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   1363篇
  免费   261篇
  国内免费   296篇
测绘学   71篇
大气科学   79篇
地球物理   282篇
地质学   766篇
海洋学   213篇
天文学   18篇
综合类   140篇
自然地理   351篇
  2024年   13篇
  2023年   32篇
  2022年   72篇
  2021年   66篇
  2020年   81篇
  2019年   68篇
  2018年   48篇
  2017年   61篇
  2016年   53篇
  2015年   66篇
  2014年   64篇
  2013年   83篇
  2012年   91篇
  2011年   64篇
  2010年   52篇
  2009年   71篇
  2008年   74篇
  2007年   101篇
  2006年   110篇
  2005年   94篇
  2004年   80篇
  2003年   73篇
  2002年   39篇
  2001年   39篇
  2000年   47篇
  1999年   40篇
  1998年   41篇
  1997年   24篇
  1996年   30篇
  1995年   25篇
  1994年   23篇
  1993年   18篇
  1992年   10篇
  1991年   9篇
  1990年   8篇
  1989年   6篇
  1987年   6篇
  1986年   3篇
  1985年   2篇
  1984年   2篇
  1980年   1篇
  1979年   1篇
  1978年   1篇
  1977年   1篇
  1976年   7篇
  1975年   1篇
  1973年   3篇
  1972年   7篇
  1971年   6篇
  1964年   1篇
排序方式: 共有1920条查询结果,搜索用时 281 毫秒
991.
George Martin 《Area》2007,39(1):66-73
The global diffusion of motorization has become a significant driver of local and regional change around the world. In the South (the developing countries), especially in China, the scale of its impact in the twenty-first century carries the potential to dwarf that of motorization in the North (the developed countries) in the twentieth century. While alarms have been sounded about the threat of greatly increased greenhouse emissions posed by China's telescoped development of motorization, this paper analyses its neglected social and ecological impacts. Through an analysis of car and land use data, China's loss of agricultural land and growing social polarization are highlighted.  相似文献   
992.
近年来中国的环境问题日益严重,中国要实现可持续发展战略,就必须将因外生环境被破坏所带来的一系列社会责任、资源消耗、人力资源等指标纳入监控范畴,使因环境问题所带来的社会外部成本可以在会计核算体系中得以披露.通过对环境经济学的剖析,结合中国实际,探寻一条中国环境会计核算的新路.  相似文献   
993.
Nick Marriner  Christophe Morhange   《Earth》2007,80(3-4):137-194
Although much has been written on the subject of ancient Mediterranean harbours, the relatively new area of harbour geoarchaeology remains dispersed in the geoscience and archaeological literature. Over a decade of research has amassed rich and varied datasets of anthropogenically forced coastal evolution, with a remarkable number of between-site analogies. This new research field also shows the rich potential of geoscience to reconcile important archaeological questions. No single publication, however, has yet drawn on these geological patterns to yield a detailed overview suitable for geoscientists and environmental archaeologists. The aim of this review article is to (1) discuss how ancient harbours have come to be preserved in the geological record; (2) expound the basic principles and palaeoenvironmental tools underpinning ancient harbour geoarchaeology; (3) outline some of the most significant research advances made; and (4) discuss a new chrono-stratigraphic model applicable to harbour sequences.  相似文献   
994.
谢学锦 《地质通报》2007,26(11):1399-1404
地球化学填图的发展属于勘查地球化学家的贡献。勘查地球化学家从发展局部矿产勘查至区域性矿产勘查,再从区域性地球化学填图至全国性乃至全球性地球化学填图。论述了西方国家、苏联和中国发展地球化学填图所走的不同道路,从而预见21世纪地球化学填图的标准化、多样化及其在解决资源与环境问题方面的重大作用。  相似文献   
995.
分析中国大陆与周边板块边界、尤其是西部地震“大三角”地区强震活动的关系认为,中国大陆与周边板块边界带的强震活动之间存在互动关系,而不完全是后者对前者的触发作用。进而根据中国大陆地震构造环境、大尺度地壳运动变形动态与强震活动状况,研究和探讨了这种“互动关系”可能的构造动力机理和我国大陆未来地震活动的发展趋势。  相似文献   
996.
