全文获取类型
收费全文 | 24555篇 |
免费 | 2853篇 |
国内免费 | 1601篇 |
专业分类
电工技术 | 1328篇 |
技术理论 | 5篇 |
综合类 | 1570篇 |
化学工业 | 5848篇 |
金属工艺 | 1256篇 |
机械仪表 | 715篇 |
建筑科学 | 1470篇 |
矿业工程 | 1053篇 |
能源动力 | 2536篇 |
轻工业 | 852篇 |
水利工程 | 566篇 |
石油天然气 | 875篇 |
武器工业 | 123篇 |
无线电 | 1437篇 |
一般工业技术 | 2641篇 |
冶金工业 | 2545篇 |
原子能技术 | 192篇 |
自动化技术 | 3997篇 |
出版年
2024年 | 69篇 |
2023年 | 686篇 |
2022年 | 951篇 |
2021年 | 1053篇 |
2020年 | 1122篇 |
2019年 | 1011篇 |
2018年 | 866篇 |
2017年 | 1014篇 |
2016年 | 1036篇 |
2015年 | 970篇 |
2014年 | 1681篇 |
2013年 | 1622篇 |
2012年 | 1897篇 |
2011年 | 2161篇 |
2010年 | 1617篇 |
2009年 | 1614篇 |
2008年 | 1490篇 |
2007年 | 1476篇 |
2006年 | 1185篇 |
2005年 | 901篇 |
2004年 | 694篇 |
2003年 | 619篇 |
2002年 | 522篇 |
2001年 | 421篇 |
2000年 | 377篇 |
1999年 | 341篇 |
1998年 | 281篇 |
1997年 | 216篇 |
1996年 | 239篇 |
1995年 | 144篇 |
1994年 | 151篇 |
1993年 | 107篇 |
1992年 | 106篇 |
1991年 | 70篇 |
1990年 | 42篇 |
1989年 | 30篇 |
1988年 | 28篇 |
1987年 | 18篇 |
1986年 | 20篇 |
1985年 | 27篇 |
1984年 | 22篇 |
1983年 | 21篇 |
1982年 | 16篇 |
1981年 | 19篇 |
1980年 | 14篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1973年 | 3篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
141.
用化学还原法制得了尼龙6表面金属(Ni)化膜材料。研究了还原条件,金属盐浓度对膜材料电性能的影响,以及膜材料的电发热性能,用光电子能谱和扫描电子显微镜对其表面及形貌进行了表征。 相似文献
142.
Zakaria Chajar Michel Primet Hélène Praliaud Michèle Chevrier Catherine Gauthier Frédéric Mathis 《Catalysis Letters》1994,28(1):33-40
The role of nitrogen dioxide in the selective reduction of NO by propane over a Cu-MFI zeolite is investigated. NO2 and NO reductions were carried out under similar conditions of reaction. In the presence of oxygen, the reduction of NO by C3H8 does not differ significantly from that of NO2. In the absence of oxygen, the reduction of NO2 by propane occurs with a partial decomposition of the nitric dioxide molecule. Such a decomposition leads to the formation of oxygen, which is responsible for the increase in catalytic activity by comparison with the same reaction performed with NO. NO2 formed and released in the gas phase during the reduction of NO by propane in the presence of oxygen does not play a predominant role in the catalytic process. 相似文献
143.
在温和条件下,研究了硒对水合肼还原芳香族硝基化合物制芳胺的催化性能。邻位或对位有取代基的芳香族硝基化合物被还原为相应芳胺的收率较低;硝基苯或间位有取代基的芳香族硝基化合物被还原为相应芳胺的收率较高。以硝基苯为底物,考察了溶剂、硒粉用量和NaOH用量等因素对反应的影响。得到的适宜条件为:以5 mL乙醇和1 mL水为溶剂,2 mmol芳香族硝基化合物,4 mmol水合肼,O.04 g NaOH和0.02 g硒粉,反应温度为75℃,反应时间为2~5 h,硝基苯或间位有取代基的芳香族硝基化合物被还原为芳胺的收率为87%~99%。催化剂重复使用4次活性没有降低。 相似文献
144.
