全文获取类型
收费全文 | 7153篇 |
免费 | 551篇 |
国内免费 | 86篇 |
专业分类
电工技术 | 17篇 |
综合类 | 406篇 |
化学工业 | 1190篇 |
金属工艺 | 9篇 |
机械仪表 | 61篇 |
建筑科学 | 60篇 |
矿业工程 | 12篇 |
能源动力 | 80篇 |
轻工业 | 5453篇 |
水利工程 | 76篇 |
石油天然气 | 27篇 |
无线电 | 47篇 |
一般工业技术 | 135篇 |
冶金工业 | 25篇 |
原子能技术 | 15篇 |
自动化技术 | 177篇 |
出版年
2024年 | 73篇 |
2023年 | 143篇 |
2022年 | 350篇 |
2021年 | 368篇 |
2020年 | 375篇 |
2019年 | 327篇 |
2018年 | 268篇 |
2017年 | 268篇 |
2016年 | 302篇 |
2015年 | 334篇 |
2014年 | 357篇 |
2013年 | 411篇 |
2012年 | 535篇 |
2011年 | 472篇 |
2010年 | 305篇 |
2009年 | 250篇 |
2008年 | 213篇 |
2007年 | 343篇 |
2006年 | 318篇 |
2005年 | 314篇 |
2004年 | 227篇 |
2003年 | 242篇 |
2002年 | 170篇 |
2001年 | 124篇 |
2000年 | 125篇 |
1999年 | 91篇 |
1998年 | 78篇 |
1997年 | 58篇 |
1996年 | 51篇 |
1995年 | 48篇 |
1994年 | 35篇 |
1993年 | 38篇 |
1992年 | 44篇 |
1991年 | 20篇 |
1990年 | 20篇 |
1989年 | 18篇 |
1988年 | 21篇 |
1987年 | 16篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有7790条查询结果,搜索用时 15 毫秒
931.
Heats of adsorption of thiosulphate, thiosulphatoargentate and p-toluenethiosulphonate to silver bromide, silver bromo"dide, silver chloride and silver sulphide were measured using a slow microcalorimeter. The results did not confirm previous evidence for the cluster mechanism for silver sulphide formation during sulphur sensitization. The possibility of this model was discussed. Heats of adsorption of silver and sulphide ions were also measured. 相似文献
932.
AbstractMesoporous material RH-MCM-41 was synthesized with rice husk silica by a hydrothermal method. It was used as a support for bimetallic platinum?iron catalysts Pt–Fe/RH-MCM-41 for phenol hydroxylation. The catalysts were prepared by co-impregnation with Pt and Fe at amounts of 0.5 and 5.0 wt.%, respectively. The RH-MCM-41 structure in the catalysts was studied with x-ray diffraction, and their surface areas were determined by nitrogen adsorption. The oxidation number of Fe supported on RH-MCM-41 was + 3, as determined by x-ray absorption near edge structure (XANES) analysis. Transmission electron microscopy (TEM) images of all the catalysts displayed well-ordered structures, and metal nanoparticles were observed in some catalysts. All the catalysts were active for phenol hydroxylation using H2O2 as the oxidant at phenol : H2O2 mole ratios of 2 : 1, 2 : 2, 2 : 3 and 2 : 4. The first three ratios produced only catechol and hydroquinone, whereas the 2 : 4 ratio also produced benzoquinone. The 2 : 3 ratio gave the highest phenol conversion of 47% at 70 °C. The catalyst prepared by co-impregnation with Pt and Fe was more active than that prepared using a physical mixture of Pt/RH-MCM-41 and Fe/RH-MCM-41. 相似文献
933.
稻壳混合贫煤燃烧对SO2排放的影响 总被引:1,自引:0,他引:1
本文利用循环流化床实验平台,分析稻壳混煤燃烧对SO2排放的影响.将稻壳与贫煤按不同质量比制成混合燃料,在流化床锅炉中燃烧,采集炉温及烟气中SO2浓度等数据进行分析.结果表明,当燃烧温度恒定时,SO2的排放量随着燃料中稻壳所占比重增加而降低;当燃料中稻壳所占比重恒定时,SO2的排放量随着燃烧温度的升高而增加. 相似文献
934.
