全文获取类型
收费全文 | 1627篇 |
免费 | 311篇 |
国内免费 | 421篇 |
专业分类
测绘学 | 132篇 |
大气科学 | 760篇 |
地球物理 | 287篇 |
地质学 | 382篇 |
海洋学 | 474篇 |
天文学 | 40篇 |
综合类 | 78篇 |
自然地理 | 206篇 |
出版年
2024年 | 12篇 |
2023年 | 26篇 |
2022年 | 38篇 |
2021年 | 64篇 |
2020年 | 63篇 |
2019年 | 97篇 |
2018年 | 64篇 |
2017年 | 92篇 |
2016年 | 67篇 |
2015年 | 88篇 |
2014年 | 97篇 |
2013年 | 124篇 |
2012年 | 110篇 |
2011年 | 114篇 |
2010年 | 81篇 |
2009年 | 129篇 |
2008年 | 116篇 |
2007年 | 119篇 |
2006年 | 108篇 |
2005年 | 71篇 |
2004年 | 89篇 |
2003年 | 73篇 |
2002年 | 96篇 |
2001年 | 57篇 |
2000年 | 36篇 |
1999年 | 41篇 |
1998年 | 47篇 |
1997年 | 38篇 |
1996年 | 50篇 |
1995年 | 35篇 |
1994年 | 26篇 |
1993年 | 20篇 |
1992年 | 17篇 |
1991年 | 14篇 |
1990年 | 9篇 |
1989年 | 4篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有2359条查询结果,搜索用时 15 毫秒
971.
Germn Rodríguez 《Ocean Engineering》2003,30(17):2255-2273
The Hartley transform, a real-valued alternative to the complex Fourier transform, is presented as an efficient tool for the analysis and synthesis of ocean surface wave records. Basic theoretical properties of this real-valued transform are briefly reviewed. Similarities and differences between Fourier and Hartley integral transforms, as well as computational benefits and disadvantages between numerical algorithms used to evaluate their discrete versions, are presented. The fast Hartley transform algorithm is used to simulate stationary Gaussian time series of the sea surface elevation and to estimate the spectral density function, the Hilbert transform and the envelope function of wave records. 相似文献
972.
973.
传统观念的底层流是指离底大于或等于2m的海流。离底小于2m的流场特征,至今研究甚少。近年来,随着养殖业的蓬勃发展,对其了解的需求愈来愈迫切。1近底层流观测全国海岛资源综合调查时,按“青岛市海岛办”的要求,在灵山岛西北侧适养区(水深12m)布设了一个近底层(离底20cm)流观测站(35℃46'N,120℃9'E),连续观测15昼夜。观测期间适逢1990年5号台风在江苏省北部登陆,该站测得11.9m/s的风速。观测仪器使用国产HJL1-1型印刷海流计。测流时将海流计悬挂于特制三角架中央,由潜水员精确… 相似文献
974.
基于乌鲁木齐市及其周边9个气象站1961-2020年气候资料以及综合气候舒适度指数模型,采用统计学方法和ArcGIS的精细化空间插值技术对近60a气候舒适度时空变化进行分析。结果表明,乌鲁木齐市气候舒适度及其变化具有明显的区域性和季节性差异:(1)气候舒适度指数的年内变化,平原地带呈双峰双谷的“M”型,山区为单峰单谷的“∩”型。(2)受气温升高、相对湿度增大、风速减小、日照时数减少的综合影响,近60a平原地带春、秋、冬季气候舒适度指数显著(P=0.05)增大,夏季显著减小;山区夏、秋季气候舒适度指数显著增大,冬、春季变化不明显。(3)近30a(199l-2020年)较前30a(196l-1990年),春季和秋季平原地带气候较舒适区海拔上限升高了100-150m,山区气候较不舒适区和不舒适区向高海拔抬升了50-100m;夏季北部平原气候较舒适区海拔上限升高了100-150m,山前倾斜平原至中山带的气候舒适区向高海拔抬升了约100m,高山带气候较不舒适区和不舒适区也向高海拔抬升并压缩了50-100m;冬季虽气候舒适度指数有所增大,但全市属于气候不舒适区的状况未发生改变。 相似文献
975.
The long-term height-resolved wind trend in China under global warming still needs to be discovered. To fill this gap, in this paper we examined the climatology and long-term(1979–2021) trends of the wintertime wind speed at the near-surface and upper atmosphere in China based on long-term radiosonde measurements. At 700, 500, and 400 hPa,much higher wind speed was found over eastern China, compared with western China. At 300, 200, and 100 hPa,maximum wind speed was observed in the latitude zone... 相似文献
976.
