全文获取类型
收费全文 | 38584篇 |
免费 | 3648篇 |
国内免费 | 1880篇 |
专业分类
电工技术 | 1654篇 |
技术理论 | 1篇 |
综合类 | 4227篇 |
化学工业 | 3732篇 |
金属工艺 | 1863篇 |
机械仪表 | 2114篇 |
建筑科学 | 11273篇 |
矿业工程 | 1416篇 |
能源动力 | 493篇 |
轻工业 | 959篇 |
水利工程 | 760篇 |
石油天然气 | 1043篇 |
武器工业 | 179篇 |
无线电 | 5231篇 |
一般工业技术 | 4505篇 |
冶金工业 | 964篇 |
原子能技术 | 1247篇 |
自动化技术 | 2451篇 |
出版年
2024年 | 132篇 |
2023年 | 428篇 |
2022年 | 826篇 |
2021年 | 1022篇 |
2020年 | 1083篇 |
2019年 | 931篇 |
2018年 | 838篇 |
2017年 | 1094篇 |
2016年 | 1162篇 |
2015年 | 1266篇 |
2014年 | 2202篇 |
2013年 | 2240篇 |
2012年 | 2842篇 |
2011年 | 3064篇 |
2010年 | 2249篇 |
2009年 | 2447篇 |
2008年 | 2340篇 |
2007年 | 2666篇 |
2006年 | 2336篇 |
2005年 | 2059篇 |
2004年 | 1630篇 |
2003年 | 1452篇 |
2002年 | 1257篇 |
2001年 | 1108篇 |
2000年 | 941篇 |
1999年 | 782篇 |
1998年 | 643篇 |
1997年 | 666篇 |
1996年 | 470篇 |
1995年 | 400篇 |
1994年 | 323篇 |
1993年 | 224篇 |
1992年 | 198篇 |
1991年 | 158篇 |
1990年 | 129篇 |
1989年 | 111篇 |
1988年 | 107篇 |
1987年 | 67篇 |
1986年 | 60篇 |
1985年 | 24篇 |
1984年 | 32篇 |
1983年 | 16篇 |
1982年 | 15篇 |
1981年 | 8篇 |
1980年 | 28篇 |
1979年 | 14篇 |
1965年 | 1篇 |
1963年 | 1篇 |
1959年 | 14篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
In the paper, a model typical for contact situations of automotive brakes is established based on the method of movable cellular automata. The processes taking place at local contacts in an automotive brake system are analysed. Based on microscopic and micro-analytical observations, the following contact situations were simulated: (i) a couple of ferritic steel against pearlitic steel, both covered by an oxide layer mixed with graphite nanoparticles and (ii) the same situation but without oxide layers. The results of calculated mean coefficients of friction of the oxide-on-oxide contact correspond well to expected values for a real braking system, whereas steel-on-steel contact are twice as high. This allows one to make some conclusions; for example, oxide formation will take place more quickly than friction layer elimination, and finally this is responsible for the stabilisation of the coefficient of friction. 相似文献
2.
Hung‐Yee Shu 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(3):273-280
Liquid–liquid two‐phase epoxidation from cyclohexene and cyclooctene in aqueous potassium peroxymonosulfate (commercially available as Oxone®) solution was studied as an application in pollution prevention. To avoid potential emissions of volatile organic compounds an aqueous solution was employed to replace the usual chlorinated solvents used in epoxide production. A droplet column reactor and stirred tank reactor were used to investigate two‐phase synthesis of epoxide. An aqueous Oxone® solution was used to oxidize a dispersion of alkene droplets and form epoxide. The study of aqueous epoxidation in both reactors showed that the epoxidation of alkenes can be represented as a first order reaction with respect to alkene. The salting out effect of Oxone® concentration was studied in both reactors and found to be very similar at optimal conditions. In comparing the two reactors, it was found that the droplet column reactor produces larger quantities of product per unit reactor volume for the same reaction time. The objective of this study is to provide an alternative reactor design and synthesis route that can meet pollution prevention goals. Copyright © 2004 Society of Chemical Industry 相似文献
3.
