全文获取类型
收费全文 | 6645篇 |
免费 | 1730篇 |
国内免费 | 2393篇 |
专业分类
测绘学 | 455篇 |
大气科学 | 2179篇 |
地球物理 | 1933篇 |
地质学 | 3712篇 |
海洋学 | 1255篇 |
天文学 | 106篇 |
综合类 | 440篇 |
自然地理 | 688篇 |
出版年
2024年 | 27篇 |
2023年 | 89篇 |
2022年 | 234篇 |
2021年 | 255篇 |
2020年 | 291篇 |
2019年 | 391篇 |
2018年 | 335篇 |
2017年 | 327篇 |
2016年 | 331篇 |
2015年 | 397篇 |
2014年 | 536篇 |
2013年 | 557篇 |
2012年 | 536篇 |
2011年 | 560篇 |
2010年 | 420篇 |
2009年 | 569篇 |
2008年 | 543篇 |
2007年 | 627篇 |
2006年 | 548篇 |
2005年 | 411篇 |
2004年 | 424篇 |
2003年 | 344篇 |
2002年 | 321篇 |
2001年 | 245篇 |
2000年 | 239篇 |
1999年 | 212篇 |
1998年 | 189篇 |
1997年 | 168篇 |
1996年 | 151篇 |
1995年 | 107篇 |
1994年 | 110篇 |
1993年 | 55篇 |
1992年 | 50篇 |
1991年 | 37篇 |
1990年 | 26篇 |
1989年 | 12篇 |
1988年 | 20篇 |
1987年 | 19篇 |
1986年 | 9篇 |
1985年 | 11篇 |
1984年 | 6篇 |
1982年 | 2篇 |
1981年 | 7篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 1篇 |
1971年 | 3篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
Testing the correctness of the sequential algorithm for simulating Gaussian random fields 总被引:2,自引:2,他引:0
X.?EmeryEmail author 《Stochastic Environmental Research and Risk Assessment (SERRA)》2004,18(6):401-413
The sequential algorithm is widely used to simulate Gaussian random fields. However, a rigorous application of this algorithm is impractical and some simplifications are required, in particular a moving neighborhood has to be defined. To examine the effect of such restriction on the quality of the realizations, a reference case is presented and several parameters are reviewed, mainly the histogram, variogram, indicator variograms, as well as the ergodic fluctuations in the first and second-order statistics. The study concludes that, even in a favorable case where the simulated domain is large with respect to the range of the model, the realizations may poorly reproduce the second-order statistics and be inconsistent with the stationarity and ergodicity assumptions. Practical tips such as the multiple-grid strategy do not overcome these impediments. Finally, extending the original algorithm by using an ordinary kriging should be avoided, unless an intrinsic random function model is sought after. 相似文献
992.
DONGSheng GANBuhong HAOXiaoli 《中国海洋大学学报(英文版)》2004,3(1):111-114
1 Introduction InChina ,coastalcitiesaremostlyregionaleconomicdevelopmentcenters.Becauseoftheirspecialgeogra phiclocations ,typhoonsandassociatedstormsurgescauseheavylossesoflivesandproperties.In 1 992 Qing daowasfloodedduetothecoincidenceoftheastrono m… 相似文献
993.
建筑结构抗震研究若干基本问题概述及讨论 总被引:3,自引:1,他引:2
本文介绍和讨论了结构抗震研究中的一些基本问题,包括地震反应分析选择地面运动输入应注意的问题,高层结构地震模拟试验问题和结构地震反应分析中的主要分析方法和存在的问题,最后简要介绍了目前常用结构反应分析程序。 相似文献
994.
To investigate the stability of the bottom boundary layer induced by tidal flow (oscillating flow) in a rotating frame, numerical experiments have been carried out with a two-dimensional non-hydrostatic model. Under homogeneous conditions three types of instability are found depending on the temporal Rossby number Rot, the ratio of the inertial and tidal periods. When Rot < 0.9 (subinertial range), the Ekman type I instability occurs because the effect of rotation is dominant though the flow becomes more stable than the steady Ekman flow with increasing Rot. When Rot > 1.1 (superinertial range), the Stokes layer instability is excited as in the absence of rotation. When 0.9 < Rot < 1.1 (near-inertial range), the Ekman type I or type II instability appears as in the steady Ekman layer. Being much thickened (100 m), the boundary layer becomes unstable even if tidal flow is weak (5 cm/s). The large vertical scale enhances the contribution of the Coriolis effect to destabilization, so that the type II instability tends to appear when Rot > 1.0. However, when Rot < 1.0, the type I instability rather than the type II instability appears because the downward phase change of tidal flow acts to suppress the latter. To evaluate the mixing effect of these instabilities, some experiments have been executed under a weak stratification peculiar to polar oceans (the buoyancy frequency N2 10−6 s−2). Strong mixing occurs in the subinertial and near-inertial ranges such that tracer is well mixed in the boundary layer and an apparent diffusivity there is evaluated at 150–300 cm2/s. This suggests that effective mixing due to these instabilities may play an important role in determining the properties of dense shelf water in the polar regions. 相似文献
995.
