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   2335篇
  免费   176篇
  国内免费   222篇
测绘学   387篇
大气科学   212篇
地球物理   195篇
地质学   470篇
海洋学   205篇
天文学   12篇
综合类   246篇
自然地理   1006篇
  2024年   57篇
  2023年   123篇
  2022年   219篇
  2021年   259篇
  2020年   196篇
  2019年   144篇
  2018年   101篇
  2017年   119篇
  2016年   82篇
  2015年   62篇
  2014年   74篇
  2013年   107篇
  2012年   122篇
  2011年   88篇
  2010年   68篇
  2009年   68篇
  2008年   62篇
  2007年   89篇
  2006年   90篇
  2005年   75篇
  2004年   60篇
  2003年   56篇
  2002年   54篇
  2001年   80篇
  2000年   69篇
  1999年   57篇
  1998年   44篇
  1997年   25篇
  1996年   10篇
  1995年   14篇
  1994年   16篇
  1993年   9篇
  1992年   4篇
  1991年   4篇
  1990年   4篇
  1989年   4篇
  1988年   6篇
  1987年   2篇
  1986年   1篇
  1985年   2篇
  1984年   4篇
  1983年   2篇
  1982年   1篇
排序方式: 共有2733条查询结果,搜索用时 46 毫秒
371.
针对教师主导的传统教学模式在地理信息系统课程教学中存在的不足,提出了将翻转课堂这一新的混合学习教学模式引入教学的想法。首先分析了地理信息系统课程实施翻转课堂的必要性和可行性,然后在综合考虑地理信息系统课程特点与中外教育文化差异的基础上进行了课程设计和组织实施。实践结果表明,实施翻转课堂确实能够提高学生学习主动性和教学质量,同时也对教师的专业水平和教学能力提出了更高的要求。  相似文献   
372.
Mineral prospectivity mapping is a classification process because in a given study area, a specific region is classified as either a prospective or non-prospective area. The cost of false negative errors differs from the cost of false positive errors because false positive errors lead to wasting much more financial and material resources, whereas false negative errors result in the loss of mineral deposits. Traditional machine learning algorithms using for mapping mineral prospectivity are aimed to minimize classification errors and ignore the cost-sensitive effects. In this study, the effects of misclassification costs on mapping mineral prospectivity are explored. The cost-sensitive neural network (CSNN) for minimizing misclassification costs is applied to map Fe polymetallic prospectivity in China’s southwestern Fujian metalorganic belt (SFMB). A CSNN with a different cost ratio ranging from 1:10 to 10:1 was used to represent various misclassification costs. The cross-validation results indicated a lower misclassification cost compared to traditional neural networks through a threshold-moving based CSNN. The CSNN’s predictive results were compared to those of a traditional neural network, and the results demonstrate that the CSNN method is useful for mapping mineral prospectivity. The targets can be used to further explore undiscovered deposits in the study area.  相似文献   
373.
Highly alkaline industrial residues (e.g., steel slag, bauxite processing residue (red mud) and ash from coal combustion) have been identified as stocks of potentially valuable metals. Technological change has created demand for metals, such as vanadium and certain rare earth elements, in electronics associated with renewable energy generation and storage. Current raw material and circular economy policy initiatives in the EU and industrial ecology research all promote resource recovery from residues, with research so far primarily from an environmental science perspective. This paper begins to address the deficit of research into the governance of resource recovery from a novel situation where re-use involves extraction of a component from a bulk residue that itself represents a risk to the environment. Taking a political industrial ecology approach, we briefly present emerging techniques for recovery and consider their regulatory implications in the light of potential environmental impacts. The paper draws on EU and UK regulatory framework for these residues along with semi-structured interviews with industry and regulatory bodies. A complex picture emerges of entwined ownerships and responsibilities for residues, with past practice and policy having a lasting impact on current possibilities for resource recovery.  相似文献   
374.
