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   415篇
  免费   62篇
  国内免费   95篇
测绘学   20篇
大气科学   106篇
地球物理   85篇
地质学   223篇
海洋学   29篇
天文学   26篇
综合类   24篇
自然地理   59篇
  2023年   6篇
  2022年   15篇
  2021年   17篇
  2020年   19篇
  2019年   15篇
  2018年   18篇
  2017年   20篇
  2016年   15篇
  2015年   15篇
  2014年   16篇
  2013年   19篇
  2012年   20篇
  2011年   26篇
  2010年   17篇
  2009年   16篇
  2008年   21篇
  2007年   14篇
  2006年   9篇
  2005年   13篇
  2004年   16篇
  2003年   8篇
  2002年   13篇
  2001年   11篇
  2000年   22篇
  1999年   24篇
  1998年   24篇
  1997年   24篇
  1996年   17篇
  1995年   14篇
  1994年   21篇
  1993年   11篇
  1992年   8篇
  1991年   9篇
  1990年   6篇
  1989年   6篇
  1988年   4篇
  1987年   3篇
  1986年   2篇
  1985年   5篇
  1984年   2篇
  1983年   1篇
  1982年   3篇
  1978年   1篇
  1971年   1篇
  1938年   1篇
  1936年   4篇
排序方式: 共有572条查询结果,搜索用时 921 毫秒
241.
Knowledge Sharing and Service is one effective way to eliminate knowledge poverty and promote social development. Existing knowledge sharing and service is mainly provided in some organizations or specific social groups. Besides, a knowledge sharing and service system about geography, natural resources and ecology has not been reported. We proposed a public welfare professional knowledge-sharing and service platform for all members of society in geography, natural resources and ecology. The construction of a knowledge-sharing and service platform is based on five aspects of work: analysis of user requirements, setting standards and drafting policies, aggregating knowledge resources, the technical realization and the maintenance of service. Knowledge resources can be aggregated by using a “two-step” strategy. A knowledge-sharing and service system can be implemented by using “four-tier” structures that are comprised of resources, resource access, application and service, based on the Hadoop-distributed cluster architecture. It has been proven that adhering to the idea of co-building and co-sharing, and using the mechanism of “payment is equal to benefit” can effectively promote the gathering of knowledge resources, and arouse the enthusiasm of all members of society to participate in knowledge sharing and service, to achieve the objective of narrowing the knowledge gap between social groups.  相似文献   
242.
Using counties as the basic analysis unit, this study established an evaluation index system for farmland function (FF) from economic, social, and ecological perspectives. The method combining entropy weighting and multiple correlation coefficient weighting was adopted to determine the weights, and the FF indices were calculated for each county. Subsequently, the spatio-temporal characteristics of farmland function evolution (FFE) were analyzed and the coupled relationships between the sub-functions were explored based on a coupling coordination model. At the same time, the dynamic mechanism of FFE was quantitatively analyzed using a spatial econometric regression analysis method. The following major conclusions were drawn: (1) The farmland economic function generally exhibited a declining trend during 1990–2010, and it is essential to point out that it was stronger in underdeveloped and agriculture-dominated counties, while it continuously weakened in developed areas. Farmland social function decreased in 60.29% of the counties, whereas some counties, which were mostly located in north of Zhengzhou and west of Dezhou and Cangzhou, Yantai, and Weihai, clearly increased. A dramatic decline in farmland ecological function occurred around Beijing, Tianjin, and Jinan. Areas located in the northern part of Henan Province and the central part of Shandong Province saw an increase in ecological function. (2) There was a significant spatial difference in the coupling degree and coordination degree of the sub-functions, and the decoupling phenomenon highlighted this. The changes in social function and ecological function lagged behind economic function in developed areas, but these were highly coupled in some underdeveloped areas. (3) FFE in the Huang-Huai-Hai Plain (HHHP) is resulted from the comprehensive effects of regional basic conditions and external driving factors. Furthermore, the transitions of population and industry under urbanization and industrialization played a decisive role in the evolution intensity and direction of farmland sub-systems, including the economy, society, and the ecology. According to the results mentioned above, promoting the transformation from traditional agriculture to modern agriculture should be regarded as an important engine driving sustainable development in the HHHP. Taking different regional characteristics of FFE into account, differentiated and diversified farmland use and management plans should be implemented from more developed urban areas to underdeveloped traditional agricultural areas.  相似文献   
243.
As the largest developing country in the world, China’s rural areas face many poverty- related issues. It is imperative to assess poverty dynamics in a timely and effective manner in China’s rural areas. Therefore, we used the poverty gap index to investigate the poverty dynamics in China’s rural areas during 2000–2014 at the national, contiguous poor areas with particular difficulties and county scales. We found that China made significant achievements in poverty alleviation during 2000–2014. At the national scale, the number of impoverished counties decreased by 1428, a reduction of 97.28%. The rural population in impoverished counties decreased by 493.94 million people or 98.76%. Poverty alleviation was closely associated with economic development, especially with industrial development. Among all 15 socioeconomic indicators, the industrial added value had the highest correlation coefficient with the poverty gap index (r = –0.458, p<0.01). Meanwhile, the inequality of income distribution in the out-of-poverty counties has been aggravated. The urban-rural income gap among the out-of-poverty counties increased by 1.67-fold, and the coefficient of variation in rural per-capita income among the out-of-poverty counties also increased by 9.09%. Thus, we argued that special attention should be paid to reducing income inequality for sustainable development in China’s rural areas.  相似文献   
244.