中国地壳运动观测网络的建设及应用   总被引:2,自引:1,他引:2  
"中国地壳运动观测网络"是国家"九五"期间建设的重大科学工程,自1998年开始观测以来,获取了大量的地壳形变GPS观测资料和相对重力观测资料,为认知中国大陆地壳运动特征及其动力学机制提供了至关重要的基础资料和定量约束。"十一五"期间,国家将实施中国地壳运动观测网络的二期工程"中国大陆构造环境监测网络",对网络中观测站点的空间密度、观测方式和应用功能进行大幅度强化。本文扼要介绍了中国地壳运动观测网络一期工程的建设内容、运行现状和主要成果及二期工程的建设规划。中国地壳运动观测网络一、二期工程将为我国地震监测和地学研究提供一个具有国际先进水平的大地测量基础平台。  相似文献   
997.
Detailed analysis of the depositional characteristics of Chinese loess is required to determine the nature of the paleoclimate record preserved in these extensive sediments. High sampling resolution optically stimulated luminescence (OSL) dating has the potential to facilitate such an analysis. However, high-resolution dating is extremely time consuming and therefore of limited practical applicability. This study assesses the luminescence characteristics of loess from three sections on the Chinese Loess Plateau in an attempt to identify methods of increasing sample throughput without compromising data quality. Using the single-aliquot regenerative-dose technique, samples yield internally consistent results. However, dose recovery data indicate that care is required in selecting preheating regimes for different sections. The standardized growth curve approach was tested and found to be applicable within, but not between, sites. Nonetheless, the use of standardized growth curves offers increases in sample throughput that will allow more routine high-resolution dating of Chinese loess. High-resolution dose rates calculated using inductively coupled plasma (ICP) methods show relative homogeneity of radioisotope concentrations and are comparable to lower resolution field gamma-spectrometry measurements. Consequently, high-resolution OSL dating has great potential to elucidate the depositional characteristics of Chinese loess and facilitate more precise use of the paleoclimatic information it preserves.  相似文献   
998.
Relative percentages of sand, silt, and clay from samples of the same till unit are not identical because of different lithologies in the source areas, sorting in transport, random variation, and experimental error. Random variation and experimental error can be isolated from the other two as follows. For each particle-size class of each till unit, a standard population is determined by using a normally distributed, representative group of data. New measurements are compared with the standard population and, if they compare satisfactorily, the experimental error is not significant and random variation is within the expected range for the population. The outcome of the comparison depends on numerical criteria derived from a graphical method rather than on a more commonly used one-way analysis of variance with two treatments. If the number of samples and the standard deviation of the standard population are substituted in at-test equation, a family of hyperbolas is generated, each of which corresponds to a specific number of subsamples taken from each new sample. The axes of the graphs of the hyperbolas are the standard deviation of new measurements (horizontal axis) and the difference between the means of the new measurements and the standard population (vertical axis). The area between the two branches of each hyperbola corresponds to a satisfactory comparison between the new measurements and the standard population. Measurements from a new sample can be tested by plotting their standard deviation vs. difference in means on axes containing a hyperbola corresponding to the specific number of subsamples used. If the point lies between the branches of the hyperbola, the measurements are considered reliable. But if the point lies outside this region, the measurements are repeated. Because the critical segment of the hyperbola is approximately a straight line parallel to the horizontal axis, the test is simplified to a comparison between the means of the standard population and the means of the subsample. The minimum number of subsamples required to prove significant variation between samples caused by different lithologies in the source areas and sorting in transport can be determined directly from the graphical method. The minimum number of subsamples required is the maximum number to be run for economy of effort.  相似文献   
999.
河北行唐大枣品质与成土母岩类型关系的探讨   总被引:3,自引:1,他引:3       下载免费PDF全文
笔者从农业地质研究的角度出发,探讨了成土母岩对行唐大枣产量和品质的影响。调查研究发现在行唐山区品质好、产量高的大枣主要分布在黑云斜长片麻岩区,其主要原因是黑云斜长片麻岩较其他类型风化层厚,裂隙发育,P、Sr、稀土元素等含量高,K含量高并以缓效态赋存在黑云母中易被植物吸收;从土壤地球化学背景分析表明,优质大枣分布区具有与P、Sr、Na和稀土元素总量的富集区吻合性最好,Ni、Cr含量低的特点,这也验证了行唐大枣优质产区分布和成土母岩黑云斜长片麻岩分布的一致性。  相似文献   
1000.
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