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921.
Inverse methods are useful tools not only for deriving estimates of unknown parameters of the subsurface, but also for appraisal of the thus obtained models. While not being neither the most general nor the most efficient methods, Bayesian inversion based on the calculation of the Jacobian of a given forward model can be used to evaluate many quantities useful in this process. The calculation of the Jacobian, however, is computationally expensive and, if done by divided differences, prone to truncation error. Here, automatic differentiation can be used to produce derivative code by source transformation of an existing forward model. We describe this process for a coupled fluid flow and heat transport finite difference code, which is used in a Bayesian inverse scheme to estimate thermal and hydraulic properties and boundary conditions form measured hydraulic potentials and temperatures. The resulting derivative code was validated by comparison to simple analytical solutions and divided differences. Synthetic examples from different flow regimes demonstrate the use of the inverse scheme, and its behaviour in different configurations. 相似文献
922.
923.
鉴于测震中电子放大地震仪放大器的输出动态范围窄的缺陷,笔者作了自动换档衰减放大倍数的电路技术设计。本设计在长周期、短周期、宽频带等各种电子放大地震仪上适当改制或重新设计放大板即可应用,从而可几十倍甚至更大地拓宽电子放大地震仪的输出动态范围,大幅度增强其适用性。 相似文献
924.
A neural network system for P and S-picking and location of earthquakes in Northeastern Italy is described. It is applied to 7108 seismograms corresponding to 1147 earthquakes occurring in Northeastern Italy and surrounding area in the period 2000–2003. Its results are compared with two sets of manual picks and with the picks performed by the existing seismic alert system. The new system recognizes 89% and 67% of P and S arrival times, respectively, which allows locating 92% of the earthquakes. P and S-picks differ from the best available manual picks by 0.00 ± 0.07 s and 0.00 ± 0.18 s, respectively. The corresponding earthquake locations differ by −0.18± 0.77 km in longitude, 0.10± 0.62 km in latitude and 0.1± 2.0 km in depth. These results suggest its use for alert purposes and rapid production of preliminary bulletins.Considering a subset of picks that are common to all the available data sets, the absolute accuracy (i.e., the inverse of the standard deviation of differences between the estimated and the true, unknown arrival times) of each picking method is estimated. The best available manual data set has standard deviation 0.03 s for P waves and 0.07 s for S waves, while for the new system it is 0.06 s and 0.18 s for P and S waves, respectively.This paper has not been submitted elsewhere in identical or similar form, nor will it be during the first three months after its submission to Journal of Seismology. 相似文献
925.
926.
Determination of nitrate in seawater first requires its reduction to nitrite. Construction of a reductor column for use during continuous flow analysis at sea is described. Novel use is made of an alloy of cadmium and copper () crushed to between 500 and 350 μm. Its performance is similar to that of the cadmium wire type of reductor but offers advantages of easier preparation and control of reductor volume. 相似文献
927.
Justyna K. Przybysz-Jarnut Remus G. Hanea Jan-Dirk Jansen Arnold W. Heemink 《Computational Geosciences》2007,11(1):73-85
A data assimilation method was applied to estimate poorly known parameters (permeabilities) in a numerical reservoir model.
Most variational methods for data assimilation are based on the assumption that the model is perfect except for the poorly
known parameters. The representer method allows also for model errors, i.e. for uncertainties in the state variables (pressures
and saturations). The method is based on minimizing a cost functional, assuming all the errors and parameters to be multivariate
Gaussian random variables with given mean and covariances. The uncertain parameters and variables are expanded into a finite
sum of basis functions called representers, and the gradients of the cost functional are obtained with an adjoint method.
This approach gives an optimal parametrization in the sense that the final result is equal to the solution of the full inverse
problem. The method was tested on a simple one-dimensional model to simulate two-phase (oil-water) flow through a heterogeneous
reservoir. The results show that the method is able to provide an acceptable estimate of the permeability field. We used pressure
measurements from a small number of observation wells in between the injection and production wells, but the representer method
could be used equally well to assimilate data from other sources. The method appears to be a promising data assimilation tool
for applications in reservoir engineering. 相似文献
928.
小比例尺地图面状水系名称注记自动配置研究 总被引:3,自引:0,他引:3
王 《武汉大学学报(信息科学版)》2007,32(6):544-547
在丰富面状水系的注记配置规则基础上,深入研究了其名称注记自动配置中两个关键算法,即要素主骨架线求取和注记配置方案的设计,并提出了基于单调链化简思想确定面状水系主骨架线的改进算法,在此基础上设计了面状水系名称注记自动配置方案。 相似文献
929.
930.
由于受基坑开挖所产生的卸载和基坑降水的影响,临近地铁隧道的受力条件将改变,造成地铁隧道的变形和位移。采用自动化技术实时监测地铁隧道的变形,对保证地铁运营安全至关重要。文中结合广州大马站商业中心项目基坑开挖对临近运营地铁1号线隧道结构变形位移自动监测工程项目的实践,对自动全站仪监测系统在地铁隧道监测方面的系统构建、测量方法、测量精度、监测效果等方面进行论述。实际应用表明,该系统以高精度、自动化的优势,及时提供可靠的动态监测数据,科学指导基坑施工,保证了地铁运营安全,取得良好的效果。 相似文献