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   557篇
  免费   78篇
  国内免费   138篇
测绘学   27篇
大气科学   111篇
地球物理   134篇
地质学   255篇
海洋学   77篇
天文学   24篇
综合类   49篇
自然地理   96篇
  2024年   1篇
  2023年   14篇
  2022年   35篇
  2021年   48篇
  2020年   32篇
  2019年   38篇
  2018年   18篇
  2017年   30篇
  2016年   48篇
  2015年   30篇
  2014年   36篇
  2013年   37篇
  2012年   28篇
  2011年   33篇
  2010年   32篇
  2009年   29篇
  2008年   16篇
  2007年   17篇
  2006年   18篇
  2005年   13篇
  2004年   15篇
  2003年   11篇
  2002年   17篇
  2001年   15篇
  2000年   10篇
  1999年   23篇
  1998年   18篇
  1997年   15篇
  1996年   13篇
  1995年   17篇
  1994年   11篇
  1993年   16篇
  1992年   9篇
  1991年   6篇
  1990年   10篇
  1989年   1篇
  1988年   2篇
  1987年   3篇
  1985年   2篇
  1984年   2篇
  1982年   2篇
  1979年   2篇
排序方式: 共有773条查询结果,搜索用时 15 毫秒
141.
介绍一种用于人卫激光测距仪的望远镜转台跟踪控制和数据处理系统。该系统具有卫星轨道计算、跟踪控制测量、数据采集和跟踪误差可实时修正以及跟踪状态在计算机屏幕实时显示等多种功能,使我国SLR网的观测水平跃上一个新的台阶。  相似文献   
142.
Research on processing geochemical data and identifying geochemical anomalies has made important progress in recent decades. Fractal/multi-fractal models, compositional data analysis, and machine learning (ML) are three widely used techniques in the field of geochemical data processing. In recent years, ML has been applied to model the complex and unknown multivariate geochemical distribution and extract meaningful elemental associations related to mineralization or environmental pollution. It is expected that ML will have a more significant role in geochemical mapping with the development of big data science and artificial intelligence in the near future. In this study, state-of-the-art applications of ML in identifying geochemical anomalies were reviewed, and the advantages and disadvantages of ML for geochemical prospecting were investigated. More applications are needed to demonstrate the advantage of ML in solving complex problems in the geosciences.  相似文献   
143.
144.
琼东南盆地深水区中央峡谷黄流组储层特征及主控因素   总被引:1,自引:1,他引:1  
李伟  左倩媚  张道军  朱继田  姚哲 《海洋学报》2016,38(11):117-124
在利用钻井和岩心资料基础上,结合铸体薄片、常规物性、压汞实验等分析测试手段,对琼东南盆地深水区中央峡谷黄流组储层特征及其影响因素进行了分析。研究表明,中央峡谷黄流组砂岩以岩屑石英砂岩为主,砂岩粒级较细且分选好,成熟度较高。原生粒间孔为主要孔隙类型,孔隙结构普遍为中孔细喉型。储层物性总体表现为中孔-特高孔、中渗-特高渗的特征。沉积微相和成岩作用是影响黄流组储层物性的主要因素,深水浊流沉积的水道砂岩是发育优质储层的前提,同时中央峡谷特殊的水深和温压条件是影响储层成岩作用的重要因素。海水深度大,而实际地层埋深浅,储层总体处于低温常压环境中,以致成岩作用程度普遍不强,但中央峡谷黄流组储层物性的内在差异仍主要受控于压实作用,中央峡谷自西向东,水深增加,实际地层埋深变浅,压实作用减弱,储层孔隙度和渗透率较好,总体上峡谷东部气层含气饱和度也较西部高。  相似文献   
145.
海岸带综合管理框架体系研究   总被引:10,自引:2,他引:10  
随着经济的发展,海岸带以其丰富而又独特的资源优势而成为开发的热点,环境压力随之出现由于海岩带生态系统的多样性和复杂性,原来的单因素管理已经不能适应发展的需要,必须要求一种全面的、综合的、系统的方法来进行管理,即海岸带综合管理(Integrated Coastal Zone Management,即ICZM)。本文通过对海岸带综合管理的概念分析,从环境经济学的角度分别对资源的功能、利用和价值进行了论  相似文献   
146.
本文利用大洋环流模式POP研究RCP4.5情景下21世纪格陵兰冰川不同的融化速率对全球及区域海平面变化的影响。结果显示:当格陵兰冰川的融化速率以每年1%增加时,全球大部分海域的动力和比容海平面变化基本不变,主要是由于格陵兰冰川在低速融化时并不会导致大西洋经向翻转流减弱。当格陵兰冰川的融化速率以每年3%和每年7%增加时,动力海平面在北大西洋副极地、大西洋热带、南大西洋副热带和北冰洋海域呈现出显著的上升趋势,这是因为格陵兰冰川快速融化导致大量的淡水输入附近海域,造成该上层海洋层化加强和深对流减弱,导致大西洋经向翻转流显著减弱;与此同时,热比容海平面在北冰洋、格陵兰岛南部海域和大西洋副热带海域显著下降,而在热带大西洋和湾流海域明显上升;此时盐比容海平面的变化与热比容海平面是反相的,这是由于大量的低温低盐水的输入,造成北大西洋副极地海域变冷变淡、大西洋经向翻转流和热盐环流显著减弱,引起了太平洋向北冰洋的热通量和淡水通量减少,导致了北冰洋海水变冷变淡,同时热带大西洋滞留了更多的高温高盐水,随着湾流被带到北大西洋,北大西洋副极地海域低温低盐的海水,被风生环流输运到副热带海域。  相似文献   
147.
