全文获取类型
收费全文 | 48158篇 |
免费 | 4968篇 |
国内免费 | 2452篇 |
专业分类
电工技术 | 3409篇 |
技术理论 | 4篇 |
综合类 | 3621篇 |
化学工业 | 7465篇 |
金属工艺 | 2589篇 |
机械仪表 | 3292篇 |
建筑科学 | 4083篇 |
矿业工程 | 1622篇 |
能源动力 | 1557篇 |
轻工业 | 3433篇 |
水利工程 | 1060篇 |
石油天然气 | 2373篇 |
武器工业 | 444篇 |
无线电 | 5595篇 |
一般工业技术 | 5575篇 |
冶金工业 | 2002篇 |
原子能技术 | 468篇 |
自动化技术 | 6986篇 |
出版年
2024年 | 223篇 |
2023年 | 835篇 |
2022年 | 1618篇 |
2021年 | 2132篇 |
2020年 | 1630篇 |
2019年 | 1302篇 |
2018年 | 1512篇 |
2017年 | 1629篇 |
2016年 | 1420篇 |
2015年 | 2053篇 |
2014年 | 2424篇 |
2013年 | 2985篇 |
2012年 | 3301篇 |
2011年 | 3399篇 |
2010年 | 3020篇 |
2009年 | 2782篇 |
2008年 | 2851篇 |
2007年 | 2574篇 |
2006年 | 2590篇 |
2005年 | 2272篇 |
2004年 | 1624篇 |
2003年 | 1609篇 |
2002年 | 1756篇 |
2001年 | 1586篇 |
2000年 | 1140篇 |
1999年 | 1132篇 |
1998年 | 745篇 |
1997年 | 688篇 |
1996年 | 591篇 |
1995年 | 461篇 |
1994年 | 391篇 |
1993年 | 295篇 |
1992年 | 249篇 |
1991年 | 179篇 |
1990年 | 147篇 |
1989年 | 116篇 |
1988年 | 98篇 |
1987年 | 47篇 |
1986年 | 43篇 |
1985年 | 33篇 |
1984年 | 26篇 |
1983年 | 16篇 |
1982年 | 12篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1979年 | 10篇 |
1959年 | 4篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Zhen Wu Jing Yao Pengfei Zhu Fusheng Yang Xiangyu Meng Sandra Kurko Zaoxiao Zhang 《International Journal of Hydrogen Energy》2021,46(19):11183-11198
Advanced biogas power generation technology has been attracting attentions, which contributes to the waste disposal and the mitigation of greenhouse gas emissions. This work proposes and models a novel biogas-fed hybrid power generation system consisting of solid oxide fuel cell, water gas shift reaction, thermal swing adsorption and proton exchange membrane fuel cell (SOFC-WGS-TSA-PEMFC). The thermodynamic, exergetic, and thermo-economic analyses of this hybrid system for power generation were conducted to comprehensively evaluate its performance. It was found that the novel biogas-fed hybrid system has a gross energy conversion efficiency of 68.63% and exergy efficiency of 65.36%, indicating high efficiency for this kind of hybrid power technology. The market sensitivity analysis showed that the hybrid system also has a low sensitivity to market price fluctuation. Under the current subsidy level for the distributed biogas power plant, the levelized cost of energy can be lowered to 0.02942 $/kWh for a 1 MW scale system. Accordingly, the payback period and annual return on investment can reach 1.4 year and about 20%, respectively. These results reveal that the proposed hybrid system is promising and economically feasible as a distributed power plant, especially for the small power scale (no more than 2 MW). 相似文献
22.
This paper presents two well-instrumented large-scale field tests of PVD-improved soft soil with vacuum and surcharge preloading, respectively. The two large-scale field tests were conducted adjacent to each other with the same preload. A comparative analysis was performed to investigate the performance of subsoil (i.e., the ground settlement, the layered settlement, the lateral displacement of subsoil and pore water pressure) under vacuum preloading and equivalent surcharge preloading. Some design methods were verified based on the field data. Cone Penetration Tests (CPT) and Vane Shear Tests (VST) were conducted to assess the improvement effects on subsoil after preloading. The results showed that as compared with surcharge preloading, vacuum preloading mitigated the differential settlement of the ground. The vacuum pressure transmitted into the soil with a minor loss through the PVD length. From a practical point of view, the improvement effects by vacuum preloading and surcharge preloading were similar in terms of influence depth and soil strength based on the in-situ tests. 相似文献
23.
