全文获取类型
收费全文 | 2937篇 |
免费 | 270篇 |
国内免费 | 112篇 |
专业分类
电工技术 | 356篇 |
技术理论 | 1篇 |
综合类 | 254篇 |
化学工业 | 243篇 |
金属工艺 | 51篇 |
机械仪表 | 91篇 |
建筑科学 | 292篇 |
矿业工程 | 97篇 |
能源动力 | 385篇 |
轻工业 | 179篇 |
水利工程 | 207篇 |
石油天然气 | 88篇 |
武器工业 | 20篇 |
无线电 | 299篇 |
一般工业技术 | 272篇 |
冶金工业 | 91篇 |
原子能技术 | 125篇 |
自动化技术 | 268篇 |
出版年
2024年 | 9篇 |
2023年 | 42篇 |
2022年 | 60篇 |
2021年 | 88篇 |
2020年 | 95篇 |
2019年 | 79篇 |
2018年 | 91篇 |
2017年 | 105篇 |
2016年 | 112篇 |
2015年 | 122篇 |
2014年 | 158篇 |
2013年 | 220篇 |
2012年 | 180篇 |
2011年 | 213篇 |
2010年 | 154篇 |
2009年 | 171篇 |
2008年 | 144篇 |
2007年 | 227篇 |
2006年 | 189篇 |
2005年 | 149篇 |
2004年 | 107篇 |
2003年 | 105篇 |
2002年 | 78篇 |
2001年 | 62篇 |
2000年 | 51篇 |
1999年 | 45篇 |
1998年 | 32篇 |
1997年 | 30篇 |
1996年 | 33篇 |
1995年 | 25篇 |
1994年 | 26篇 |
1993年 | 19篇 |
1992年 | 16篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 2篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1980年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1961年 | 2篇 |
1956年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有3319条查询结果,搜索用时 0 毫秒
91.
The objective of the study was to optimize the nutrition sources in a culture medium for the production of xylanase from Penicillium sp.WX-Z1 using Plackett-Burman design and Box-Behnken design. The Plackett-Burman multifactorial design was first employed to screen the important nutrient sources in the medium for xylanase production by Penicillium sp.WX-Z1 and subsequent use of the response surface methodology (RSM) was further optimized for xylanase production by Box-Behnken design. The important nutrient sources in the culture medium, identified by the initial screening method of Placket-Burman, were wheat bran, yeast extract, NaNO(3), MgSO(4), and CaCl(2). The optimal amounts (in g/L) for maximum production of xylanase were: wheat bran, 32.8; yeast extract, 1.02; NaNO(3), 12.71; MgSO(4), 0.96; and CaCl(2), 1.04. Using this statistical experimental design, the xylanase production under optimal condition reached 46.50 U/mL and an increase in xylanase activity of 1.34-fold was obtained compared with the original medium for fermentation carried out in a 30-L bioreactor. 相似文献
92.
针对低温环境条件下热泵逆循环除霜存在的诸多问题,提出了一套具备预热除霜功能的新型空气-水双热源复合热泵系统(new air-water double source composite heat pump system,AWDSHPS-N),通过阀门切换和低温水源侧水泵的启停控制可直接进入除霜模式,除霜过程中可保证制热的连续性,每次除霜时长不超过5 min。利用恒温恒湿环境仓模拟室外环境条件,可调控水温的低温水箱模拟太阳能等低温热源搭建AWDSHPS-N实验台,对不同测试工况下,单空气源制热模式(air source heating mode,ASHM)、单水源制热模式(water source heating mode,WSHM)、空气-水双热源制热模式(air-water source heating mode,AWSHM)3种制热模式将水从18℃加热至51℃的系统性能系数(coefficient of performance,COP)进行了实验,结果表明:AWSHM的COP比ASHM提高了6.1%~20.5%;当环境温度和低温水源温度均高于15℃时,系统COP高低顺序为AWSHM、ASHM和WSHM。 相似文献
93.
94.
按照现行的锅炉设计及运行情况,天然气锅炉的效率都在80%左右,锅炉的总体运行效率不高,能源浪费仍然较大。通过对相关设备进行改造,减少热能损失和充分回收利用各种余热,可以将锅炉的热效率提高到85%以上,提高天然气锅炉的热效率,从而节约能源。 相似文献
95.
Nitrogen was supplied from two fast release sources, ammonium sulfate ((NH4)2SO4) and calcium nitrate (Ca(NO3)2) and a slow release source, isobutylidene diurea (IBDU) to boronia, a new flower crop native to Australia. At lower rates (25 kg per ha), N availability from different sources, as indicated by the leaf N concentration, did not differ within a month after application but three months after application, N availability was higher from IBDU than from (NH4)2SO4 or Ca(NO3)2. At 50 or 100 kg per ha, N availability was higher throughout the year from (NH4)2SO4 or Ca(NO3)2 than from IBDU, thereby allowing luxury consumption and causing toxicity. The flower yield increased with increasing N rates. Complete doses of all N rates which were applied early during the vegetative growth gave the highest yields and the same N rates applied in split doses at different phases of plant growth decreased the yields. In addition, high N availability during flowering (caused by a split dose) further decreased the yield. At all application times, IBDU gave the highest yield and the differences in yields with (NH4)2SO4 and Ca(NO3)2 were not significant. The leaf N concentration associated with maximum yield declined as the plant advanced towards flowering. 相似文献
96.
97.
Rui Marques Linda Mazri Stphanie Da Costa Franck Delacroix Grald Djga-Mariadassou Patrick Da Costa 《Catalysis Today》2008,137(2-4):185
The aim of the present work is to study the selective reduction of NOx from natural gas sources using unburned methane or hydrogen as reducing agents. The results suggest that the NOx are reduced by H2 at low temperature, when methane is not activated and at higher temperature the methane is then the main reducing agent. Similar results are obtained for alumina supported palladium and alumina supported cobald-palladium catalysts at low temperature in presence of hydrogen suggesting that the active phase for the reaction NO/H2 is the palladium. However, at high temperature the higher activity is obtained on bimetallic catalyst. The presence of cobalt enhances the catalytic activity. This result suggests that cobalt and palladium both in cationic form are the active sites when the reducing agent is the methane. 相似文献
98.
This paper treats supercapacitors matrix characterization. In order to cut off transient power peaks and to compensate for the intrinsic limitations in embedded sources, the use of supercapacitors as a storage system is quite suitable, because of their appropriate electrical characteristics (huge capacitance, small series resistance, high specific energy, high specific power), direct storage (energy ready for use), and easy control by power electronic conversion. This use requires supercapacitors modules where several cells connected in serial and/or in parallel, thus a bypass system to balance the charging or the discharging of supercapacitors is required. In the matrix of supercapacitors, six elements of three parallel BCAP0350 supercapacitors in serial connections have been considered. This topology permits to reduce the number of the bypass circuits and it can work in degraded mode. Actually, it allows the system to have more reliability by providing power continually to the load even when there are one or more cells failed. Simulation and experimental results are presented and discussed. 相似文献
99.
根据金属冶炼建设项目安全设施设计编写提纲,围绕安全设施设计编写中常遇到的几个问题进行分析和思考,主要阐述编写安全设施设计的前期准备工作和编写重点。 相似文献
100.