全文获取类型
收费全文 | 5393篇 |
免费 | 581篇 |
国内免费 | 360篇 |
专业分类
电工技术 | 35篇 |
技术理论 | 1篇 |
综合类 | 340篇 |
化学工业 | 2909篇 |
金属工艺 | 177篇 |
机械仪表 | 38篇 |
建筑科学 | 80篇 |
矿业工程 | 206篇 |
能源动力 | 69篇 |
轻工业 | 1086篇 |
水利工程 | 38篇 |
石油天然气 | 371篇 |
武器工业 | 115篇 |
无线电 | 42篇 |
一般工业技术 | 379篇 |
冶金工业 | 393篇 |
原子能技术 | 32篇 |
自动化技术 | 23篇 |
出版年
2024年 | 26篇 |
2023年 | 63篇 |
2022年 | 96篇 |
2021年 | 143篇 |
2020年 | 137篇 |
2019年 | 127篇 |
2018年 | 116篇 |
2017年 | 162篇 |
2016年 | 208篇 |
2015年 | 195篇 |
2014年 | 306篇 |
2013年 | 352篇 |
2012年 | 395篇 |
2011年 | 414篇 |
2010年 | 302篇 |
2009年 | 338篇 |
2008年 | 261篇 |
2007年 | 364篇 |
2006年 | 343篇 |
2005年 | 314篇 |
2004年 | 267篇 |
2003年 | 232篇 |
2002年 | 209篇 |
2001年 | 163篇 |
2000年 | 158篇 |
1999年 | 137篇 |
1998年 | 97篇 |
1997年 | 68篇 |
1996年 | 57篇 |
1995年 | 45篇 |
1994年 | 54篇 |
1993年 | 36篇 |
1992年 | 28篇 |
1991年 | 19篇 |
1990年 | 13篇 |
1989年 | 15篇 |
1988年 | 13篇 |
1987年 | 25篇 |
1986年 | 11篇 |
1985年 | 3篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有6334条查询结果,搜索用时 46 毫秒
101.
从原子经济性出发,对以碳酸铈为原料合成硝酸铈铵的绿色化学工艺与传统工艺进行了对比.与传统工艺相比,绿色化学工艺的原子利用率提高30.01个百分点,原子效率因子提高24.44个百分点. 相似文献
102.
103.
104.
105.
高分子型阳离子抗静电剂性质的研究 总被引:3,自引:0,他引:3
设计合成了聚丙烯酰胺季铵盐类的抗静电剂。当高聚物的溶液浓度为1.44%,涤纶织物在25℃、RH66%的半衰期为0秒.静电压为0KV,15次水洗后半衰期为1.7秒,静电压为0.35KV。研究结果表明:这种阳离子型高聚物具有优良的抗静电性和耐水洗性。 相似文献
106.
107.
Craig A Beyrouty Darrell W Nelson Lee E Sommers 《Nutrient Cycling in Agroecosystems》1986,10(2):135-146
A field study was conducted in 1982 to measure the effect of no-till (NT) and conventional till (CT) systems on N transformation after surface and subsurface applications of N fertilizers. Urea, urea-ammonium nitrate (UAN) solution, (NH4)2SO4 (AS), and CA(NO3)2 were applied to NT and CT plots (5.95 m2) at a rate of 448 kg N ha–1. A comparison of fertilizer N recovered in soils receiving incorporated or surface applied N was used to estimate NH3 volatilization while denitrification was estimated from fertilizer N recovered in the presence and absence of nitrapyrin with incorporated N. Immobilization was assessed in microplots (0.37 m2) after surface application of (15NH4)2SO4 to NT and CT systems at a rate of 220 kg N ha–1.The results indicate little difference between NT and CT systems on urea hydrolysis rates and immobilization of surface applied fertilizer N. Approximately 50% and 10% of the surface applied N was recovered in the inorganic and organic fractions, respectively, on both tillage systems. The N not recovered was likely lost from plot areas through soil runoff. Incorporation of UAN, urea and AS resulted in 20 to 40% greater inorganic N recovery than from surface application. Nitrification rates were greater under the NT than the CT system. The similarities in concentration in the various N pools observed between the two tillage systems may be partially due to the short length of time that NT was imposed in this field study (<1 year) since other researchers using established tillage systems (>5 y) indicate that NT tends to promote decreased efficiency of fertilizer N. 相似文献
108.
109.
一般的酸性染料溶解度较小,而本文所介绍的单或双偶氮酸性染料,实际上是以碱金属盐的形式存在,由于加入了(按重量计)80%~30%的木质素磺酸铵,改善了室温的冷水溶解度。木质素磺酸铵既作为标准化试剂,用来调节高强度染料到稳定的商品染料,同时又能提高染料在室温时冷水溶解度。 相似文献
110.
A field experiment was conducted on an acid sulfate soil in Thailand to determine the effect of N fertilization practices on the fate of fertilizer-N and yield of lowland rice (Oryza sativa L.). A delayed broadcast application of ammonium phosphate sulfate (16-20-0) or urea was compared with basal incorporation of urea, deep placement of urea as urea supergranules (USG), and amendment of urea with a urease inhibitor. Deep placement of urea as USG significantly reduced floodwater urea- and ammoniacal-N concentrations following N application but did not reduce N loss, as determined from an15N balance, in this experiment where runoff loss was prevented. The urease inhibitor, phenyl phosphorodiamidate (PPD), had little effect on floodwater urea- and ammoniacal-N, and it did not reduce N loss. The floodwater pH never exceeded 4.5 in the 7 days following the first N applications, and application of 16-20-0 reduced floodwater pH by 0.1 to 0.3 units below the no-N control. The low floodwater pH indicated that ammonia volatilization was unimportant for all the N fertilization practices. Floodwater ammoniacal-N concentrations following application of urea or 16-20-0 were greater on this Sulfic Tropaquept than on an Andaqueptic Haplaquoll with near neutral pH and alkaline floodwater. The prolonged, high floodwater N concentrations on this Sulfic Tropaquept suggested that runoff loss of applied N might be a potentially serious problem when heavy rainfall or poor water control follow N fertilization. The unaccounted-for15N in the15N balances, which presumably represented gaseous N losses, ranged from 20 to 26% of the applied N and was unaffected by urea fertilization practice. Grain yield and N uptake were significantly increased with applied N, but grain yield was not significantly affected by urea fertilization practice. Yield was significantly lower (P = 0.05) for 16-20-0 than for urea; however, this difference in yield might be due to later application of P and hence delayed availability of P in the 16-20-0 treatment. 相似文献