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   812篇
  免费   120篇
  国内免费   210篇
测绘学   66篇
大气科学   95篇
地球物理   117篇
地质学   574篇
海洋学   134篇
天文学   22篇
综合类   40篇
自然地理   94篇
  2024年   5篇
  2023年   9篇
  2022年   16篇
  2021年   29篇
  2020年   23篇
  2019年   38篇
  2018年   27篇
  2017年   29篇
  2016年   35篇
  2015年   41篇
  2014年   55篇
  2013年   75篇
  2012年   64篇
  2011年   72篇
  2010年   58篇
  2009年   46篇
  2008年   59篇
  2007年   69篇
  2006年   55篇
  2005年   51篇
  2004年   31篇
  2003年   35篇
  2002年   30篇
  2001年   25篇
  2000年   19篇
  1999年   24篇
  1998年   20篇
  1997年   11篇
  1996年   14篇
  1995年   8篇
  1994年   19篇
  1993年   9篇
  1992年   11篇
  1991年   5篇
  1990年   6篇
  1989年   3篇
  1988年   2篇
  1987年   6篇
  1986年   2篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
  1981年   1篇
  1979年   1篇
排序方式: 共有1142条查询结果,搜索用时 640 毫秒
941.
The article reviews some learning objectives in the Norwegian core curriculum for four subjects in compulsory school education, namely science, social science, mathematics, and physical education. The subjects are examined with respect to maps, including map use, digital mapping tools, coordinate systems, and scales. Primary and lower secondary school pupils’ knowledge of maps was investigated before and after a group mapping project. Among three indicators, two showed statistically significant improvements in the pupils’ level of confidence when studying data with the aid of maps. The learning outcome is discussed in an inquiry-based and interdisciplinary pedagogical frame. In addition, the findings reveal that the four subjects have significantly different objectives and rates of progression regarding maps and map use. Based on the results of the group project, the author argues in favour of bringing the four curricula into more parallel learning curves. In order to facilitate interdisciplinary projects, he considers it would be interesting to coordinate the different subject curricula in the future, and recommends that attempts should be made to harmonise competence objectives that are part of several subjects in order to facilitate interdisciplinary projects in the next revision of the core curriculum in Norway.  相似文献   
942.
Experimental studies on pathway patterns of secondary oil migration   总被引:2,自引:1,他引:1  
The oil migration patterns in porous medium are discussed based on the results of diphasic expulsing experiments. In the experiments, dyed kerosene was used as expulsing phase to expulse water saturated in a glass cylinder filled with sorted glass beads. Two series of experiments were done: one with different initial oil column heights and the other with variable oil injection rates. Three secondary migration patterns, including stable displacement pattern, fingering pattern and stringing pattern may be recognized in each series of experiments. Two classic dimensionless parameters, the modified Bond number and the Capillary number, were used to construct a phase diagram that may characterize the patterns. A new method was proposed to calculate the Darcian velocity of moving kerosene in the cylinder when only buoyancy force acts. It is found that when Darcian velocity is used to get the two dimensionless parameters, the data from both series of experiments, as well as those obtained from literatures, may be reasonably drawn in a phase diagram to identify the three migration patterns.  相似文献   
943.
In order to study the spatial-temporal change and environmental management of regional karst LUCC (land use and land cover change) and its causative environmental effect-rocky dcsertification by integrating qualitative analysis and quantitative analysis, and relying on RS, GIS and GPS (3S) techniques, karst land rocky derification dynamic monitoring and visualization management information system (KLRD.DMVM.IS) is framed, which includes design aim and structure model, function design, database design and model system design. The model system design gives priority to dynamic monitoring, drive force diagnosis, comprehensive evaluation and decision support of karst rocky desertification. From the viewpoint of model type, mathematic expression and its meaning, the dynamic monitoring models are concretely devised to reflect the spatial and temporal changing features and the trend of karst LUCC and rocky desertification. Taking Du‘an Yao Autonomic County of Guangxi as an example, the KLRD.DMVM.1S is systematically analyzed in the application of the process and trend of karst LUCC and rocky desertiflcation in Du‘an County, and it provides the technical support for the study on karst land rocky desertification.  相似文献   
944.
(903) Nealley moves on an orbit of low eccentricity with a mean motion that is slightly larger than the 2/1 value of resonance. This orbit and some related fictious orbits are studied by numerical integrations of the four-body problem Sun-Jupiter-Saturn-asteroid over an interval of 110000 yr. The author's experience on related cases of resonance allows a study of the variation of suitably defined orbital parameters. The long-term evolution of the orbits is compared with earlier predictions. Some of the librating orbits are temporarily captured in a secondary resonance that refers to three-dimensional motion and is demonstrated by a special example.  相似文献   
945.