科学数据共享实践:以国家地球系统科学数据中心为例   总被引:2,自引:0,他引:2  
地球系统科学是一门综合性交叉学科,起源于全球变化研究,受益于遥感技术进步,现已进入大数据时代,人工智能技术成为解决地球系统科学前沿问题的新手段。科学数据共享是推动科学发展、提升数据价值的关键,经过长期的探索和实践,全球已形成完善的数据资源管理政策与机制、持续的数据共享服务体系、多元化的科学数据整合模式,并且新的理念不断推动数据共享创新发展,其中“可发现、可访问、可互操作和可重用”原则和数据出版备受推崇。我国颁布了国家层面的政策法规,着重推动国家级科学数据中心建设、科技项目数据资源汇交及数据出版。借鉴国外数据共享经验,结合国内实际发展情况,我国探索出具有中国特色的地球系统科学数据资源分类体系,在元数据、分布式互操作、大数据分析和共享服务等关键技术方面都取得了重大突破。本文以国家地球系统科学数据中心为例,系统梳理了国内地球系统科学领域的数据共享实践进展,详细介绍了国家在地球系统科学领域的数据共享实践及其成效。国家地球系统科学数据共享工作已探索形成成熟稳定的运行服务机制、研制出适用于多源分散地球系统科学数据的标准体系、 建成多学科多时空尺度的地球系统科学数据库群、自主研发海量异构数据共享网络技术体系与服务系统,促进了地球系统科学的科学发展,同时也推动了数据共享理念的传播与推广。然而,数据孤岛现象、共享服务系统标准化程度低、系统技术标准未对接国际规范等问题仍然较为突出,阻碍了地球系统科学数据开放与共享。未来,随着共享个性化需求被激活,定制化的“数据+知识”服务有望成为主流趋势,将给数据共享带来新的机遇和挑战。  相似文献   
245.
罗霞  屠周益  牛萍  田德宝 《气象科技》2016,44(2):344-346
建筑物内低压电源系统电涌保护器(SPD)设计和安装等依据的技术规范为GB 50057-2010和GB 50343-2012。由于两个规范对SPD的相关规定存在较大差异,导致防雷工作中SPD设计、安装等标准无法统一。从SPD术语、安装位置、放电电流、级别设置相关条款进行对比分析,发现:1SPD术语仅翻译不同。2GB 50343对SPD安装位置要求较准确;GB 50057关于SPD放电电流的规定更合理。3SPD级别设置的计算方法不同。  相似文献   
246.
247.
We explore the use of high-rate GPS, strong-motion records and their joint use for earthquake monitoring, the data collected during 2011 Mw 9.0 Tohoku earthquake was studied. We compared the recorded co-seismic movement, analyzed the displacements in both time-frequency domain. Meanwhile, the comparison of P wave detection was shown and the dynamic velocity waves were discussed. The results suggest that the GPS-only solution is good for low-frequency signal, and the strong-motion-only solution is good for high-frequency signal, thus, the integration of two datasets best complement the advantages of each, more details of co-seismic motions and broader frequency band of seismic signals. This is crucial for earthquake monitoring and early warning.  相似文献   
248.
The complementary advantages of GPS and seismic measurements are well recognized in seismotectonic monitoring studies. Therefore, integrated processing of the two data streams has been proposed recently in an attempt to obtain accurate and reliable information of surface displacements associated with earthquakes. A hitherto still critical issue in the integrated processing is real-time detection and precise estimation of the transient baseline error in the seismic records. Here, we report on a new approach by introducing the seismic acceleration corrected by baseline errors into the state equation system. The correction is performed and regularly updated in short epochs (with increments which may be as short as seconds), so that station position, velocity, and acceleration can be constrained very tightly and baseline error can be estimated as a random-walk process. With the adapted state equation system, our study highlights the use of a new approach developed for integrated processing of GPS and seismic data by means of sequential least-squares adjustment. The efficiency of our approach is demonstrated and validated using simulated, experimental, and real datasets. The latter were collected at collocated GPS and seismic stations around the 4 April 2010, E1 Mayor-Cucapah earthquake (Mw, 7.2). The results have shown that baseline errors of the strong-motion sensors are corrected precisely and high-precision seismic displacements are real-timely obtained by the new approach.  相似文献   
249.
在华北地台西缘与秦祁地槽东部的国家湾盆地和固关盆地中下白垩统砂岩中赋存铀矿。以长石砂岩为主的铀矿源层和灰色层为主的积铀层,构成了双层结构的特征。通过对901砂岩型铀矿床地质及水文地质因素的分析,认为地浸的有利条件是具备的,可用地下浸出法采铀。为该区开发提供了新的思路,前景乐观。  相似文献   
250.
基于GIS的青藏高原人口统计数据空间化   总被引:93,自引:6,他引:87  
根据2000年第5次全国人口普查数据分析,西藏、青海2省区各市县平均人口密度与海拔高度、土地利用、主要道路有较强的相关关系,河流水系对居民点分布的影响较为明显,而居民点是人口分布的重要指示因子。以GIS软件为工具,通过较为客观的方式赋予各影响因子人口分布影响权重,运用多源数据融合技术进行了人口统计数据的空间化。结果显示,通过数据融合产生的人口密度与各市县实际人口密度的相关系数大于0.80,与试验区各乡镇的实际人口密度的相关系数大于0.75。最终生成的栅格人口密度数据既与各市县统计型人口数据保持一致,又反映了各市县内部人口分布的空间变化。  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