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   453篇
  免费   9篇
  国内免费   6篇
测绘学   15篇
大气科学   35篇
地球物理   97篇
地质学   153篇
海洋学   24篇
天文学   88篇
自然地理   56篇
  2020年   3篇
  2019年   4篇
  2018年   8篇
  2017年   9篇
  2016年   8篇
  2015年   8篇
  2014年   10篇
  2013年   19篇
  2012年   12篇
  2011年   12篇
  2010年   16篇
  2009年   21篇
  2008年   21篇
  2007年   14篇
  2006年   22篇
  2005年   10篇
  2004年   13篇
  2003年   10篇
  2002年   11篇
  2001年   5篇
  2000年   12篇
  1999年   11篇
  1998年   11篇
  1997年   5篇
  1996年   8篇
  1995年   10篇
  1994年   8篇
  1993年   9篇
  1992年   5篇
  1991年   12篇
  1990年   8篇
  1989年   11篇
  1988年   9篇
  1987年   3篇
  1986年   8篇
  1985年   10篇
  1984年   9篇
  1983年   9篇
  1982年   7篇
  1981年   3篇
  1980年   7篇
  1979年   6篇
  1977年   6篇
  1976年   7篇
  1975年   6篇
  1974年   5篇
  1973年   4篇
  1972年   3篇
  1971年   4篇
  1970年   4篇
排序方式: 共有468条查询结果,搜索用时 15 毫秒
341.
Historical and modern scientific contexts are provided for the 2006 Binghamton Geomorphology Symposium on the Human Role in Changing Fluvial Systems. The 2006 symposium provides a synthesis of research concerned with human impacts on fluvial systems — including hydrologic and geomorphic changes to watersheds — while also commemorating the 50th anniversary of the 1955 Man's Role in Changing the Face of the Earth Symposium [Thomas, Jr., W. L. (Ed.), 1956a. Man's Role in Changing the Face of the Earth. Univ. Chicago Press, Chicago. 1193 pp]. This paper examines the 1955 symposium from the perspective of human impacts on rivers, reviews current inquiry on anthropogenic interactions in fluvial systems, and anticipates future directions in this field.Although the 1955 symposium did not have an explicit geomorphic focus, it set the stage for many subsequent anthropogeomorphic studies. The 1955 conference provided guidance to geomorphologists by recommending and practicing interdisciplinary scholarship, through the use of diverse methodologies applied at extensive temporal and geographical scales, and through its insistence on an integrated understanding of human interactions with nature. Since 1956, research on human impacts to fluvial systems has been influenced by fundamental changes in why the research is done, what is studied, how river studies are conducted, and who does the research. Rationales for river research are now driven to a greater degree by institutional needs, environmental regulations, and aquatic restoration. New techniques include a host of dating, spatial imaging, and ground measurement methods that can be coupled with analytical functions and digital models. These new methods have led to a greater understanding of channel change, variations across multiple temporal and spatial scales, and integrated watershed perspectives; all changes that are reflected by the papers in this volume. These new methods also bring a set of technical demands for the training of geomorphologists. The 2006 Binghamton Geomorphology Symposium complements the 1956 symposium by providing a more specific and updated view of river systems coupled with human interactions. The symposium focuses on linkages between human land use, structures, and channel modification with geomorphology, hydrology, and ecology. The emergence of sustainability as a central policy guideline in environmental management should generate greater interest in geomorphic perspectives, especially as they pertain to human activities. The lack of theories of anthropogeomorphic change, however, presents a challenge for the next generation of geomorphologists in this rapidly growing subfield.  相似文献   
342.
Henry Darcy and the Fountains of Dijon   总被引:4,自引:0,他引:4  
  相似文献   
343.
