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   109篇
  免费   31篇
  国内免费   34篇
测绘学   26篇
大气科学   56篇
地球物理   13篇
地质学   42篇
海洋学   6篇
天文学   2篇
综合类   21篇
自然地理   8篇
  2023年   2篇
  2022年   10篇
  2021年   9篇
  2020年   7篇
  2019年   14篇
  2018年   8篇
  2017年   3篇
  2016年   11篇
  2015年   14篇
  2014年   8篇
  2013年   6篇
  2012年   4篇
  2011年   3篇
  2010年   12篇
  2009年   6篇
  2008年   6篇
  2007年   4篇
  2006年   3篇
  2005年   12篇
  2004年   2篇
  2003年   6篇
  2002年   2篇
  2001年   2篇
  2000年   3篇
  1999年   3篇
  1998年   3篇
  1996年   1篇
  1995年   5篇
  1993年   2篇
  1992年   1篇
  1991年   1篇
  1983年   1篇
排序方式: 共有174条查询结果,搜索用时 500 毫秒
81.
本文向读者介绍一种高精度,低成本,具有自动峰值保持功能,且同时显示峰值和瞬时值两种状态数显表的设计实现方案。  相似文献   
82.
基于位姿传感器的户外ARGIS注册技术   总被引:1,自引:0,他引:1  
针对传统基于计算机视觉注册方法的局限性,提出并实践将GPS与位姿传感器进行组合应用于户外环境下增强现实地理信息系统的注册过程。设计了一套在户外注册单元硬件设备系统,推导阐释了实虚融合坐标转换关系,解决了不同设备间涉及的硬件配准集成问题。实验结果表明,该系统的实时性与准确性指标能够达到校园环境下户外注册的技术要求。  相似文献   
83.
Most vein minerals deposited in fractures of the Jialingjiang Formation from Libixia section,Hechan area include a large amount of saddle dolomite and accompanying celestite,calcite and fluorite.This study analyzed the nature,source,evolution of the fluids by plane-light petrography,fluid-inclusion methods,cathodoluminescence images,and stable isotopic compositions.The homogenization temperatures of two-phase aqueous fluid inclusions in dolomite range between100 and 270℃.Combined with theδ~(18)O data,it is suggested that the fluid responsible for the precipitation of fracture fillings haveδ~(18)O values between 10‰and 18‰(relative to SMOW).The saddle dolomite and the accompanying minerals were the result of activity of dense brines at elevated temperatures.Moreover,analysis shows that the fluid was derived from a mixture of marine-derived brine and deeper circulating flow.This fluid was enriched in Sr during diagenesis and formed celestite in fracture and for regional mineralization.Dissolution of saddle dolomite was attributed to the cooling of Mg/Ca-decreased fluids,which may relate to a leaching of gypsum to celestite in surrounding carbonates.  相似文献   
84.
Theoretical and Applied Climatology - The East Asian summer monsoon (EASM) can change the spatio-temporal distribution of aerosols by influencing the aerosol horizontal and vertical transports and...  相似文献   
85.
柯坪地区下志留统储层性质及控制因素   总被引:3,自引:0,他引:3  
野外露头浅钻取样分析发现,柯坪地区志留系下统柯坪塔格组的储层性质与塔北及塔中地区差别较大。柯坪地区的砂岩储层以粉细粒岩屑砂岩为主,处于晚成岩A2期,孔隙度主要为2%~6%,平均4.47%,渗透率主要为(0.01~0.1)×10-3μm2,平均0.06×10-3μm2,属于特低孔特低渗储层,而塔北及塔中地区以低孔低渗和中孔中渗为主。研究表明柯坪地区成岩压实、石英次生加大是储层物性的主控因素,储层经历长期深埋藏和短期浅埋藏,使成岩压实减孔率达30.4%;胶结作用所减少的孔隙量一般为1.5%~8%,致密胶结段可达10%~11%,石英次生加大所减少的孔隙量一般2%~4%,致密胶结段可达6%~8%;溶蚀作用及次生裂缝对储层物性改善不大,一般增孔量4%左右;成岩中后期强烈挤压构造运动对储层性质有重要影响。储层演化史表明晚二叠世、晚白垩世—早第三纪是油气聚集成藏期,随后遭后期构造运动破坏,油气逸散或发生氧化作用,柯坪塔格组含沥青砂岩即是这一过程的产物。  相似文献   
86.
