全文获取类型
收费全文 | 55132篇 |
免费 | 7429篇 |
国内免费 | 4797篇 |
专业分类
电工技术 | 5393篇 |
技术理论 | 1篇 |
综合类 | 5444篇 |
化学工业 | 7026篇 |
金属工艺 | 3726篇 |
机械仪表 | 3811篇 |
建筑科学 | 4010篇 |
矿业工程 | 2065篇 |
能源动力 | 1359篇 |
轻工业 | 6396篇 |
水利工程 | 2075篇 |
石油天然气 | 2291篇 |
武器工业 | 858篇 |
无线电 | 6129篇 |
一般工业技术 | 4585篇 |
冶金工业 | 2287篇 |
原子能技术 | 1335篇 |
自动化技术 | 8567篇 |
出版年
2024年 | 199篇 |
2023年 | 1019篇 |
2022年 | 2382篇 |
2021年 | 3011篇 |
2020年 | 2170篇 |
2019年 | 1505篇 |
2018年 | 1580篇 |
2017年 | 1668篇 |
2016年 | 1543篇 |
2015年 | 2469篇 |
2014年 | 3119篇 |
2013年 | 3614篇 |
2012年 | 4545篇 |
2011年 | 4820篇 |
2010年 | 4632篇 |
2009年 | 4591篇 |
2008年 | 4533篇 |
2007年 | 4442篇 |
2006年 | 3776篇 |
2005年 | 3099篇 |
2004年 | 2244篇 |
2003年 | 1471篇 |
2002年 | 1377篇 |
2001年 | 1367篇 |
2000年 | 1023篇 |
1999年 | 409篇 |
1998年 | 117篇 |
1997年 | 106篇 |
1996年 | 109篇 |
1995年 | 69篇 |
1994年 | 54篇 |
1993年 | 44篇 |
1992年 | 38篇 |
1991年 | 25篇 |
1990年 | 24篇 |
1989年 | 31篇 |
1988年 | 15篇 |
1987年 | 11篇 |
1986年 | 19篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 11篇 |
1982年 | 3篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1979年 | 10篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1959年 | 8篇 |
1951年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 875 毫秒
1.
4.
本文采用QuEChERS技术结合超高效液相色谱-串联质谱(UHPLC-MS/MS)技术建立同时检测丙烯酰胺(AA)、亚硝胺(NAs)和杂环胺(HAAs)含量的方法,用于分析热加工肉制品中产生的胺类物质。结果表明:该方法检测出的三类成分20种胺类物质在相应浓度范围内显示出良好的线性关系(R2>0.991),检测限和定量限分别为0.01~1.6 ng/g和0.03~4.8 ng/g,日内回收率介于66.3%~116.5%之间,日内精密度介于0.78%~9.0%之间。每个胺类物的5×LOQ加标水平计算的日间精度范围为3.4%~9.4%。该方法应用于煎烤的四种肉制品中AA、NAs和HAAs的分析,共检测出9种胺类物质,浓度范围为0.03~31.26 ng/g。 相似文献
5.
6.
Suisui Zhang Jingying Li Yan Nie Luyao Qiang Boyang Bai Zhiwei Peng Xiaoxun Ma 《中国化学工程学报》2022,42(2):236-244
HFC-134a is a widely used environment-friendly refrigerant. At present, China is the largest producer of HFC-134a in the world. The production of HFC-134a in China mainly adopts the calcium carbide acetylene route. However, the production route has high resource and energy consumption and large waste emission, and few of the studies addressed on the environmental performance of its production process. This study quantified the environmental performance of HFC-134a production by calcium carbide route via carrying out a life cycle assessment (LCA) using the CML 2001 method. And uncertainty analysis by Monte-Carlo simulation was also carried out. The results showed that electricity had the most impact on the environment, followed by steam, hydrogen fluoride and chlorine, and the impact of direct CO2 emissions in calcium carbide production stage on the global warming effect also could not be ignored. Therefore, the clean energy (e.g., wind, solar, biomass, and natural gas) was used to replace coal-based electricity and coal-fired steam in this study, showing considerable environmental benefits. At the same time, the use of advanced production technologies could also improve environmental benefits, and the environmental impact of the global warming category could be reduced by 4.1% via using CO2 capture and purification technology. The Chinese database of HFC-134a production established in this study provides convenience for the relevant study of scholars. For the production of HFC-134a, this study helps to better identify the specific environmental hotspots and proposes useful ways to improve the environmental benefits. 相似文献
7.