996.
《海洋数值模拟》是淮海工学院面向海洋技术专业本科生开设的专业选修课程。以培养海洋科学专业学生的数值模拟技能为目标,以研究海洋环境动力机制为导向,研究了《海洋数值模拟》课程的教学案例,提出了关于该课程建设上的思考,教学实践表明,学生的基本技能得到明显提高,学习兴趣普遍增强。 相似文献
997.
从动量定理和水量平衡原理出发,以Saint Venant方程为基础推导出自然降雨条件下不同生态措施(即同时考虑变雨强、降雨动量和不同生态措施影响下的坡地径流过程)坡地的径流基本方程。在考虑一般问题定解条件的基础上,采用Preissmann隐式格式对模型进行数值求解。利用3个处理(裸地、百喜草覆盖和百喜草+果树覆盖)、5组实测资料(不同雨型)对模型进行了验证,结果表明3个处理的计算值与实测值的平均相对误差分别为:14.97%、13.59%、15.15%,说明模型的计算结果是可靠的,对于模拟预测自然降雨条件下不同生态措施坡地径流过程是可行的。 相似文献
998.
Based on remote sensing snow water equivalent (SWE) data, the simulated SWE in 20C3M experiments from 14 models attending
the third phase of the Coupled Models for Inter-comparison Project (CMIP3) was first evaluated by computing the different
percentage, spatial correlation coefficient, and standard deviation of biases during 1979–2000. Then, the diagnosed ten models that
performed better simulation in Eurasian SWE were aggregated by arithmetic mean to project the changes of Eurasian SWE in
2002–2060. Results show that SWE will decrease significantly for Eurasia as a whole in the next 50 years. Spatially, significant
decreasing trends dominate Eurasia except for significant increase in the northeastern part. Seasonally, decreasing proportion will
be greatest in summer indicating that snow cover in warmer seasons is more sensitive to climate warming. However, absolute decreasing
trends are not the greatest in winter, but in spring. This is caused by the greater magnitude of negative trends, but smaller
positive trends in spring than in winter. The changing characteristics of increasing in eastern Eurasia and decreasing in western
Eurasia and over the Qinghai-Tibetan Plateau favor the viewpoint that there will be more rainfall in North China and less in the
middle and lower reaches of the Yangtze River in summer. Additionally, the decreasing rate and extent with significant decreasing
trends under SRES A2 are greater than those under SRES B1, indicating that the emission of greenhouse gases (GHG) will speed
up the decreasing rate of snow cover both temporally and spatially. It is crucial to control the discharge of GHG emissions for
mitigating the disappearance of snow cover over Eurasia. 相似文献
999.
基于情景模拟的天津市滨海新区2020年暴雨内涝风险评估 总被引:4,自引:0,他引:4
基于多灾种复合动态风险评估理论,依据滨海新区2020年人口规划、土地利用规划以及社会经济发展计划,根据地面沉降和海平面上升预测结果设计了最不利、适中和最理想化三种情景;在此基础上,自行开发了基于GIS的洪水淹没区计算模块,模拟计算不同重现期暴雨内涝的淹没范围、淹没深度及淹没损失。结果表明:2020年,发生1 000 a一遇、200 a一遇和50 a一遇暴雨时,在最不利的情景一下:天津市滨海新区分别将有32.73%,29.34%和26.01%的土地不同程度受淹,受淹人口分别为338万、305万和264万,淹没损失分别达220.89亿元、181.39亿元和139.12亿元。 相似文献
1000.
库姆塔格沙漠春季近地面风场、温度场特征 总被引:1,自引:1,他引:0
利用中尺度区域预报模式系统对库姆塔格沙漠及其周边地区春季近地层风场与温度场分布特征进行了模拟和分析。结果发现,受青藏高原地形影响,偏北气流向南运行在途经库姆塔格沙漠的过程中发生3个分支:①在沙漠东部气流逐渐转变为西北风吹向甘肃省;②中西部气流以较强的东北风流向塔克拉玛干沙漠;③另一部分气流继续顺势南下流入青海省。沙漠区域温度从北向南逐渐降低,在青海省的边界上出现一个低温带,然后温度又开始增加。 相似文献