全文获取类型
收费全文 | 448636篇 |
免费 | 40675篇 |
国内免费 | 22002篇 |
专业分类
电工技术 | 78358篇 |
技术理论 | 33篇 |
综合类 | 41697篇 |
化学工业 | 46120篇 |
金属工艺 | 14013篇 |
机械仪表 | 28646篇 |
建筑科学 | 38851篇 |
矿业工程 | 18255篇 |
能源动力 | 21170篇 |
轻工业 | 19415篇 |
水利工程 | 26634篇 |
石油天然气 | 16890篇 |
武器工业 | 4776篇 |
无线电 | 39320篇 |
一般工业技术 | 25936篇 |
冶金工业 | 15218篇 |
原子能技术 | 5536篇 |
自动化技术 | 70445篇 |
出版年
2024年 | 1603篇 |
2023年 | 5026篇 |
2022年 | 11376篇 |
2021年 | 13345篇 |
2020年 | 12494篇 |
2019年 | 9877篇 |
2018年 | 9414篇 |
2017年 | 12850篇 |
2016年 | 15486篇 |
2015年 | 17265篇 |
2014年 | 29408篇 |
2013年 | 26193篇 |
2012年 | 32733篇 |
2011年 | 33864篇 |
2010年 | 26026篇 |
2009年 | 26370篇 |
2008年 | 25496篇 |
2007年 | 32514篇 |
2006年 | 29982篇 |
2005年 | 26275篇 |
2004年 | 20971篇 |
2003年 | 18912篇 |
2002年 | 14792篇 |
2001年 | 11945篇 |
2000年 | 9971篇 |
1999年 | 7627篇 |
1998年 | 5507篇 |
1997年 | 4466篇 |
1996年 | 3861篇 |
1995年 | 3272篇 |
1994年 | 2715篇 |
1993年 | 1847篇 |
1992年 | 1569篇 |
1991年 | 1160篇 |
1990年 | 951篇 |
1989年 | 829篇 |
1988年 | 570篇 |
1987年 | 429篇 |
1986年 | 298篇 |
1985年 | 315篇 |
1984年 | 319篇 |
1983年 | 231篇 |
1982年 | 188篇 |
1981年 | 127篇 |
1980年 | 129篇 |
1979年 | 88篇 |
1978年 | 54篇 |
1977年 | 50篇 |
1962年 | 70篇 |
1959年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
The proliferating need for sustainability intervention in food grain transportation planning is anchoring the attention of researchers in the interests of stakeholders and environment at large. Uncertainty associated with food grain supply further intensifies the problem steering the need for designing robust, cost-efficient and sustainable models. In line with this, this paper aims to develop a robust and sustainable intermodal transportation model to facilitate single type of food grain commodity shipments while considering procurement uncertainty, greenhouse gas emissions, and intentional hub disruption. The problem is designed as a mixed integer non-linear robust optimisation model on a hub and spoke network for evaluating near optimal shipment quantity, route selection and hub location decisions. The robust optimisation approach considers minimisation of total relative regret associated with total cost subject to several real-time constraints. A version of Particle Swarm Optimisation with Differential Evolution is proposed to tackle the resulting NP-hard problem. The model is tested with two other state-of the art meta-heuristics for small, medium, and large datasets subject to different procurement scenarios inspired from real time food grain operations in Indian context. Finally, the solution is evaluated with respect to total cost, model and solution robustness for all instances. 相似文献
3.
4.
大型综合室内亲子乐园属于高大空间,设有游乐设施和游戏的特殊性使得对空间的舒适性要求一致,但是送风气流遇阻严重,室内存在较多气流死角,影响室内空气质量和儿童健康。因此其空调设计不仅需要考虑温度、风速的空间均匀度,还要考虑各点的空气龄和PMV-PPD指标。以天津某亲子乐园为研究对象,利用scSTREAM软件对适用于该房间的辐射供冷加新风、置换通风、混合通风三种空调方式的送风效果进行数值模拟分析,从流场的均匀性、人员的热舒适性等方面对模拟结果进行探讨,研究结果表明辐射供冷加新风方式的空间均匀性和PMV指标最佳,混合通风方式的空气龄最小。 相似文献
5.