A reexamination of the sequences of planktonic foraminifers and calcareous nannoplankton in the Plio-Pleistocene sediments beneath the Louisiana continental shelf has been undertaken in order to modernize correlation schemes that were established 10–20 y.a. As a consequence, it can be shown that (1) a new correlation of marine micropaleontological and continental glacial events is necessary; (2) the Gulf Coast faunal events can be reliably correlated with those in the type Italian Pleistocene section and in the deep-sea cores; (3) it is becoming increasingly evident that it is invalid to correlate the Plio-Pleistocene boundary, as defined by paleontology, with a climatically defined boundary.  相似文献   
344.
Rural areas in developed economies are becoming increasingly multi-functional in that their character is being shaped by a mix of production, consumption and conservation values. Agriculture may remain the dominant land use, but many landholders do not see themselves as farmers by occupation. Researchers have demonstrated that occupational identity influences land use and management. However, efforts to explore the influence of occupational identity often rely on surrogate measures and have largely ignored identity theory. We build on research demonstrating that collective identity theory can be used to develop a valid and reliable measure of farmer identity and to then classify rural landholders across a natural resource management (NRM) region. The contribution of this paper is to explain how that measure of farmer identity can be mapped and then demonstrate the relevance of doing so for regional NRM in Australia. As expected, farmer identity varied across the case study region with distance from urban centres, and across different environmental assets. Those findings should lead to a more targeted approach to landholder engagement in NRM. We suggest that farmer identity (i.e. farmer-collective occupational identity construct; F-COIC) might provide a next step for responding to the challenges of interpreting and mapping multi-functionality.  相似文献   
345.
We present two metrics (utility functions based on observational requirements) for specifying agent behaviour in the eSTAR autonomous observing system. Together, these metrics provide an agent with tools to analyse the phase coverage and interconnectivity properties of partial datasets, and to modify the subsequent observing strategy in order to fulfill the astronomical constraints expressed by the astronomer. We discuss the behaviour of the metrics for evenly sampled and randomly sampled datasets, and present a use case that demonstrates how the metrics could be applied in an agent‐based observing scenario. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
346.
Using longitudinal survey data, this paper explores stability and change in values, beliefs, attitudes, and knowledge among rural landholders. Existing theories predict varying degrees of stability in these constructs. This paper tests these assumptions through data collected by four cross-sectional surveys of rural landowners (>10?ha), completed in one region between 2002 and 2016. The study area includes a mix of social landscapes but agriculture is the dominant land use. Results reveal significant change in measured constructs over time. Nearly all of the items assessing values changed significantly across the study period (seven of eight held values, ten of eleven assigned values). Most belief items (three of five), half of the attitude items (two of four), and all eleven knowledge items also experienced change. While statistically significant, most of the identified changes were relatively modest in scope. Findings suggest the value of longitudinal research to better understand dynamic psychological and social constructs.  相似文献   
347.
348.
349.
The XVIth International Congress of Photogrammetry and Remote Sensing, organised by the International Society for Photogrammetry and Remote Sensing, was held in the Kyoto International Conference Hall from 1st to 10th July, 1988. The activities of the seven technical commissions of ISPRS were described at a meeting of the Photogrammetric Society on 18th October, 1988. The meeting also heard about the Congress Exhibition and the deliberations of the General Assembly during the Congress. Papers from the Congress were published in the International Archives of Photogrammetry and Remote Sensing 27.  相似文献   
350.
An atomic oxygen flow system and a C14 radiochemical technique have been used to show that the reactions O + CO → CO2 and O + O → O2, are heterogeneously catalysed by solid CO2 at 77 K.The O-CO recombination is first order in CO and inhibited by O, whereas the O-O recombination is first order in O and weakly inhibited by CO. Assuming simple first order kinetics, recombination coefficients γco = 1.3(±0.9) × 10?5 and γO = 0.05± 0.02 are determined. A recombination mechanism involving an intermediate adsorbed CO3 is proposed. If the kinetic results are assumed to apply under Martian surface conditions, then conversion of CO to CO2 by reaction on the solid CO2 at the polar caps occurs at ~10 times the total column recombination rates for homogeneous reactions previously proposed; night-side CO2 ice clouds would also constitute an important recombination surface.  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