全文获取类型
收费全文 | 8208篇 |
免费 | 339篇 |
国内免费 | 95篇 |
专业分类
测绘学 | 199篇 |
大气科学 | 566篇 |
地球物理 | 1933篇 |
地质学 | 2979篇 |
海洋学 | 749篇 |
天文学 | 1209篇 |
综合类 | 19篇 |
自然地理 | 988篇 |
出版年
2021年 | 89篇 |
2020年 | 113篇 |
2019年 | 114篇 |
2018年 | 166篇 |
2017年 | 162篇 |
2016年 | 227篇 |
2015年 | 194篇 |
2014年 | 196篇 |
2013年 | 469篇 |
2012年 | 249篇 |
2011年 | 308篇 |
2010年 | 282篇 |
2009年 | 338篇 |
2008年 | 321篇 |
2007年 | 279篇 |
2006年 | 314篇 |
2005年 | 237篇 |
2004年 | 291篇 |
2003年 | 262篇 |
2002年 | 264篇 |
2001年 | 174篇 |
2000年 | 170篇 |
1999年 | 141篇 |
1998年 | 142篇 |
1997年 | 104篇 |
1996年 | 114篇 |
1995年 | 115篇 |
1994年 | 129篇 |
1993年 | 114篇 |
1992年 | 115篇 |
1991年 | 109篇 |
1990年 | 101篇 |
1989年 | 85篇 |
1988年 | 87篇 |
1987年 | 123篇 |
1986年 | 100篇 |
1985年 | 163篇 |
1984年 | 187篇 |
1983年 | 145篇 |
1982年 | 126篇 |
1981年 | 131篇 |
1980年 | 108篇 |
1979年 | 124篇 |
1978年 | 118篇 |
1977年 | 103篇 |
1976年 | 96篇 |
1975年 | 91篇 |
1974年 | 67篇 |
1973年 | 83篇 |
1972年 | 49篇 |
排序方式: 共有8642条查询结果,搜索用时 31 毫秒
211.
The U.S. and U.K. literatures have discussed “food deserts,” reflecting populated, typically urban, low‐income areas with limited access to full‐service supermarkets. Less is known about supermarket accessibility within Canadian cities. This article uses the minimum distance and coverage methods to determine supermarket accessibility within the city of Edmonton, Canada, with a focus on high‐need and inner‐city neighborhoods. The results show that for 1999 both of these areas generally had higher accessibility than the remainder of the city, but six high‐need neighborhoods had poor supermarket accessibility. We conclude by examining potential reasons for differences in supermarket accessibility between Canadian, U.S., and U.K. cities. 相似文献
212.
Robert Gilbert Sarah Crookshanks Kyle R. Hodder John Spagnol Roland B. Stull 《Journal of Paleolimnology》2006,35(4):737-745
Severe rainfall in mid October, 2003 produced the largest floods in almost a century of record on rivers in the Cordillera
of southwestern British Columbia. Sediment deposited in Lillooet Lake as a result of this event is clearly distinguished by
stratigraphy, colour, texture, magnetic properties, and organic content. Each of these physical properties is related to the
lacustrine processes, especially turbid underflow, that distributed the sediment through the lake. The flood, which lasted
less than a week, delivered 8–12 times the amount of sediment that accumulates in most entire years in the deepest, central
parts of the lake. Recognition of events of this type in the stratigraphic record offers a means of assessing the changing
nature of extreme hydroclimatic events, and their relation to more ubiquitous, lower-energy processes. 相似文献
213.
This study investigates the extent to which people's views on the causes and preventability of earthquake damage might be influenced by their degree of exposure to hazard as well as what information they have been given about the hazard. The results show that the provision of hazard zoning information influences judgements on preventability and causes of damage, but this effect depends on the degree of hazard faced by residents. In low hazard zones, information leads to the view that causes are manageable, whereas in high hazard zones information may induce a degree of fatalism. The use of public information in risk management needs to take into account the degree of risk faced by the recipients. 相似文献
214.
On the Social Lives of Maps and the Politics of Diagrams: A story of power, seduction, and disappearance 总被引:1,自引:0,他引:1
John Pickles 《Area》2006,38(3):347-350
215.