It is essential to automate the scanning path generation process to effectively implement the micro-stereolithography. However, a scanning path that is generated based only on a 3D CAD model introduces dimensional inaccuracies. In micro-stereolithography, the photopolymer solidification is affected by fabrication conditions, such as the optical properties (laser power, laser scanning speed, laser scanning pitch focusing condition, etc.) and material properties of the photopolymer. Thus, the photopolymer solidification phenomena must be considered when generating a laser scanning path. In this paper, a scanning path generation algorithm that uses 3D CAD data and considers the photopolymer solidification phenomena is proposed to improve the dimensional accuracy in micro-stereolithography. Multi-line photopolymer solidification experiments were performed for various laser scanning conditions to examine the photopolymer solidification phenomena. From these experiments, linear relations between the solidification length (width) and scanning length (width) were acquired and stored in a database. Subsequently, these data were utilized to compensate the scanning path of the laser beam. In addition, experiments for determining the layer thickness in the z-direction were performed and these results were also used in the scanning path generation algorithm.This research was supported by the Highly Advanced National Project (http://www.most.go.kr), which performs some of the National R&D Program, and sponsored by the Korean Ministry of Science and Technology under the contract project code M10214000116-02B1500-02010. 相似文献
4.
R. GRAY† M. HILARY STEVENSON‡ 《International Journal of Food Science & Technology》1991,26(6):669-672
One hundred and twenty-five pairs of chicken drumsticks were randomly allocated to one of five dose rates: 5, 10, 15, 20 or 600 kGyh-. The highest dose rate was obtained using a linear accelerator whilst the remaining dose rates were provided using a 60 Co gamma source. Each batch of 25 pairs was further divided into groups five of which were stored at 4°C for 0, 7, 14, 21 or 28 days. ESR spectroscopy was used to measure the intensity of the radiation-induced signal. There was a quadratic relationship between ESR signal strength and dose rate, which although statistically significant is unlikely to be of practical importance. The magnitude of the ESR signal declined by about 20% over the first 14 days of storage at 4°C and thereafter the decrease was minimal. 相似文献
5.
6.
预应力钢-混凝土组合梁的应用与研究 总被引:1,自引:0,他引:1
回顾了预应力钢 混凝土组合梁国内外应用与研究历史 ,分析了现有规范及理论的不足 ,并指出了有待解决的问题。 相似文献
7.
The pyrolysis of tertiarybutylphosphine (TBP) has been studied in the low pressure conditions used for chemical beam epitaxy
(CBE). The pyrolysis studies were carried out in low pressure reactors of two different configurations, one of which is a
cracker cell designed for use in a CBE system. The reaction products were studied using a quadrupole mass spectrometer. The
products observed are accounted for by a reaction mechanism involving homolysis of the parent TBP molecule to produce PH2 and C4H9 radicals. These undergo subsequent reactions to form the stable products C4H8, PH3 and H2, with smaller amounts of P and P2 being produced. The production of the sub-hydride PH2 using this cracker cell design indicates that the use of partially cracked TBP may be a promising technique for reducing
the amount of carbon incorporated into the growing epitaxial layer. 相似文献
8.
磁偏转电子枪研制核靶 总被引:3,自引:3,他引:0
文章叙述了磁偏转电子枪的原理和结构以及用EQD-3型电子枪研制各种核靶的工艺过程。 相似文献
9.
Abstract The whole DNA of soybean was implanted into four varieties of wheat of Zhongyu5, Huaiyin 9628, Wenyou 1, Jimai 5 respectively via ion-beam mediation. There were 5 plantsobtained whose protein content was higher than 18.5%, the highest one was 21.44%. There were 3plants obtained whose protein content was lower than 11.5%, the lowest one was 10.96%. We cansee that the whole DNA of soybean transformed into wheat via ion beam implantation can inducethe increase in wheat protein content dramatically. The result also shows that the transformationefficiency of different gene types of wheat receptor varies greatly that the implanting time has acertain effect on the efficiency of transformation. 相似文献
10.
给出平凹谐振腔和凹平凹谐振腔失调时光轴确定方法。在二维轴对称折迭-组合腔 激光器小角度失调运行时,对非相干并和和相干并和后的输出光束的近场强度分布做了分析和模拟。结果表明:小角度失调对4cm以内的近场影响不大,光强分布仍具有高斯状分布;对4cm以外的近场影响较大,光强分布发生相应的形变,且随着失调角度变大而变大。 相似文献