The Tahe Oilfield is a complex petroleum reservoir of Ordovician carbonate formation and made up of spatially overlapping fracture-cavity units. The oilfield is controlled by a cave system resulting from structure-karst cyclic sedimentation. Due to significant heterogeneity of the reservoir, the distribution of oil and water is complicated. Horizontally, a fresh water zone due to meteoric water can be found in the north part of the Akekule uplift. A marginal freshening zone caused by water released from mudstone compaction is found at the bottom of the southern slope. Located in a crossformational flow discharge zone caused by centripetal and the centrifugal flows, the main part of the Tahe Oilfield, featuring high salinity and concentrations of CI^- and K^++Na^+, is favorable for accumulation of hydrocarbon. Three types of formation water in the Tahe Ordovician reservoir are identified: (1) residual water at the bottom of the cave after oil and gas displacement, (2) residual water in fractures/pores around the cave after oil and gas displacement, and (3) interlayer water below reservoirs. The cave system is the main reservoir space, which consists of the main cave, branch caves and depressions between caves. Taking Cave System S48 in the Ordovician reservoir as an example, the paper analyzes the fluid distribution and exploitation performance in the cave system. Owing to evaporation of groundwater during cross-formational flow, the central part of the main cave, where oil layers are thick and there is a high degree of displacement, is characterized by high salinity and Br^- concentration. With high potential and a long stable production period, most wells in the central part of the main cave have a long water-free oil production period. Even after water breakthrough, the water content has a slow or stepwise increase and the hydrochemistral characteristics of the produced water in the central part of the main cave are uniform. From the center to the edge of the main cave, displacement and enri  相似文献   
148.
选取第五次耦合模式比较计划(CMIP5)模式中较适宜于南海海表面温度(SST)模拟的加拿大地球系统模式(CanESM2),并获取其在IPCC RCP2.6、RCP4.5和RCP8.5温室气体排放情景下模拟的2006-2100年南海SST数据。基于南海诸岛珊瑚礁和线性回归方法分析了RCPs情景下的珊瑚礁区夏季SST上升趋势,并基于热周指数(DHW, Degree Heating Weeks)及年白化时间指数分析了RCPs情景下的南海诸岛珊瑚礁热压力临时避难所,主要得出以下结论:①RCPs情景下,明显变暖的珊瑚礁海域均为南沙群岛;②年白化时间不晚于全球珊瑚礁平均年白化时间的珊瑚礁像元占南海诸岛总珊瑚礁像元的比例,在RCP2.6、RCP4.5和RCP8.5情景下分别为17%、29%和42%,均分布在南沙群岛;③RCPs情景下,较高纬度的西沙群岛、中沙群岛和南沙群岛北部为未来南海诸岛珊瑚礁热压力临时避难所。  相似文献   
149.
Three approaches, i.e., the harmonic analysis (HA) technique, the thermal diffusion equation and correction (TDEC) method, and the calorimetric method used to estimate ground heat flux, are evaluated by using observations from the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) in July, 2008. The calorimetric method, which involves soil heat flux measurement with an HFP01SC self-calibrating heat flux plate buried at a depth of 5 cm and heat storage in the soil between the plate and the surface, is here called the ITHP approach. The results show good linear relationships between the soil heat fluxes measured with the HFP01SC heat flux plate and those calculated with the HA technique and the TDEC method, respectively, at a depth of 5 cm. The soil heat fluxes calculated with the latter two methods well follow the phase measured with the HFP01SC heat flux plate. The magnitudes of the soil heat flux calculated with the HA technique and the TDEC method are close to each other, and they are about 2 percent and 6 percent larger than the measured soil heat flux, respectively, which mainly occur during the nighttime. Moreover, the ground heat fluxes calculated with the TDEC method and the HA technique are highly correlated with each other (R2 = 0.97), and their difference is only about 1 percent. The TDEC-calculated ground heat flux also has a good linear relationship with the ITHP-calculated ground heat flux (R2 = 0.99), but their difference is larger (about 9 percent). Furthermore, compared to the HFP01SC direct measurements at a depth of 5 cm, the ground heat flux calculated with the HA technique, the TDEC method, and the ITHP approach can improve the surface energy budget closure by about 6 percent, 7 percent, and 6 percent at SACOL site, respectively. Therefore, the contribution of ground heat flux to the surface energy budget is very important for the semi-arid grassland over the Loess Plateau in China. Using turbulent heat fluxes with common corrections, soil heat storage between the surface and the heat flux plate can improve the surface energy budget closure by about 6 to 7 percent, resulting in a closure of 82 to 83 percent at the SACOL site.  相似文献   
150.
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