全文获取类型
收费全文 | 328篇 |
免费 | 41篇 |
国内免费 | 32篇 |
专业分类
测绘学 | 54篇 |
大气科学 | 21篇 |
地球物理 | 19篇 |
地质学 | 24篇 |
海洋学 | 244篇 |
天文学 | 2篇 |
综合类 | 17篇 |
自然地理 | 20篇 |
出版年
2024年 | 3篇 |
2023年 | 10篇 |
2022年 | 9篇 |
2021年 | 19篇 |
2020年 | 26篇 |
2019年 | 25篇 |
2018年 | 17篇 |
2017年 | 16篇 |
2016年 | 13篇 |
2015年 | 19篇 |
2014年 | 14篇 |
2013年 | 13篇 |
2012年 | 10篇 |
2011年 | 16篇 |
2010年 | 14篇 |
2009年 | 21篇 |
2008年 | 14篇 |
2007年 | 19篇 |
2006年 | 13篇 |
2005年 | 11篇 |
2004年 | 13篇 |
2003年 | 13篇 |
2002年 | 5篇 |
2001年 | 14篇 |
2000年 | 8篇 |
1999年 | 5篇 |
1998年 | 10篇 |
1997年 | 2篇 |
1996年 | 11篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1988年 | 3篇 |
排序方式: 共有401条查询结果,搜索用时 15 毫秒
101.
The spatial and temporal variations in aerosols and precursor gases over oceanic regions have special importance in the estimation
of radiative forcing parameters and thereby in the refinement of general circulation models. Extensive observations of the
columnar aerosol optical depth (AOD), total column ozone (TCO) and precipitable water content (PWC) have been carried out
using the on-line, multi-band solar radiometers onboard ORV Sagar Kanya (Cruise # SK 147B) over Bay of Bengal during 11th–28th
August 1999. Aerosol optical and physical properties (optical depth and angstrom parameter) have been estimated at six wavelengths
covering from UV to NIR (380–1020 nm) while TCO and PWC have been determined using the UV band around 300 nm and NIR band
around 940 nm, respectively. Added, concurrent meteorological and satellite observations during this field phase of BOBMEX-99
have been utilized to investigate spectral-temporal variations of AOD, TCO and PWC in marine environment.
The results indicate lower AODs (around 0.4 at characteristic wavelength of 500 nm) and size distributions with abundance
of coarse-mode particles as compared to those aerosols of typical land origin. An interesting result that is found in the
present study is the significant reduction in AOD at all wavelengths from initial to later part of observation period due
to cloud-scavenging and rain-washout effects as well as signature of coastal aerosol loading. The clear-sky daytime diurnal
variation of TCO shows gradual increase during post-sunrise hours, broad maximum during afternoon hours and gradual decrease
during pre-sunset hours, which is considered to be due to photochemical reactions. The diurnal variation curve of PWC showed
maximum (~ 4 cm) during morning hours and gradual decrease (~ 3.5 cm) towards evening hours, which are found to be greater
as compared to typical values over land. Another interesting feature observed is that although the PWC values are very high,
there was no proportionate or appreciable enhancement in AOD—a feature that can be utilized to infer composition of aerosols
over the study region. 相似文献
102.
The problem of wake geometry characterization downstream of a collector for getting water out of advection fog is investigated combining the results coming from wind tunnel trials and an experimental campaign in Peru (Lomas de Mejia), where a fog collection project was running. Results from a physical model of the fog collector at a 1:100 scale tested in a wind tunnel through anemometer velocity measurements and flow visualization techniques showed, at different heights from the ground, the general direction of the flow in the vicinity of the obstacle and the extension of the downstream-disturbed area. Wind speed data collection in Peru showed the reduction in wind speed depending on its intensity. The preliminary results show the utility of such an approach in order to improve the understanding of the flow motion downstream of permeable surfaces. The possibility of spatially characterizing the wake presence has a practical utilization whenever the knowledge of the geometry of the wake downstream of an obstacle is required. 相似文献
103.
屋盖MR智能隔震系统对升船结构顶部厂房地震鞭梢效应的模糊控制 总被引:8,自引:0,他引:8
基于抑制升船结构顶部厂房地震鞭梢效应的目的,本文提出了升船结构顶部厂房屋盖MR智能隔震模糊控制的思想。文中,在建立屋盖智能隔震升船结构计算力学模型的基础上,建立了屋盖MR智能隔震系统对升船结构顶部厂房地震反应模糊控制的设计计算方法。文中并以中国某大坝巨型升船结构为背景,设计了屋盖MR智能隔震系统对升船结构顶部厂房地震反应模糊控制的控制系统。仿真分析和对MR阻尼器的参数研究表明,安装合适的屋盖MR智能隔震系统并采用模糊控制策略能有效地抑制具有不确定参数升船结构顶部厂房地震反应的鞭梢效应,且模糊控制器能保持较好的稳定性能。 相似文献
104.
