全文获取类型
收费全文 | 143篇 |
免费 | 2篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 4篇 |
地球物理 | 21篇 |
地质学 | 50篇 |
海洋学 | 25篇 |
天文学 | 9篇 |
综合类 | 1篇 |
自然地理 | 36篇 |
出版年
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2017年 | 5篇 |
2016年 | 4篇 |
2015年 | 3篇 |
2014年 | 6篇 |
2013年 | 4篇 |
2012年 | 4篇 |
2011年 | 9篇 |
2010年 | 1篇 |
2009年 | 11篇 |
2008年 | 9篇 |
2007年 | 6篇 |
2006年 | 4篇 |
2005年 | 9篇 |
2004年 | 10篇 |
2003年 | 4篇 |
2002年 | 8篇 |
2001年 | 3篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有147条查询结果,搜索用时 781 毫秒
91.
Buck J.R. Preisig J.C. Johnson M. Catipovic J. 《Oceanic Engineering, IEEE Journal of》1997,22(2):281-291
The shallow-water acoustic channel supports far-field propagation in a discrete set of modes. Ocean experiments have confirmed the modal nature of acoustic propagation, but no experiment has successfully excited only one of the suite of mid-frequency trapped modes propagating in a coastal environment. The ability to excite a single mode would be a powerful tool for investigating shallow-water ocean processes. A feedback control algorithm incorporating elements of adaptive estimation, underwater acoustics, array processing, and control theory to generate a high-fidelity single mode is presented. This approach also yields a cohesive framework for evaluating the feasibility of generating a single mode with given array geometries, noise characteristics, and source power limitations. Simulations and laboratory wave guide experiments indicate the proposed algorithm holds promise for ocean experiments 相似文献
92.
Gregory Buck 《Celestial Mechanics and Dynamical Astronomy》1991,51(4):305-317
Moulton's Theorem says that given an ordering of masses m 1, ..., m nthere exists a unique collinear central configuration. The theorem allows us to ask the questions: What is the distribution of n equal masses in the collinear central configuration? What is the behavior of the distribution as n → ∞? These questions are due to R. Moekel (personal conversation). Central configurations are found to be attracting fixed points of a flow — a flow we might call an auxiliary flow (in the text it is denoted F(X)), since it has little to do with the equations of motion. This flow is studied in an effort to characterize the mass distribution. Specifically, for a collinear central configuration of n equal masses, a bound is found for the position of the masses furthest from the center of mass. Also some facts concerning the distribution of the inner masses are discovered. 相似文献
93.
Yuko Ogata Kaoruko Mizukawa Satoru Iwasa Yukie Mato Keiji Okuda Michio Murakami Ruchaya Booyatumanondo Le Quang Dung Carlos Miguez Charles Moore Steven Weerts Erick Burres Michael Van Velkenburg Richard C. Lang Brenda Danner Richard C. Thompson 《Marine pollution bulletin》2009,58(10):1437-1446
Samples of polyethylene pellets were collected at 30 beaches from 17 countries and analyzed for organochlorine compounds. PCB concentrations in the pellets were highest on US coasts, followed by western Europe and Japan, and were lower in tropical Asia, southern Africa and Australia. This spatial pattern reflected regional differences in the usage of PCBs and was positively correlated with data from Mussel Watch, another monitoring approach. DDTs showed high concentrations on the US west coast and in Vietnam. In Vietnam, DDT was predominant over its metabolites (DDE and DDD), suggesting the principal source may be current usage of the pesticide for malaria control. High concentrations of pesticide HCHs were detected in the pellets from southern Africa, suggesting current usage of the pesticides in southern Africa. This study demonstrates the utility and feasibility of the International Pellet Watch approach to monitor POPs at a global scale. 相似文献
94.
A history of Holocene glaciation in the Antarctic and sub-Antarctic affords insight into questions concerning present and future ice-sheet and mountain-glacier behavior and global climate and sea-level change. Existing records permit broad correlation of Holocene ice fluctuations within the region. In several areas, ice extent was less than at present in mid-Holocene time. An important exception to this is the West Antarctic Ice Sheet, which has undergone continued recession throughout the Holocene, probably in response to internal dynamics. The first Neoglacial ice advances occurred at 5.0 ka, although some sites (e.g., western Ross Sea) lack firm evidence for glacial expansion at that time. Glaciers in all areas underwent renewed growth in the past millennium, and most have subsequently undergone recession in the past 50 years, ranging from near-catastrophic in parts of the Antarctic Peninsula to minor in the western Ross Sea region and sections of East Antarctica. This magnitude difference likely reflects the much greater warming that is taking place in the Antarctic Peninsula region today as compared to East Antarctica. 相似文献
95.
