全文获取类型
收费全文 | 6802篇 |
免费 | 677篇 |
国内免费 | 313篇 |
专业分类
电工技术 | 59篇 |
技术理论 | 1篇 |
综合类 | 409篇 |
化学工业 | 3846篇 |
金属工艺 | 280篇 |
机械仪表 | 80篇 |
建筑科学 | 121篇 |
矿业工程 | 249篇 |
能源动力 | 118篇 |
轻工业 | 532篇 |
水利工程 | 61篇 |
石油天然气 | 389篇 |
武器工业 | 121篇 |
无线电 | 136篇 |
一般工业技术 | 677篇 |
冶金工业 | 574篇 |
原子能技术 | 94篇 |
自动化技术 | 45篇 |
出版年
2024年 | 42篇 |
2023年 | 79篇 |
2022年 | 146篇 |
2021年 | 220篇 |
2020年 | 221篇 |
2019年 | 204篇 |
2018年 | 163篇 |
2017年 | 241篇 |
2016年 | 281篇 |
2015年 | 258篇 |
2014年 | 382篇 |
2013年 | 431篇 |
2012年 | 513篇 |
2011年 | 535篇 |
2010年 | 373篇 |
2009年 | 386篇 |
2008年 | 311篇 |
2007年 | 402篇 |
2006年 | 393篇 |
2005年 | 316篇 |
2004年 | 294篇 |
2003年 | 255篇 |
2002年 | 217篇 |
2001年 | 184篇 |
2000年 | 176篇 |
1999年 | 147篇 |
1998年 | 123篇 |
1997年 | 80篇 |
1996年 | 61篇 |
1995年 | 53篇 |
1994年 | 51篇 |
1993年 | 52篇 |
1992年 | 34篇 |
1991年 | 27篇 |
1990年 | 21篇 |
1989年 | 18篇 |
1988年 | 15篇 |
1987年 | 25篇 |
1986年 | 12篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1951年 | 3篇 |
排序方式: 共有7792条查询结果,搜索用时 15 毫秒
21.
制备低硫可膨胀石墨的研究 总被引:18,自引:3,他引:15
研究了以过二硫酸铵作氧化剂低硫可膨胀石墨的制备,找到了在较低温度下,制备低硫可膨胀石墨的最佳条件。即过二硫酸铵和石墨的重量比为15%;反应温度为55℃;反应时间为40min;硫酸浓度为98%;硫酸与石墨的重量比为4∶1,草酸和硝酸(浓度为65%)的重量比为7.5%时,所制得的可膨胀石墨含硫量为0.65%,膨胀容积为200mL/g可膨胀石墨。并且,其终端产品柔性石墨具有优良的力学性能和抗氧化性能。 相似文献
22.
23.
Rafael S. Pinto João P. Serra João C. Barbosa Renato Gonçalves Maria M. Silva Senentxu Lanceros-Méndez Carlos M. Costa 《大分子材料与工程》2021,306(11):2100372
Considering the high levels of materials used in the fields of electronics and energy storage systems, it is increasingly necessary to take into consideration environmental impact. Thus, it is important to develop devices based on environmentally friendlier materials and/or processes, such as additive manufacturing techniques. In this work, poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) are prepared by direct-ink-writing (DIW) by varying solvent evaporation temperature and fill density percentage. Different morphologies for both polymers are obtained, including dense films and porous membranes, as well as different electroactive β-phase content, thermal and mechanical properties. The dielectric constant and piezoelectric d33 coefficient for dense films reaches up to 16 at 1 kHz and 4 pC N−1, respectively for PVDF-HFP with a fill density of 80 and a solvent evaporation temperature of 50 °C. Porous structures are developed for battery separator membranes in lithium-ion batteries, with a highest ionic conductivity value of 3.8 mS cm−1 for the PVDF-HFP sample prepared with a fill density of 100 and a solvent evaporation temperature of 25 °C, the sample showing an excellent cycling performance. It is demonstrated that electroactive films and membranes can be prepared by direct-ink writing suitable for sensors/actuators and energy storage systems. 相似文献
24.
采用硝酸-氢氟酸混合酸为消解溶剂,通过微波消解技术对粗制氟化钠进行快速消解,并用氟硅酸钾滴定法测定其二氧化硅含量。选择饱和氯化钾溶液替代固体氯化钾作为沉淀剂,考察了消解酸体系、饱和氯化钾溶液用量、沉淀温度、沉淀放置时间、共存元素干扰及指示剂选择等条件对测定结果的影响并进行优化。确定了最优测试条件:以8 mL硝酸+2 mL氢氟酸为消解溶剂,以8 mL饱和氯化钾溶液为沉淀剂,控制沉淀温度为20~25 ℃、沉淀放置时间为15 min,选择50 g/L氯化钾-50%乙醇溶液洗涤沉淀,采用溴麝香草酚蓝-酚红指示剂。该方法应用于回收粗制氟化钠中二氧化硅含量的测定可大幅度缩短分解试样的时间,有效降低检测成本,回收率为99.15%~100.63%,相对标准偏差(RSD,n=8)小于1%,与传统高温碱熔法测定结果相符,方法的准确度和精密度较好。 相似文献
25.
季胺萃取锌的动力学研究 总被引:1,自引:0,他引:1
以恒界面池法研究了氯化物介质中季胺萃锌的动力学。考查了搅拌转速、传质界面积和温度对萃取速率的影响,判定季爱萃锌为界面化学反应的动力学模式。进一步研究了季胺萃取剂浓度和水相Zn^2+浓度对萃取速率的影响,得到了与理论推断相吻合的速率方程。 相似文献
26.
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
27.
28.
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
29.
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
30.
氧化铁生产废液的治理和利用 总被引:1,自引:0,他引:1
氧化铁生产产生的含铁硫酸铵废液和洗涤废水中含有铁、硫酸根、铵等离子。采用化学沉淀、过滤、蒸发等方法处理该废水可回收废水中的硫酸铵、氧化铁、处理后的废水可回用于生产。 相似文献