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   2107篇
  免费   235篇
  国内免费   239篇
测绘学   172篇
大气科学   180篇
地球物理   340篇
地质学   555篇
海洋学   363篇
天文学   34篇
综合类   161篇
自然地理   776篇
  2024年   10篇
  2023年   41篇
  2022年   78篇
  2021年   124篇
  2020年   111篇
  2019年   85篇
  2018年   57篇
  2017年   120篇
  2016年   91篇
  2015年   74篇
  2014年   125篇
  2013年   164篇
  2012年   93篇
  2011年   105篇
  2010年   91篇
  2009年   73篇
  2008年   111篇
  2007年   106篇
  2006年   91篇
  2005年   95篇
  2004年   98篇
  2003年   93篇
  2002年   82篇
  2001年   57篇
  2000年   78篇
  1999年   62篇
  1998年   52篇
  1997年   40篇
  1996年   39篇
  1995年   30篇
  1994年   14篇
  1993年   17篇
  1992年   12篇
  1991年   11篇
  1990年   8篇
  1989年   5篇
  1988年   6篇
  1987年   7篇
  1986年   6篇
  1985年   4篇
  1984年   6篇
  1983年   3篇
  1982年   3篇
  1980年   1篇
  1978年   1篇
  1973年   1篇
排序方式: 共有2581条查询结果,搜索用时 15 毫秒
161.
材料科学和地质学的发展及前景(英文)   总被引:1,自引:1,他引:0  
材料科学可定义为一门涉及化学、物理学、矿物学、地质学、冶金学和合成材料等领域的科学。“工具制造者的人类” ,主要是使用石器 ,并由此而增进了其智能的发育。燧石、石灰岩中氧化硅富集体提供了制作武器和工具的材料 ,土壤则可用于制陶业和陶瓷业。材料科学主要是由研究工业矿物演化而来 ,它与地质学的关系密切 ;合成材料以其特殊的性能满足了人们的需求。火和压力在处理天然材料的工艺发展中起着头等作用 ;金银铜铁及其它金属能用作装饰品、防御武器和制造工具。有些金属的使用显示了人类各历史时期的特点。人们后来发现某些结晶体具有特殊的性质 ,如石英的压电性、红宝石激光 ,钻石和刚玉的高硬度 (可用作磨料 ,将来仍具开发潜力 )。合成材料和在太空合成的材料具有远大前景 (如碳的同素异形体carbyne car bynoid)。在材料科学中 ,特种玻璃 ,硬而防火的陶瓷、磨料、特殊耐火材料 ,只不过是材料科学中业已开发的几种工艺矿物而已。材料科学的发展对于现代文明和解决人类当今和未来所遇到的各种问题都极其重要。与世界人口增长相关的问题 ,可以通过科学、绿色革命和生物技术 ,以及一切天然资源的合理开发来解决 ,这将有助于避免“南北对抗”。肯定地说 ,材料科学及其未来的发展 ,会有助于人类去应付  相似文献   
162.
The spatially distributed soil erosion and sediment delivery model WATEM/SEDEM was used to simulate the impact of riparian vegetated filter strips (RVFSs) on river sediment delivery at different spatial scales. For a field plot with a straight slope, sediment reduction by the RVFSs is comparable to results obtained through experimental set‐ups elsewhere (i.e. >70%). However, at the scale of an entire catchment, sediment reduction is much less (i.e. ±20%) due to (1) overland flow convergence, which reduces the sediment trapping efficiency of an RVFS, and (2) because part of the sediment bypasses the RVFSs through ditches, sewers and road surfaces. These results suggest that, at the catchment scale, RVFSs should be accompanied with other conservation techniques that are more appropriate for reducing river sediment loads, and that also reduce on‐site soil erosion. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
163.
水文科技发展回顾及思考   总被引:5,自引:0,他引:5  
张建云  章树安 《水文》2006,26(3):13-17
水文科技是水文工作和水利科技一个重要组成部分,长期以来水文科学技术对我国水文与水利事业的发展和国民经济建设起到了巨大的推动作用,我国水文科学技术发展随着水文、水利与国民经济的发展和科学技术的进步取得了巨大成就,有些技术达到获接近国际先进水平。本文对我国水文科技取得的主要成就进行了总结,对目前水文科技存在主要问题进行了分析;结合水资源可持续利用支持社会经济可持续发展的需求,对水文科技发展的重点和策略进行了分析和探讨。  相似文献   
164.