145.
Evaluation of rainfall networks using entropy: II. Application 总被引:2,自引:0,他引:2
This paper, the second in the series, applies the entropy approach to space and time evaluation of rainfall networks in Louisiana. The evaluation is made for five sampling intervals: daily, 2-day, weekly, monthly, and yearly, and for two separate seasons. In each case, the best combination of raingages is suggested and the lines of equal information (isoinformation contours) are constructed showing the areas of greater or less information transfer. The isoinformation lines are especially suitable in decisions concerning the expansion of the existing network or deleting the unnecessary raingages. 相似文献
146.
A new evaluation model for SK combinator expressions is presented and used as a basis for the design of a novel processor. The resulting machine architecture resembles a dataflow ring, but executions are constrained to be fully lazy. An automatic dynamic load sharing mechanism for a distributed multiprocessor architecture is suggested, and initial simulation results are presented. 相似文献
147.
针对催化裂化装置汽油和液态烃精制产生的含硫废弃物的碱渣处理,讨论了碱渣提酚、碱渣湿式氧化脱臭两种处理工艺的环境治理效果,并就碱渣湿式氧化脱臭工艺如何降低运行成本、减少污水排放等内容进行了探讨。 相似文献
148.
Potential control under thin aqueous layers using a Kelvin Probe 总被引:1,自引:0,他引:1
Kelvin Probes can be modified to control as well as monitor potential. The design and operation of two different Kelvin Probe Potentiostats (KPPs) are described in this paper. One approach uses a permanent magnet and double coil to oscillate the needle at a fixed frequency, an AC backing potential, and software analysis and control schemes. This technique can also control the distance between the tip and sample, thereby tracking the topography of the sample. Both KPPs were used to make measurements on Type 304L stainless steel under thin layers of electrolyte. Cathodic polarization curves exhibited a limiting current density associated with oxygen reduction. The limiting current density varied with solution layer thickness over a finite range of thickness. Anodic polarization curves on 304L in a thin layer of chloride solution resulted in pitting corrosion. The breakdown potential did not vary with solution layer thickness. However, the thin layer was observed to increase in volume remarkably during pit growth owing to the absorption of water from the high humidity environment into the layer with ionic strength increased by the pit dissolution. The open circuit potential (OCP) and solution layer thickness were monitored during drying out of a thin electrolyte layer. Pitting corrosion initiated, as indicated by a sharp drop in the OCP, as the solution thinned and increased in concentration. 相似文献
149.
稠油由于富含沥青质、胶质等重质组分而具有很高的黏度,给稠油的开采和运输带来了很大的困难。降低稠油黏度进而改善其流动性成为一项十分重要的工作。以植物油、脂肪酸及植物油甲酯为掺稀介质,以塔河油田稠油为研究对象,考察对比了3种不同的掺稀介质对稠油的掺稀降黏效果。研究结果表明,3种掺稀介质对稠油具有良好的掺稀降黏效果,在同一掺稀比下,植物油甲酯对稠油的降黏效果最显著,其次是脂肪酸,再次是植物油。通过斑点试验考察了掺稀介质和稠油的相容性和体系稳定性。结果显示,植物油甲酯与稠油相容性和稳定性最好,脂肪酸和植物油与稠油的相容性和稳定性相对较差。 相似文献
150.
Cu ion co-ordination-location in zeolites of MFI, erionite, mordenite matrices has been determined and the activity of the individual Cu sites compared for NO decomposition and its selective reduction by hydrocarbons or ammonia. It appears that Cu ions in the vicinity of one framework Al (site II), able to form stable Cu+-dinitrosyl complexes, and abundant in MFI structure, are responsible for high activity in NO decomposition. The Cu ions neighbouring two framework Al atoms (site I), and forming mostly mononitrosyl complexes, which dominate in erionite structure, provide a high activity in selective reduction of NO. 相似文献