《Journal of Nuclear Science and Technology》2013,50(1):120-129
Carbon-14 (14C) is of great interest in the assessment of dose due to the nuclear industry because of the biological importance of carbon. We collected atmospheric CO2, rice grain, leafy vegetable, and Japanese mugwort samples at various locations at different time intervals, and measured their 14C concentrations to show the spatiotemporal distribution of 14C around the Tokai reprocessing plant (TRP). The results consistently gave the picture of a 14C dispersion pattern brought about by the prevailing wind in this area, which conveys the 14C plume, and as a result, caused elevated 14C concentrations in the area 2–3 km southwest of the main stack of the TRP. The increases in 14C concentration were, however, quite temporary, and the baseline concentration remained at the background level even in the elevated area. The 14C concentrations in vegetations generally followed those in atmospheric CO2, but seemed different in 14C uptake response between vegetation types, emphasizing the importance of this nature not only in its application as bioindicators in environmental monitoring but also in establishing a more realistic dose evaluation model for 14C. Through a series of investigations, we found the highest 14C concentrations of 374, 287, and 361 Bq kg-C?1 in atmospheric CO2, rice grains, and leafy vegetables, respectively. They corresponded to a maximum of ~110 Bq kg-C?1 excess above the background. The annual effective dose delivered from the concentrations was estimated to be around 0.7 μSv yr?1, only 0.07% of the annual effective dose limit for the public. Thus, we conclude that the 14C releases from the TRP have a very slight impact both on the environment and on the public. 相似文献
935.
Hallah Ahmad Alyosef André Eilert Julia Welscher Suzan S. Ibrahim Reinhard Denecke Wilhelm Schwieger 《Particulate Science and Technology》2013,31(5):524-532
This study presents two routes to produce amorphous silica from an Egyptian rice husk under conditions optimized for least environmental impact and low cost. The first route includes thoroughly washing of the husk sample with water, dry milling and leaching with citric acid. The leaching process was applied in two stages, that is, at 323 K for 180 min and then at 353 K for 60 min. After washing and drying, the leached sample was subjected to a heat treatment in a muffles furnace at four sequential steps. The second route includes all the previously mentioned steps, except the citric acid leaching. The final products were characterized using x-ray fluorescence analysis, carbon content analysis, x-ray diffraction, differential thermal analysis, nitrogen adsorption, mercury intrusion, and scanning electron microscopy. The results show that the citric acid leaching has many advantages with respect to silica yield and porosity as well. 相似文献
936.
采用稻壳纤维素,通过硝化、碱化、老化、交联、胺化等制备工艺,制得了表面具有甲胺基团的阴离子交换剂。直接耐晒翠蓝阴离子交换的性能实验表明,选择三甲胺盐酸盐作为胺化剂,胺化温度为65℃时,制备的离子交换剂的交换率最高。通过正交实验得出在pH值为4,反应温度为60℃,反应时间为120 min的条件下,稻壳基离子交换剂对直接耐晒翠蓝阴离子交换效果较好。离子交换过程的动力学研究表明,在反应前期(前80 min),离子交换行为为膜扩散所控制;在反应后期(80 min后),为内部扩散所控制。 相似文献
937.
938.
939.
[目的]研制长效控释性防治稻瘟病的水稻种衣剂.[方法]通过对不同分散剂、成膜剂以及增稠剂的筛选,采用湿式超微粉碎加工工艺,获得一种新型水稻种衣剂成膜剂及种衣剂制备方法.[结果]10%嘧菌酯悬浮种衣剂的最佳制剂配方为嘧菌酯原药10%,YUS-FS3000 8%,黄原胶0.12%,快T0.5%,皂土0.5%,成膜剂8%.[结论]砂磨转速500 r/min、砂磨时间2h条件下,得到的种衣剂粒径小于3μm,其成膜性良好,脱落率小于5%,包衣后的水稻种子发芽率达到98.25%,符合水稻悬浮种衣剂要求. 相似文献
940.
利用中低品位磷矿生产钙镁磷肥,然后制成养分配方为12-10-8复混肥,为研究含钙镁磷肥的复混肥在作物上的肥效,在早稻上进行了田间试验。结果表明:含钙镁磷肥的复混肥处理与农民习惯施肥处理比较,早稻平均增产15.1%;与高浓度复合肥处理相比,稻谷产量不会降低;含钙镁磷肥复混肥处理均能促进早稻的生长发育,有利于促进早稻的增产。 相似文献