Brenda Matthews Edwin Bergin Antonio Crapsi Michiel Hogerheijde Jes Jørgensen Dan Marrone Ramprasand Rao 《Astrophysics and Space Science》2008,313(1-3):65-68
We present our most recent results from an ongoing study of the Class 0 source Barnard 1c in Perseus. This source is of particular
interest because it exhibits evidence of strong alignment of grains all the way to the core’s centre, which is contrary to
all other low-mass protostellar cores observed to date. Our goal is to clarify the source of poor alignment in other sources
by identifying the source of strong alignment in B1c. A central cavity has been identified in N2H+ emission; its anticorrelation with C18O emission suggests that heating in the centre has released CO from grain mantles, in turn destroying N2H+. We present sensitivity-limited, high spatial resolution polarimetry data from the SubMillimeter Array and discuss the potential
implications of these data. 相似文献
96.
Brenda Parker 《The Professional geographer》2006,58(4):470-484
Despite the growing practice of community mapping, empirical research remains limited. Extant studies have focused primarily on “counter‐maps” and indigenous maps, leaving many locally produced maps and their authors' perspectives unexplored. This article identifies the mapping process as critical to the definition and understanding of community mapping. It links critical cartography literature to goals of community‐mapping practitioners through themes of inclusion, transparency, and empowerment. The discussion highlights the social construction and practice of “community,” the relationship between maps and power, the definitional difficulties associated with community mapping, and the figurative and literal boundaries that constrain community cartography. Finally, it points to areas for further research and exploration. 相似文献
97.
It has been assumed that soil pendants form in a similar manner as stalactites, in which innermost laminae are the oldest and outer laminae are the youngest. This study presents a new interpretation for soil pendant development. Pahranagat Valley, Nevada, pendants contain features indicating continued precipitation through time at the clast–pendant contact, implying that the oldest deposits are not always found at the pendant–clast contact, as other studies have assumed. These features include a void at the clast–pendant contact where minerals such as calcium carbonate, silica, and/or fibrous silicate clays precipitate. In addition, fragments of the parent clast and detrital grains are incorporated into the pendant and are displaced and/or dissolved and result in the formation of sepiolite. This study indicates that pendants are complex, open systems that during and after their formation undergo chemical changes that complicate their usefulness for dating and paleoenvironmental analyses. 相似文献
98.
The burgeoning literature on transnationalism involving skilled migrants--based largely on the view from the developed world--have generally paid little heed to “elite” women and the reproductive sphere. We argue that women play many roles in elite transnational migration streams and must be given full consideration as part of the “transnational elite.” Attention is given to the way women--both “tied” and “lead” migrants--negotiate gendered identities as they participate in Singapore's regionalisation process, a state-driven initiative to extend the national economy by leveraging on growth in the region. Empirical material for the paper is mainly based on in-depth interviews with married women who were part of a larger project involving interviews with 150 Singaporeans who had lived, or were living, in China. In examining the movements through transnational space between Singapore and China, it is clear that patriarchal norms continue to shape women's understandings of their own identities vis--vis men's. Singapore women who move as accompanying spouses (the majority) find themselves giving up careers to focus on their domestic role in China (in the absence of access to “suitable” paid domestic service), and are not so much “deskilled” but “re-domesticated”. The exceptional few women who ventured into China as entrepreneurs experienced considerable strain holding together geographically separate spheres of productive and reproductive work across the transnational terrain. Both sets of “stories” alert us to the need to include “elite” women--whether accompanying spouses or independent entrepreneurs--in our understanding of “transnational elites.” This will contribute to the urgent task of ensuring that both productive and reproductive work are valorized in equal measure in conceptualizing transnationalism. 相似文献
99.
100.
Wolfgang Lutz Mahendra Shah Richard E. Bilsborrow John Bon-gaarts Partha DasGupta Barbara Entwisle Günther Fischer Brigida Garcia Daniel J. Hogan Arne Jernelöv Zhenghua Jiang Robert W. Kates Sanjaya Lall F. Landis MacKellar P.K. Makinwa-Adebusoye Anthony J. McMichael Vinod Mishra Norman Myers Nebojsa Nakicenovic Sten Nilsson Brian C. O'Neill Xizhe Peng Harriet B. Presser Nafis Sadik Warren C. Sanderson Gita Sen Barbara Torrey Dirk van de Kaa Hans J.A. van Ginkel Brenda Yeoh Huda Zurayk 《Global Change & Human Health》2002,3(1):33-35
The forthcoming World Summit on Sustainable Development (WSSD) in Johannesburg (August 26-September 4, 2002) has been set
by the United Nations to consider strategies toward sustainable development in all its dimensions. Hence, its mandate is broader
than that of the Rio 1992 United Nations Conference on Environment and Development (UNCED). Population issues have so far
been discussed in a separate series of World Population Conferences (Bucharest 1974, Mexico City 1984, Cairo 1994). With no
new World Population Conference scheduled for 2004 and Johannesburg having a mandate that is stated to explicitly include
social and economic aspects, population as a key component of sustainable development should figure prominently on the Johannesburg
agenda. Yet, after the third of four preparatory meetings for Johannesburg (which ended in New York on April 5th), consideration
of population is completely absent. The reasons for this are not entirely clear. We assume that they have to do with the fear
of entering into political controversies over abortion. We are concerned that, despite its broader mandate, in most countries
inputs to Johannesburg are being prepared mainly by environment ministries who have little experience in dealing with population
questions.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献