胡续礼  杨树江  吴迪  潘剑君 《水文》2006,26(5):45-47
本文简要分析了我国水文资料的基本特点及其在水土保持中的应用情况,并结合水文资料在水土保持中的研究实例,探讨了加强水文资料在水土保持中应用范围与价值,在新一轮的站网调整建设中应与水土保持监测站网建设结合起来,避免重复建设,加强水文站网功能,发挥现有水文站网作用。  相似文献   
165.
1 Introduction The mean meridional circulation plays an important role in the transportation and balance of heat, momen- tum, vortex and vapor between different latitudes. According to the data analysis, there are three circula- tions from the equator to the polar area: the Hadley circulation, a heat-driven circulation which rises around the equator and sinks at a certain latitude; the subpolar circulation, another heat-driven circulation around the polar area; and the Ferrel circulation, an i…  相似文献   
166.
Brian H. King 《Geoforum》2007,38(1):207-219
The idealization of natural landscapes and peoples during colonialism, coupled with the popularity of sustainable development in the postcolonial era, has contributed to the expansion of conservation planning throughout the African continent. Concerns surrounding the promotion of national and international conservation agendas at the expense of local livelihood needs have generated interest in community conservation projects that attempt to include local participation and knowledge in natural resource management. The early excitement associated with community conservation has waned in light of recent assessments that it has been unsuccessful in meeting its ecological and social goals. This parallels other research that suggests communities are understood in generic or homogenous ways that influence how these initiatives are understood. Using a case study of the Mahushe Shongwe Game Reserve, this paper evaluates how rural households access environmental and economic resources to produce livelihoods, and how these access patterns impact their views of the project. It is argued that there are significant livelihood variations within the community that shape the ways households engage with, and benefit from, conservation planning. Rather than strictly viewing Mahushe Shongwe as a constraint to environmental resource access or site for limited employment, community members identify a number of benefits from its existence including education and development opportunities. Additionally, transformations in governance systems in the region impact community views of the project since younger residents are less likely to engage with the Matsamo Tribal Authority, which participates in managing the reserve. The consequence is that conservation has various impacts and meanings within a specific community that remain tied to the livelihood and governance systems being renegotiated in the post-apartheid era.  相似文献   
167.
本文介绍了山西省气象局气象科技数字图书馆的构架及服务功能,从数字图书馆技术方面分析了气象科技图书馆的主要特点,同时对数字图书馆开通以来的使用情况进行了统计分析,为数字图书馆的进一步完善和发展提出构想。  相似文献   
168.
重视科技论文摘要的编写提高期刊的办刊质量   总被引:1,自引:0,他引:1  
王蕾 《广西气象》2007,28(2):75-77
针对目前气象科技论文提要撰写中经常出现的一些问题,对科技信息传播方面的影响,重申提要编写的重要性,并提出:(1)应举办面向有关摘要编写的论文作者、编辑的培训班或学习班。(2)编辑工作者应加强各种知识的学习和积累,严把英文摘要关(3)广泛招揽一些学术水平高,各方面素质较高的人才加入到编辑行列中来(4)编辑部应经常开展一些工作研讨,就英文摘要中经常发现的问题进行探讨,不断提高中英文摘要的编写水平等改进摘要编写,提高期刊办刊质量的措施和建议。  相似文献   
169.
Catchments in the Loess Plateau have been under the influence of human activities for centuries. In the last four decades, soil conservation measures have accelerated and intensified. These measures were designed to reduce soil erosion, improve agricultural productivity, and enhance environmental quality. It is important to evaluate the effects of these measures on hydrology in order to develop sustainable catchment management plans in the region. This study evaluated changes in stream flow data for four selected catchments in the Loess Plateau following large‐scale soil conservation measures. The non‐parametric Mann–Kendall test was used to identify trends in annual stream flow and the results showed significant downward trends in three of the four catchments. The Pettitt test indicated that a change point occurred in 1978 in these three catchments. Annual precipitation in all the catchments showed no significant trend during the period of record. Comparison of daily flow duration curves for two 20‐year periods (1957–1978) and (1979–2003) showed significant changes in stream flow regime. Reduction in most percentile flows varied between 20 and 45%, and the reduction in low flows was greatest. Overall, the reductions in daily flow were increasing with time, with significant changes occurring in the 1990s. However, it is not clear whether these catchments have seen the full effects of the soil conservation measures, so the results of this study might underestimate the final impact of soil conservation on stream flow regime. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
170.
Conservation of wetlands especially as waterfowl habitat in northeast China   总被引:2,自引:0,他引:2  
Wetland,withveryhighbiologicalproductivity,tremendousresourcepotentialandenvironmentfunction,isaspecialecosystemintheearthan...  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