全文获取类型
| 收费全文 | 278篇 |
| 免费 | 21篇 |
| 国内免费 | 2篇 |
专业分类
| 测绘学 | 14篇 |
| 大气科学 | 18篇 |
| 地球物理 | 69篇 |
| 地质学 | 71篇 |
| 海洋学 | 51篇 |
| 天文学 | 53篇 |
| 综合类 | 3篇 |
| 自然地理 | 22篇 |
出版年
| 2022年 | 3篇 |
| 2021年 | 4篇 |
| 2020年 | 10篇 |
| 2019年 | 2篇 |
| 2018年 | 4篇 |
| 2017年 | 8篇 |
| 2016年 | 17篇 |
| 2015年 | 7篇 |
| 2014年 | 8篇 |
| 2013年 | 10篇 |
| 2012年 | 11篇 |
| 2011年 | 10篇 |
| 2010年 | 8篇 |
| 2009年 | 15篇 |
| 2008年 | 17篇 |
| 2007年 | 9篇 |
| 2006年 | 7篇 |
| 2005年 | 5篇 |
| 2004年 | 7篇 |
| 2003年 | 9篇 |
| 2002年 | 9篇 |
| 2001年 | 11篇 |
| 2000年 | 8篇 |
| 1999年 | 10篇 |
| 1998年 | 6篇 |
| 1997年 | 3篇 |
| 1996年 | 6篇 |
| 1995年 | 3篇 |
| 1994年 | 4篇 |
| 1992年 | 4篇 |
| 1991年 | 7篇 |
| 1990年 | 3篇 |
| 1989年 | 2篇 |
| 1988年 | 4篇 |
| 1987年 | 3篇 |
| 1986年 | 5篇 |
| 1985年 | 3篇 |
| 1984年 | 8篇 |
| 1983年 | 6篇 |
| 1982年 | 2篇 |
| 1981年 | 2篇 |
| 1979年 | 2篇 |
| 1978年 | 3篇 |
| 1977年 | 2篇 |
| 1976年 | 2篇 |
| 1975年 | 3篇 |
| 1972年 | 2篇 |
| 1968年 | 1篇 |
| 1966年 | 2篇 |
| 1964年 | 1篇 |
排序方式： 共有301条查询结果，搜索用时 102 毫秒
141.
Use of the conditional spectrum to incorporate record‐to‐record variability in simplified seismic assessment of RC wall buildings 
下载免费PDF全文
下载免费PDF全文 A procedure for incorporating record‐to‐record variability into the simplified seismic assessment of RC wall buildings is presented. The procedure relies on the use of the conditional spectrum to randomly sample spectral ordinates at relevant periods of vibration. For inelastic response, displacement reduction factors are then used to relate inelastic displacement demand to the spectral displacement at the effective period for single‐degree‐of‐freedom systems. Simple equations are used to convert back and forth between multi‐degree‐of‐freedom RC wall buildings and equivalent single‐degree‐of‐systems so that relevant engineering demand parameters can be obtained. Consideration is also given to higher‐mode effects by adapting existing modal combination rules. The proposed method is applied to several case study buildings, showing promising results in the examination of inter‐storey drift ratio and shear forces. The proposed method captures the variation in the distribution of structural response parameters that occurs with variations in structural configuration, intensity, engineering demand parameter of interest and site characteristics. Discussion is provided on possible ways to improve the accuracy of the procedure and suggestions for additional future work. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
142.
