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   364篇
  免费   59篇
  国内免费   44篇
测绘学   82篇
大气科学   95篇
地球物理   126篇
地质学   101篇
海洋学   18篇
天文学   1篇
综合类   22篇
自然地理   22篇
  2023年   2篇
  2022年   4篇
  2021年   9篇
  2020年   10篇
  2019年   10篇
  2018年   6篇
  2017年   17篇
  2016年   11篇
  2015年   17篇
  2014年   22篇
  2013年   29篇
  2012年   15篇
  2011年   26篇
  2010年   21篇
  2009年   31篇
  2008年   24篇
  2007年   34篇
  2006年   28篇
  2005年   14篇
  2004年   23篇
  2003年   14篇
  2002年   11篇
  2001年   16篇
  2000年   14篇
  1999年   10篇
  1998年   4篇
  1997年   9篇
  1996年   6篇
  1995年   6篇
  1994年   6篇
  1993年   6篇
  1992年   2篇
  1991年   3篇
  1990年   3篇
  1989年   3篇
  1988年   1篇
排序方式: 共有467条查询结果,搜索用时 31 毫秒
91.
测量数据的质量控制理论探讨   总被引:4,自引:1,他引:4  
欧吉坤 《测绘工程》2001,10(2):6-10
从可靠性和粗差检测两方面分析了质控制理论研究的进展;介绍了新的统一的可靠性指标,它完全由系统的结构决定,不包含受主观因素影响的概率因子(非中心参数λ0)。详细介绍了拟准检定法的原理和实施办法,特别是初选拟准观测的一些技巧,通过一个算例比较了拟准检定法与假设检验的三种形式的计算结果,后者存在部分粗差不能发现的问题,而前者能发现全部粗差,效果较好。  相似文献   
92.
Quality Mapping of Surface Water and Assessment of Treated and Untreated Waste-water Inputs into the Rhine and Main River Based on Microbial Enzyme Activities Microbial enzyme activities are used for an extension of the traditional quality mapping of surface water. In the following study, the enzymatic parameters were proved and validated on samples from various creeks and rivers in Baden-Württemberg and on samples gathered from the Rhine and Main Rivers (Germany). The test parameters should also be used for the control and the preservation of the capacity of the biological self-purification, which is the only natural and essential process in drinking-water conditioning of surface water. Main subject of the surveys was the development of criteria for an assessment of the measured enzymatical inhibition effects. Therefore, classes of inhibition and indices of inhibition are defined.  相似文献   
93.
钟智琼 《城市地质》2016,(2):98-100
地质档案是已完成地质工作的凭证,要求在档案汇交的时候对完整性进行严格控制;地质档案是开展新的地质工作的重要参考资料,存在利用率高的特点;地质档案含有关系国土安全的涉密测绘数据,在管理中对安全保密有特殊要求。针对这些特点,本文为了提高地质档案管理水平,针对基层地勘单位在地质档案管理中遇到的涉密地质资料利用安全意识薄弱问题,以及档案丢失和损耗率高的问题,提出通过不同涉密级别的档案分类管理和完善借阅防抵赖机制,达到增强档案使用者重视的目的来解决问题;针对地质档案汇交完整性不高的问题,提出引入质量管理体系文件作为客观证据,快速有效确定汇交范围的方法来解决。通过地质档案管理办法创新,更好的为地质工作服务。  相似文献   
94.
《China Geology》2023,6(2):208-215
The Qilian Mountain permafrost area located in the northern of Qinghai-Tibet Plateau is a favorable place for natural gas hydrate formation and enrichment, due to its well-developed fractures and abundant gas sources. Understanding the formation and distribution of multi-component gas hydrates in fractures is crucial in accurately evaluating the hydrate reservoir resources in this area. The hydrate formation experiments were carried out using the core samples drilled from hydrate-bearing sediments in Qilian Mountain permafrost area and the multi-component gas with similar composition to natural gas hydrates in Qilian Mountain permafrost area. The formation and distribution characteristics of multi-component gas hydrates in core samples were observed in situ by X-ray Computed Tomography (X-CT) under high pressure and low temperature conditions. Results show that hydrates are mainly formed and distributed in the fractures with good connectivity. The ratios of volume of hydrates formed in fractures to the volume of fractures are about 96.8% and 60.67% in two different core samples. This indicates that the fracture surface may act as a favorable reaction site for hydrate formation in core samples. Based on the field geological data and the experimental results, it is preliminarily estimated that the inventory of methane stored in the fractured gas hydrate in Qilian Mountain permafrost area is about 8.67×1013 m3, with a resource abundance of 8.67×108 m3/km2. This study demonstrates the great resource potential of fractured gas hydrate and also provides a new way to further understand the prospect of natural gas hydrate and other oil and gas resources in Qilian Mountain permafrost area.©2023 China Geology Editorial Office.  相似文献   
95.
