首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   66篇
  免费   4篇
  国内免费   3篇
测绘学   3篇
大气科学   22篇
地球物理   15篇
地质学   20篇
天文学   4篇
综合类   3篇
自然地理   6篇
  2023年   1篇
  2022年   1篇
  2020年   1篇
  2019年   4篇
  2017年   2篇
  2015年   3篇
  2014年   2篇
  2013年   2篇
  2012年   2篇
  2011年   3篇
  2010年   1篇
  2009年   5篇
  2008年   11篇
  2007年   2篇
  2006年   1篇
  2005年   4篇
  2004年   2篇
  2003年   2篇
  2002年   1篇
  2001年   2篇
  2000年   1篇
  1999年   2篇
  1995年   1篇
  1994年   2篇
  1993年   2篇
  1992年   1篇
  1990年   3篇
  1988年   1篇
  1986年   1篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1982年   2篇
  1980年   1篇
  1976年   1篇
排序方式: 共有73条查询结果,搜索用时 15 毫秒
21.
近40年拉萨霜期变化的气候特征分析   总被引:11,自引:1,他引:10  
采用气候统计学方法,对拉萨无霜期、初(终)霜日气候特征及其气候变化进行了分析。结果表明:无霜期的绝对变率要比初、终霜日的绝对变率大,终霜日推迟的概率比初霜日提早的概率大。1954~1988年总的趋势是初霜日提早、终霜日推迟、无霜期缩短;1989年后表现为无霜期延长、初霜日推迟、终霜日提早。  相似文献   
22.
利用焉耆盆地3个气象站1961-2014年的初终霜冻日、无霜期资料,采用线性倾向估计法、多项式趋势、M-K检测等统计方法,分析焉耆盆地54a来霜冻气候变化特征。结果表明:(1)焉耆盆地平均初、终霜冻整体均呈显著线性后推趋势,平均分别后推了3d和21d,终霜冻推后速率大于初霜冻,无霜期呈缩短趋势,平均缩短了18d,具有明显的年代际特征。(2)平均初、终霜冻及无霜期分别于1987年、1985年、1967年发生了气候突变,初、终霜冻均表现为由提前转为明显推迟,无霜期表现为由延长转为缩短.(3)焉耆盆地特早、偏早初霜冻发生频率分别为7%和22%,发生在60年代到90年代,特晚、偏晚终霜冻发生频率分别为4%和11%,多发生在70年代和90年代,21世纪各出现一次。(4)终霜日显著推后,无霜期缩短,是今后焉耆盆地农业生产结构优化关注的重点。  相似文献   
23.
对温宿核桃物候期、生长气象条件及主要气象灾害进行了统计分析,以期为有效防灾减灾措施的提出提供参考依据。结果表明:2000年至今核桃花芽膨大期、果实成熟期差异变化不明显,展叶期和开花期逐年均呈偏早趋势;花期与开花期间≥3℃积温、4月日照时数呈显著正相关,积温越高、日照时数越多,花期越早;果实成熟期与6月日照时数相关最为显著,日照时数越多,成熟期越早,反之越晚;越冬期日最低气温-25℃以下持续7天以上,或极端低温-28℃以下持续24小时以上,核桃树就可能遭受冻害。花期主要影响气象灾害为大风浮尘、高温,果实生长期为高温、持续降水,越冬休眠期主要为低温冻害。  相似文献   
24.
冻结地层加固法是一种环境影响小、加固效果好的地层加固方法,人工冻结壁的形成是一个复杂的热-力耦合问题。依托实际盾构隧道始发施工中冻结加固工程,采用有限差分软件Flac3D建立数值模型分析了地铁隧道水平冻结施工中温度场随时间的发展和分布特征,同时采用准热-力耦合的方法,分析了冻结施工中地表冻胀隆起变形规律。分析结果表明:冻结壁模拟交圈时间和设计交圈时间基本一致;冻结壁交圈前,地表冻胀隆起位移速率快,冻结壁交圈之后,地表冻胀变形逐渐趋近稳定。计算结论可供设计和施工参考,提供了一种简便的人工冻结加固施工的数值模拟方法。  相似文献   
25.