利用Visual Basic对象嵌入技术(OLE Automation),将MapInfo作为一个对象使用,应用GIS空间分析和数据处理等功能,对地理信息系统平台MapInfo进行二次开发,实现了对滑坡快速有效的统计、分析和预测,并建立了区域滑坡稳定的综合判定标准。通过友好的人机交互界面实现对地震滑坡稳定性分析和综合评价,提高了地震诱发滑坡灾害稳定性分析的可操作性和空间地理信息的传输能力。  相似文献   
946.
The spatial thinking skills and attitudes of geography majors were compared with those of future teachers majoring in elementary education and secondary social studies education. Scores were obtained for each group on two measures: the spatial skills test and the attitude toward spatial thinking inventory. Mean differences were examined based on five factors: major, gender, travel experience, geography courses, and experience using geographic information systems (GIS). For both outcome measures, results showed that the mean scores for elementary education majors were significantly lower than scores from secondary social studies majors and geography majors. Geography majors outperformed both groups of education majors on both measures. Implications for the preparation of geography teachers are discussed.  相似文献   
947.
The increased opportunity to choose one’s school of preference has been raised as a key factor in many countries to promote equal opportunities and a higher quality of education. This has been endorsed by policymakers who assume that students make well-informed rational choices and that students stress only academic quality when deciding which school to attend. If this is true, it will benefit schools of high academic quality, rendering improved school quality overall. To date, little research has examined the validity of these assumptions despite the profound effects they have had for changing the school systems in many countries. This article describes an experiment to investigate the relative importance of factors in school choice. The aim is to test the validity of the theoretical assumptions that guided the school choice reforms in Sweden. Specifically, we draw on experimental data from prospective upper secondary school students in Sweden to contrast the principal school quality attributes behind the policy change (knowledge reputation and program feasibility), with the presence of friends and geographical attributes such as distance, location and accessibility, while controlling for individual characteristics. The results have important policy implications as they show that geographical factors are highly relevant for school choice preferences. In contrast to the reforms’ intentions, geography appears to have become more important than ever before. The findings thus reveal significant flaws in the assumptions that motivated the school choice policy reform.  相似文献   
948.
15口井岩芯和众多储层实验资料研究表明,沾化凹陷北部陡坡带始新统沙河街组扇三角洲砂体由长石砂岩、岩屑长石砂岩等构成。在埋藏成岩演化过程中,该砂岩储层经历了多种成岩作用,现储层埋深1800~4000m,处于中成岩演化阶段,总体形成了中孔中渗储层(平均孔隙度为19.7%,平均渗透率为111.5×10-3μm2)。但在成岩演化过程中,溶蚀作用对于改善储层质量起到了重要作用,主要在2800~3300m深度段,有机酸对长石颗粒的溶蚀,形成的粒间和粒内孔隙不仅增加了孔隙度,而且提高了储层渗透率,改善了储层质量(孔隙度可达到30%,渗透率达到1000×10-3μm2)。可以看出,确定次生孔隙发育深度段有利于有利储层和油气富集层段预测。  相似文献   
949.
2014年2月4—7日河南暴雪过程的环流特征及其持续原因   总被引:1,自引:0,他引:1  
顾佳佳  武威 《湖北气象》2015,(2):117-125
利用常规观测资料、地面自动站资料、NCEP 1°×1°间隔6 h再分析资料、云顶亮温(TBB)资料以及多普勒天气雷达资料,对2014年2月4—7日河南省大范围暴雪过程的环流特征及其持续原因进行了分析。在此基础上,总结出此次暴雪过程的三维空间结构特征。结果表明:河套地区低槽东移发展配合近地层冷空气活动,有利于冷暖气流在黄淮地区交汇,是暴雪发生的大尺度环流背景,干冷东北急流与强盛暖湿急流在暴雪区交汇,为暴雪提供了有利的水汽和动力条件;从卫星云图和雷达回波变化特征看,暴雪发生在TBB≤-30℃的冷云团边缘等值线梯度最大处,雷达回波的移动与强度变化与降雪落区和强度实况相吻合;持续的水汽辐合为暴雪提供了充沛的水汽条件;干冷空气从低层南下导致暖湿气流抬升形成强烈上升运动,两支干冷下沉气流在对流层中层(600—400 h Pa)形成明显干层,致使底层形成饱和层,导致大量能量堆积;冷暖空气交汇处出现明显锋生,形成垂直于锋面的次级环流,导致上升运动进一步增强,对暴雪维持和发展具有重要作用。  相似文献   
950.
随着经济高速发展和城市的快速扩张,城市河道污染问题越来越严重,已经影响到人们的正常生产生活;城市河流污染治理已列入政府工作日程.文中结合某城市次级河流入河排污口污染源勘查工作,对排水管线污染源头进行了追踪调查和测量,并以GIS对成果进行直观展示,为城市管理者规划提供技术支持.  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