全文获取类型
收费全文 | 51篇 |
免费 | 3篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 1篇 |
地球物理 | 11篇 |
地质学 | 17篇 |
海洋学 | 3篇 |
天文学 | 11篇 |
自然地理 | 9篇 |
出版年
2023年 | 1篇 |
2021年 | 1篇 |
2017年 | 1篇 |
2016年 | 1篇 |
2013年 | 1篇 |
2010年 | 3篇 |
2008年 | 2篇 |
2007年 | 4篇 |
2006年 | 3篇 |
2005年 | 1篇 |
2004年 | 5篇 |
2003年 | 1篇 |
2002年 | 1篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1998年 | 2篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1971年 | 2篇 |
排序方式: 共有55条查询结果,搜索用时 270 毫秒
11.
12.
M. Fadavi A. Verveer J. Aymon D. Merlin K. Situ C. Pennypackker J. D. Biggs G. White A. Gould G. Greenberg V. Hoette K. McCarron K. Archer F. Pino M. Hibbs M. Ford J. Wetsch 《Astronomische Nachrichten》2006,327(8):811-813
The Pilot Small Telescope Network (PSTN) is a state‐of the art system of easily replicable and scalable hardware, software, servers, eXtensible Markup Language (XML) protocols, and network middleware connecting and developing a pilot array of robotic telescopes to one another and the user community. The PSTN is a developmental project that will allow growing access to these telescopes, and make available data to faculty, students and others in an environment of collaboration. The underlying goal of the PSTN is to broaden the quantity and quality of astronomical education and research, particularly with a focus on traditionally underserved populations. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
13.
J. J. Pereira J. Ziskowski R. Mercaldo-Allen C. Kuropat D. Luedke E. Gould 《Estuaries and Coasts》1992,15(3):289-297
Vitellogenin is an egg-yolk precursor protein in teleosts which is crucial to the survival of larvae. Manufactured in the liver, where pollutants are known to accumulate, and transported to the ovary by the blood, its synthesis by the liver or uptake by the gonad can be compromised by accumulation of xenobiotics. In three studies, winter flounder (Pleuronectes americanus) blood samples were taken to determine normal levels of vitellogenin during the reproductive cycle, and to learn how its production might be affected in degraded environments. Specifically, these studies followed the seasonal cycle of vitellogenin production in winter flounder through monthly sampling at relatively clean (Shoreham, New York) and degraded areas (Black Rock and New Haven harbors, Connecticut) in Long Island Sound; examined the relationship between parental vitellogenin levels and survival of offspring by sampling fish that had been spawned at the Milford Laboratory for a reproductive success study; and determined the effect of gross liver lesions on vitellogenin production by sampling flounder from Boston Harbor, Massachusetts, which have been reported to have a high prevalence of liver tumors. Blood vitellogenin levels were determined by measuring alkali-labile phosphate (ALP). Large fish (>30 cm) from the two degraded sites had elevated serum ALP levels relative to those from the clean area. Lowered total ovarian lipid levels in large fish from Black Rock Harbor suggested impaired vitellogenin uptake. There were no significant differences in serum ALP among the small (≤30 cm) fish from the three sampling sites. Boston Harbor flounder with gross liver lesions had lower ALP values than fish without such lesions. There were no significant differences in ALP values among the spawned fish. 相似文献
14.
Gould WT 《Applied geography (Sevenoaks, England)》1995,15(3):203-218
It is argued that the research agenda on fertility decline needs to be explanatory rather than operational and not tied to government policy justification. The research agenda should be set in the broader developmental and geographic contexts and with consideration of cultural practices. Demographic and Health Surveys provide limited biosocial data, which does not provide a fuller analysis of the factors affecting contraceptive use and effectiveness. Clear associations are drawn between rising contraceptive use and fertility decline and are used as supports for national and international policy makers. Although policy formation may be justified by this research agenda, the view is taken that this is "bad science." Kenya has been used as a model for population change in Africa. Kenya is viewed as a country with obvious direct government involvement in policies on fertility reduction, which mirror the ideological biases of the global model. The global model assumes a universal relationship between fertility and contraceptive prevalence and attaches little significance to cultural differences. However, research recognizes that in Africa family relationships, land tenure, and economic organization are different and highly variable. If economic and social variables on Kenya were available, it is possible that the economic change hypothesis could be proven. Kenya has great regional differences and wide gaps in levels of development. For many countries population growth is the key factor in development, and policies reflect the threat of loan conditions or reductions in foreign aid. Many African countries moved in the direction of reducing population growth through improved health and education, more jobs, improved status of women, and other indirect measures. This approach relies on the Western model of demographic transition. This author argues that knowledge and conclusions about fertility in Africa are more conditioned by ideology rather than technical concerns. In the case of Kenya ideology is supported by research, but a fuller explanation of family formation is not yet available. Kenya's population policy is based on the contraception hypothesis, and data are not yet available for testing other alternative child mortality or economic change hypotheses and constructively informing policy makers about fertility decline. 相似文献
15.
