental changes,
which could be regarded as biotic indicators for evaluating soil quality. The analysis of community diversity showed that
the abundance index (d), the Shannon-Wiener index (H′), the evenness index (J) and the density-group index (DG) were significantly higher in the forest zone, lower in the forest-steppe zone, and lowest in the meadow-steppe zone. Seasonal
variations in community composition correlated with changes in average air temperature and precipitation in this ecotone.
Groups and individuals of soil arthropod communities in the three zones were present in greater numbers in the middle of the
rainy season than in the early or late periods of the rainy season as a whole. At the same time, seasonal changes in soil
arthropod communities from different plots were also influenced by habitat condition. 相似文献