全文获取类型
收费全文 | 226351篇 |
免费 | 29617篇 |
国内免费 | 9570篇 |
专业分类
电工技术 | 13811篇 |
技术理论 | 17篇 |
综合类 | 14841篇 |
化学工业 | 45186篇 |
金属工艺 | 10806篇 |
机械仪表 | 12145篇 |
建筑科学 | 15936篇 |
矿业工程 | 5304篇 |
能源动力 | 6174篇 |
轻工业 | 23574篇 |
水利工程 | 4195篇 |
石油天然气 | 8662篇 |
武器工业 | 1830篇 |
无线电 | 27500篇 |
一般工业技术 | 31307篇 |
冶金工业 | 10791篇 |
原子能技术 | 2182篇 |
自动化技术 | 31277篇 |
出版年
2024年 | 879篇 |
2023年 | 3113篇 |
2022年 | 6486篇 |
2021年 | 8660篇 |
2020年 | 7604篇 |
2019年 | 7858篇 |
2018年 | 8408篇 |
2017年 | 9423篇 |
2016年 | 9247篇 |
2015年 | 11673篇 |
2014年 | 13641篇 |
2013年 | 16712篇 |
2012年 | 15973篇 |
2011年 | 16828篇 |
2010年 | 15228篇 |
2009年 | 14491篇 |
2008年 | 13854篇 |
2007年 | 12928篇 |
2006年 | 12027篇 |
2005年 | 9769篇 |
2004年 | 7448篇 |
2003年 | 6548篇 |
2002年 | 6676篇 |
2001年 | 5619篇 |
2000年 | 4708篇 |
1999年 | 3693篇 |
1998年 | 3362篇 |
1997年 | 2454篇 |
1996年 | 2113篇 |
1995年 | 1504篇 |
1994年 | 1210篇 |
1993年 | 981篇 |
1992年 | 730篇 |
1991年 | 526篇 |
1990年 | 421篇 |
1989年 | 355篇 |
1988年 | 296篇 |
1987年 | 233篇 |
1986年 | 209篇 |
1985年 | 211篇 |
1984年 | 119篇 |
1983年 | 128篇 |
1982年 | 120篇 |
1981年 | 137篇 |
1980年 | 141篇 |
1979年 | 77篇 |
1977年 | 105篇 |
1976年 | 203篇 |
1975年 | 54篇 |
1973年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Zhang Li Chun Jin Hai Yan Ye Hong Fei Gao Yu Zhi Ning Bao Jun Mo Bang Xian 《Electron Devices, IEEE Transactions on》2002,49(6):1075-1076
A polysilicon emitter RCA transistor (an ultra-thin interfacial oxide layer exists between polysilicon and silicon emitter) is presented which can operate at 77 K for the first time. An ultra-thin (1.5 nm) interfacial oxide layer is grown deliberately between polysilicon and silicon emitter using RCA oxidation and excellent device stability is obtained after rapid thermal annealing (RTA) treatment in nitrogen atmosphere. The RCA transistor exhibits good electrical performance at very low temperature for an emitter area of 3 × 8 μm2. The maximum toggle frequency of a 1:2 static divider is 1.2 GHz and 732 MHz at 300 K and 77 K, respectively 相似文献
63.
Summary The influence of draw ratio on macroscopic and crystallographic density of polyethylene with different initial morphologies, has been investigated by solid-state extrusion. An initial drop followed by an increase in macroscopic density as a function of draw ratio has been observed. Since precision X-ray measurements of unit cell parameters showed no variation of crystallographic density, it was concluded that plastic deformation of polyethylene upon drawing proceeds with a decrease of the degree of crystallinity. This was confirmed by differential scanning calorimetry. 相似文献
64.
65.