16.
Countries need to know what species are present within their waters to effectively manage the issue of non-indigenous marine species. Five survey methods are currently employed to detect introduced marine species: the Hewitt and Martin protocols (66% of effort; 73 ports, 12 countries); Rapid Assessment Surveys (7% of effort; 8 regions, 4 countries); the Bishop Museum protocols (7% of effort; 8 ports, 3 countries); the Chilean aquaculture surveys (1% of effort; numerous regions; 1 country); and Passive Sampling protocols (18% of effort; 20 ports, 2 countries). These methods use either quantitative, qualitative, or a mixture of the two sampling techniques and tend to target locations that are potential inoculation sites (i.e., such as ports, marinas and aquaculture facilities). To date, introduced marine species surveys have been implemented in 19 countries and have detected more than 1185 non-indigenous, 735 cryptogenic and 15,315 native species. 相似文献
17.
— Simulation of the complete earthquake generation process requires assimilation of observational data on long-term behavior of faults over multiple rupture cycles. Paleoseismology, the study of pre-instrumental earthquakes from geological field investigations, provides the only observations of long-term fault behavior. Paleoseismic data present challenges for assimilation into models because data sets are small, sparse, analog, and contain qualitative uncertainties. Observations can be categorized as primary measurements from field data, or non-primary extrapolations or interpretations of primary data. Assimilation of non-primary data could yield biased simulation results. We present a primary data set for the San Andreas and Imperial faults for comparison with non-primary data in existing databases, and propose standard formats and structure for paleoseismic data assimilation into numerical simulation models . 相似文献
18.
Polarimetric observations of 300 pulsars have been conducted with the 76-m Lovell telescope at Jodrell Bank at radio frequencies centred around 230, 400, 600, 920, 1400 and 1600 MHz. More than half of the pulsars have no previously published polarization profiles and this compilation represents about three times the sum of all previously published pulsar polarization data. A selection of integrated polarization profiles is provided. Tables of pulse widths and the degree of both linear and circular polarization are given for all pulsars, and these act as an index for all the data, which are available by anonymous ftp in numerical and graphical form. 相似文献
19.
The sources of reservoired liquid hydrocarbons in Australia differ substantially from their Northern Hemisphere counterparts. Not only are Australian source rocks largely of terrigenous origin but the concepts accepted as defining the hydrocarbon potential of source rocks have recently been challenged. Although isotopic measurements on Australian source rocks and liquid hydrocarbon products closely parallel those published from elsewhere, new interpretations of these data have been made, particularly with regard to D/H ratios in coals. As interesting as such results may be, the most important findings relate to the origins and histories of methane, the higher gaseous hydrocarbons and carbon dioxide, and the interpretation of these data in terms of hydrocarbon genesis. Simple Northern Hemisphere concepts which characterize gases as being biogenic, oil-associated, etc., on the bases of their isotopic and chemical compositions are clearly not applicable to the Australian scene. Indeed justification of such precise classifications in the Northern Hemisphere on the available evidence is also questioned.Isotopic and compositional data from gases from the Cooper, Bowen, Sydney and Gippsland Basins and from the North West Shelf (Australia) are reviewed, and assessed in terms of generation pathways. 相似文献
20.
B. K. Maheshwari K. Z. Truman M. H. El Naggar P. L. Gould 《Soil Dynamics and Earthquake Engineering》2004,24(4):343-356
A three-dimensional method of analysis is presented for the seismic response of structures constructed on pile foundations. An analysis is formulated in the time domain and the effects of material nonlinearity of soil on the seismic response are investigated. A subsystem model consisting of a structure subsystem and a pile-foundation subsystem is used. Seismic response of the system is found using a successive-coupling incremental solution scheme. Both subsystems are assumed to be coupled at each time step. Material nonlinearity is accounted for by incorporating an advanced plasticity-based soil model, HiSS, in the finite element formulation. Both single piles and pile groups are considered and the effects of kinematic and inertial interaction on seismic response are investigated while considering harmonic and transient excitations. It is seen that nonlinearity significantly affects seismic response of pile foundations as well as that of structures. Effects of nonlinearity on response are dependent on the frequency of excitation with nonlinearity causing an increase in response at low frequencies of excitation. 相似文献