全文获取类型
收费全文 | 2300篇 |
免费 | 94篇 |
国内免费 | 65篇 |
专业分类
电工技术 | 161篇 |
综合类 | 80篇 |
化学工业 | 402篇 |
金属工艺 | 256篇 |
机械仪表 | 148篇 |
建筑科学 | 156篇 |
矿业工程 | 162篇 |
能源动力 | 75篇 |
轻工业 | 146篇 |
水利工程 | 6篇 |
石油天然气 | 11篇 |
武器工业 | 26篇 |
无线电 | 114篇 |
一般工业技术 | 332篇 |
冶金工业 | 246篇 |
原子能技术 | 70篇 |
自动化技术 | 68篇 |
出版年
2024年 | 6篇 |
2023年 | 13篇 |
2022年 | 26篇 |
2021年 | 34篇 |
2020年 | 42篇 |
2019年 | 34篇 |
2018年 | 35篇 |
2017年 | 60篇 |
2016年 | 64篇 |
2015年 | 56篇 |
2014年 | 89篇 |
2013年 | 128篇 |
2012年 | 120篇 |
2011年 | 184篇 |
2010年 | 131篇 |
2009年 | 148篇 |
2008年 | 134篇 |
2007年 | 131篇 |
2006年 | 141篇 |
2005年 | 125篇 |
2004年 | 95篇 |
2003年 | 97篇 |
2002年 | 66篇 |
2001年 | 47篇 |
2000年 | 72篇 |
1999年 | 63篇 |
1998年 | 51篇 |
1997年 | 41篇 |
1996年 | 38篇 |
1995年 | 41篇 |
1994年 | 42篇 |
1993年 | 24篇 |
1992年 | 28篇 |
1991年 | 16篇 |
1990年 | 10篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
排序方式: 共有2459条查询结果,搜索用时 15 毫秒
1.
Through improved synthesis process, resistance reduction effect of (K0.5Bi0.5)TiO3 (KBT) doping in Y–Mn co-doped BaTiO3 (BT) lead free ceramics was investigated. By different doping methods (doping K2O, Bi2O3 and TiO2 or synthesized KBT), medium Curie temperature (around 130 °C) lead free BT ceramics were obtained with ultra-low resistivity (13.84 Ωcm) with a temperature maintaining process at 700 °C. In this contribution, effect of sintering process and doping methods is discussed in detail. 相似文献
2.
Environmental contaminants such as trace elements may be present in all foods. Foods, raw materials and ingredients for food production are to an increasing extent traded across borders. Hence, there is a need for international legislation on trace elements as contaminants in food. In 1961, the FAO and WHO established the Codex Alimentarius to elaborate international food legislation. Contaminants in food are handled by the Codex Committee for Food Additives and Contaminants (CCFAC). The Codex Alimentarius system for developing legislation concerning trace elements as contaminants in food is based upon the Codex General Standard for Contaminants and Toxins in Food (GSCTF). By October 2001, the principles for setting maximum limits (MLs) for contaminants in food are agreed, and work is in progress on MLs for trace elements such as lead and cadmium in the various food categories. The status for the proposals is presented and discussed. The EU Regulation 466/2001 of 8 March 2001 sets MLs for lead and cadmium in various foods. This regulation will apply from 5 April 2002. The EU regulation is more detailed but similar to the Codex draft standards for lead and cadmium in food. In future, legislators and administrators in the Codex and EU and analytical chemists will discuss how to use more and better analytical data as risk-management tools to protect public health. Trace elements' speciation is an important aspect of this discussion. 相似文献
3.
4.
Anodic oxidation of mecoprop herbicide at lead dioxide 总被引:1,自引:0,他引:1
The electrochemical oxidation of an aqueous solution containing mecoprop (2-(2-methyl-4-chlorophenoxy)propionic acid) has
been studied at PbO2 anodes by cyclic voltammetry and bulk electrolysis. The influence of current density, hydrodynamic conditions, temperature
and pH on the degradation rate and current efficiency is reported. The results obtained show that the use of PbO2 leads to total mineralization of mecoprop due to the production of oxidant hydroxyl radical electrogenerated from water discharge.
The current efficiency for the electro-oxidation of mecoprop is enhanced by low current density, high recycle flow-rates and
high temperature. In contrast, the pH effect was not significant. It has also been observed that mecoprop decay kinetics follows
a pseudo-first-order reaction and the rate constant increases with rising current density. 相似文献
5.
6.
1 INTRODUCTIONLead-brass has excellent cutting ability , me-chanical and physical properties and is one of themost widely used copper alloys . The occupationratio of brass tube to all kinds of tubes reaches90 % in developed countries . The cutting lead-brass is a dual-phase brass and fine lead particlesdistribute dispersivelyin grains and on grain boun-ries . Theleadin wasted brass can easily beleachedand dissolvedinto soil .If the wasted lead-brass isburned in air ,the lead will become p… 相似文献
7.
8.
采用正交设计法和对比试验法,考察了硫黄、氧化锌、促进剂、炭黑以及某些工艺条件对胶料与镀铜钢丝帘线粘合力的影响。结果表明,硫黄品种对粘合力的影响不大;氧化锌用量增大,粘合力增大;用1.0份促进剂CZ时的粘合力大于用1.3份促进剂DZ;使用高结构炭黑可增大粘合力;胶料的混炼方法和硫化时间对粘合力的影响较大。 相似文献
10.