全文获取类型
收费全文 | 1043篇 |
免费 | 28篇 |
国内免费 | 38篇 |
专业分类
测绘学 | 22篇 |
大气科学 | 45篇 |
地球物理 | 266篇 |
地质学 | 364篇 |
海洋学 | 85篇 |
天文学 | 163篇 |
综合类 | 6篇 |
自然地理 | 158篇 |
出版年
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 15篇 |
2020年 | 10篇 |
2019年 | 13篇 |
2018年 | 25篇 |
2017年 | 19篇 |
2016年 | 24篇 |
2015年 | 13篇 |
2014年 | 44篇 |
2013年 | 64篇 |
2012年 | 29篇 |
2011年 | 55篇 |
2010年 | 37篇 |
2009年 | 48篇 |
2008年 | 54篇 |
2007年 | 41篇 |
2006年 | 37篇 |
2005年 | 52篇 |
2004年 | 45篇 |
2003年 | 45篇 |
2002年 | 46篇 |
2001年 | 26篇 |
2000年 | 24篇 |
1999年 | 27篇 |
1998年 | 15篇 |
1997年 | 17篇 |
1996年 | 26篇 |
1995年 | 14篇 |
1994年 | 22篇 |
1993年 | 17篇 |
1992年 | 9篇 |
1991年 | 8篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 20篇 |
1984年 | 16篇 |
1983年 | 15篇 |
1982年 | 12篇 |
1981年 | 4篇 |
1980年 | 11篇 |
1979年 | 14篇 |
1978年 | 11篇 |
1977年 | 4篇 |
1976年 | 11篇 |
1975年 | 3篇 |
1973年 | 5篇 |
排序方式: 共有1109条查询结果,搜索用时 15 毫秒
1.
2.
Lance B. Morrissey Philippe Janvier Simon J. Braddy John P. Bennett Susan B. Marriott Peter R. Tarrant 《Geology Today》2006,22(2):66-67
Armoured jawless fish, or 'ostracoderms', lived 450–360 million years ago, and display unusual morphologies, unlike any modern fish group. Since they left no living descendants, their mode of swimming has, until recently, remained speculative, although this is a crucial question as the first true pectoral fins evolved within the 'ostracoderms'. The discovery of the oldest-known fish trails, from the Early Devonian (400 million year old) 'Lower Old Red Sandstone' of south-east Wales offers new insights into the swimming behaviour of these early fish, notably the osteostracan 'ostracoderms' (or cephalaspids), whose horseshoe-shaped head and paddle-shaped pectoral fins have remained a functional riddle. 相似文献
3.
Quick-look assessments to identify optimal CO2 EOR storage sites 总被引:1,自引:0,他引:1
Vanessa Núñez-López Mark H. Holtz Derek J. Wood William A. Ambrose Susan D. Hovorka 《Environmental Geology》2008,54(8):1695-1706
A newly developed, multistage quick-look methodology allows for the efficient screening of an unmanageably large number of
reservoirs to generate a workable set of sites that closely match the requirements for optimal CO2 enhanced oil recovery (EOR) storage. The objective of the study is to quickly identify miscible CO2 EOR candidates in areas that contain thousands of reservoirs and to estimate additional oil recovery and sequestration capacities
of selected top options through dimensionless modeling and reservoir characterization. Quick-look assessments indicate that
the CO2 EOR resource potential along the US Gulf Coast is 4.7 billion barrels, and CO2 sequestration capacity is 2.6 billion metric tons. In the first stage, oil reservoirs are screened and ranked in terms of
technical and practical feasibility for miscible CO2 EOR. The second stage provides quick estimates of CO2 EOR potential and sequestration capacities. In the third stage, a dimensionless group model is applied to a selected set
of sites to improve the estimates of oil recovery and storage potential using appropriate inputs for rock and fluid properties,
disregarding reservoir architecture and sweep design. The fourth stage validates and refines the results by simulating flow
in a model that describes the internal architecture and fluid distribution in the reservoir. The stated approach both saves
time and allows more resources to be applied to the best candidate sites. 相似文献
4.
5.
6.
