全文获取类型
收费全文 | 230602篇 |
免费 | 26362篇 |
国内免费 | 16026篇 |
专业分类
电工技术 | 13604篇 |
技术理论 | 1篇 |
综合类 | 14154篇 |
化学工业 | 47756篇 |
金属工艺 | 51769篇 |
机械仪表 | 10624篇 |
建筑科学 | 12733篇 |
矿业工程 | 5780篇 |
能源动力 | 6423篇 |
轻工业 | 14133篇 |
水利工程 | 3220篇 |
石油天然气 | 9238篇 |
武器工业 | 2099篇 |
无线电 | 16809篇 |
一般工业技术 | 31789篇 |
冶金工业 | 17045篇 |
原子能技术 | 2505篇 |
自动化技术 | 13308篇 |
出版年
2024年 | 1195篇 |
2023年 | 4332篇 |
2022年 | 9207篇 |
2021年 | 10448篇 |
2020年 | 8637篇 |
2019年 | 7604篇 |
2018年 | 7516篇 |
2017年 | 9411篇 |
2016年 | 10370篇 |
2015年 | 11066篇 |
2014年 | 14006篇 |
2013年 | 14712篇 |
2012年 | 15018篇 |
2011年 | 15731篇 |
2010年 | 11793篇 |
2009年 | 12710篇 |
2008年 | 10722篇 |
2007年 | 14210篇 |
2006年 | 13993篇 |
2005年 | 11506篇 |
2004年 | 9434篇 |
2003年 | 8446篇 |
2002年 | 6870篇 |
2001年 | 5819篇 |
2000年 | 5000篇 |
1999年 | 4066篇 |
1998年 | 3101篇 |
1997年 | 2804篇 |
1996年 | 2383篇 |
1995年 | 2068篇 |
1994年 | 1812篇 |
1993年 | 1297篇 |
1992年 | 1173篇 |
1991年 | 861篇 |
1990年 | 846篇 |
1989年 | 706篇 |
1988年 | 373篇 |
1987年 | 264篇 |
1986年 | 181篇 |
1985年 | 154篇 |
1984年 | 170篇 |
1983年 | 113篇 |
1982年 | 132篇 |
1981年 | 88篇 |
1980年 | 112篇 |
1979年 | 47篇 |
1964年 | 36篇 |
1962年 | 68篇 |
1959年 | 45篇 |
1951年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
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
4.
5.
6.
Akira Yamamoto Kentaro Teramura Saburo Hosokawa Tsunehiro Tanaka 《Science and Technology of Advanced Materials》2015,16(2)
The effect of SO2 gas was investigated on the activity of the photo-assisted selective catalytic reduction of nitrogen monoxide (NO) with ammonia (NH3) over a TiO2 photocatalyst in the presence of excess oxygen (photo-SCR). The introduction of SO2 (300 ppm) greatly decreased the activity of the photo-SCR at 373 K. The increment of the reaction temperature enhanced the resistance to SO2 gas, and at 553 K the conversion of NO was stable for at least 300 min of the reaction. X-ray diffraction, FTIR spectroscopy, thermogravimetry and differential thermal analysis, x-ray photoelectron spectroscopy (XPS), elemental analysis and N2 adsorption measurement revealed that the ammonium sulfate species were generated after the reaction. There was a strong negative correlation between the deposition amount of the ammonium sulfate species and the specific surface area. Based on the above relationship, we concluded that the deposition of the ammonium sulfate species decreased the specific surface area by plugging the pore structure of the catalyst, and the decrease of the specific surface area resulted in the deactivation of the catalyst. 相似文献
7.
通过制备不同晶相结构〔单斜相(m-ZrO_2)、四方相(t-ZrO_2)和无定型(a-ZrO_2)〕ZrO_2载体,再通过沉积沉淀法制得Cu/m-ZrO_2、Cu/t-ZrO_2和Cu/a-ZrO_2催化剂,分别用于催化二乙醇胺脱氢合成亚氨基二乙酸反应。采用XRD、氮气物理吸附脱附、XPS、H_2-TPR、CO_2-TPD对催化剂的结构进行了表征。结果表明,Cu/m-ZrO_2催化剂界面更加有利于Cu~+/Cu~0稳定存在,具有更多的碱性位点,且抗氧化性较好。在二乙醇胺脱氢反应中,Cu/m-ZrO_2催化剂性能最好,反应时间为2.5 h,亚氨基二乙酸收率为97.64%。 相似文献
8.
9.
10.
《Displays》2015
Modern liquid crystal displays (LCDs) require novel technologies, such as new alignment methods to eliminate alignment layers, fast response and long operation time. To this end, we report an overview of recent efforts in LCD technologies devoted to realize more display modes having no alignment layer, faster switching time and low battery consumption. In particular, we overview recent advances on the liquid crystals (LCs) alignment for display applications, which includes superfine nanostructures, polymeric microchannels and polymer stabilized LCs. Furthermore, we analyze the main optical and electro-optical properties of new generation LCDs displays addressing a particular attention to LCs blue phase hosting gold nanoparticles. Moreover, we focus on the progress of electrofluidic displays, which demonstrates characteristics that are similar to LCDs, with attention on various pixel designs, operation principles and possible future trends of the technology. 相似文献