A physical retrieval approach based on the one-dimensional variational(1 D-Var) algorithm is applied in this paper to simultaneously retrieve atmospheric temperature and humidity profiles under both clear-sky and partly cloudy conditions from FY-4 A GIIRS(geostationary interferometric infrared sounder) observations. Radiosonde observations from upper-air stations in China and level-2 operational products from the Chinese National Satellite Meteorological Center(NSMC)during the periods from December 2019 to January 2020(winter) and from July 2020 to August 2020(summer) are used to validate the accuracies of the retrieved temperature and humidity profiles. Comparing the 1 D-Var-retrieved profiles to radiosonde data, the accuracy of the temperature retrievals at each vertical level of the troposphere is characterized by a root mean square error(RMSE) within 2 K, except for at the bottom level of the atmosphere under clear conditions. The RMSE increases slightly for the higher atmospheric layers, owing to the lack of temperature sounding channels there.Under partly cloudy conditions, the temperature at each vertical level can be obtained, while the level-2 operational products obtain values only at altitudes above the cloud top. In addition, the accuracy of the retrieved temperature profiles is greatly improved compared with the accuracies of the operational products. For the humidity retrievals, the mean RMSEs in the troposphere in winter and summer are both within 2 g kg–1. Moreover, the retrievals performed better compared with the ERA5 reanalysis data between 800 h Pa and 300 h Pa both in summer and winter in terms of RMSE.  相似文献   
87.
INTRODUCTIONMyxosporeansareverycommonparasitesoffish .Theirseasonalfluctuationsinprevalenceandintensityofinfectionweredescribedbysomeauthors (Mitchell,1 989;Sitja BobadillaandAlvarez Pellitero,1 990 ;Cone ,1 994 ) .However,almostnorelatedinformationisavailableinChin…  相似文献   
88.
???t??????λ??????λ????????????GPS?????????????????д?????????????????????????????·????????????????λ????????????????з????????????λ??????????е?EW??NS???????????7.3??7.1??16.0 mm??????λ??EW??NS???????????5.0??5.2??14.7 mm????????????λ???????????λ?????1.9~2.3 mm?????ù????????????о??????λ??????????????????????????????????????е?????????????????????λ??????????0.1 Hz??????????????????????????0.1 Hz??????????????????????????λ??????????????????????????????????????????????????????????????????????????????????????????????????????????λ????????????????????????????????????????????????λ?????????????????????????????????  相似文献   
89.
We have investigated the contributions of three dominant macrophyte species, Deyeuxia angustifolia, Carex lasiocarpa, and Carex pseudocuraica (covering about 10 304 km2), to carbon (C), nitrogen (N), and phosphorus (P) stocks in the largest freshwater marsh (17 300 km2) in China for a 3‐year period (from 2002 to 2004). The monthly biomass, seasonal, and annual net primary productivity (NPP), and nutrient concentrations of three species were measured. All three plant species showed rapid growth in the rainy season. The maximum and minimum production rates in the freshwater marsh were ~36.19 and ~9.92 g m?2 day?1, respectively. The total NPP accounts 1900–2700 g m?2 year?1 in the studied area. Total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) concentrations in roots were higher than those in stem and leaf tissues. The vast beds of the three studied species comprise 80% of the grass covered marsh of Sanjiang plain, contributing annual nutrient stocks of ~10.99 × 106, ~788.36 × 103, and ~18.10 × 103 t (tonnes) for TOC, TN, and TP, respectively. Our results suggest that the nutrient bioaccumulation capacity in freshwater marshes depend mainly on plant species, which are decided by hydrological conditions. The nutrient stocks in the Sanjiang plain marsh have been greatly reduced because some of the area occupied by C. lasiocarpa was replaced by D. angustifolia as a result of succession caused by the changes of water table.  相似文献   
90.
自动与人工观测气压的差异及原因分析   总被引:6,自引:0,他引:6  
鞠晓慧  任芝花  曹丽娟  刘小宁 《气象》2010,36(1):104-110
利用全国373个基准基本站自动与人工平行观测期间的气压对比观测资料,进行了自动与人工观测气压的差异分析,重点从本站气压计算公式和环境温度方面分析了两种观测方式引起气压观测数据差异的原因。结果表明:(1)自动观测的气压值比人工观测气压值普遍偏低0.1~0.2 hPa。日最低气压差异最大,可达到0.34 hPa。自动与人工观测气压的差值有较明显的日变化和季节变化;(2)从分布区域看,自动与人工观测气压差异较大的区域位于海拔较高的西部地区,我国中东部地区则差异较小,绝大多数在0.2 hPa以内;(3)由于人工观测气压计算公式的问题,在2004年之前人工观测的本站气压值偏大,海拔高度越高的地方,偏大程度越高。统计结果还表明,30℃以上的高温环境和-30℃以下的低温环境,自动与人工观测气压差异明显。  相似文献   
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