K. W. Helen Lau Keith E. Louden Sharon Deemer Jeremy Hall John R. Hopper Brian E. Tucholke W. Steven Holbrook Hans Christian Larsen † 《Geophysical Journal International》2006,167(1):157-170
New multichannel seismic reflection data were collected over a 565 km transect covering the non-volcanic rifted margin of the central eastern Grand Banks and the Newfoundland Basin in the northwestern Atlantic. Three major crustal zones are interpreted from west to east over the seaward 350 km of the profile: (1) continental crust; (2) transitional basement and (3) oceanic crust. Continental crust thins over a wide zone (∼160 km) by forming a large rift basin (Carson Basin) and seaward fault block, together with a series of smaller fault blocks eastwards beneath the Salar and Newfoundland basins. Analysis of selected previous reflection profiles (Lithoprobe 85-4, 85-2 and Conrad NB-1) indicates that prominent landward-dipping reflections observed under the continental slope are a regional phenomenon. They define the landward edge of a deep serpentinized mantle layer, which underlies both extended continental crust and transitional basement. The 80-km-wide transitional basement is defined landwards by a basement high that may consist of serpentinized peridotite and seawards by a pair of basement highs of unknown crustal origin. Flat and unreflective transitional basement most likely is exhumed, serpentinized mantle, although our results do not exclude the possibility of anomalously thinned oceanic crust. A Moho reflection below interpreted oceanic crust is first observed landwards of magnetic anomaly M4, 230 km from the shelf break. Extrapolation of ages from chron M0 to the edge of interpreted oceanic crust suggests that the onset of seafloor spreading was ∼138 Ma (Valanginian) in the south (southern Newfoundland Basin) to ∼125 Ma (Barremian–Aptian boundary) in the north (Flemish Cap), comparable to those proposed for the conjugate margins. 相似文献
216.
217.
218.
Matthew J. Spittal Frank H. Walkey John McClure Richard J. Siegert Kimberley E. Ballantyne 《Natural Hazards》2006,39(1):15-29
Preparedness is a key dependent variable in many studies examining people’s response to disasters such as earthquakes. A feature
of many studies on this issue, however, is the lack of attention given to psychometric issues when constructing measures of
preparedness. With regard to earthquake preparation, for example, many studies could be greatly improved by the use of a valid
and reliable measure of preparedness. This research developed such a measure that assessed both low-level preparedness, such
as having an emergency kit, and high-level preparedness, such as altering home structures to mitigate damage. Studies of Wellington
(New Zealand) residents using two samples totalling n=652 showed that 23 items measuring these different aspects of earthquake preparation could be combined into a reliable, valid,
unifactorial scale. This brief scale should have utility in multivariate studies of earthquake preparation, either as a dependent
variable, where preparation is the outcome variable of primary interest, or as one of several independent variables, where
preparation and other measures predict another outcome variable. 相似文献
219.
Zr-in-rutile thermometry in blueschists from Sifnos, Greece 总被引:1,自引:0,他引:1
Frank S. Spear David A. Wark John T. Cheney John C. Schumacher E. Bruce Watson 《Contributions to Mineralogy and Petrology》2006,152(3):375-385
Zr-in-rutile thermometry on samples of blueschist from Sifnos, Greece, yields temperatures that reflect progressive crystallization of rutile from ca. 445 to 505°C with an analytical precision of + 18/−27 and ± 10°C using the electron microprobe and ± 1.5–3.5°C using the ion microprobe. Individual grains are generally homogeneous within analytical uncertainty. Different grains within a single sample record temperature differences as large 55°, although in most samples the range of temperatures is on the order of 25°. In several samples, Zr-in-rutile temperatures from grains within garnet are lower than temperatures from matrix grains, reflecting growth of rutile with increasing temperature of metamorphism. Although the specific rutile-producing reactions have not been identified, it is inferred that rutile grows from either continuous reaction involving the breakdown of lower grade phases (possibly ilmenite), or from pseudomorph reactions involving the breakdown of relic igneous precursors at blueschist-facies conditions. No systematic variation in rutile temperatures was observed across the blueschist belt of northern Sifnos, consistent with the belt having behaved as a coherent block during subduction. 相似文献
220.
Seismic Hazards Assessment for Radioactive Waste Disposal Sites in Regions of Low Seismic Activity 总被引:4,自引:0,他引:4
Clark H. Fenton John Adams Stephen Halchuk 《Geotechnical and Geological Engineering》2006,24(3):579-592
A comparative tectonic quiescence and lack of earthquakes make the stable centres of continents attractive for siting long-term
radioactive waste storage facilities. The low rates of deformation in such regions, however, make it difficult to characterize
their long-term seismotectonic behaviour, leading to uncertain estimates for the very low probability hazard estimates required
by society. In an attempt to overcome the deficiency of both contemporary seismicity and paleoseismic data in central Canada,
we have used earthquake histories from regions with similar seismotectonic characteristics from around the world. Substituting
space for time, we estimate a long-term rate per 106 km2 of 0.004 magnitude ≥6 earthquakes per annum, of which 33–100% might rupture to the surface. 相似文献