全文获取类型
收费全文 | 39135篇 |
免费 | 4749篇 |
国内免费 | 2802篇 |
专业分类
电工技术 | 4046篇 |
技术理论 | 5篇 |
综合类 | 5218篇 |
化学工业 | 3337篇 |
金属工艺 | 1163篇 |
机械仪表 | 4052篇 |
建筑科学 | 9112篇 |
矿业工程 | 1267篇 |
能源动力 | 1314篇 |
轻工业 | 327篇 |
水利工程 | 970篇 |
石油天然气 | 925篇 |
武器工业 | 1554篇 |
无线电 | 3468篇 |
一般工业技术 | 3962篇 |
冶金工业 | 555篇 |
原子能技术 | 215篇 |
自动化技术 | 5196篇 |
出版年
2024年 | 146篇 |
2023年 | 704篇 |
2022年 | 1189篇 |
2021年 | 1486篇 |
2020年 | 1615篇 |
2019年 | 1275篇 |
2018年 | 1181篇 |
2017年 | 1444篇 |
2016年 | 1531篇 |
2015年 | 1808篇 |
2014年 | 3280篇 |
2013年 | 2510篇 |
2012年 | 3505篇 |
2011年 | 3556篇 |
2010年 | 2615篇 |
2009年 | 2706篇 |
2008年 | 2412篇 |
2007年 | 2797篇 |
2006年 | 2251篇 |
2005年 | 1775篇 |
2004年 | 1426篇 |
2003年 | 1142篇 |
2002年 | 886篇 |
2001年 | 676篇 |
2000年 | 549篇 |
1999年 | 442篇 |
1998年 | 332篇 |
1997年 | 288篇 |
1996年 | 230篇 |
1995年 | 224篇 |
1994年 | 186篇 |
1993年 | 120篇 |
1992年 | 106篇 |
1991年 | 71篇 |
1990年 | 59篇 |
1989年 | 43篇 |
1988年 | 35篇 |
1987年 | 18篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 3篇 |
1959年 | 2篇 |
1956年 | 1篇 |
1954年 | 1篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
11.
Incorporating microgrids coupling with utilization of flexible switching to enhance self-healing ability of electric distribution systems 下载免费PDF全文
Saeed Mousavizadeh Arman Alahyari Seyed Reza Movahhed Ghodsiny Mahmoud-Reza Haghifam 《电力系统保护与控制》2021,6(3):300-310
Electric distribution networks have to deal with issues caused by natural disasters. These problems possess unique characteristics, and their severity can make load restoration methods impotent. One solution that can help in alleviating the aftermath is the use of microgrids (MGs). Employing the cumulative capacity of the generation resources through MG coupling facilitates the self-healing capability and leads to better-coordinated energy management during the restoration period, while the switching capability of the system should also be considered. In this paper, to form and schedule dynamic MGs in distribution systems, a novel model based on mixed-integer linear programming (MILP) is proposed. This approach employs graph-related theories to formulate the optimal formation of the networked MGs and management of their proper participation in the load recovery process. In addition, the Benders decomposition technique is applied to alleviate computability issues of the optimization problem. The validity and applicability of the proposed model are evaluated by several simulation studies. 相似文献
12.
Günther Huber Otto Machhammer Maren Lepple Claudia Weidlich Cord-Henrich Dustmann Akane Hartenbach 《化学,工程师,技术》2021,93(4):664-672
A photovoltaic system could supply a single-family house with electrical power, warm water, and room heat if the energy would be distributed over the year to suit the load profile. However, storage systems for this are not state of the art yet. A concrete example is used to estimate which parameters such a power storage system should have. A suitable electrochemical reaction system based on inorganic salt mixtures is proposed. The German Federal Ministry of Education and Research is currently funding the development of a world storage facility based on the same reaction system. 相似文献
13.
针对在役公路梁式桥梁由于材料性能退化及外部环境等因素共同作用而导致承载力不足、耐久性降低等问题,开展旧桥力学性能的快速诊断试验研究。通过诊断性载荷试验的理论分析和有限元模型标定流程研究,快速、高效地完成在役公路桥梁的承载力性能测量和评估,从而为在役公路桥梁结构的养护管理提供可靠的技术支持。 相似文献
14.
