全文获取类型
收费全文 | 85512篇 |
免费 | 11579篇 |
国内免费 | 6428篇 |
专业分类
电工技术 | 9900篇 |
技术理论 | 4篇 |
综合类 | 8248篇 |
化学工业 | 8519篇 |
金属工艺 | 2955篇 |
机械仪表 | 7326篇 |
建筑科学 | 5640篇 |
矿业工程 | 3255篇 |
能源动力 | 6657篇 |
轻工业 | 4388篇 |
水利工程 | 2257篇 |
石油天然气 | 4340篇 |
武器工业 | 1093篇 |
无线电 | 8067篇 |
一般工业技术 | 7077篇 |
冶金工业 | 2874篇 |
原子能技术 | 799篇 |
自动化技术 | 20120篇 |
出版年
2024年 | 270篇 |
2023年 | 1780篇 |
2022年 | 3215篇 |
2021年 | 3541篇 |
2020年 | 3821篇 |
2019年 | 3287篇 |
2018年 | 2986篇 |
2017年 | 3656篇 |
2016年 | 4068篇 |
2015年 | 4485篇 |
2014年 | 6503篇 |
2013年 | 6294篇 |
2012年 | 7118篇 |
2011年 | 7324篇 |
2010年 | 5222篇 |
2009年 | 5451篇 |
2008年 | 4862篇 |
2007年 | 5375篇 |
2006年 | 4572篇 |
2005年 | 3616篇 |
2004年 | 2956篇 |
2003年 | 2414篇 |
2002年 | 2029篇 |
2001年 | 1664篇 |
2000年 | 1346篇 |
1999年 | 978篇 |
1998年 | 818篇 |
1997年 | 690篇 |
1996年 | 616篇 |
1995年 | 530篇 |
1994年 | 437篇 |
1993年 | 312篇 |
1992年 | 256篇 |
1991年 | 228篇 |
1990年 | 183篇 |
1989年 | 154篇 |
1988年 | 100篇 |
1987年 | 57篇 |
1986年 | 55篇 |
1985年 | 35篇 |
1984年 | 37篇 |
1983年 | 31篇 |
1982年 | 34篇 |
1981年 | 23篇 |
1980年 | 15篇 |
1979年 | 16篇 |
1978年 | 9篇 |
1977年 | 6篇 |
1959年 | 7篇 |
1951年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
This paper focuses on the configuration design of flexure hinges with a prescribed compliance matrix and preset rotational center position. A new method for the topology optimization of flexure hinges is proposed based on the adaptive spring model and stress constraint. The hinge optimization model is formulated by maximizing the bending displacement with a spring while optimizing the compliance matrix to a prescribed value. To avoid numerical instability, an artificial spring is used as an auxiliary calculation, and a new strategy is developed for adaptively adjusting the spring stiffness according to the prescribed compliance matrix. The maximum stress of flexure hinge is limited by using a normalized P-norm of the effective von Mises stress, and a position constraint of rotational center is proposed to predetermine the position of the rotational center. In addition, to reduce the error of the stress measurement, a simple but effective filtering method is presented to obtain a complete black-and-white design. Numerical examples are used to verify the proposed method. Topology results show that the obtained flexure hinges have the prescribed compliance matrix and preset rotational center position while also meeting the stress requirements. 相似文献
2.
3.
This study proposes a multiperiod mixed integer linear programming model for the management of a single municipal solid waste (MSW) treatment plant with sustainability as the objective. Discrete and continuous variables define the capacity selections for diverse MSW technologies, and the operation of the MSW network, respectively. The economic target is considered to maximize the net present value. The environmental impact is the minimization of a normalized environmental objective function (NEOF). The social target is the maximization of jobs. An interesting feature about the research work is the requirement of biodrying technologies for MSW moisture content control. Due to the conflicted nature among the sustainability components, a multiobjective optimization (MO) is carried out to find the Pareto optimal solutions. The MO results show that the Pareto optimal solutions vary around profit range of $4.9–8.5 billion, NEOF impact range of 3.2–3.6 units, and social benefit range of 2700–4828 jobs. 相似文献
4.
Thomas R. Savage Fernando Almeida-Trasvina Ehecatl A. del-Rio Chanona Robin Smith Dondga Zhang 《American Institute of Chemical Engineers》2021,67(11):e17358
With liquefied natural gas becoming increasingly prevalent as a flexible source of energy, the design and optimization of industrial refrigeration cycles becomes even more important. In this article, we propose an integrated surrogate modeling and optimization framework to model and optimize the complex CryoMan Cascade refrigeration cycle. Dimensionality reduction techniques are used to reduce the large number of process decision variables which are subsequently supplied to an array of Gaussian processes, modeling both the process objective as well as feasibility constraints. Through iterative resampling of the rigorous model, this data-driven surrogate is continually refined and subsequently optimized. This approach was not only able to improve on the results of directly optimizing the process flow sheet but also located the set of optimal operating conditions in only 2 h as opposed to the original 3 weeks, facilitating its use in the operational optimization and enhanced process design of large-scale industrial chemical systems. 相似文献
5.
