全文获取类型
收费全文 | 300908篇 |
免费 | 26244篇 |
国内免费 | 13192篇 |
专业分类
电工技术 | 18313篇 |
技术理论 | 37篇 |
综合类 | 29390篇 |
化学工业 | 41687篇 |
金属工艺 | 10992篇 |
机械仪表 | 13298篇 |
建筑科学 | 42596篇 |
矿业工程 | 17111篇 |
能源动力 | 13259篇 |
轻工业 | 21232篇 |
水利工程 | 28994篇 |
石油天然气 | 18825篇 |
武器工业 | 3392篇 |
无线电 | 15329篇 |
一般工业技术 | 20110篇 |
冶金工业 | 14503篇 |
原子能技术 | 2694篇 |
自动化技术 | 28582篇 |
出版年
2024年 | 1266篇 |
2023年 | 3862篇 |
2022年 | 7338篇 |
2021年 | 9457篇 |
2020年 | 9498篇 |
2019年 | 7305篇 |
2018年 | 6987篇 |
2017年 | 8709篇 |
2016年 | 10356篇 |
2015年 | 10977篇 |
2014年 | 19943篇 |
2013年 | 18194篇 |
2012年 | 21876篇 |
2011年 | 23579篇 |
2010年 | 17415篇 |
2009年 | 17793篇 |
2008年 | 16130篇 |
2007年 | 20133篇 |
2006年 | 18385篇 |
2005年 | 16233篇 |
2004年 | 13310篇 |
2003年 | 11713篇 |
2002年 | 9735篇 |
2001年 | 7956篇 |
2000年 | 6722篇 |
1999年 | 5273篇 |
1998年 | 3778篇 |
1997年 | 3248篇 |
1996年 | 2620篇 |
1995年 | 2216篇 |
1994年 | 1816篇 |
1993年 | 1321篇 |
1992年 | 1062篇 |
1991年 | 767篇 |
1990年 | 634篇 |
1989年 | 606篇 |
1988年 | 354篇 |
1987年 | 308篇 |
1986年 | 251篇 |
1985年 | 279篇 |
1984年 | 219篇 |
1983年 | 162篇 |
1982年 | 86篇 |
1981年 | 82篇 |
1980年 | 95篇 |
1979年 | 52篇 |
1978年 | 24篇 |
1977年 | 30篇 |
1975年 | 18篇 |
1959年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
Wenshu Chen Jiajun Gu Yongping Du Fang Song Fanxing Bu Jinghan Li Yang Yuan Ruichun Luo Qinglei Liu Di Zhang 《Advanced functional materials》2020,30(25)
Large‐scale production of hydrogen from water‐alkali electrolyzers is impeded by the sluggish kinetics of hydrogen evolution reaction (HER) electrocatalysts. The hybridization of an acid‐active HER catalyst with a cocatalyst at the nanoscale helps boost HER kinetics in alkaline media. Here, it is demonstrated that 1T–MoS2 nanosheet edges (instead of basal planes) decorated by metal hydroxides form highly active / heterostructures, which significantly enhance HER performance in alkaline media. Featured with rich / sites, the fabricated 1T–MoS2 QS/Ni(OH)2 hybrid (quantum sized 1T–MoS2 sheets decorated with Ni(OH)2 via interface engineering) only requires overpotentials of 57 and 112 mV to drive HER current densities of 10 and 100 mA cm?2, respectively, and has a low Tafel slope of 30 mV dec?1 in 1 m KOH. So far, this is the best performance for MoS2‐based electrocatalysts and the 1T–MoS2 QS/Ni(OH)2 hybrid is among the best‐performing non‐Pt alkaline HER electrocatalysts known. The HER process is durable for 100 h at current densities up to 500 mA cm?2. This work not only provides an active, cost‐effective, and robust alkaline HER electrocatalyst, but also demonstrates a design strategy for preparing high‐performance catalysts based on edge‐rich 2D quantum sheets for other catalytic reactions. 相似文献
4.