Junjie Li Mei Liang Wanjing Cheng Shuhao Wang 《International Journal of Hydrogen Energy》2021,46(14):9553-9566
Electric vehicles (EVs) are considered a promising alternative to conventional vehicles (CVs) to alleviate the oil crisis and reduce urban air pollution and carbon emissions. Consumers usually focus on the tangible cost when choosing an EV or CV but overlook the time cost for restricting purchase or driving and the environmental cost from gas emissions, falling to have a comprehensive understanding of the economic competitiveness of CVs and EVs. In this study, a life cycle cost model for vehicles is conducted to express traffic and environmental policies in monetary terms, which are called intangible cost and external cost, respectively. Battery electric vehicles (BEVs), fuel cell electric vehicles (FCEVs), and CVs are compared in four first-tier, four new first-tier, and 4 s-tier and below cities in China. The comparison shows that BEVs and FCEVs in most cities are incomparable with CVs in terms of tangible cost. However, the prominent traffic and environmental policies in first-tier cities, especially in Beijing and Shanghai, greatly increase the intangible and external costs of CVs, making consumers more inclined to purchase BEVs and FCEVs. The main policy benefits of BEVs and FCEVs come from three aspects: government subsidies, purchase and driving restrictions, and environmental taxes. With the predictable reduction in government subsidies, traffic and environmental policies present important factors influencing the competitiveness of BEVs and FCEVs. In first-tier cities, BEVs and FCEVs already have a competitive foundation for large-scale promotion. In new first-tier and second-tier and below cities, stricter traffic and environmental policies need to be formulated to offset the negative impact of the reduction in government subsidies on the competitiveness of BEVs and FCEVs. Additionally, a sensitivity analysis reveals that increasing the mileage and reducing fuel prices can significantly improve the competitiveness of BEVs and FCEVs, respectively. 相似文献
15.
《International Journal of Hydrogen Energy》2021,46(64):32665-32675
The thermal management of a proton exchange membrane fuel cell (PEMFC) is crucial for fuel cell vehicles. This paper presents a new simulation model for the water-cooled PEMFC stacks for automotive vehicles and cooling systems. The cooling system model considers both the cooling of the stack and cooling of the compressed air through the intercooler. Theoretical analysis was carried out to calculate the heat dissipation requirements for the cooling system. The case study results show that more than 99.0% of heat dissipation requirement is for thermal management of the PEMFC stack; more than 98.5% of cooling water will be distributed to the stack cooling loop. It is also demonstrated that controlling cooling water flow rate and stack inlet cooling water temperature could effectively satisfy thermal management constraints. These thermal management constraints are differences in stack inlet and outlet cooling water temperature, stack temperature, fan power consumption, and pump power consumption. 相似文献
16.
17.
《Ceramics International》2022,48(7):9527-9533
In this work, a magnetodielectric coupling observed in barium titanate–cobalt ferrite composites synthesized using high-energy ball milling assisted via a thermal treatment is discussed. Vibrating sample magnetometry and dielectric spectroscopy showed that multiferroic composites possess both ferromagnetic and dielectric behaviors inherited from the parent ferromagnetic cobalt ferrite and ferroelectric barium titanate phases. The magnetocapacitance (up to 35%) recorded for x = 0.3, (1-x)BaTiO3–xCoFe2O4, can be attributed to the spin-dependent filtering mechanism. The composite with the aforementioned composition exhibited a homogeneous matrix–particle composite microstructure, which was achieved via high-energy ball milling during the mixing stage. 相似文献
18.
大直径厚壁气瓶内部淬火时的流动换热过程极其复杂,受到多种因素的影响,而研究气瓶内部压强和温度的变化规律对改善流动换热效果、提高产品组织性能具有重要的理论指导意义。以914 mm厚壁气瓶和瓶内流体为研究对象,建立了二维等效流 固耦合模型;采用多喷嘴系统对气瓶内外进行喷水淬火,研究了气瓶总长、喷水流速及淬火时间对瓶内压强及内壁温度的影响,通过间歇淬火试验验证了数学模型的正确性。结果发现,气瓶长度对瓶内压强和瓶壁温度的影响显著,喷水流速次之,当喷水流速大于8 m/s后,水量对瓶壁的冷却效果大大降低;气瓶内壁长度方向的温度梯度分别随气瓶总长的增加和淬火时间的延长而减小,但基本不受喷水量的影响。 相似文献
19.
Numerous design choices need to be made at several levels when designing high-tech products: technology, processes, architecture, components, materials… and these choices need to be made in relation to the product life cycle with the corresponding experts for each stage of the life cycle. At the same time, to ensure product sustainability, a specific focus on the future potential environmental impacts is highly recommended. In this research, an agile model is proposed to help designers make decisions while monitoring environmental performance indicators of high-tech solutions. The concept of Critical Product Life Cycle Parameters had to be introduced to facilitate the eco-design of the final product. The approach is illustrated by the Electric Vehicle Li-Ion Batteries case study. 相似文献
20.
针对多角度下车辆出现一定的尺度变化和形变导致很难被准确识别的问题,提出基于多尺度双线性卷积神经网络(MS-B-CNN)的车型精细识别模型。首先,对双线性卷积神经网络(B-CNN)算法进行改进,提出MS-B-CNN算法对不同卷积层的特征进行了多尺度融合,以提高特征表达能力;此外,还采用基于中心损失函数与Softmax损失函数联合学习的策略,在Softmax损失函数基础上分别对训练集每个类别在特征空间维护一个类中心,在训练过程中新增加样本时,网络会约束样本的分类中心距离,以提高多角度情况下的车型识别的能力。实验结果显示,该车型识别模型在CompCars数据集上的正确率达到了93.63%,验证了模型在多角度情况下的准确性和鲁棒性。 相似文献