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981.
In the present paper, a new stochastic framework is introduced to decompose random variables. This decomposition method is
shown to better capture and reflect the medium heterogeneity for multimodal porous media than the classical Reynolds decomposition
does. In particular, with this decomposition method, the variance of log conductivity is decomposed into two parts. The first
one measures the mean differences of log conductivity across different units having high contrasting conductivity. The second
part measures the variation of log conductivity arisen within individual units. Based on this localized decomposition, a new
stochastic model is proposed for flow in a highly heterogeneous porous media. This stochastic model shall produce much sharper
approximations under the assumption that only the second part of the variance of log conductivity is small. Therefore, the
proposed model can partially overcome the assumption of small composite variance for log conductivity in current theory for
both flow and transport. 相似文献
982.
983.
984.
The fast update rate and good performance of new generation electronic sector scanning sonars is now allowing practicable use of temporal information for signal processing tasks such as object classification and motion estimation. Problems remain, however, as objects change appearance, merge, maneuver, move in and out of the field of view, and split due to poor segmentation. This paper presents an approach to the segmentation, two-dimensional motion estimation, and subsequent tracking of multiple objects in sequences of sector scan sonar images. Applications such as ROV obstacle avoidance, visual servoing, and underwater surveillance are relevant. Initially, static and moving objects are distinguished in the sonar image sequence using frequency-domain filtering. Optical flow calculations are then performed on moving objects with significant size to obtain magnitude and direction motion estimates. Matches of these motion estimates, and the future positions they predict, are then used as a basis for identifying corresponding objects in adjacent scans. To enhance robustness, a tracking tree is constructed storing multiple possible correspondences and cumulative confidence values obtained from successive compatibility measures. Deferred decision making is then employed to enable best estimates of object tracks to be updated as subsequent scans produce new information. The method is shown to work well, with good tracking performance when objects merge, split, and change shape. The optical flow is demonstrated to give position prediction errors of between 10 and 50 cm (1%-5% of scan range), with no violation of smoothness assumptions using sample rates between 4 and 1 frames/s 相似文献
985.
作者从发生白点综合征的中国对虾中,提取了一株白点综合征病毒,用电镜对纯化的病毒进行了形态学观察,并对病毒纯化过程中蛋白酶抑制剂的使用及离心速度的选择进行了探讨。经蔗糖密度梯度离心,分取各带负染后电镜观察,病毒条带位于40%~50%蔗糖梯度之间,其完整毒粒长225~270nm,直径75~88nm,有的完整毒粒带有很长的尾,病毒衣壳长250~320nm,直径60~80nm。在匀浆使用的缓冲液中加入蛋白酶抑制剂PMSF,可得到完整的带包膜的病毒颗粒,比不使用PMSF的提纯效果要好。经3000r/min离心5min,5000r/min离心25min,去除大部分的组织碎片,经10000r/min离心1h,可使大部分病毒沉淀。并采用传统的方法对病毒核酸进行了提取,其基因组经初步分析为dsDNA。 相似文献
986.
In almost all frozen soil models used currently, three variables of temperature, ice content and
moisture content are used as prognostic variables and the rate term, accounting for the contribution of the
phase change between water and ice, is shown explicitly in both the energy and mass balance equations. The
models must be solved by a numerical method with an iterative process, and the rate term of the phase change
needs to be pre-estimated at the beginning in each iteration step. Since the rate term of the phase change
in the energy equation is closely related to the release or absorption of the great amount of fusion heat, a
small error in the rate term estimation will introduce greater error in the energy balance, which will amplify
the error in the temperature calculation and in turn, cause problems for the numerical solution convergence. In
this work, in order to first reduce the trouble, the methodology of the variable transformation is applied to a
simplified frozen soil model used currently, which leads to new frozen soil scheme used in this work. In the new
scheme, the enthalpy and the total water equivalent are used as predictive variables in the governing equations to
replace temperature, volumetric soil moisture and ice content used in many current models. By doing so, the rate
terms of the phase change are not shown explicitly in both the mass and energy equations and its pre-estimation is
avoided. Secondly, in order to solve this new scheme more functionally, the development of the numerical scheme to
the new scheme is described and a numerical algorithm appropriate to the numerical scheme is developed. In order
to evaluate the new scheme of the frozen soil model and its relevant algorithm, a series of model evaluations are
conducted by comparing numerical results from the new model scheme with three observational data sets. The
comparisons show that the results from the model are in good agreement with these data sets in both the change trend
of variables and their magnitude values, and the new scheme, together with the algorithm, is more efficient and saves
more computer time. 相似文献
987.
本文利用模型子群概念,引入了L-Fuzzy子群概念。基于模糊集合的层次结构特征,得到L-Fuzzy了群若干重要性质;给出并证明L-Fuzzy子群的一系列等价刻划;文章最后讨论L-Fuzzy子群同态性质 。 相似文献
988.
在实行“两个转变”中,地勘单位的设备管理要适应市场经济需要,紧密结合地勘单位在开发新产品、新工艺以及生产装备更新的需求,实现管理科学化、现代化、集约化,步入良性循环。 相似文献
989.
????μ???????????????????????????????????????????????????????????????????????Simulink???湤????????????????????????????????????????????仯???????????????????????侫???????????????????????? 相似文献
990.
With a global GSSTF2 and NCEP/NCAR reanalysis database and observation data at the Yong Xing station of Xisha Island in the South China Sea, we simulated the turbulent sensible and latent heat flux at sea surface in Chinese and neighboring seas (hereafter termed as China seas) using a common bulk method with some improved parameters. Comparing the simulated results with the observed and reanalyzed data, the improvement yielded higher accuracy, a smaller mean square deviation within 10 W/m2, and a smaller average relative error at about 25%. In addition, spatial resolution was improved to 0.1°×0.1°. The simulation is able to replay the main features of regional and seasonal variation in turbulent heat fluxes, and also the general pattern of heat flux changes during the summer monsoon outbreak in the South China Sea. 相似文献