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81.
数值模式初值的敏感性程度对四维同化的影响 总被引:3,自引:0,他引:3
用著名的Lorenz系统作了共轭变分同化的数值试验。发现随着模式对初值敏感性程度的增加,用这种方法得到和模式相协调的初始场愈来愈困难,直到某些情况下的完全失败。这表明四维同化和可预报期限是联系在一起的。另一方面,随着方程不精确程度的增加,变分同化的效果愈来愈差,直到所做的预报无任何意义可言。如果在做变分同化的同时对模式参数也进行反演,就可使得基于Lorenz系统所做的预报效果大大提高。 相似文献
82.
83.
Transport and deposition of suspended particles in saturated porous media: hydrodynamic effect 总被引:1,自引:1,他引:1
Nasre-Dine Ahfir Hua Qing Wang Ahmed Benamar Adbellah Alem Nicolas Massei Jean-Paul Dupont 《Hydrogeology Journal》2007,15(4):659-668
A laboratory study was undertaken to determine the transport and deposition rate of suspended particles in columns of saturated porous media (gravel and glass beads), where the porous media were subjected to steady-state flow. Silt particles with a mode of 14 μm diameter (used as the suspended particles) and fluorescein (as the conservative tracer) were injected into the columns in short pulses. The breakthrough curves were competently described with the analytical solution of a convection–dispersion equation with a first-order deposition rate. The experiments were performed using different flow rates. The suspended particle size distribution, the porous media, and the flow rates themselves were the main factors retained in this study to investigate the mechanisms governing the transport and deposition kinetics in detail. The results showed the existence of a flow rate, beyond which suspended particles travel faster than the conservative tracer. A decrease of the deposition rate of suspended particles beyond a critical flow velocity was also observed. Such behaviour led to consideration of the couple hydrodynamic-gravity forces at high flow rates. As the hydrodynamic force increases, particle deposition rates are reduced due to the effect of hydrodynamic forces inhibiting the deposition. 相似文献
84.
S. Abhilash Someshwar Das S. R. Kalsi M. Das Gupta K. Mohankumar John P. George S. K. Banerjee S. B. Thampi D. Pradhan 《Pure and Applied Geophysics》2007,164(8-9):1491-1509
Pre-monsoon rainfall around Kolkata (northeastern part of India) is mostly of convective origin as 80% of the seasonal rainfall
is produced by Mesoscale Convective Systems (MCS). Accurate prediction of the intensity and structure of these convective
cloud clusters becomes challenging, mostly because the convective clouds within these clusters are short lived and the inaccuracy
in the models initial state to represent the mesoscale details of the true atmospheric state. Besides the role in observing
the internal structure of the precipitating systems, Doppler Weather Radar (DWR) provides an important data source for mesoscale
and microscale weather analysis and forecasting. An attempt has been made to initialize the storm-scale numerical model using
retrieved wind fields from single Doppler radar. In the present study, Doppler wind velocities from the Kolkata Doppler weather
radar are assimilated into a mesoscale model, MM5 model using the three-dimensional variational data assimilation (3DVAR)
system for the prediction of intense convective events that occurred during 0600 UTC on 5 May and 0000 UTC on 7 May, 2005.
In order to evaluate the impact of the DWR wind data in simulating these severe storms, three experiments were carried out.
The results show that assimilation of Doppler radar wind data has a positive impact on the prediction of intensity, organization
and propagation of rain bands associated with these mesoscale convective systems. The assimilation system has to be modified
further to incorporate the radar reflectivity data so that simulation of the microphysical and thermodynamic structure of
these convective storms can be improved. 相似文献
85.
A probabilistic fog forecast system was designed based on two high resolution numerical 1-D models called COBEL and PAFOG.
The 1-D models are coupled to several 3-D numerical weather prediction models and thus are able to consider the effects of
advection. To deal with the large uncertainty inherent to fog forecasts, a whole ensemble of 1-D runs is computed using the
two different numerical models and a set of different initial conditions in combination with distinct boundary conditions.
Initial conditions are obtained from variational data assimilation, which optimally combines observations with a first guess
taken from operational 3-D models. The design of the ensemble scheme computes members that should fairly well represent the
uncertainty of the current meteorological regime. Verification for an entire fog season reveals the importance of advection
in complex terrain. The skill of 1-D fog forecasts is significantly improved if advection is considered. Thus the probabilistic
forecast system has the potential to support the forecaster and therefore to provide more accurate fog forecasts. 相似文献
86.
基于进化方向遗传算法的四维变分资料同化方法 总被引:7,自引:5,他引:7
数值天气预报模式初始时刻要素场的变分同化问题是一个非线性最优化问题。利用进化方向遗传算法(EDGA)求解该最优化问题,并对理想初始场作数值模拟,结果表明模拟的效果较好。 相似文献
87.
使用共轭码技术,构造了中尺度模式的伴随模式,研究了模式侧边界条件。基于伴随模式技术的原理,设计了伴随同化和Derber同化方法两套方案;下降算法采用共轭梯度法,使用准真实资料,进行子同化数值试验和预报试验。结果表明,两套同化方案都取得了一定的同化效果,Derber同化方法比伴随同化更令人满意。证明了变分同化是提高预报准确率的一种非常有效的手段。 相似文献
88.
89.
基于正交设计的复杂坝基弹塑性力学参数反演 总被引:8,自引:1,他引:8
复杂坝基弹塑性力学参数反演的计算工作量直接取决于采用何种优化方法。根据大坝在运行期的实测资料,运用有限元正交数值试验、回归分析和优化相结合的方法,反演了坝基岩体的弹塑性力学参数。实例研究表明了该方法的有效性和实用性。 相似文献
90.
基于GIS与空间统计分析的可持续发展度量方法研究——以缅甸Myingyan District为例 总被引:15,自引:0,他引:15
利用空间信息系统所提供的强大空间数据处理和分析能力,并将之与统计分析软件包的统计分析功能进行有效的集成,建立了基于空间统计分析的可持续发展定量分析评价模型(SBSA)。从在缅甸中部Myingyan县的应用实例来看,该模型能够提示影响Myingyan县可持续发展能力的主导因子,通过对这些因子和可持续发展综合指数的定量化、空间化的分析,为政府部门规划区域综合发展方案,制定发展政策提供很好的决策支持。 相似文献