采用超高效液相色谱⁃四极杆⁃飞行时间高分辨质谱(UPLC⁃Q⁃TOF)对4类不同类型的含聚对苯二甲酸乙二醇酯(PET)材质的食品接触材料在4 %乙酸和50 %乙醇模拟物中的迁移出的非挥发性未知物进行筛查解析。结果表明,产品在4 %乙酸模拟物的迁移风险远小于50 %乙醇模拟物,主要迁移物质为聚合单体形成的寡聚物,抗氧剂、润滑剂、胶黏剂等加工助剂以及生产加工、迁移过程中形成的非有意添加物(NIAS)物质;纯PET材质的产品迁移物质较少,多层复合材料迁移物质较多。复合材质的产品中,PET材质可能在生产时添加了己二酸、癸二酸、新戊二醇等物质,进行了改性处理;此外,部分迁移物质会与模拟物中的乙醇发生反应,生成新的NIAS物质。 相似文献
8.
Yu Yang Zhiwei Zhou Bingchu Mei Yongqiang Zhang Xinwen Liu 《Ceramics International》2021,47(12):17139-17146
SrF2 transparent ceramic is a promising upconversion material due to the low phonon energy. The effect of different sintering temperatures on Er:SrF2 transparent ceramics was investigated. The suitable sintering temperature for Er:SrF2 transparent ceramics was 900 °C by hot-pressed sintering in this study. High quality of Er:SrF2 transparent ceramics with different doping concentrations were obtained. The upconversion luminescence spectra and decay behavior were compared between Er:SrF2 and Er:CaF2 transparent ceramics with different Er3+ doping concentration. The green emission of 5 at.% Er:SrF2 ceramic was much stronger than that of 5 at.% Er:CaF2 ceramic, while the red emission of Er:SrF2 ceramic was almost the same as that of Er:CaF2 ceramic. The upconversion luminescence lifetime of Er:SrF2 transparent ceramics was longer than that of Er:CaF2.All the results indicated Er:SrF2 transparent ceramics was a candidate for green fluorescent upconversion materials. 相似文献
9.
Huimin Tang Zhiwei Peng Foquan Gu Lei Yang Weiguang Tian Qiang Zhong Mingjun Rao Guanghui Li Tao Jiang 《Ceramics International》2021,47(8):10809-10818
The chromium-promoted preparation of forsterite refractory materials from ferronickel slag was investigated by microwave sintering of the slag with the additions of sintered magnesia and 0–10 wt% chromium oxide (Cr2O3). The thermodynamic calculations revealed that the addition of Cr2O3 can promote the formations of spinel and liquid phase and maintain high content of forsterite below 1500 °C. The experimental results showed that there existed a stronger promoting effect of Cr2O3 additive on the properties of refractory materials in the microwave field than that in conventional sintering. It was attributed to the preferential formation and growth of spinel with stronger microwave absorption than other phases (e.g., enstatite), the existence of more forsterite, and the enhanced densification in association with the presence of more liquid phase at the same temperature. By microwave sintering of the mixture of ferronickel slag, 25 wt% sintered magnesia, and 4 wt% Cr2O3 at 1350 °C for 20 min, a superior refractory material with refractoriness of 1801 °C, thermal shock resistance of 6 times, bulk density of 2.97 g/cm3, apparent porosity of 1.4%, and compressive strength of 197 MPa was obtained. Compared with that prepared by conventional sintering at 1350 °C for 2 h, the refractoriness and thermal shock resistance were increased by 175 °C and 100%, respectively. The present study provided a novel method for preparing high-quality refractory materials from ferronickel slag and relevant industrial wastes. 相似文献
10.