针对致密砂岩油藏大规模体积压裂开发后能量补充困难的问题,利用自主设计制作的大型人造三维岩心物理模型和物理模拟实验舱,开展致密砂岩油藏能量补充方式优化研究。实验结果表明:致密砂岩油藏压裂开发过程中,地层能量损耗严重,采取注水或注气的方式可有效进行能量补充;地层中裂缝规模越大,越有利于原油渗流,后续补充能量的传播范围越广,有助于进一步提高原油采收率;从提高驱油效率和扩大波及系数方面优选吞吐渗吸介质,CO2均优于活性水,CO2吞吐开发在矿场试验中取得了显著的增油效果,因此,CO2吞吐作为一种有效的能量补充方式在致密油开发中展现了良好的应用前景。该文分析了致密砂岩储层水平井压裂开发的渗流规律,优选出致密砂岩储层大规模压裂开发后最佳渗吸介质,可为致密砂岩油藏开发设计提供重要的理论依据。 相似文献
6.
文中提出了一种利用有限数量的相量测量单元(PMU)和相量数据集中器(PDC)设计最优监控结构的方法。通过在大量的设定值场景下,使电力系统可观测性曲线的期望值最大化,同时使通信基础设施成本最小化,最终确定PMU和PDC的最佳位置。提出了一种非线性动态扩展卡尔曼滤波(EFK)状态观测器。这种状态观测器可以将暂态行为转换为由代数微分方程描述的广域电力系统,而无需非线性反演技术。最后以IEEE-5电力系统为例,说明了该方法的有效性。 相似文献
7.
《International Journal of Hydrogen Energy》2022,47(7):4328-4345
This paper proposes a parameter adjustable dynamic mass and energy balance simulation model for an industrial alkaline water electrolyzer plant that enables cost and energy efficiency optimization by means of system dimensioning and control. Thus, the simulation model is based on mathematical models and white box coding, and it uses a practicable number of fixed parameters. Zero-dimensional energy and mass balances of each unit operation of a 3 MW, and 16 bar plant process were solved in MATLAB functions connected via a Simulink environment. Verification of the model was accomplished using an analogous industrial plant of the same power and pressure range having the same operational systems design. The electrochemical, mass flow and thermal behavior of the simulation and the industrial plant were compared to ascertain the accuracy of the model and to enable modification and detailed representation of real case scenarios so that the model is suitable for use in future plant optimization studies. The thermal model dynamically predicted the real case with 98.7 % accuracy. Shunt currents were the main contributor to relative low Faraday efficiency of 86 % at nominal load and steady-state operation and heat loss to ambient from stack was only 2.6 % of the total power loss. 相似文献
8.
9.
《International Journal of Hydrogen Energy》2022,47(14):8943-8955
In this research, a technical, economic and environmental analysis has been proposed to a Hybrid Solid Oxide Fuel Cell (SOFC) system-based hybrid system including biomass, gas turbine, and Proton Exchange Membrane Electrolyzer. A multi-objective optimization technique has been utilized to improve the overall product cost and the exergy effectiveness based on a developed version of Aquila Optimizer (DAO). The main idea of using the developed version is to improve the accuracy and the precision of the original Aquila optimizer. The system is then authenticated in terms of energy/exergy effectiveness, and energy-economic efficiency. The achievements indicate that employing the optimization algorithm for different configurations provided satisfying results for the system. 相似文献
10.
磨矿动力学是描述被磨物料的磨碎速率与磨矿时间之间关系规律的一种数学模型,对分析物料在磨矿过程中的粒级及能量变化具有重要作用。为充分发挥磨矿动力学在磨矿过程中的作用,论文在分析国内外研究现状的基础上,系统介绍了两种典型的磨矿动力学模型:m阶磨矿动力学模型和磨矿总体平衡动力学模型,分析了模型中各参数的含义;以磨矿总体平衡动力学模型为重点,分析了破碎速率函数和破碎分布函数的求解方式,包括零阶产出率法、奥-勒理论简算法、卡普尔G-H算法以及经验公式法等;从物料性质、磨矿介质及配比、磨矿方式及参数、化学添加剂等几个方面分析了影响磨矿动力学模型的因素;指出了磨矿动力学模型在矿物加工工程领域的应用现状并对其未来的研究方向提出展望。研究表明磨矿动力学在矿物加工领域具有广泛而重要的应用,为进一步改善磨矿工艺提供了理论依据。 相似文献