全文获取类型
收费全文 | 9383篇 |
免费 | 1015篇 |
国内免费 | 400篇 |
专业分类
电工技术 | 75篇 |
技术理论 | 1篇 |
综合类 | 656篇 |
化学工业 | 5383篇 |
金属工艺 | 372篇 |
机械仪表 | 62篇 |
建筑科学 | 376篇 |
矿业工程 | 443篇 |
能源动力 | 104篇 |
轻工业 | 945篇 |
水利工程 | 88篇 |
石油天然气 | 618篇 |
武器工业 | 118篇 |
无线电 | 74篇 |
一般工业技术 | 634篇 |
冶金工业 | 763篇 |
原子能技术 | 59篇 |
自动化技术 | 27篇 |
出版年
2024年 | 50篇 |
2023年 | 103篇 |
2022年 | 247篇 |
2021年 | 278篇 |
2020年 | 267篇 |
2019年 | 250篇 |
2018年 | 243篇 |
2017年 | 308篇 |
2016年 | 366篇 |
2015年 | 370篇 |
2014年 | 545篇 |
2013年 | 595篇 |
2012年 | 700篇 |
2011年 | 696篇 |
2010年 | 508篇 |
2009年 | 539篇 |
2008年 | 437篇 |
2007年 | 566篇 |
2006年 | 542篇 |
2005年 | 505篇 |
2004年 | 435篇 |
2003年 | 391篇 |
2002年 | 340篇 |
2001年 | 280篇 |
2000年 | 257篇 |
1999年 | 221篇 |
1998年 | 166篇 |
1997年 | 109篇 |
1996年 | 92篇 |
1995年 | 69篇 |
1994年 | 73篇 |
1993年 | 51篇 |
1992年 | 37篇 |
1991年 | 26篇 |
1990年 | 23篇 |
1989年 | 15篇 |
1988年 | 16篇 |
1987年 | 28篇 |
1986年 | 15篇 |
1985年 | 4篇 |
1984年 | 11篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1962年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
氨法处理硫酸装置尾气生产亚铵的实践 总被引:1,自引:0,他引:1
介绍用氨法处理硫酸装置尾气生产亚硫酸铵的工艺流程、控制指标、主要设备和生产运行情况。实践表明,氨法SO2吸收率高,可实现装置尾气达标排放,但也存在产品品位较低的问题。对问题进行了分析并提出改进意见。 相似文献
62.
63.
Soil incubation studies were undertaken in controlled environment cabinets at 15°C to investigate the effect of increasing application rates of calcium ammonium nitrate (CAN) on net nitrification in two grassland soils. Granular CAN was applied to the surface of freshly collected, moist soil, at a rate equivalent to 0, 100, 200, 400, 800 and 1600µg NH
4
+
-N and NO
3
-
-N per gram of oven dry soil. In half the treatments finely ground CaCO3 was incorporated into the moist soil to raise the starting pH. Changes in soil mineral N and pH were measured at weekly intervals up to six-weeks. The most probable number (MPN) technique was used to enumerate the NH
4
+
-N and NO
2
-
-N oxidizers at the beginning and end of the incubation.At low rates of CAN application there was considerable NH
4
+
-N oxidation to NO
3
-
-N during the incubation of both soils. Lime stimulated this N transformation. At high application rates (i.e. 800 and 1600 ppm) there was little change in NH
4
+
-N or NO
3
-
-N on either soil during the 6 week incubation, in the presence or absence of lime. The rate of NO
3
-
-N produced peaked at 5.6 and 3.8 mg NO
3
-
-N kg–1 d–1 on soil 1 and 2 respectively, in the presence of lime. Above a level of 400 ppm CAN (equivalent to 38 kg N ha–1) the rate of NO
3
-
-N produced decreased. The higher rate of net nitrification in soil 1 compared with soil 2 was probably due to a higher number of nitrifying bacteria. Although high rates of CAN decreased the nitrifying activity of both soils there was little difference between treatments in the actual numbers of NH
4
+
-N and NO
2
-
-N oxidizers determined by the MPN technique.The results showed that the rate of granular CAN applied to the soil surface can influence the local activity of nitrifying bacteria and subsequent N transformations. At application rates of CAN generally used agriculturally for grass production, it is likely that net nitrification of the NH
4
+
-N in the fertilizer granule will be inhibited. 相似文献
64.
Slow growth and high seedling mortality limit direct seeding establishment of guayule (Parthenium argentatum G.). This study was conducted to assess seedling growth enhancement by the addition of different rates and forms of N fertilizers and Ca salts. Experiments were conducted in a greenhouse with cultivar 593 under both surface and subirrigated conditions using water low in salts (salinity of 0.8 dSm–1, SAR of 5.0 and 10 mg Ca L–1). Under surface-irrigated conditions, seedling height and fresh plant weight increased with N application to the irrigation water to 70 mg L–1. The best seedling growth was observed when (NH4)2SO4 was added in combination with CaCl2 or CaSO4. Progressively less growth was observed by addition of (NH4)2SO4 alone, CO(NH2)2 plus CaSO4, CO(NH2)2 alone and Ca(NO3)2. When seedlings were subirrigated, however, the best growth was observed with Ca(NO3)2. Intermediate growth was obtained with (NH4)2SO4 plus CaSO4 and lowest growth rates with (NH4)2SO4 alone. These differential responses may be explained by the differences in leaching and volatile characteristics of the N forms. Growth enhancement from N and Ca additions increased with time with significant increases 45 days after seeding. Nitrogen application with Ca may be effective amendment in promoting subsequent growth of direct seeded guayule. 相似文献
65.
66.
硫酸铜灭藻影响因素的试验研究 总被引:1,自引:0,他引:1
目的通过对硫酸铜灭藻影响因素的试验研究,确定出硫酸铜灭藻的最佳工况条件.方法以叶绿素a法作为检测方法,通过烧杯试验,确定处理含藻水的最佳硫酸铜投加量、接触反应时间、pH等参数.结果硫酸铜最佳投加量为1.5 mg/L;硫酸铜适宜的接触反应时间为8~12 h;pH值6.6左右时,硫酸铜藻类去除率较高,pH值>9时,藻类去除率显著降低.结论 pH值对硫酸铜灭藻效果的影响较大;温度对硫酸铜灭藻有一定的影响;水中还原物质浓度对硫酸铜灭藻影响较小;藻类浓度不同对硫酸铜灭藻效果有一定的影响. 相似文献
67.
68.
69.
70.
Stakheev A. Yu. Gabrielsson P. Gekas I. Teleguina N. S. Bragina G. O. Tolkachev N. N. Baeva G. N. 《Topics in Catalysis》2007,42(1-4):143-147
Pt/Al2O3 and Pt/BaO/Al2O3 catalysts (1 wt% Pt, 10 wt%BaO) were sulfated under conditions simulating a real NSR catalyst operation. Comparative TPR
and XPS studies of sulfur removal from Pt/Al2O3 and Pt/BaO/Al2O3 catalysts indicate that the sulfur removal from Al2O3 surface precedes reductive decomposition of BaSO4 (250–400 °C). Barium sulfate decomposition started with further increase in desulfation temperature at the point of surface
atomic ratio Ba:S = 1 (~450o). Simultaneously, an intensive formation of sulfide species on the catalyst surface was observed. Thermodynamic analysis
of the desulfation process allows us to hypothesize that barium sulfide formation may hinder sulfur removal under reducing
conditions. 相似文献