The glacial buzzsaw hypothesis suggests that efficient erosion limits topographic elevations in extensively glaciated orogens. Studies to date have largely focussed on regions where large glaciers (tens of kilometres long) have been active. In light of recent studies emphasising the importance of lateral glacial erosion in lowering peaks and ridgelines, we examine the effectiveness of small glaciers in limiting topography under both relatively slow and rapid rock uplift conditions. Four ranges in the northern Basin and Range, Idaho, Montana, and Wyoming, USA, were chosen for this analysis. Estimates of maximum Pleistocene slip rates along normal faults bounding the Beaverhead–Bitterroot Mountains (~ 0.14 mm y− 1), Lemhi Range (~ 0.3 mm y− 1) and Lost River Range (~ 0.3 mm y− 1) are an order of magnitude lower than those on the Teton Fault (~ 2 mm y− 1). We compare the distribution of glacial erosion (estimated from cirque floor elevations and last glacial maximum (LGM) equilibrium line altitude (ELA) reconstructions) and fault slip rate with three metrics of topography in each range: the along-strike maximum elevation swath profile, hypsometry, and slope-elevation profiles. In the slowly uplifting Beaverhead–Bitterroot Mountains, and Lemhi and Lost River Ranges, trends in maximum elevation parallel ELAs, independent of variations in fault slip rate. Maximum elevations are offset ~ 500 m from LGM ELAs in the Lost River Range, Lemhi Range, and northern Beaverhead–Bitterroot Mountains, and by ~ 350 m in the southern Beaverhead–Bitterroot Mountains, where glacial extents were less. The offset between maximum topography and mean Quaternary ELAs, inferred from cirque floor elevations, is ~ 350 m in the Lost River and Lemhi Ranges, and 200–250 m in the Beaverhead–Bitterroot Mountains. Additionally, slope-elevation profiles are flattened and hypsometry profiles show a peak in surface areas close to the ELA in the Lemhi Range and Beaverhead–Bitterroot Mountains, suggesting that small glaciers efficiently limit topography. The situation in the Lost River Range is less clear as a glacial signature is not apparent in either slope-elevation profiles or the hypsometry. In the rapidly uplifting Teton Range, the distribution of ELAs appears superficially to correspond to maximum topography, hypsometry, and slope-elevations profiles, with regression lines on maximum elevations offset by ~ 700 and ~ 350 m from the LGM and mean Quaternary ELA respectively. However, Grand Teton and Mt. Moran represent high-elevation “Teflon Peaks” that appear impervious to glacial erosion, formed in the hard crystalline bedrock at the core of the range. Glacier size and drainage density, rock uplift rate, and bedrock lithology are all important considerations when assessing the ability of glaciers to limit mountain range topography. In the northern Basin and Range, it is only under exceptional circumstances in the Teton Range that small glaciers appear to be incapable of imposing a fully efficient glacial buzzsaw, emphasising that high peaks represent an important caveat to the glacial buzzsaw hypothesis.  相似文献   
26.
作物霜冻与低温强度及冰核菌密度的关系   总被引:4,自引:0,他引:4       下载免费PDF全文
应用辐射型霜箱进行控制试验,研究玉米霜冻害程度与低温强度和冰核菌密度的关系。结果表明逻辑斯蒂克(logistic)方程只有在没有冰核菌或冰核菌密度很小的条件下才能描述霜冻与温度的关系,而理查兹(Richards)方程能够在各种冰核菌密度下很好地描述三者的关系。进而讨论了这种关系在确定霜冻指标,制作霜冻预报,选用防霜方法等方面的应用。  相似文献   
27.
