首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4604篇
  免费   828篇
  国内免费   625篇
测绘学   716篇
大气科学   571篇
地球物理   1547篇
地质学   1074篇
海洋学   564篇
天文学   426篇
综合类   426篇
自然地理   733篇
  2024年   6篇
  2023年   35篇
  2022年   102篇
  2021年   128篇
  2020年   148篇
  2019年   210篇
  2018年   145篇
  2017年   187篇
  2016年   179篇
  2015年   192篇
  2014年   229篇
  2013年   256篇
  2012年   274篇
  2011年   294篇
  2010年   226篇
  2009年   297篇
  2008年   256篇
  2007年   338篇
  2006年   331篇
  2005年   258篇
  2004年   237篇
  2003年   225篇
  2002年   176篇
  2001年   178篇
  2000年   144篇
  1999年   144篇
  1998年   169篇
  1997年   89篇
  1996年   93篇
  1995年   94篇
  1994年   92篇
  1993年   80篇
  1992年   54篇
  1991年   38篇
  1990年   25篇
  1989年   47篇
  1988年   21篇
  1987年   19篇
  1986年   10篇
  1985年   9篇
  1984年   5篇
  1983年   1篇
  1982年   4篇
  1981年   3篇
  1980年   3篇
  1979年   2篇
  1978年   1篇
  1954年   3篇
排序方式: 共有6057条查询结果,搜索用时 31 毫秒
151.
地图数字化位置误差的协方差函数   总被引:3,自引:1,他引:3  
针对数字化地图的精度 ,利用平稳随机过程的理论来估计位置数据的不确定性 ,提出了一套计算方法 ,主要内容包括运用平稳随机过程的各态历经性 ,对任意点坐标的X、Y按距离拟合求定其协方差 ,其特点是应用了统计估计原理 ,使得到的结果更为合理和简便。  相似文献   
152.
航天GPS接收机设计   总被引:1,自引:0,他引:1  
航天GPS接收机为航天器提供航迹、姿态、时问和相对距离等导航信息,提高航天嚣运行的自主性。文中介绍了清华宇航中。航天GPS接收的硬件和软件设计,给出测试结果和分析。  相似文献   
153.
Sampling and testing are conducted on groundwater depth and vegetation coverage in the 670 km2 of the Sangong River Basin and semi-variance function analysis is made afterwards on the data obtained by the application of geo-statistics. Results showed that the variance curve of the groundwater depth and vegetation coverage displays an exponential model. Analysis of sampling data in 2003 indicates that the groundwater depth and vegetation coverage change similarly in space in this area. The Sangong River Basin is composed of upper oasis, middle ecotone and lower sand dune. In oasis and ecotone, influenced by irrigation of the adjoining oasis, groundwater level has been raised and soil water content also increased compared with sand dune nearby, vegetation developed well. But in the lower reaches of the Sangong River Basin, because of descending of groundwater level, soil water content decreased and vegetation degenerated. From oasis to abandoned land and desert grassland, vegetation coverage and groundwater level changed greatly with significant difference respectively in spatial variation. Distinct but similar spatial variability exists among the groundwater depth and vegetation coverage in the study area, namely, the vegetation coverage decreasing (increasing) as the groundwater depth increases (decreases). This illustrates the great dependence of vegetation coverage on groundwater depth in arid regions and further implies that among the great number of factors affecting vegetation coverage in arid regions, groundwater depth turns out to be the most determinant one.  相似文献   
154.
利用SMART 1台阵三次地震记录拟合了各个测点在地震中的竖向地震动强度包络曲线及Amin 和Ang的强度包络函数中各模型参数值,分析了各模型参数的空间变化规律,建立了各模型参数随二维空间坐标及土层厚度变化的随机模型,为多点地震动合成中竖向强度包络函数的计算提供了理论依据。  相似文献   
155.
If the site at which receiver functions are constructed is filled by sediments, then the waveforms from these receiver functions are dominantly controlled by the sedimentary structures within the first few seconds after the direct P arrival. Based on this observation, waveform data collected at 44 temporary seismic stations have been used to image the sedimentary structure of the Bohai Bay Basin, a major continental petroliferous basin in Eastern China. An adapted hybrid global waveform inversion method was applied to the receiver functions to extract structural information beneath each of the stations. The derived S-velocity structure provides for the first time, a basin-scale seismic image of detailed sedimentary stratification. The sedimentary cover of the basin is about 2-12 km thick, consisting of Cenozoic, Mesozoic, and Paleozoic strata from top to bottom. The structural features presented in the S-velocity image coincide quite well with the depression-uplift type of tectonic system in the Bohai Bay Basin. The reconstructed morphology of the sedimentary layers provides seismological evidence for the two-stage evolution of the intracontinental basin that were caused by an intensive tectonic regime transition in late Mesozoic immediately following the lithospheric reforming of the Eastern China continent.  相似文献   
156.
Based on one type of practical Biot's equation and the dynamic-stiffness matrices of a poroelastic soil layer and half-space, Green's functions were derived for uniformly distributed loads acting on an inclined line in a poroelastic layered site. This analysis overcomes significant problems in wave scattering due to local soil conditions and dynamic soil-structure interaction. The Green's functions can be reduced to the case of an elastic layered site developed by Wolf in 1985. Parametric studies are then carried out through two example problems.  相似文献   
157.
Since the sign up of CTBT (Comprehensive Test Ban Treaty), the nuclear monitoring and distinguishing has gained great attention by the treaty countries. Seismology is one of the primary technical means available for monitoring compliance to a CTBT. However, there does not exist a single criterion, so far, that can effectively distinguish explorations from earthquakes. It has been known that source time function (abbreviated to STF) of an underground nuclear explosion contains important p…  相似文献   
158.
付兵先  唐飞  李天降 《岩土工程技术》2005,19(6):284-286,322
根据对一低液限粉土路基的现场工程地质调查及检测,确定了影响该路基长期稳定性的主要影响因素,并结合AHP法,应用两级模糊综合评判的方法对该路基的长期稳定性进行了评价。  相似文献   
159.
160.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号