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601.
602.
荒漠戈壁下垫面表面动量和感热湍流通量参数化研究 总被引:9,自引:0,他引:9
用合理筛选以后的野外观测资料,研究了荒漠戈壁地表湍流通量参数化的问题。首先,分析了Monin-obukhov相似函数的特征,并拟台出了其经验公式。结果表明,风速和温度相似性函数随稳定度参数的变化曲线与典型经验曲线差异较小,并且在经验曲线分布范围以内,但中性时的值有所不同。同时,还用该资料给出了动量和标量粗糙度(感热粗糙度)长度的平均值及其标量粗糙度随摩擦速度的变化关系。发现标量粗糙度的平均值大约比动量粗糙度的小一个量级,并且随摩擦速度的增大而减小,但明显比其理论预测值要大。 相似文献
603.
The Influence of Vegetation Cover on Summer Precipitation in China: a Statistical Analysis of NDVI and Climate Data 总被引:18,自引:0,他引:18
This study provides new evidence for the feedback effects of vegetation cover on summer precipitation in different regions of China by calculating immediate (same season), and one-and two-season lagged correlations between the normalized difference vegetation index (NDVI) and summer precipitation. The results show that the correlation coefficients between NDVI in spring and the previous winter and precipitation in summer are positive in most regions of China, and they show significant difference between regions. The stronger one-and two-season lagged correlations occur in the eastern arid/semi-arid region, Central China,and Southwest China out of the eight climatic regions of China, and this implies that vegetation cover change has more sensitive feedback effects on summer precipitation in the three regions. The three regions are defined as sensitive regions. Spatial analyses of correlations between spring NDVI averaged over each sensitive region and summer precipitation of 160 stations suggest that the vegetation cover strongly affects summer precipitation not only over the sensitive region itself but also over other regions, especially the downstream region. 相似文献
604.
605.
地震动输入能量衰减规律的研究 总被引:6,自引:1,他引:6
对所收集到的266条强震记录,将其按场地条件分类,计算了不同场地条件、不同延性系数下的“绝对”和“相对”输入能量反应谱,然后利用两步回归法,得出了不同场地条件下地震动“绝对”和“相对”两种输入能量的衰减规律,分析了场地条件、延性系数、震级及距离等参数对地震动能量谱的影响,并对两种输入能量衰减规律进行了比较。 相似文献
606.
607.
608.
时间项分析法中,应用广义最小二乘法进行反演,对长白山天池火山区岩浆系统的长白—敦化(L1)剖面的Pg波到时进行了计算处理,得到了Pg波时间项及基底速度值;取上部地壳的介质平均速度为4.5km/s,经反演求得了各点的深度值,给出了长白山天池火山区结晶基底的厚度分布。结晶基底厚度一般在2.0km左右,而在长白山天池下方结晶基底最厚处接近4.0km;在万宝和敦化附近各有一不太明显的凹陷,其原因可能与在这两个位置处有几条断裂穿过有关。 相似文献
609.
610.
Numerical simulation of a South China Sea typhoon Leo (1999) 总被引:6,自引:0,他引:6
K.-H. Lau Z.-F. Zhang H.-Y. Lam S.-J. Chen 《Meteorology and Atmospheric Physics》2003,83(3-4):147-161
Summary ?A South China Sea typhoon, Leo (1999), was simulated using the Penn State/NCAR mesoscale model MM5 with the Betts-Miller
convective parameterization scheme (BMEX). The simulation had two nested domains with resolutions at 54 and 18 km, and the
forecast duration was 36 hours. The model was quite successful in predicting the track, the rapid deepening, the central pressure,
and the maximum wind speed of typhoon Leo as verified with reports from the Hong Kong Observatory (HKO). The structure of
the eye, the eye wall, and the spiral convective cloud band simulated in the model are found to be comparable to corresponding
features identified in satellite images for the storm, and also with those reported by other authors.
A trajectory analysis was performed. Three kinds of trajectory were found: (1) spirally rising trajectories near the eye wall;
(2) spirally rising/descending trajectories in the convective/cloud free belt; (3) straight and fast rising trajectories in
a heavy convection zone along one of the cloud bands on the periphery of the tropical cyclone.
Both the HKO and the U.S. Joint Typhoon Warning Center (JTWC) reported the rapid deepening of Leo started around 00 UTC 29
April. In the model, the eye was first formed in the lower troposphere, and it extended to the upper troposphere within a
few hours. We speculate that the spin-up of cyclonic rotation in the low-level eye enhanced the positive vorticity along the
low-level eye wall. The positive vorticity was then transported to the upper troposphere by convection, leading to an extension
and growth of the eye into the upper troposphere.
To examine the impact of convective parameterization scheme (CPS) on the simulation, the Grell scheme (GLEX) was also tested.
The GLEX predicted a weaker typhoon with a wilder eye that extended not as high up in the upper troposphere as BMEX. The different
structures of the eye between the BMEX and GLEX suggest that the mesoscale features of the eye are dependent on the convection.
In other words, the vertical and horizontal distribution of convective heating is essential to the development and structure
of the eye.
Received December 18, 2001; accepted May 7, 2002
Published online: March 20, 2003 相似文献