Kelvin wake is one of the common wakes generated by moving ships and contains rich information about ships. In this paper, free wave elevations of Kelvin wake are calculated based on the Michell thin ship theory combined with a point source perturbation model. The probability density function of sea surface slopes is introduced to calculate the specular reflection of sunlight and skylight and the refraction of scattered light underwater. Satellite-detected Kelvin wakes are then simulated by adding surface specular reflectance and water-leaving reflectance. Simulation results agree well with satellite measurements. The specular reflection of sunlight is the decisive factor affecting the features of Kelvin wakes according to the simulation results. The main factors that influence the specular reflection of sunlight, such as the incident direction and observation direction, ship parameters, and background environment, are discussed. This study is helpful for wake detection and provides a preliminary theoretical method for the retrieval of ship information. 相似文献
105.
This paper is the continuation of the work described in [14], dedicated to the presentation of the results of propeller performance in behind-hull during straight ahead motion obtained by a novel experimental set-up for the measurements of single blade loads. In the present case, the study shows and discusses the single blade and propeller loads developed during steady turning conditions, that were simulated by means of free running, self propelled maneuvering tests for a twin screw configuration. Maneuvering conditions are critical for the ship propulsion system, because the performance of the propeller and the side effects related to its functioning (propeller–hull induced pressure and vibrations, noise) are completely different with respect to the design condition in straight ahead motion. Thrust and torque and generation of in-plane loads (force and moments), developed by the blade during the period, evolve differently for the two propellers, due to different propeller–wake interactions. The understanding and the accurate quantification of propeller loads, in these realistic operative scenarios, are pivotal to design low emission and comfortable ships, fulfilling the requirements of safety and continuity of operations at sea. The analysis is carried out revisiting the investigation in [14] for three different speeds (FN = 0.26, 0.34 and 0.40) and a large set of rudder angles that span moderate and tight maneuvers. 相似文献
106.
107.
108.
It is well known that the Reynolds number has a significant effect on the vortex-induced vibrations (VIV) of cylinders. In this paper, a novel in-line (IL) and cross-flow (CF) coupling VIV prediction model for circular cylinders has been proposed, in which the influence of the Reynolds number was comprehensively considered. The Strouhal number linked with the vortex shedding frequency was calculated through a function of the Reynolds number. The coefficient of the mean drag force was fitted as a new piecewise function of the Reynolds number, and its amplification resulted from the CF VIV was also taken into account. The oscillating drag and lift forces were modelled with classical van der Pol wake oscillators and their empirical parameters were determined based on the lock-in boundaries and the peak-amplitude formulas. A new peak-amplitude formula for the IL VIV was developed under the resonance condition with respect to the mass-damping ratio and the Reynolds number. When compared with the results from the experiments and some other prediction models, the present model could give good estimations on the vibration amplitudes and frequencies of the VIV both for elastically-mounted rigid and long flexible cylinders. The present model considering the influence of the Reynolds number could generally provide better results than that neglecting the effect of the Reynolds number. 相似文献
109.
由于前后桨的相互干扰,对转桨的推力和扭矩呈现非常明显的非定常特点。一些主要的设计参数,如前后桨叶数比、推力比以及桨盘面间距对对转桨的水动力性能皆有一定的影响。分别对它们进行系统的研究有助于减弱对转桨的不利干扰,最大程度地回收周向动能。本文采用CFD方法首先分析了叶数比的影响,推力和扭矩的预报结果与试验值吻合良好,结果显示,叶数比为4∶5的对转桨拥有较好的稳定性。另外,对转桨的效率比等效单桨高8.73%~10.2%左右。最后研究了前后桨不同间距和不同推力比的影响,结果显示,增加前后桨的间距可以有效减小前后桨的不利干扰,但是在一定间距内或者推力比在1附近,对转桨水动力均值变化影响不大。 相似文献
110.
基于CFD技术和重叠网格技术完成了黏性流场中KVLCC2船模的操纵性水动力导数的数值计算。为保证计算的精确性,进行了网格的收敛性分析,给出了合适的网格划分方法;通过数值模拟斜航运动、纯横荡运动和纯艏摇运动计算出的水动力与相应条件下的试验值对比,计算结果与试验值吻合良好,计算出的水动力导数准确度较高。基于MMG分离建模方法建立KVLCC2船模的操纵性数学模型,利用龙格-库塔算法求解微分方程组,对船舶操纵运动进行仿真。回转试验和Z形操舵试验的仿真结果与试验结果对比,其回转直径和轨迹都非常吻合,表明采用的船舶操纵性预报是可行的。 相似文献