全文获取类型
收费全文 | 289093篇 |
免费 | 23960篇 |
国内免费 | 13038篇 |
专业分类
电工技术 | 17411篇 |
技术理论 | 25篇 |
综合类 | 19758篇 |
化学工业 | 47219篇 |
金属工艺 | 16633篇 |
机械仪表 | 18620篇 |
建筑科学 | 22469篇 |
矿业工程 | 9410篇 |
能源动力 | 7942篇 |
轻工业 | 19765篇 |
水利工程 | 5235篇 |
石油天然气 | 18787篇 |
武器工业 | 2400篇 |
无线电 | 31799篇 |
一般工业技术 | 32895篇 |
冶金工业 | 15217篇 |
原子能技术 | 3144篇 |
自动化技术 | 37362篇 |
出版年
2024年 | 1372篇 |
2023年 | 4878篇 |
2022年 | 8802篇 |
2021年 | 12095篇 |
2020年 | 9324篇 |
2019年 | 7641篇 |
2018年 | 8593篇 |
2017年 | 9683篇 |
2016年 | 8587篇 |
2015年 | 11607篇 |
2014年 | 14913篇 |
2013年 | 17511篇 |
2012年 | 19129篇 |
2011年 | 20514篇 |
2010年 | 18255篇 |
2009年 | 17073篇 |
2008年 | 16609篇 |
2007年 | 15991篇 |
2006年 | 15861篇 |
2005年 | 13597篇 |
2004年 | 9299篇 |
2003年 | 7657篇 |
2002年 | 6798篇 |
2001年 | 5964篇 |
2000年 | 6399篇 |
1999年 | 7132篇 |
1998年 | 5781篇 |
1997年 | 4776篇 |
1996年 | 4485篇 |
1995年 | 3733篇 |
1994年 | 2977篇 |
1993年 | 2102篇 |
1992年 | 1630篇 |
1991年 | 1295篇 |
1990年 | 980篇 |
1989年 | 795篇 |
1988年 | 583篇 |
1987年 | 354篇 |
1986年 | 295篇 |
1985年 | 202篇 |
1984年 | 156篇 |
1983年 | 119篇 |
1982年 | 129篇 |
1981年 | 110篇 |
1980年 | 89篇 |
1979年 | 44篇 |
1978年 | 26篇 |
1977年 | 22篇 |
1976年 | 36篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Ning-Cong Xiao Hong-Zhong Huang Zhonglai Wang Yu Liu Xiao-Ling Zhang 《Structural and Multidisciplinary Optimization》2012,46(6):803-812
Uncertainties exist in products or systems widely. In general, uncertainties are classified as epistemic uncertainty or aleatory uncertainty. This paper proposes a unified uncertainty analysis (UUA) method based on the mean value first order saddlepoint approximation (MVFOSPA), denoted as MVFOSPA-UUA, to estimate the systems probabilities of failure considering both epistemic and aleatory uncertainties simultaneously. In this method, the input parameters with epistemic uncertainty are modeled using interval variables while input parameters with aleatory uncertainty are modeled using probability distribution or random variables. In order to calculate the lower and upper bounds of system probabilities of failure, both the best case and the worst case scenarios of the system performance function need to be considered, and the proposed MVFOSPA-UUA method can handle these two cases easily. The proposed method is demonstrated to be more efficient, robust and in some situations more accurate than the existing methods such as uncertainty analysis based on the first order reliability method. The proposed method is demonstrated using several examples. 相似文献
992.
Jie Zhang Souma Chowdhury Achille Messac 《Structural and Multidisciplinary Optimization》2012,46(2):223-238
The determination of complex underlying relationships between system parameters from simulated and/or recorded data requires advanced interpolating functions, also known as surrogates. The development of surrogates for such complex relationships often requires the modeling of high dimensional and non-smooth functions using limited information. To this end, the hybrid surrogate modeling paradigm, where different surrogate models are combined, offers an effective solution. In this paper, we develop a new high fidelity surrogate modeling technique that we call the Adaptive Hybrid Functions (AHF). The AHF formulates a reliable Crowding Distance-Based Trust Region (CD-TR), and adaptively combines the favorable characteristics of different surrogate models. The weight of each contributing surrogate model is determined based on the local measure of accuracy for that surrogate model in the pertinent trust region. Such an approach is intended to exploit the advantages of each component surrogate. This approach seeks to simultaneously capture the global trend of the function as well as the local deviations. In this paper, the AHF combines four component surrogate models: (i) the Quadratic Response Surface Model (QRSM), (ii) the Radial Basis Functions (RBF), (iii) the Extended Radial Basis Functions (E-RBF), and (iv) the Kriging model. The AHF is applied to standard test problems and to a complex engineering design problem. Subsequent evaluations of the Root Mean Squared Error (RMSE) and the Maximum Absolute Error (MAE) illustrate the promising potential of this hybrid surrogate modeling approach. 相似文献
993.
