全文获取类型
收费全文 | 4667篇 |
免费 | 350篇 |
国内免费 | 83篇 |
专业分类
电工技术 | 141篇 |
综合类 | 280篇 |
化学工业 | 2764篇 |
金属工艺 | 100篇 |
机械仪表 | 66篇 |
建筑科学 | 242篇 |
矿业工程 | 112篇 |
能源动力 | 199篇 |
轻工业 | 269篇 |
水利工程 | 73篇 |
石油天然气 | 264篇 |
武器工业 | 5篇 |
无线电 | 66篇 |
一般工业技术 | 235篇 |
冶金工业 | 223篇 |
原子能技术 | 17篇 |
自动化技术 | 44篇 |
出版年
2024年 | 12篇 |
2023年 | 56篇 |
2022年 | 86篇 |
2021年 | 125篇 |
2020年 | 114篇 |
2019年 | 75篇 |
2018年 | 65篇 |
2017年 | 122篇 |
2016年 | 104篇 |
2015年 | 149篇 |
2014年 | 306篇 |
2013年 | 293篇 |
2012年 | 348篇 |
2011年 | 318篇 |
2010年 | 267篇 |
2009年 | 264篇 |
2008年 | 176篇 |
2007年 | 250篇 |
2006年 | 229篇 |
2005年 | 212篇 |
2004年 | 180篇 |
2003年 | 209篇 |
2002年 | 155篇 |
2001年 | 173篇 |
2000年 | 121篇 |
1999年 | 137篇 |
1998年 | 102篇 |
1997年 | 96篇 |
1996年 | 75篇 |
1995年 | 56篇 |
1994年 | 70篇 |
1993年 | 26篇 |
1992年 | 19篇 |
1991年 | 17篇 |
1990年 | 23篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 13篇 |
1984年 | 11篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1951年 | 4篇 |
排序方式: 共有5100条查询结果,搜索用时 15 毫秒
101.
Ammonium acetate was more attractive than other ammonium salts to Mexican fruit flies (Anastrepha ludens) in an orchard test. We hypothesized that acetic acid enhanced the attractiveness of ammonia in the orchard test and that acetic acid may similarly enhance attractiveness of AMPu, an attractant consisting of a mixture of ammonium bicarbonate or ammonium carbonate, methylamine HCl, and putrescine. In laboratory experiments, acetic acid was attractive to flies deprived of either yeast hydrolysate or both sugar and yeast hydrolysate but not to flies fed both sugar and yeast hydrolysate. AMPu/acetic acid combinations were more attractive than AMPu alone to flies deprived of both sugar and yeast hydrolysate but not to flies fed sugar, regardless of yeast hydrolysate deprivation status. Acetic acid is the first attractant found that has become more attractive with both sugar and protein deprivation in studies withA. ludens. It is also the first that has enhanced the attractiveness of another attractant type. In orchard tests, yellow sticky panels baited with either AMPu or 17 mg of acetic acid were at least six times more attractive than unbaited panels. However, panels baited with both acetic acid (17–68 mg) and AMPu were less attractive than AMPu alone. These results differed from the laboratory data in which combinations were never less attractive than AMPu alone. 相似文献
102.
介绍中石油宁夏石化分公司二化肥尿素装置的现状,拟采用二氧化碳汽提法对装置进行50%扩能改造,分析改造方案的可行性。 相似文献
103.
Field studies were conducted for two years on a rapidly percolating loamy sand (Typic Ustochrept) to evaluate the effect of green manure (GM) on the yield,15N recovery from urea applied to flooded rice, the potential for ammonia loss and uptake of residual fertilizer N by succeeding crops. The GM crop ofSesbania aculeata was grownin situ and incorporated one day before transplanting rice. Urea was broadcast in 0.05 m deep floodwater, and incorporated with a harrow. Green manure significantly increased the yield and N uptake by rice and substituted for a minimum of 60 kg fertilizer N ha–1. The recovery of fertilizer N as indicated by15N recovery was higher in the GM + urea treatments. The grain yield and N uptake by succeeding wheat in the rotation was slightly higher with GM. The recovery of residual fertilizer N as indicated by the15N recovery in the second, third and fourth crops of wheat, rice and wheat was only 3, 1 and 1 per cent of the urea fertilizer applied to the preceding rice crop. Floodwater chemistry parameters showed that the combined use of the GM and 40 kg N ha–1 as urea applied at transplanting resulted in a comparatively higher potential for NH3 loss immediately after fertilizer application. The actual ammonia loss as suggested by the15N recoveries in the rice crop, however, did not appear to be appreciably larger in the GM treatment. It appeared the ammonia loss was restricted by low ammoniacal-N concentration maintained in the floodwater after 2 to 3 days of fertilizer application. 相似文献
104.
105.
以缙云天然丝光沸石为载体,考察了载体预处理、不同活性组分、负载量等因素对氨、吡啶、二乙胺吸附容量的影响。结果表明,负载CuSO_4对氨的吸附容量明显提高,具有物理吸附和化学吸附双重功能,但吡啶、二乙胺略有下降。随着焙烧温度的提高,其对氨的吸附能力也提高,水份的存在对氨的吸附容量影响不大。 相似文献
106.
The reductive alkylation of Illinois No. 6 coal was investigated using alkali metals and alkyl halides in liquid ammonia. Potassium is the most effective reducing agent and butyl iodide is the most effective alkylating agent for the preparation of coal alkylate that is soluble in tetrahydrofuran. The overall yield of soluble product is often improved through the reaction of the tetrahydrofuran-insoluble portion of the initial reaction products with an alkylating agent in the presence of tetrabutylammonium hydroxide. The infrared spectra of these materials suggest that the phase transfer agent catalyses the esterification of residual carboxylic acid functions. The intermolecular interactions between such acid groups and acceptor groups markedly restrict the solubility of the coal alkylate. The gel permeation chromatograms of the soluble reaction products are essentially featureless with only modest maxima at short and long elution volumes. The proton and carbon nuclear magnetic resonance spectra of the reductive methylation products, prepared using methyl-13C iodide, suggest that carbon alkylation exceeds oxygen alkylation and that the alkylation of phenolic groups is the dominant O-alkylation reaction. The spectra also suggest that fewer ethers are cleaved in the reaction in liquid ammonia than under the conditions of the Sternberg reaction. 相似文献
107.
对合成氨造气工艺流程中的自动加煤系统、专用炉箅、洗气箱、废热锅炉、吹风气余热回收系统等关键工艺环节进行了工艺优化、设备选型和工艺实践论证;对比了技术优化前后的运行数据和产生的经济效益。 相似文献
108.
109.
为了探讨膜技术在城市污水回用中的适用性,总结了城市污水的回用现状和技术措施,研究了膜技术在洗浴废水和高氨氮生活污水回用中的应用.结果表明,膜出水水质均符合市政和生活杂用水水质标准.膜技术用于城市污水回用具有明显的环境效益,可有效缓解水资源不足和水环境污染的矛盾. 相似文献
110.
以升流式曝气生物滤池(UBAF)深度处理某焦化厂废水处理站二级未达标生化出水,在投加30%双氧水(H2O2/COD cr质量比为3)预处理后,并在气水比为3∶1,回流比为(0.5~1)∶1的运行条件下,系统对CODcr、NH3-N的平均去除率分别为53.1%、91.6%,系统出水CODcr和NH3-N浓度分别达到《污水综合排放标准》(GB8987—1996)的二级和一级排放标准. 相似文献