Development of a model-based high-resolution extreme surface wind climatology for Switzerland 总被引:1,自引:0,他引:1
Stéphane Goyette 《Natural Hazards》2008,44(3):329-339
An innovative methodology aimed at establishing a numerical model-based high-resolution climatology of extreme winds over
Switzerland is described, that makes use of the Canadian Regional Climate Model where a new windgust parameterization has
been implemented. Self-nesting procedures allow windstorms to be studied at resolution as high as 2-km. The analysis of ten
major windstorms concludes that the average spatial pattern and magnitude of the simulated windspeeds are well captured, and
the areas that experienced extreme winds correspond well with observations and to the location where forest damage was reported
following the last two of these storms. This climatology would eventually serve to form risk assessment maps based on the
exceedance of windspeed thresholds. There is, however, a need for further investigations to encompass the full range of potential
extreme wind cases. The ultimate goal of this methodology is to assess the change in the behaviour of extreme winds for a
climate forced by enhanced greenhouse gas concentrations, and the impact of future windstorms over the Alpine region at high
resolution. 相似文献
977.
Feras Youssef Gunay Erpul Pieter Bogman Wim M. Cornelis Donald Gabriels 《Environmental Geology》2008,55(4):741-750
The trap efficiency of a catcher in wind erosion measurements plays a significant role, and in many cases suspension trap
efficiencies at high wind velocities are still unknown. The sediment trap efficiency generally changes with particles size
and with wind speed. In this study, the efficiency of Vaseline Slide (VS) and Modified Wilson and Cooke (MWAC) catchers were
determined with different sand particle sizes (<50, <75, 50–75, 200–400, and 400–500 μm) at a fixed wind speed (13.3 ms−1) and with different soil textures at different wind velocities (10.3, 12.3, and 14.3 ms−1) in the wind tunnel of the International Center for Eremology (ICE), Ghent University, Belgium. The traps were placed at
different heights (4, 6.5, 13, 20, 120, and 192 cm for VS and 1.5, 3, 5, 8, 11, and 30 cm for MWAC) to catch saltating and
suspended sediments in a 12-m long, 1.2-m wide and 3.2-m high working section of the wind tunnel. In the sand particle experiments,
the efficiency of the VS catcher was 92% for particles smaller than 50 μm and decreased with increasing particles size, falling
to 2.2% for 400–500 μm particle size at 13.4 ms−1. However, the MWAC’s efficiency was 0% for particles smaller than 50 μm and increased with increasing particle size to 69.5%
at 400–500 μm. In the experiments with different soil textures, the efficiency of each catcher significantly changed with
soil and with wind speed. It also considerably varied with the catchers: for instance, for sand (S), the MWAC efficiency was
very high (67.4, 113.4, and 90.5% at 10.3, 12.3, and 14.4 ms−1, respectively) while the efficiency of VS was relatively very low (5.2, 4.4, and 1.9% at 10.3, 12.3, and 14.4 ms−1, respectively). Results indicated that the efficiency depends critically on the particle size, type of catcher, and wind
speed, and these could be helpful to increase the robustness of wind erosion measurements. 相似文献
978.
979.
Shulin Liu Tao Wang Guangting Chen Jian Guo Xian Xue Shaoxiu Ma 《Environmental Geology》2008,53(6):1225-1233
The characteristics of sand and dust movement over different sandy grasslands in China’s Otindag Sandy Land were explored
based on field observations and laboratory analyses. Threshold wind speeds (the speed required to initiate sand movement)
at a height of 2 m above the ground were estimated in the field for different surface types. Threshold wind speed above shifting
dunes in the study area is about 4.6 m s−1 at this height. This value was smaller than values observed above other surfaces, resulting in a greater risk of blowing
sand above these dunes. Differences in sand transport rates (STR) as a function of the severity of desertification resulted
primarily from differences in surface vegetation cover and secondarily from the soil’s grain-size distribution. STR increased
exponentially with increasing near-bed wind velocity. Under the same wind conditions, STR increased with increasing severity
of desertification: from 0.08 g cm−2 min−1 above semi-fixed dunes to 8 g cm−2 min−1 above semi-shifting dunes and 25 g cm−2 min−1 above shifting dunes. Vegetation’s affect on STR was clearly large. Different components of sand and dust were trapped over
different lands: mostly sand grains but little dust were trapped above shifting dunes, but much dust was collected over semi-shifting
and semi-fixed dunes. Human disturbance is likely to produce dust even from fixed dunes as a result of trampling by animals
and vehicle travel. In addition, spring rainfall decreased the risk of sand and dust movement by accelerating germination
of plants and the formation of a soil crust. 相似文献
980.
综合分析国内外风速预报相关文献,从物理方法、统计与机器学习方法、组合方法3个方面对超短期风速预报方法的研究现状进行归纳总结,对比了主要预报方法的优缺点,给出了不确定分析和误差评价指标,探讨了在超短期风速预报研究中应重点解决的问题和发展方向。 相似文献