Abstract. Four sites were sampled in kelp (Macrocysiis pyrifera) forests occupying rocky bottom habitats along a wave exposure gradient in central California. Consistent betwecn-site differences were found in the three major structural elements - the surface canopy, the undcrstory assemblage, and the ground cover/turf assemblage - of kelp forest communities. Macrocysiis pyrifera was found at all four sites. Nereucyslis tuelkeana only at the most exposed site. The understory kelps Laminaria setchellii and Pterygopltora californica were also characteristic of exposed sites. Articulated coralline algae were more abundant at exposed sites than protected, while fleshy red algae showed the opposite pattern. All four study sites were located along 8.5 km of coastline, and thus were assumed to have available to them the same species pool for colonization. The substrate composition was the same and the amount of unconsolidated substrate was similar at all four sites. We suggest that exposure to wave-generated water motion, through its influence on the surface canopy and therefore on the amount of light reaching the bottom, is responsible for these between-site differences. 相似文献
7.
We developed light requirements for eelgrass in the Pacific Northwest, USA, to evaluate the effects of short- and long-term
reductions in irradiance reaching eelgrass, especially related to turbidity and overwater structures. Photosynthesis-irradiance
experiments and depth distribution field studies indicated that eelgrass productivity was maximum at a photosynthetic photon
flux density (PPFD) of about 350–550 μmol quanta m−2 s−1. Winter plants had approximately threefold greater net apparent primary productivity rate at the same irradiance as summer
plants. Growth studies using artificial shading as well as field monitoring of light and eelgrass growth indicated that long-term
survival required at least 3 mol quanta m−2 day−1 on average during spring and summer (i.e., May-September), and that growth was saturated above about 7 mol quanta m−2 day−1. We conclude that non-light-limited growth of eelgrass in the Pacific Northwest requires an average of at least 7 mol quanta
m−2 day−1 during spring and summer and that long-term survival requires a minimum average of 3 mol quanta m−2 day−1. 相似文献
8.
GI Science, Disasters, and Emergency Management 总被引:6,自引:1,他引:6
Susan L Cutter 《Transactions in GIS》2003,7(4):439-446
Societal responses to disasters begin with the initial post‐event rescue and relief operations, followed by recovery, reconstruction, and then transcend into mitigation actions including the development of pre‐impact preparedness measures, collectively known as the emergency response cycle. This paper highlights some of the applications of GI Science to the emergency response cycle, citing examples from natural hazards and from the World Trade Center disaster on 11th September 2001. More importantly, the paper describes some of the constraints on the utilization of GI Science by the practitioner community: understandable user interfaces; data quantity, quality, and integration; real‐time data and information. Finally, the paper suggests some important GI Science research areas based on the needs of the disasters and emergency management research and practitioner communities. 相似文献
9.
This paper examines historical and spatial trends in hazardous materials transportation spills from 1971 to 1991. While the number of spills Inc.reased steadily during the 1970s, peaking in 1978–1979, there has been a decline in frequency sInc.e then largely due to modifications in reporting. Monetary damages have the opposite temporal pattern, with major Inc.reases recorded from 1982 onward. Death and injury statistics are more variable. Spatially, accidents are more prevalent in the Rust Belt extending from the Northeast corridor westward to the Great Lakes states, as well as in the Southeast. The greatest potential risk to the public is found in smaller, more densely populated industrial states such as New Jersey, Delaware, and Maryland. The spatial distribution, however, has not changed. Potential risk sources (e.g., chemical industry, number of hazardous waste facilities, number of railroad miles) are the best predictors of hazmat Inc.ident frequency. Mitigation efforts (statewide regulatory and/or management policies) also help explain the variability in hazmat Inc.idents. 相似文献
10.
Ellis L. Krinitzsky 《Engineering Geology》1996,45(1-4):45-58
Fisk's work provided a three-dimensional pattern of occurrence and composition of sediments in the alluvial valley and deltaic plain of the lower Mississippi River. He also interpreted the processes by which the sediments were deposited and the relevance of tectonism in their history. These data provide site characterizations that are basic for all major categories of engineering. His work has found applications in better methods for control of the river, stabilizing its banks, locating sources of aggregate for concrete, management of groundwater, maintenance of wetlands, and generally for more reliable, timely and economical evaluations in selecting optimum site locations and determining foundation conditions. Since then, work in the Lower Mississippi Valley (LMV) has expanded enormously and continues to be greatly indebted to formative interpretations by Fisk. 相似文献