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701.
构建了基于双高速摄像机的立体摄影测量与大范围PIV测量系统,实现了对高坝泄洪的水面曲面和流速场的原型观测.摄影测量系统将相机内外参数分开标定,既保证了相机标定精度,又减少了布置标定点的工作量;使用SIFT关键点标识法提取不同照片中水流表面流动纹理的特征点.大范围PIV系统中,使用灰度标准化、背景移除、中值滤波等方法提取水流表面流动纹理作为PIV计算的示踪物,解决了原型观测中释放示踪物的难题.根据重构出的水面曲面形态对大范围PIV所得流场进行尺度换算与水面贴合,得到真实的表面流场.在向家坝消力池运用实例表明,本方法的计算结果合理. 相似文献
702.
A turbulent microstructure experiment was undertaken at a low latitude of 10°N in the South China Sea in late August 2012. The characteristics of the eddy diffusivity above 650 m were analyzed, which is one order of magnitude larger than that in the open ocean at that low latitude. Enhanced eddy diffusivities by strong shears and sharp changes in topography were observed. The strongest eddy diffusivity occurred in the mixed layer, and it reached O(10–2 m2/s). Strong stratification in the thermocline inhibited the penetration of surface eddy diffusivities through the thermocline, where the mixing was weakest. Below the thermocline, where the background eddy diffusivity was approximately O(10–6 m2/s), the eddy diffusivity increased with depth, and its largest value was O(10–3 m2/s). 相似文献
703.
704.
A modified cross-twinning growth mechanism is put forward to explain the anomalous morphology of a spinel multiple-twin from Sri Lanka, flattened crosswise the twin
planes. Cross-twinning in spinel was found also in other specimens from Pegu (Myanmar), and the results were published in
a previous paper. This particular type of twinning is derived from the combination of cyclic
twinning with lamellar
twinning, so that these samples may be thought of as partial fivelings (cubic cyclic {111} twins with five components sharing a common <110> pseudo-fivefold axis). In the present paper, the sample
from Sri Lanka has been suitably cut with the aim of focusing the study on the cross-twinning region. The transformation matrices
that link the orientation states of each couple of twin components have been determined by means of White Beam Synchrotron
Radiation Topography. They showed that the specimen is made up of four twin components (A, B, C and D), with three twin planes:
and They also showed that the cross-twinned individuals (B and D) actually are not twinned to each other, and that a simple crystallographic
relationship holds between them. X-ray diffraction topography by conventional source allowed to image the crossing-region
and to determine that the cross-twinned individuals are in contact through a semi-coherent boundary, with twinning dislocations contributing to relieve the coherency strains. Electron probe microanalyses with wave dispersive spectroscopy showed that
the chemical composition is almost homogeneous, at least within the spatial resolution limit of this technique. The similar
growth features observed in the spinel sample from Sri Lanka and in those from Myanmar are interpreted as growth marks, indicators of a similar origin: in both cases they are found in impure dolomitic marbles. In particular, the specimen from
Sri Lanka results from the interaction of thermal and metasomatic effects due to contact metamorphism. An unusual stepped
morphology of the face close to the twin boundary, possibly due to corrosion and re-growth processes acted preferentially at a re-entrant corner by metasomatic
fluids, is interpreted as indicator of a metasomatic event that succeeded to the crystal growth, the latter occurred by thermal
effect.
相似文献
Rosa Anna FregolaEmail: |
705.
南极普里兹湾是我国南极中山站建站的重要依托海域 ,是科考船前往中山站进出的必由之路。本文根据普里兹湾近岸的中山站附近海域概略水深 ,研究分析了地形基本概况 ,崎岖不平的中山站近海湾部水下地形 ,沿其湾顶部轴线SN向形成了一条绵延弯曲的水深达 80 0m以浅的海底峡谷 ,通往冰盖底部。峡谷两侧地形复杂 ,水下丘岭嶙峋。从冰盖沿峡谷崩裂下来的冰山 ,最终依其适宜的水深 ,绕过地形障碍 ,沿海底峡谷西侧随风和流往西离去。除中山锚地抛锚区域属于浅水低洼的平缓台地外 ,湾内其它水域可供科考船抛锚的优越水下地形极少 相似文献
706.
707.
708.
In this paper, we try to calculate precipitation in Miyake Island, Japan. In order to know the temporal and spatial variations of precipitation, we have set 15 rain gauges randomly in the island to collect the monthly precipitation data since June 1994. It is found that the precipitation is very different from point to point. First, we used statistical methods to get the correlations between the monthly precipitation at our survey points and that at the weather station. Next, regression analyses were used to establish formulae to calculate precipitation as a function of altitude, aspect of the geomorphological surface and wind direction. Based on these results, distributions of monthly and yearly precipitation and δ18O over the island were assessed. The results show that landscape patterns strongly influence precipitation distribution over the island, with the highest precipitation being found on the windward side, about 400–600 m above sea level. Even at places at the same altitude, the precipitation was different because of the aspect of the landscape. At the same time, altitude effects for δ18O on both the windward and leeward sides were −0·10‰/100 m and −0·15‰/100 m, respectively. Comparing with the distribution of precipitation distribution, it was also found that δ18O for the windward and leeward sides was different from that for precipitation, which means that both topographical effects must be considered separately. © 1998 John Wiley & Sons, Ltd. 相似文献
709.
710.
Satellite gradiometry is an observation technique providing data that allow for evaluation of Stokes’ (geopotential) coefficients.
This technique is capable of determining higher degrees/orders of the geopotential coefficients than can be achieved by traditional
dynamic satellite geodesy. The satellite gradiometry data include topographic and atmospheric effects. By removing those effects,
the satellite data becomes smoother and harmonic outside sea level and therefore more suitable for downward continuation to
the Earth’s surface. For example, in this way one may determine a set of spherical harmonics of the gravity field that is
harmonic in the exterior to sea level.
This article deals with the above effects on the satellite gravity gradients in the local north-oriented frame. The conventional
expressions of the gradients in this frame have a rather complicated form, depending on the first-and second-order derivatives
of the associated Legendre functions, which contain singular factors when approaching the poles. On the contrary, we express
the harmonic series of atmospheric and topographic effects as non-singular expressions. The theory is applied to the regions
of Fennoscandia and Iran, where maps of such effects and their statistics are presented and discussed. 相似文献