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581.
582.
高精度低频振动台及伺服隔振 总被引:8,自引:0,他引:8
本文提出了一种复合速度反馈技术,用以建造高精度大行程低频标准振动,同时,这种伺服隔振技术可大幅度降低地基振支对台面的干扰,降低地基造价。 相似文献
583.
F. A. El-Awar J. W. Labadie T. B. M. J. Ouarda 《Stochastic Environmental Research and Risk Assessment (SERRA)》1998,12(4):247-266
: As with all dynamic programming formulations, differential dynamic programming (DDP) successfully exploits the sequential
decision structure of multi-reservoir optimization problems, overcomes difficulties with the nonconvexity of energy production
functions for hydropower systems, and provides optimal feedback release policies. DDP is particularly well suited to optimizing
large-scale multi-reservoir systems due to its relative insensitivity to state-space dimensionality. This advantage of DDP
encourages expansion of the state vector to include additional multi-lag hydrologic information and/or future inflow forecasts
in developing optimal reservoir release policies. Unfortunately, attempts at extending DDP to the stochastic case have not
been entirely successful. A modified stochastic DDP algorithm is presented which overcomes difficulties in previous formulations.
Application of the algorithm to a four-reservoir hydropower system demonstrates its capabilities as an efficient approach
to solving stochastic multi-reservoir optimization problems. The algorithm is also applied to a single reservoir problem with
inclusion of multi-lag hydrologic information in the state vector. Results provide evidence of significant benefits in direct
inclusion of expanded hydrologic state information in optimal feedback release policies. 相似文献
584.
The effect of cloud feedback on the response of a radiative-convective model to a change in cloud model parameters, atmospheric CO2 concentration, and solar constant has been studied using two different parameterization schemes. The method for simulating the vertical distribution of both cloud cover and cloud optical thickness, which depends on the relative humidity and on the saturation mixing ratio of water vapor, respectively, is the same in both approaches, but the schemes differ with respect to modeling the water vapor profile. In scheme I atmospheric water vapor is coupled to surface parameters, while in scheme II an explicit balance equation for water vapor in the individual atmospheric layers is used. For both models the combined effect of feedbacks due to variations in lapse rate, cloud cover, and cloud optical thickness results in different relationships between changes in surface temperature, planetary temperature, and cloud cover. Specifically, for a CO2 doubling and a 2% increase in solar constant, in both models the surface warming is reduced by cloud feedback, in contrast to no feedback, with the greater reduction in scheme I as compared to that of scheme II. 相似文献
585.
586.
单片机控制的锁相频率合成技术 总被引:1,自引:2,他引:1
余朝琨 《华东地质学院学报》2001,24(3):224-227
叙述了由单片机、定时计数器8253-5及单片集成锁相环路组成的可程控频率合成技术,而标频可经单片机设定预置值给定时器T1而形成,并经锁相环路产生各种离散的频率输出。 相似文献
587.
根据低纬地区地表温度高、蒸发及降水量大、辐合上升运动剧烈等特点,本文构造了一个正压模式的方程组,提示出影响低纬大气波动的一个重要因素——海表温度SST。研究指出:(1)当SST<25℃时,含蒸发风反馈机制的Rossby波向西传播,当SST>25℃时.含蒸发风反馈机制的Rossby波向东传播。(2)SST的数值越高,空气越潮湿,含蒸发风反馈机制的Rossby波传播速度就越小。当SST超过29℃时,会形成周期为30天的低频振荡。 相似文献
588.
A conceptual model is proposed to explain the observed aperiodicity in the short term climate fluctuations of the tropical
coupled ocean-atmosphere system. This is based on the evidence presented here that the tropical coupled ocean-atmosphere system
sustains a low frequency inter-annual mode and a host of higher frequency intra-seasonal unstable modes. At long wavelengths,
the low frequency mode is dominant while at short wavelengths, the high frequency modes are dominant resulting in the co-existence
of a long wave low frequency mode with some short wave intra-seasonal modes in the tropical coupled system. It is argued that
due to its long wavelength, the low frequency mode would behave like a linear oscillator while the higher frequency short
wave modes would be nonlinear. The conceptual model envisages that an interaction between the low frequency linear oscillator
and the high frequency nonlinear oscillations results in the observed aperiodicity of the tropical coupled system. This is
illustrated by representing the higher frequency intra-seasonal oscillations by a nonlinear low order model which is then
coupled to a linear oscillator with a periodicity of four years. The physical mechanism resulting in the aperiodicity in the
low frequency oscillations and implications of these results on the predictability of the coupled system are discussed. 相似文献
589.
Total Catchment Management (TCM) has been implemented in New South Wales to provide a more integrated, participatory' approach to natural resource management. This change in direction poses significant challenges for obtaining and integrating environmental information. This paper examines the adequacy of environmental information in terms of both the participatory turn in government policy and the management imperatives of the integrated, catchment‐wide approach of TCM. Drawing on empirical studies in the Hunter Valley, it is suggested that current information available for TCM is inadequate and reflects a fragmented approach that is primarily concerned with biophysical phenomena and is generated at inappropriate scales. Furthermore, most information is generated by government agencies, ignoring the substantial contribution that catchment occupiers could make. It is argued that the utilisation of the knowledge and experience of occupiers could provide more integrated catchment perspectives while meeting the participatory goals espoused in TCM. 相似文献
590.
一个自组织气候模型 总被引:7,自引:1,他引:7
本文选择全球平均地表温度#AT#a和全球平均云量#An#a为状态变量。通过对气候系统中物理过程的研究与在气候意义上的合理近似,得到行星反照率α和大气有效发射率ε与状态变量的参数化关系,它们给出了气候系统内部几个重要的反馈过程。利用这些结果,建立起一个云和辐射相互作用的零维的非线性气候模型。在Hopf分支点附近,得到极限环的解析解,它们同数值解吻合得相当好,由解析解得到振幅,周期和位相差与太阳常数和CO2的近似关系,依此可估计它们在气候振荡中的作用,尤其,我们发现CO2的增加除有增温效应外,还能使气候振荡的振幅增加,这个结果意味着CO2的增加可能导致自然灾害周期性地出现或加剧。 相似文献