H. W. Liu 《International Journal of Fracture》1989,39(1-3):63-77
A fatigue crack may propagate by the mechanism of crack tip cyclic plastic deformation, by the mechanism of fracture of brittle particles and embrittled grain boundaries,or, often, by a combination of both. Neutnann and Vehoff have made in situ observations of alternate shear decohhesions on two intersecting conjugate slip bands at a crack tip as the basic mechanism of fatigue crack growth. It is a mechanism by plastic deformation.
A micro-mechanism based finite element model is made to simulate the unzipping process of the crack tip shear decohesion mechanism. The calculated crack growth rates by the finite element model agree very well with the measured rates in the intermediate K region of a number of materials
Résumé La propagation d'une fissure de fatigue peut être due au mécanisme de déformation plastique cyclique de l'extrémité de la fissure, au mécanisme de rupture de portions fragiles et de frontières de grains fragilisées ou, souvent, à une combinaison de ces deux mécanismes.Neumann et Vehoff ont procédé à des observations in situ des décohésions par cisaillement alterné dans deux bandes de glissement s'intersectant à l'extrémité d'une fissure, et ont décrit ce mécanisme par déformation plastique comme un mécanisme de base de la propagation d'une fissure de fatigue.En vue de simuler le processus d'ouverture qui régit le mécanisme de décohésion par cisaillement à l'extrémité dame fissure, on élabore un modèle par éléments finis basé sur un mécanisme à échelle microscopique. On trouve que les vitesses de propagation d'une fissure calculées grâce à ce modèle par éléments finis sont en très bon accord lvee les vitesses mesurées dans la zone des K intermédiaries et pour plusieurs matériaux.相似文献
994.
995.
Jian Liu 《时间序列分析杂志》1992,13(4):319-325
Abstract. We provide a stochastic proof of the inequality ρ(A?A+B?B) ≥ρ(A?A), where ρ(M) denotes the spectral radius of any square matrix M, i.e. max{|eigenvalues| of M}, and M?N denotes the Kronecker product of any two matrices M and N. The inequality is then used to show that stationarity of the bilinear model will imply stationarity of the linear part, i.e. the linear ARMA model for r= 1 and q= 1. Furthermore, it is shown that stationarity of the subdiagonal model, i.e. the bilinear model with bij=0 for i< j, again implies stationarity of its linear part, provided that the stationarity condition given by Bhaskara Rao and his colleagues is met. Interestingly, the conclusion that stationarity of the subdiagonal models, implies that the linear component models cannot be extended to the general non-subdiagonal bilinear models. The last observation is demonstrated via a simple example with p=m= 1, r= 0 and q= 2. 相似文献
996.
A method capable of estimating the hydrograph from a prescribed storm for a practical mild slope upstream catchment is proposed. This method makes use of two new characteristic parameters, andS, in conjunction with the kinematic wave equation to compute lateral inflows of the main stream of the catchment. The depth profile of overland flow at any instant within the catchment and hydrograph at any location can be easily found. Lag times for individual lateral inflows are then considered and are linearly combined to obtain the hydrograph at the outlet of the catchment or depth profile of the main stream at any instant. The validity of the excess rainfall-surface runoff linear relationship in this study has also been verified with Tatsunokuchiyama catchment, and it shows good results for this computed runoff. 相似文献
997.
对于集成电路设计、生产过程中的多目标、多约束统计优化问题,本文提出了“合格率足够高”的优化宗旨,并从概率论的基本原理出发,结合集成电路的特点,导出了一种合格率的近似表述方法,提出的变权重Monte Carlo法编程简便,效率高。采用这些优化策略设计的集成电路合格率优化系统取得了比较好的结果。 相似文献
998.
999.
无线传感器网络是无线通讯技术、网络技术、传感器技术交叉融合的新兴产物。无线传感器网络具备小型化、智能化、网络化和能够无线通讯等特点,能够满足人们在生产生活、科学研究、军事、医疗等众多领域对于实时信息获取的需求。由于人类获取信息的80%以上是通过视觉获取的,因此,无线图像传感器网络作为人类获取视觉图像信息的重要工具在无线传感器网络中占有重要的地位。无线图像传感器网络要想实现小型化、智能化、集成化等要求,采用与标准CMOS工艺兼容的CMOS图像传感器技术将是最为理想的选择。随着CMOS图像传感器工艺和设计水平的进步,CMOS图像传感器在成像质量、生产成本、小型化、智能化等方面显示出巨大的优势,同时由于与VLSI电路兼容的天然特性,基于CMOS图像传感器的无线图像传感器网络拥有巨大的发展潜力和广阔的市场前景。基于CMOS的无线图像传感器网络目前呈现多元化的发展趋势,高分辨率、高速、低功耗、智能化等方向是基于CMOS的无线图像传感器网络未来发展的方向。 相似文献
1000.