We identify and describe a series of east–west left-lateral strike-slip faults (named the Songino-Margats, the Hag Nuur, the Uliastay and the South Hangay fault systems) in the Hangay mountains of central Mongolia: an area that has little in the way of recorded seismicity and which is often considered as a rigid block within the India–Eurasia collision zone. The strike-slip faults of central Mongolia constitute a previously unrecognized hazard in this part of Mongolia. Each of the strike-slip faults show indications of late Quaternary activity in the form of aligned sequences of sag-ponds and pressure-ridges developed in alluvial deposits. Total bed-rock displacements of ∼3 km are measured on both the Songino-Margats and South Hangay fault systems. Bed-rock displacements of 11 km are observed across the Hag Nuur fault. Cumulative offset across the Uliastay fault systems are unknown but are unlikely to be large. We have no quantitative constraint on the age of faulting in the Hangay. The ≤20 km of cumulative slip on the Hangay faults might, at least in part, be inherited from earlier tectonic movements. Our observations show that, despite the almost complete absence of instrumentally recorded seismicity in the Hangay, this part of Mongolia is cut through by numerous distributed strike-slip faults that accommodate regional left-lateral shear between Siberia and China. Central Mongolia is thus an important component of the India–Eurasia collision that would be overlooked in models of the active tectonics based on the distribution of seismicity. We suggest that active faults such as those identified in the Hangay of Mongolia might exist in other, apparently aseismic, regions within continental collision zones. 相似文献
143.
The non-thermal escape of neutral O atoms from Mars at the current epoch is largely due to dissociative recombination of :
144.
We analyze here the behavior of the magnitudes of the F1 and E peaks of the electron density profiles measured by the Radio Science Subsystem of the Mars Global Surveyor spacecraft, as a function of solar zenith angle χ and solar flux. For each of the 658 days of data in the six occultation seasons in the northern hemisphere, we choose one profile to analyze, which is that for which the F1 peak is the median value. We assume that the variations of the measured peak densities can be represented as Aa(cosχ) and as Bb(F10.7), where F10.7 is the usual solar flux proxy, appropriately shifted to the orbital position of Mars. To minimize the effect of solar activity, we divide the data into 6 F10.7 bins, fit the data in each bin, and derive the values of the exponent a and the coefficient AF10.7 for each bin. The median values that we derive for the exponent a is 0.46 for the F1 peak, and 0.395 for the E peak. To minimize the effect of SZA, we divide the data into eight SZA bins, and derive the exponent b and the coefficient Bχ for each SZA bin. We argue that the last three SZA bins should be excluded because the fits were poor, due partly to the small number of data points in each of these bins. If we do so, the median values of b that we derive are 0.27 and 0.40 for the F1 and E peaks, respectively. Finally we derive a 3-parameter fit to all the data, which expresses the variability of the peak densities as a function of a′(cosχ) and b′(F10.7) simultaneously. The fitted values of the exponents a′ and b′ for the F1 peak are 0.45 and 0.26, respectively; for the E peak, the values are 0.39 and 0.46, respectively. We compare our results to Chapman theory, and to those of other investigators. 相似文献
145.
A mathematical model has been developed to forecast or hindcast wind, waves, and longshore currents during the passage of a coastal storm. Storm intensity is a function of the barometric pressure gradient which is modeled by rotating an inverted normal curve around the center of an ellipse. The length and orientation of the major and minor axes of the ellipse control the size and shape of the storm. The path of the storm is determined by a sequence of storm positions for the hindcast mode, and by interpolated positions assuming constant speed and direction for the forecast mode. The site location, shoreline orientation, and nearshore bottom slope provide input data for the shore position. The geostrophic wind speed and direction at the shore site are computed from the latitude and barometric pressure gradient. The geostrophic wind is converted into surface wind speed and direction by applying corrections for frictional effects over land and sea. The surface wind speed and direction, effective fetch, and wind duration are used to compute wave period, breaker height, and breaker angle at the shore site. The longshore current velocity is computed as a function of wave period, breaker height and angle, and nearshore slope. The model was tested by comparing observed data for several coastal locations with predicted values for wind speed, wave period and height, and longshore current velocity. Forecasts were made for actual storms and for hypothetical circular and elliptical storms. 相似文献
146.
