全文获取类型
收费全文 | 82314篇 |
免费 | 6076篇 |
国内免费 | 4950篇 |
专业分类
电工技术 | 3032篇 |
技术理论 | 1篇 |
综合类 | 4344篇 |
化学工业 | 27799篇 |
金属工艺 | 7739篇 |
机械仪表 | 2573篇 |
建筑科学 | 4166篇 |
矿业工程 | 1115篇 |
能源动力 | 2188篇 |
轻工业 | 6844篇 |
水利工程 | 547篇 |
石油天然气 | 4302篇 |
武器工业 | 610篇 |
无线电 | 7551篇 |
一般工业技术 | 9046篇 |
冶金工业 | 3322篇 |
原子能技术 | 1564篇 |
自动化技术 | 6597篇 |
出版年
2024年 | 308篇 |
2023年 | 1397篇 |
2022年 | 4064篇 |
2021年 | 4194篇 |
2020年 | 2534篇 |
2019年 | 2129篇 |
2018年 | 1882篇 |
2017年 | 2445篇 |
2016年 | 2928篇 |
2015年 | 2959篇 |
2014年 | 3989篇 |
2013年 | 4513篇 |
2012年 | 4868篇 |
2011年 | 6051篇 |
2010年 | 4391篇 |
2009年 | 5120篇 |
2008年 | 4367篇 |
2007年 | 4887篇 |
2006年 | 4562篇 |
2005年 | 3734篇 |
2004年 | 3087篇 |
2003年 | 2935篇 |
2002年 | 2468篇 |
2001年 | 2049篇 |
2000年 | 1814篇 |
1999年 | 1523篇 |
1998年 | 1149篇 |
1997年 | 931篇 |
1996年 | 841篇 |
1995年 | 753篇 |
1994年 | 672篇 |
1993年 | 515篇 |
1992年 | 459篇 |
1991年 | 363篇 |
1990年 | 339篇 |
1989年 | 234篇 |
1988年 | 185篇 |
1987年 | 162篇 |
1986年 | 188篇 |
1985年 | 155篇 |
1984年 | 153篇 |
1983年 | 110篇 |
1982年 | 111篇 |
1981年 | 124篇 |
1980年 | 116篇 |
1979年 | 99篇 |
1978年 | 87篇 |
1977年 | 86篇 |
1976年 | 99篇 |
1975年 | 98篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
The effect of rare earth oxides Y203 or Ce02 on sintering properties of Si3N4 ceramics was studied and the mechanism of assisting action during sintering was analyzed. The results in dicate that the best sintering properties appear in Si3N4 ceramics with 5% Y203 or 8% CeO2. Secondary crystallites are formed at grain boundaries after heat treatment,which decreases the amount of glass phase and contributes to the improvement of high-temperature mechanical properties of silicon nitride. 相似文献
53.
54.
55.
An efficient, convenient and quantitative method for characterising polyester end-groups is described. We have found that trichloroacetyl isocyanate (TAI) reacts rapidly and quantitatively with both carboxyl [C(O)OH] and hydroxyl (OH) chain ends to form derivatives that can be readily determined by 1H NMR spectroscopy. The TAI capped end-groups give rise to characteristic imidic NH resonances in a normally clear region of the 1H NMR spectrum [δ∼10-11.5 for C(O)-O-C(O)-NH-C(O)CCl3 from C(O)OH, δ∼8-9 for O-C(O)-NH-C(O)CCl3 from OH]. The method has been successfully applied to quantitative determination of the end-groups of a wide variety of oligomeric polyesters. It has also been applied to higher molecular weight polyesters including commercial, bottle grade, poly(ethylene terephthalate) (PET) and PET based copolyesters (e.g. PETG). 相似文献
56.
Yi‐Hung Chen Ching‐Yuan Chang Wei‐Ling Su Chun‐Yu Chiu Yue‐Hwa Yu Pen‐Chi Chiang Chiung‐Fen Chang Je‐Lueng Shie Chyow‐San Chiou Sally IM Chiang 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(1):68-75
This study investigates the ozonation of CI Reactive Black 5 (RB5) by using the rotating packed bed (RPB) and completely stirred tank reactor (CSTR) as ozone contactors. The RPB, which provides high gravitational force by adjusting the rotational speed, was employed as a novel ozone contactor. The same ozone dosage was separately introduced into either the RPB or the CSTR for the investigation, while the experimental solution was continuously circulated within the apparatus consisting of the RPB and CSTR. The decolorization and mineralization efficiencies of RB5 in the course of ozonation are compared for these two methods. Moreover, the dissolved and off‐gas ozone concentrations were simultaneously monitored for the further analysis. As a result, the ozone mass transfer rate per unit volume of the RPB was significantly higher because of its higher mass transfer coefficient and gas–liquid concentration driving force. Furthermore, ozonation kinetics was found to be independent of the gravitational magnitude of an ozone gas–liquid contactor. Therefore, the results suggest employing RPBs as ozone‐contacting devices with the advantage of volume reduction. The experimental results, which can be used for further modeling of the ozonation process in the RPB, also show the requirement of correct design for the RPB. Consequently, the present study is useful for the understanding of practical application of RPBs. Copyright © 2004 Society of Chemical Industry 相似文献
57.
We succeeded in the fabrication of bonded laser crystals composed of a neodymium-doped YVO4 laser crystal (Nd:YVO4) and its host crystals YVO4 by a newly developed dry etching technique using an argon ion beam. The optical distortion caused by the bonded interface of size 5 mm × 6 mm was estimated to be 0.05λ at 633 nm. From the comparison of laser performance pumped by a laser diode, the bonded crystals could increase the laser output power by nearly twice that of the non-bonded crystals with the same degree of polarization of 99.2%. To analyze the mechanism of the enhanced reduction of the thermal load in the bonded crystals, numerical simulations with a finite-element method were also performed. 相似文献
58.
59.
论述了2,4-二氯氟苯合成的新方法。以对氯硝基苯为起站原料,经氟化反应、硝化反应及氯化反应制得2,4-二氯氟苯,总收率达59.0%。本合成路线工艺简单、操作安全、原料易得、成本低廉,适合于工业化生产。 相似文献
60.