Climate change increases the complexity and uncertainty of regional natural resource management (NRM), calling into question the appropriateness of linear knowledge-transfer approaches. In this paper we reflect on knowledge practices among a partnership of researchers and NRM planners, under a federal program of NRM investment intended to ‘deliver information’ to regional NRM planners to support planning for climate change. We unpack ‘container’ and ‘conduit’ metaphors of linear, one-way communication invoked by the starting conditions, and explore whether more relational ways of communicating were achieved. A key theme emerged early in the research that NRM planners felt overwhelmed by the sheer volume of information available and discouraged by the irrelevance of much of it to their climate change planning. Our research-practice collaboration unfolded in this context and through ongoing face-to-face and virtual engagement over a period of two years. The collaborative approach featured joint identification of priority activities, co-design of planning approaches, and the iterative co-development of an online ‘information portal’, which acted as a boundary object. We report the emergence of a ‘knowing system’, resulting from these efforts to foster relationships and co-produce boundary objects in a particular geographic context. Our findings highlight the potential benefits of investing in the capacity of researchers and NRM practitioners to engage in collaborative research partnerships premised on the emergence of knowing systems.  相似文献   
375.
This paper analyzes how Mexican hometown associations in New York City practice solidarity so that they might best meet the needs of the transnational communities that they serve. Commonly formed by immigrants in the United States, hometown associations are organizations which send money collectively to their home countries, supporting public infrastructure and community projects. Scholars have debated both the merits of remittance programs that channel migrant funds as economic development and the agency of immigrant economies in neoliberal development structures. Through primary data collected from interviews in New York City, I review the frustrations that hometown associations have with one such program: Mexico's programa tres por uno para migrantes. Concurrently, I examine how the same hometown associations engage ethical economic practices of collective remittance sending and community service provision in New York City. Drawing on feminist literature on diverse economies, I argue that the solidarity work of hometown associations disrupts the dominant remittance as development discourse. Migrants are not content to participate in tres por uno and through practicing solidarity they distance themselves from this neoliberal policy.  相似文献   
376.
One of the most prominent stylized facts about contemporary capitalism concerns its “financialization.” Like all economic stylized facts, however, facts about financialization are recognized by some commentators and not by others. This article offers one explanation why. It argues that the claims we can make about “the economy” depend upon how we envision that economy in the first place. The economy can be pictured in myriad ways – it is multiple, not singular – and different pictures of it enable the identification of different stylized facts about it. So it is with financialization. The article illustrates this by examining the history of two different traditions of picturing the economy. One – national accounting – increasingly has enabled financialization to be seen; the other – mainstream economics – generally has not.  相似文献   
377.
区域作为人类、自然、社会共同作用和互相影响的复杂系统,对区域进行生态量化建模与模拟仿真,是实现区域可持续发展战略的关键。传统机器学习方法对区域生态系统建模取得了一定的成果,但难以确定学习特征和实现时空模拟。深度学习不需事先确定训练特征,具有优异的特征学习能力,能够提高模型预测精度,因此利用深度学习进行建模具有显著优势。本文使用植被净初级生产力(NPP)、气溶胶光学厚度(AOD)和人口格网数据,充分利用深度学习的优点,采用最优深度神经网络时空模拟,得到了河南省2007-2014年3 km分辨率的生态赤字空间分布图和河南省2015-2020年的生态赤字时间预测结果并进行分析,为区域生态的科学管理和建设供科学依据和参考。  相似文献   
378.
周凡涵  刘丙军 《水文》2022,42(1):59-66
受潮汐、径流、风速风向、地形变化等多种海陆要素交互作用,河口区盐水入侵呈高度不确定性与非线性特征,盐度预报难度较大.利用在线学习算法与误差自回归修正方法在水文预报中时效性更强的优点,构建一种耦合在线序列极限学习机-误差修正(OSELM-EC)盐水入侵预报模型,选取珠江河口区磨刀门水道为典型研究区进行逐日盐度预报.结果表...  相似文献   
379.
平度市国土资源局全面推进“双保”行动的探索   总被引:1,自引:1,他引:0  
王强先 《山东国土资源》2010,26(5):55-56,59
为应对国际金融危机,平度市国土资源局积极响应国土资源部在全国范围内部署开展的"保增长、保红线"双保行动,立足部门职能,扎实工作,加强和改善土地宏观调控新机制,有效保障扩大内需,保障重点项目用地,促进经济平稳较快发展。  相似文献   
380.
菏泽市挖掘节约用地潜力的探索   总被引:1,自引:1,他引:0  
菏泽市国土资源局在学习科学发展观过程中,在挖掘土地潜力上下功夫,寻求突破口,通过向节约投资要效益、向低效用地要效益、向标准厂房要效益、向调整结构要效益、向集约用地要效益、向压缩用地面积要效益、向闲置土地要效益、向废弃未利用土地要效益、向旧村改造要效益九条措施破解了土地制约瓶颈,缓解了用地矛盾,确保了全市经济又好又快发展。  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