Matthias Braun Jefferson Cardia Sim“非汉字符号”es N.Blindow Steffen Vogt U.F.Bremer M.Pfender H.Saurer F.E.Aquino F.A.Ferron 《地球空间信息科学学报》2001,4(2):47-51
1 ＩｎｔｒｏｄｕｃｔｉｏｎＡｔｐｒｅｓｅｎｔ,ＫｉｎｇＧｅｏｒｇｅＩｓｌａｎｄ (ＫＧＩ)ｉｓｏｎｅｏｆｔｈｅｍｏｓｔｆｒｅｑｕｅｎｔｅｄｓｉｔｅｓｉｎＡｎｔａｒｃｔｉｃａ .Ｉｎｔｏｔａｌ,9ｐｅｒｍａｎｅｎｔｒｅｓｅａｒｃｈｓｔａｔｉｏｎｓａｒｅｉｎｏｐｅｒａｔｉｏｎａｎｄｓｅｖｅｒａｌｒｅｓｅａｒｃｈｃａｂｉｎｓｈａｖｅｂｅｅｎｃｏｎｓｔｒｕｃｔｅｄ .ＤｕｅｔｏｔｈｅｅａｓｙａｃｃｅｓｓｖｉａｔｈｅＣｈｉｌｅａｎａｉｒｓｔｒｉｐｔｈｅｎｕｍ ｂｅｒｏｆｔｈｅｉｓｌａｎｄ’ｓｉｎｈａｂｉｔａｎｔｓｒ… 相似文献
147.
Automatic digital elevation model (DEM) generation has become an established technique within mapping agencies. This paper assesses the effectiveness of automatic DEM generation using area-based matching for glaciated terrain in Antarctica. DEM accuracy is assessed by comparison with check data acquired using analytical photogrammetry and independent field measurements.An optimum DEM collection strategy is identified. DEM success is linked to ground terrain type and it is found that areas of a DEM which can be collected successfully are relatively insensitive to changes in the collection strategy. A method of isolating unsuccessful areas of a DEM for manual editing is tested for Antarctic terrain. In this example, over 90% success is achieved in identifying erroneous DEM results measured against check data. 相似文献
148.
The level of hydrocarbons present in the sediments of real estate canals on the east and west coast of Florida was determined using gas chromatography. Although the amount of alkanes present was found to be comparatively low, the ratio of the amount of odd carbon-numbered alkanes to even carbon-numbered alkanes suggested that canals on the Gulf of Mexico are receiving an influx of petroleum products. In addition, the most probable number technique was used to enumerate total aerobic heterotrophic bacteria, aerobic hydrocarbon-degrading bacteria, sulfate reducing bacteria, and sulfate-reducing hydrocarbon-degrading bacteria present in the canal sediments. Results showed significantly higher numbers of hydrocarbon degrading bacteria in the sediments of the west coast canals. 相似文献
149.
Paul A. Delcourt Hazel R. Delcourt Patricia A. Cridlebaugh Jefferson Chapman 《Quaternary Research》1986,25(3)
Human occupation and utilization of plant resources have affected vegetation in the lower Little Tennessee River Valley of East Tennessee for 10,000 yr. Changes in Indian cultures and land use are documented by radiocarbon chronologies, lithic artifacts, ceramics, settlement patterns, and ethnobotanical remains from 25 stratified archaeological sites within the Holocene alluvial terrace. The ethnobotanical record consists of 31,500 fragments (13.7 kg) of wood charcoal identified to species and 7.7 kg of carbonized fruits, seeds, nutshells, and cultigens from 956 features. Pollen and plant macrofossils from small ponds both in the uplands and on lower stream terraces record local vegetational changes through the last 1500 to 3000 yr. Human impact increased after cultigens, including squash and gourd, were introduced ca. 4000 yr B.P. during the Archaic cultural period. Forest clearance and cultivation disturbed vegetation on both the floodplain and lower terraces after 2800 yr B.P., during the Woodland period. Permanent Indian settlements and maize and bean agriculture extended to higher terraces 1.5 km from the floodplain by the Mississippian period (1000 to 300 yr B.P.). After 300 yr B.P., extensive land clearance and cultivation by Historic Overhill Cherokee and Euro-Americans spread into the uplands beyond the river valley. 相似文献
150.
Lewis E. Fox 《Geochimica et cosmochimica acta》1984,48(4):879-884
Dissolved humic acid and soluble iron appear to be chemically unassociated in estuaries despite their coincident removal. This conclusion is supported by differences in the aggregation kinetics of soluble iron and dissolved humic acid, the inability of extracted humic acid to stabilize laboratory preparations of ferric hydroxide, and decreasing ratios of humic acid carbon to soluble iron along the axes of some estuaries. 相似文献