《Food Control》2015
The aim of the study was to investigate annual and regional differences in the level of aflatoxin B1 (AFB1) in grains and dairy cattle feed. Maize (n = 972), wheat (n = 201), barley (n = 147), oat (n = 136), grain mixtures (n = 168), and dairy cattle feed (n = 325) were sampled from 2009 to 2013 on different farms and in different farm factories situated in four Croatian regions. The samples were analysed for AFB1 using the validated ELISA immunoassay. AFB1 was determined in 16.4% of all investigated samples, among which maize was proven to be the most contaminated, with 21.7% of the samples recovered during 2013 harbouring AFB1 in concentrations over the permissible ones. Levels higher than permitted were observed in 17.9% and 12.3% of grain mixtures and dairy cattle feed, respectively, whereas concentrations of AFB1 determined in other crops throughout the investigated period met the stipulated requirements. The results revealed the AFB1 occurrence to be significantly (p < 0.05) dependent on the cultivation region, with the highest levels generally found in maize harvested in 2013 and consequently in grain mixtures and cattle feed that can most likely be associated with climatic conditions as the most critical factor for mould formation, and thus also AFB1 production. 相似文献
5.
为检查工程质量,查找输水系统可能存在的问题并消除隐患,保障电站安全运行,福建仙游抽水蓄能电站在投产发电前,要对输水发电系统进行充水试验与放空排水试验,在试验过程中监测输水系统的应力、应变与渗漏水情况。本文以尾水系统为例,介绍了试验所应具备的工程条件、工作程序及技术要求、试验成果分析和存在问题处理等。试验表明,仙游抽水蓄能电站尾水系统设计合理,施工质量优良,结构可靠,可供同类工程参考与借鉴。 相似文献
6.
High dimensionality in real-world multi-reservoir systems greatly hinders the application and popularity of evolutionary algorithms, especially for systems with heterogeneous units. An efficient hierarchical optimization framework is presented for search space reduction, determining the best water distributions, not only between cascade reservoirs, but also among different types of hydropower units. The framework is applied to the Three Gorges Project (TGP) system and the results demonstrate that the difficulties of multi-reservoir optimization caused by high dimensionality can be effectively solved by the proposed hierarchical method. For the day studied, power output could be increased by 6.79 GWh using an optimal decision with the same amount of water actually used; while the same amount of power could be generated with 2.59 × 107 m3 less water compared to the historical policy. The methodology proposed is general in that it can be used for other reservoir systems and other types of heterogeneous unit generators. 相似文献
7.
8.
《石油化工》2015,44(4):506
采用便携式微量水分析仪和库仑法微量水分析仪测定了乙烯、丙烯试样中的微量水含量,对试样的传输系统、进样量的控制、液体试样的气化和水标准气体的制备方法进行了改进,优化了测试条件。以低吸附惰性管线和小死体积单进单出的不锈钢减压器为试样传输系统,缩短了测试时间。采用液态烃闪蒸气化取样进样器气化液体试样并准确控制试样的进样量,可避免液体试样渐次气化对水含量测定结果的影响及对采样钢瓶大小的限制。采用渗透管发生器制备水标准气体,可验证分析结果的准确度。采用库仑法微量水分析仪测定水含量时,试样流量选择600 m L/min较适宜,开封保存15 d之内的卡尔·费休试剂对测定结果无影响。采用便携式微量水分析仪测定水含量时,选择试样流量在400~800 m L/min之间较适宜。两种仪器的测量结果相近,稳定性好,准确度高,回收率在102%~107%之间,相对偏差小于10%。 相似文献
9.
文章通过对黑龙江省高效节水现状,存在问题的分析,结合黑龙江省高效节水发展的支撑能力,阐述黑龙江省节水增粮目标、任务及总体布局,为黑龙江省2012—2015年节水增粮实施提供依据。 相似文献
10.