张皓博 《重庆电力高等专科学校学报》2015,(3):5-6,17
以可编程控制器课程为例,介绍"任务驱动"教学法在教学过程中的具体应用,并探讨了实施过程中存在的问题与解决方法。 相似文献
6.
7.
The supervision of a hybrid power plant, including solar panels, a gas microturbine and a storage unit operating under varying solar power profiles is considered. The Economic Supervisory Predictive controller assigns the power references to the controlled subsystems of the hybrid cell using a financial criterion. A prediction of the renewable sources power is embedded into the supervisor. Results deteriorate when the solar power is unsteady, owing to the inaccuracy of the predictions for a long-range horizon of 10 s. The receding horizon is switched between an upper and a lower value according to the amplitude of the solar power trend. Theoretical results show the relevance of horizon switching, according to a tradeoff between performance and prediction accuracy. Experimental results, obtained in a Hardware In the Loop (HIL) framework, show the relevance of the variable horizon approach. Power amplifiers allow us to simulate virtual components, such as a gas microturbine, and to blend their powers with that of real devices (storage unit, real solar panels). In this case, fuel savings, reaching 15%, obtained under unsteady operating conditions lead to a better overall performance of the hybrid cell. The overall savings obtained in the experiments amount to 12%. 相似文献
8.
The development of a sustainable energy system throughout an enterprise is a complex task, which requires an agile holistic approach. Such an approach needs to include a variety of objectives including energy strategy formation and strategic decision-making, which are directly related to the analysis and management of the main areas of sustainable development:The economic, technological, environmental, and social. These multidimensional requirements of sustainability are often difficult to achieve within the enterprise, because these aspects are interrelated and influenced by various internal and external environment factors. This paper first reviews the main challenges for an energy system, and then demonstrates how a strategic agile enterprise architecture driven approach could effectively guide the sustainable energy system development. The study presented in this paper provides a holistic approach that contributes to the advancement and usage of literature dealing with issues of sustainable energy system development and agile enterprise architecture, which has not been discussed before to any great extent. 相似文献
9.
Novel organic dyes containing N-bridged oligothiophene coplanar cores for dye-sensitized solar cells
Three novel organic dyes adopting fully-fused coplanar heteroarene as the donor moieties end-capped with two cyanoacrylic acids as acceptors and anchoring groups have been synthesized, characterized, and used as the sensitizers for dye-sensitized solar cells (DSSCs). The photophysical and electrochemical properties of the novel dyes and the characteristics of the DSSCs based on the novel organic dyes were investigated. The incorporation of the coplanar cores with electron-donating N-bridges are beneficial for the better intramolecular charge transfer (ICT), giving these new dyes good light-harvesting capability. The LUMO energy levels of these coplanar heteroacene-based dyes are sufficiently high for the efficient electron injection to TiO2 upon photo-excitation, while the suitable HOMOs allow the regeneration of oxidized dyes with the electrolyte redox (I−/I3−). The structural features of the coplanar cores (penta vs. hexa heteroarene) as well as the alkyl substitutions play crucial roles in governing the physical properties and device performance. Among these three novel organic sensitizers, the EHTt dye composed of a fully fused hexa-arene core and less bulky N-alkyl groups caused the DSSC to show the best photovoltaic performance with an open-circuit voltage (VOC) of 0.58 V, a short-circuit photocurrent density (JSC) of 13.72 mA/cm2, and a fill factor (FF) of 0.69, yielding an overall power conversion efficiency (PCE) of 5.52% under AM 1.5G solar irradiation. 相似文献
10.
对鞍钢股份无缝钢管厂连轧机前毛管坯横移装置存在的设计缺陷进行了分析,并提出改进方案,将原横移装置由高架轨道横移机构及上下升降链传动装置,改进为地面轨道横移系统及同步旋转臂实现取管、放管过程。实施后消除了生产故障,缩短了轧制周期,降低生产成本。 相似文献