随着风廓线雷达组网观测系统建设的推进,质量控制是提高风廓线雷达观测资料应用效益的重要环节。通过介绍风廓线雷达回波信号的产生机理、信号与数据处理流程,研究了风廓线雷达多普勒功率谱的湍流回波与干扰回波的特征,给出了功率谱的特征量,提出了基于模糊逻辑提取大气湍流回波信息的质量控制方法,改进了多普勒速度估算的准确性。为检验质量控制方法的可靠性,以合肥2008年6月4日10:42:16(北京时,下同)东波束和8日10:36:20西波束的多普勒功率谱数据处理为例开展了风廓线观测资料质量控制的个例试验分析,结果表明处理后观测资料的可用性较好。  相似文献   
96.
本文利用中尺度非静力WRF(Weather Research Forecast, Version 3.4)模式, 针对1013号“鲇鱼”台风个例, 通过对红外高光谱AIRS(Atmospheric Infrared Sounder)资料经过基于空间梯度信息的质量控制之后同化进入模式, 来评估新的质量控制方法对同化效果的影响以及对台风数值模拟的改善情况。研究结果发现, 如果仅仅基于WRFDA(WRF Data Assimilation system, Version 3.4)模式自带的质量控制系统, 将会有部分梯度距平值明显较大超过阈值的资料被同化进入模式, 而这些可能受到“污染”且误差较大的资料同化进入模式必将会导致同化结果有较大误差, 影响分析结果的质量。而对AIRS资料经过基于空间梯度信息质量控制之后再同化进入模式, 确实可将梯度距平值大于阈值的“坏点”剔除掉, 从而使初始场的描述更加准确, 台风路径的模拟精度在一定程度上得到提高。综上可知, 基于空间梯度信息的质量控制方法整体上对改善同化效果有较好的正效应, 对台风的数值模拟也起到一定的促进作用。  相似文献   
97.
地基微波辐射计亮温观测数据的综合质量控制与效果分析   总被引:2,自引:0,他引:2  
针对北京一地基微波辐射计,研究其Level-1级数据的质量控制方案,提出极值检查、时间一致性检查、辐射传输计算检查和多通道亮温交叉检查。并用实际亮温观测数据进行质量控制实验,分析其应用效果。研究结果表明了提出的综合质量控制方案的可行性,为本资料的后续应用提供选择依据。  相似文献   
98.
针对现有研究较少关注时空特征对服务质量的影响,预测准确性有限的不足,该文提出了一种基于时区聚类协同过滤的空间信息服务质量预测算法:利用时区特征进行用户和空间信息服务的聚类,并采用时区优化的相似度计算方法寻找相似用户和相似服务,通过构建时区约束的邻近用户—服务矩阵进行空间信息服务质量的综合预测。最后,实验结果证明基于时区聚类协同过滤方法可以显著提高空间信息服务质量预测的准确性。  相似文献   
99.
Estuaries have long been regarded as environmentally naturally stressed areas because of the high degree of variability in their physico-chemical characteristics, for example oxygen, temperature and salinity in the water column and bed sediment dynamics. However, their biota is well-adapted to cope with that stress and so the areas may be regarded as resilient because of that inherent variability; their ability to absorb stress without adverse effects is regarded here as Environmental Homeostasis. Hence these areas may only be regarded as stressful for marine or freshwater-adapted organisms and that for estuarine organisms this environmental stress is regarded as a subsidy whereby they successfully capitalise on the stressful conditions. In addition, using examples of the estuarine fauna and flora, this article indicates that the characteristics of natural stress in estuaries are similar to those for anthropogenic stress. An over-reliance on ecosystem structural features, such as diversity, in quality indicators therefore makes the detection of the anthropogenic stress more difficult. This difficulty is termed the Estuarine Quality Paradox. Because of these difficulties, the article argues that functional characteristics either as well as or rather than structural ones should be used in detecting environmental perturbations in estuaries.  相似文献   
100.
International trade in fishery commodities reached US 58.2 billion dollars in 2002, a 5% improvement relative to 2000 and a 45% increase over 1992 levels. Within this global trade, developing countries registered a net trade surplus of US 17.4 billion dollars in 2002 and accounted for almost 50% by value and 55% of fish exports by volume. This globalization of fish trade, coupled with technological developments in food production, handling, processing and distribution, and the increasing awareness and demand of consumers for safe and high quality food have put food safety and quality assurance high in public awareness and a priority for many governments. Consequently, many countries have tightened food safety controls, imposing additional costs and requirements on imports. As early as 1980, there was an international drive towards adopting preventative HACCP-based safety and quality systems. More recently, there has been a growing awareness of the importance of an integrated, multidisciplinary approach to food safety and quality throughout the entire food chain. Implementation of this approach requires an enabling policy and regulatory environment at national and international levels with clearly defined rules and standards, establishment of appropriate food control systems and programmes at national and local levels, and provision of appropriate training and capacity building. This paper discusses the international framework for fish safety and quality, with particular emphasis on the United Nation's Food and Agricultural Organization's (FAO) strategy to promote international harmonization and capacity building.  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