Aline Kövilein Christin Kubisch Liyin Cai Katrin Ochsenreither 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2020,95(3):513-526
Malic acid derived from fossil resources is currently applied in the food and beverage industries with a medium global production capacity. However, in the transition from a fossil-based to a bio-based economy, biotechnologically produced l -malic acid may become an important platform chemical with many new applications, especially in the field of biopolymers. In this review, currently used petrochemical production routes to dl -malic acid are outlined and insights into possible bio-based alternatives for microbial l -malic acid production are provided. Besides ecological reasons, the possibility to produce enantiopure l -malic acid by microbial fermentation is the biggest advantage over chemical synthesis. State-of-the-art and open challenges concerning production host engineering, substrate choice and downstream processing are addressed. With regard to production hosts, a literature overview is given covering the leading natural production strains of Aspergillus, Ustilago and Aureobasidium, as well as Escherichia coli as the most important engineered recombinant host. The utilization of renewable substrates as an alternative to glucose is emphasized in particular as a key aspect for a competitive bio-based production. Out of the alternative substrates discussed in this review, the industrial side-streams crude glycerol and molasses seem to be most promising for large-scale l -malic acid production. © 2019 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. 相似文献
24.
中国大陆PCB产业自动化的现况与未来 总被引:1,自引:1,他引:0
从中国大陆PCB发展的现况分析实行设备自动化连线为企业所创造的价值。设备自动化连线是中国大陆PCB必须面临的改革出路。 相似文献
25.
26.
蔡存岭 《石油化工管理干部学院学报》2006,(1):72-74
论述了当前腐败现象的表现和特点,分析了产生腐败现象的主要原因,提出了治理腐败现象的对策措施: 建立有效的教育机制、严格的用人机制、规范的决策机制、健全的管理机制、完善的监督机制和有力的责任追究机制,建立科学的法人治理结构并实行纪检监察机构派驻制。 相似文献
27.
螺旋折流板换热器传热系数与压降实验研究 总被引:3,自引:2,他引:1
以螺旋角18°为例,研究了螺旋折流板换热器传热系数与压降的变化,并给出了螺旋折流板换热器的传热系数与压降相关的计算公式。该结果可为系统仿真和螺旋折流板换热器的设计计算提供借鉴。 相似文献
29.
蔡剑锋 《信息安全与通信保密》2006,(9):142-144
论文通过对病毒及反病毒技术的发展分析,总结了现有一些较优秀的杀毒软件的优缺点,提出了基于新理念的攻防查杀型杀毒软件的实现模型。 相似文献
30.
802.22 工作组的主要任务是开发和建立一套基于认知无线电(CR)技术, 在现有电视频段利用暂时空闲的频道进行无线通信的区域网空中接口标准。由于基于802.22 协议的无线区域网(WRAN)工作在现有电视频段中 , 要求不能对正在广播的电视频道产生干扰 , 所以WRAN采用了认知无线电技术 , 对电视频段进行感知和测量 , 利用动态频谱管理技术找到空闲频道进行再分配。认知无线电技术将是未来无线通信的发展方向之一。本讲座分3 期对无线区域网和认知无线电技术进行介绍, 第1 讲已经介绍无线区域网络和IEEE 802.22工作组情况 , 包括WRAN背景、802.22 系统、802.22空中接口等;第2讲已经介绍认知无线电技术和实现其的基础软件无线电(SDR)技术 , 包括无线电知识描述语言(RKRL)和认知循环、无线电频谱礼仪等;本讲介绍802.22 WRAN频谱共存问题和认知无线电技术的应用。 相似文献