全文获取类型
收费全文 | 841篇 |
免费 | 100篇 |
国内免费 | 347篇 |
专业分类
测绘学 | 211篇 |
大气科学 | 76篇 |
地球物理 | 194篇 |
地质学 | 578篇 |
海洋学 | 113篇 |
天文学 | 17篇 |
综合类 | 63篇 |
自然地理 | 36篇 |
出版年
2023年 | 14篇 |
2022年 | 25篇 |
2021年 | 26篇 |
2020年 | 34篇 |
2019年 | 58篇 |
2018年 | 31篇 |
2017年 | 37篇 |
2016年 | 44篇 |
2015年 | 46篇 |
2014年 | 54篇 |
2013年 | 72篇 |
2012年 | 68篇 |
2011年 | 66篇 |
2010年 | 66篇 |
2009年 | 56篇 |
2008年 | 64篇 |
2007年 | 73篇 |
2006年 | 66篇 |
2005年 | 56篇 |
2004年 | 48篇 |
2003年 | 53篇 |
2002年 | 55篇 |
2001年 | 25篇 |
2000年 | 14篇 |
1999年 | 20篇 |
1998年 | 31篇 |
1997年 | 12篇 |
1996年 | 19篇 |
1995年 | 7篇 |
1994年 | 13篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1982年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有1288条查询结果,搜索用时 234 毫秒
121.
This paper presents an examination of the timescale of phase transition behaviour of a series of salts known to cause damage
to wall paintings and other cultural property. The rate of deliquescence and crystallisation of single salts (nitromagnesite
and halite) under different RH regimes, and the extent to which this was affected when mixed with other salts (niter, nitratite
and gypsum), was investigated. The study was conducted using simple conventional techniques (mass measurements over time)
and also using an innovative new method: timelapse video imaging with online data annotation. The results demonstrate the
synergy gained from combining video imaging with environmental data in reference to time in the study of salt phase changes:
where it revealed new information concerning the kinetics of deliquescence and crystallisation. The implications of these
results for the implementation of environmental control measures within historic buildings are discussed.
相似文献
Alison SawdyEmail: |
122.
We analyse data obtained by different ground-based video camera systems during the 1999 Leonid meteor storm. We observe similar
activity profiles at nearby observing sites, but significant differences over distances in the order of 4,000 km. The main
peak occured at 02:03 UT (λ⊙=235.286, J2000, corrected for the time of the topocentric stream encounter). At the Iberian peninsula quasi-periodic activity
fluctuations with a period of about 7 min were recorded. The camera in Jordan detected a broad plateau of activity at 01:39–01:53
UT, but no periodic variations. The Leonid brightness distribution derived from all cameras shows a lack of faint meteors
with a turning point close to +3m, which corresponds to meteoroids of approximately 10-3 g. We find a pin-point radiant at αalpha=153.65 ±0.1, δ=21.80 ±0. (λ⊙=235.290). The radiant positionis identical before and after the storm, and also during the storm no driftis observed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
123.
Concentrations of Hg0 in surface waters and atmosphere of the Scheldt estuary and the North Sea are presented and their relationship with biological processes is discussed. Hg0 concentrations in the Scheldt estuary range from 0.1 to 0.38 pmol·l−1 in the winter and from 0.24 to 0.65 pmol·l−1 in the summer and show a positive relationship with phytoplankton pigments. In the North Sea Hg0 concentrations range from 0.06 to 0.8 pmol·l−1 and are higher in coastal stations. Transfer velocities across the air–sea interface were calculated using a classical shear turbulence model. Volatilization fluxes of Hg0 were calculated for the Scheldt estuary and the North Sea. For the Scheldt estuary the fluxes range from 226–284 pmol·m−2·d−1 in winter and 500–701 pmol·m−2·d−1 in summer and for the North Sea the fluxes range from 59–1110 pmol·m−2·d−1 for an average windspeed of 8.1 m·s−1. These fluxes are comparable to the wet and dry depositional fluxes to the North Sea. Hg0 formation rates necessary to balance the volatilization fluxes vary from 0.2 to 4% d−1. 相似文献
124.
提出了一种基于图像恢复技术的遥感图像压缩技术,在提高遥感图像压缩比的同时,使压缩后的重建图像质量达到准无损的技术要求。对SRTF、TM图像的试验结果表明,该技术是可行的。 相似文献
125.
介绍了武汉市供电局110联动报修计算机管理系统的设计和实现方法。系统利用ATM网络和PSTN网络,在SQLServer数据库环境中实现配电故障的信息处理。 相似文献
126.
127.
A video analysis method for monitoring sediment transport and sorting processes in a laboratory flume is presented. Video taken through the glass side‐wall of a laboratory flume is captured using a digital CCD (charge‐coupled device) camera and significant movements between individual frames are detected using image analysis. This method involves direct subtraction of the brightness numbers of pixels in sequential video frames, followed by thresholding to produce binarized images of significant change, above the inherent level of system noise. Experimental results showing dilation of a gravel framework and rapid infiltration of fines just prior to entrainment are discussed. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
128.
Cusp formation was continuously monitored on a manually flattened, plane section of a coarse clastic, microtidal, pocket beach on the Pacific coast of Japan using a CCD camera suspended in the air. Vertical video pictures enabled the examination of the temporal change in foreshore morphologies and swash pattern. Boulders on the beach face appeared to have triggered the formation of beach cusps, which gradually and successively grew up alongshore. In 2·5 h, two well defined beach cusps had developed with a spacing of 2·2 and 2·5 m, respectively. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
129.
为了研究近代海相沉积软土的变形特征,本文对珠江三角洲河口地区的全新世海相沉积的软土进行了室内单轴压缩与不同围压下作用下的三轴固结不排水(CU)、不固结不排水(UU)的剪切试验。试验结果表明:原状土和重塑土样的孔隙比随压力的增大而下降,且与加压方式有密切关系,加压幅度越小,土的扰动破坏越小;原状土样固结系数随着压力增加而递减,整体近似符合指数函数分布,重塑土样固结系数随着压力增加逐渐增大,整体近似符合线性函数分布。在相同的固结压力下,原状土样的强度低于重塑土样的强度。土样的应力应变曲线为应变硬化型,且围压对重塑土的影响小于原状土。 相似文献
130.