两种探空仪观测湿度垂直分布及其应用比较   总被引:2,自引:2,他引:2       下载免费PDF全文
对2010年8月在云南腾冲利用芬兰Vaisala RS80和低温霜点仪 (Cryogenic Frostpoint Hygrometer,CFH) 两种探空仪测量大气湿度的垂直分布进行对比分析,同时比较它们白天和夜间测量误差的差别,并对国产GTS1,RS80和CFH共3种探空仪测量水汽总量与地基GPS遥测结果进行比较。结果表明:RS80湿度测值在整个对流层比CFH测值偏干 (23.7±18.5)%;因太阳辐射白天RS80偏干较夜间更明显,比夜间偏干 (13.5±14.8)%。而在对流层上层向平流层过渡区域内RS80湿度数据基本无效。CFH在低温、低湿环境下对湿度能有效测量,但在湿度较高的对流层低层测值偏高,导致比较中CFH水汽总量平均比GPS遥测的水汽总量偏高 (4.3±2.0) mm (样本数为11),而RS80,GTS1与GPS的水汽总量差别分别是 (0.2±1.4) mm (样本数为12), (-0.2±2.2) mm (样本数为43)。地基GPS遥测的水汽总量对对流层上层至平流层的水汽变化不敏感。由于RS80测量相对湿度在高空偏低,通过RS80相对湿度测值来确定中、高云结果是偏低的,特别是对6000 m以上的高云判别上,RS80相对湿度的探测几乎很难甄别到云的存在。  相似文献   
28.
This paper presents the results of a physical model study of the performance of landfill clay cover liners subjected to extended freezing periods. Three proposed designs for a prototype cover liner were evaluated with a primary objective being the determination of frost penetration resulting from the sub-freezing temperatures imposed as an upper boundary condition to the model. The ultimate performance of the three liner designs were compared on the basis of frost penetration, leakage through the liner, and frost heave. The observed depth of frost penetration was compared to that predicted using a simplified analytical solution of the thermodynamic problem, in addition to measured field behavior.

The laboratory experiment utilizes a 1.8 m2 tank, of ca 2.1 m depth. The tank is loaded with clay to the specifications required for landfill liners. Three different landfill cover liner designs were modeled in the experimental tank. The performance of the three designs, as measured by a variety of observations, were compared. Frost heave was measured for each design and was found to vary between 3.8 and 4.3 cm. The results indicate the depth of frost penetration was similar for all designs tested (29.2–31.7 cm), although the design which included a soil drainage layer had superior leakage performance.  相似文献   

29.
The surficial deposits and landforms of the middle Dyfi Valley, Wales, are examined and a sequence of glacial, glacio-fluvial and glacio-lacustrine sediments is identified. This is considered to relate to a late stage in the wastage of the Late-Devensian Merioneth ice-cap. A sequence of terrace gravels overlying the giacigenic succession represents dissection during early Flandrian times.  相似文献   
30.
In boreal and nemoboreal forests, tree frost hardiness is modified in reaction to cues from day length and temperature. The dehardening processes in Norway spruce, Picea abies, could be estimated to start when the daily mean temperature is above 5 °C for 5 days. Bud burst will occur approximately after 120–170 degree-days above 5 °C, dependent on genetic differences among provenances. A reduced cold hardiness level during autumn and spring and an advanced onset of bud burst are expected impacts of projected future global warming. The aim of this study was to test if this will increase the risk for frost damage caused by temperature backlashes. This was tested for Sweden by comparing output from the Hadley Centre regional climate model, HadRM3H, for the period 1961–1990 with future IPCC scenario SRES A2 and B2 for 2070–2099. Different indices for calculating the susceptibility to frost damage were used to assess changes in frost damage risk. The indices were based on: (1) the start of dehardening; (2) the severity of the temperature backlash; (3) the timing of bud burst; and (4) the cold hardiness level. The start of dehardening and bud burst were calculated to occur earlier all over the country, which is in line with the overall warming in both climate change scenarios. The frequency of temperature backlashes that may cause frost damage was calculated to increase in the southern part, an effect that became gradually less pronounced towards the north. The different timing of the onset of dehardening mainly caused this systematic latitudinal pattern. In the south, it occurs early in the year when the seasonal temperature progression is slow and large temperature variations occur. In the north, dehardening will occur closer to the spring equinox when the temperature progression is faster.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号