减压渣油与FCC油浆共炭化的化学组成变化 总被引:6,自引:2,他引:4
考察了齐鲁石化胜利炼油厂催化油浆(FCC)和胜利减压渣油(VR)在490℃,0.8MPa下不同混合比的原料和不同反应时间的中间产物的HS、TS、PS、P及其1h中间产物的HS和TS的^1H-NMR。数据结果反映了体系的反应速度。掺入FCC油浆抑制了VR的反应活性,降低了体系的反应速度,增加了基质的溶解度;1h中间产物的组成结构更接近于原料及反应体系的反应性和基质的溶解度;1h中间产物的芳香度越高,取代基越少,侧链越短,基质对VR中的活性反应组分在炭化早期生成的高度缩合物质的溶解度越大。 相似文献
66.
Hong Jeong Jeong‐Ho Park 《International Journal of Adaptive Control and Signal Processing》2002,16(1):1-23
Tracking targets of interest is one of the major research areas in radar surveillance systems. We formulate the problem as incomplete data estimation and apply EM to the MAP estimate. The resulting filter has a recursive structure analogous to the Kalman filter. The advantage is that the measurement‐update deals with multiple measurements in parallel and the parameter‐update estimates the system parameters on the fly. Experiments tracking separate targets in parallel show that tracking maintenance ratio of the proposed system is better than that of NNF and RMS position error is smaller than that of PDAF. Also, the system parameters are correctly obtained even from incorrect initial values. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
67.
健康住宅正在走近我们 总被引:1,自引:1,他引:0
人类居住健康的问题越来越受到全世界居住者和舆论的关注.长期以来人类过于不当的城市建设行为,人口的过于集中,城市建筑的高层化倾向,过分的人造环境造成土地失水性严重、热岛现象衍生.城市作为人类居住生活的功能区,在很大程度上被削弱,居住条件恶化、环境受到污染.让城市功能朝着人居、健康的目标发展,包括生理和心理的、社会的和人文的、近期的和长期的多层次的健康,是我们今天的历史责任. 相似文献
68.
Qin‐Tao Liu Malcolm R Clench Judith L Kinderlerer 《Journal of the science of food and agriculture》2002,82(5):553-558
Structural isomers of monoacylglycerols (monoglycerides, MAGs) were identified and compared after degradation of butter oil by two strains of Penicillium roquefortii and a commercial lipase from P roquefortii (EC 3.1.1.3) at pH 7.0 and 10 °C. The conditions were selected as they were comparable with those used in the manufacture of blue mould‐ripened cheese. The commercial lipase was selected to compare with the fungal strains in terms of acyl migration. Results showed that the main isomers formed by lipolysis with the commercial lipase were sn‐2 MAGs (64 mol%), whilst spores and emerging mycelia of P roquefortii produced mainly sn‐1(3) MAGs (83–90 mol%). The work reported here may lead to further assessment of different MAG structural isomers as natural preservatives in foods and dairy products. © 2002 Society of Chemical Industry 相似文献
69.
Yu‐Qing Cao Zhan Zhang Yan‐Xin Guo 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(10):1441-1444
A new efficient method for synthesising nitriles, important organic reagents, is reported in this paper. In an environmentally benign solvent‐free system, aryl carboxylic acids were converted into the corresponding nitriles via one‐pot reactions, by amidation with ethyl carbamate followed by dehydration with thionyl chloride, in excellent yields. The results showed that the method has the advantages of lower cost, higher yield, less pollution and greater ease of work‐up. Copyright © 2008 Society of Chemical Industry 相似文献
70.
The cooling and solidification of melted drops during their movement in an immiscible cooling medium is widely employed for granulation in the chemical industry, and a study of these processes to provides a basis for the design of the granulation tower height and the temperature of the cooling medium is reported. A physical model of the cooling and solidification of the drop is established and the numerical calculation is performed. The influences of the key factors in the solidification, i.e., Bi number, drop diameter, temperature of the cooling medium, etc. are presented. The cooling and solidification during wax granulation in a water‐cooling tower and during urea granulation in an air‐cooling tower (spraying tower) are described in detail. Characteristics of the solidification and temperature distribution within the particle at different times are shown. The model and calculations can be used for structure design of the granulation tower and optimization of the operation parameters. 相似文献