全文获取类型
收费全文 | 54166篇 |
免费 | 15634篇 |
国内免费 | 64篇 |
专业分类
电工技术 | 1013篇 |
综合类 | 75篇 |
化学工业 | 21091篇 |
金属工艺 | 760篇 |
机械仪表 | 1292篇 |
建筑科学 | 2263篇 |
矿业工程 | 55篇 |
能源动力 | 1551篇 |
轻工业 | 9925篇 |
水利工程 | 489篇 |
石油天然气 | 148篇 |
武器工业 | 2篇 |
无线电 | 7920篇 |
一般工业技术 | 14059篇 |
冶金工业 | 2333篇 |
原子能技术 | 157篇 |
自动化技术 | 6731篇 |
出版年
2024年 | 61篇 |
2023年 | 214篇 |
2022年 | 571篇 |
2021年 | 1028篇 |
2020年 | 1921篇 |
2019年 | 3707篇 |
2018年 | 3745篇 |
2017年 | 4071篇 |
2016年 | 4546篇 |
2015年 | 4395篇 |
2014年 | 4519篇 |
2013年 | 6229篇 |
2012年 | 3761篇 |
2011年 | 3626篇 |
2010年 | 3458篇 |
2009年 | 3416篇 |
2008年 | 2876篇 |
2007年 | 2559篇 |
2006年 | 2207篇 |
2005年 | 1770篇 |
2004年 | 1701篇 |
2003年 | 1716篇 |
2002年 | 1652篇 |
2001年 | 1402篇 |
2000年 | 1321篇 |
1999年 | 676篇 |
1998年 | 598篇 |
1997年 | 457篇 |
1996年 | 316篇 |
1995年 | 201篇 |
1994年 | 159篇 |
1993年 | 141篇 |
1992年 | 84篇 |
1991年 | 78篇 |
1990年 | 74篇 |
1989年 | 54篇 |
1988年 | 61篇 |
1987年 | 41篇 |
1986年 | 46篇 |
1985年 | 46篇 |
1984年 | 38篇 |
1983年 | 37篇 |
1982年 | 24篇 |
1981年 | 29篇 |
1980年 | 29篇 |
1979年 | 22篇 |
1978年 | 18篇 |
1977年 | 36篇 |
1976年 | 53篇 |
1975年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Adaptive backstepping repetitive learning control design for nonlinear discrete‐time systems with periodic uncertainties
下载免费PDF全文
![点击此处可从《International Journal of Adaptive Control and Signal Processing》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Qiao Zhu Jian‐Xin Xu Shiping Yang Guang‐Da Hu 《International Journal of Adaptive Control and Signal Processing》2015,29(4):524-535
This paper addresses a tracking problem for uncertain nonlinear discrete‐time systems in which the uncertainties, including parametric uncertainty and external disturbance, are periodic with known periodicity. Repetitive learning control (RLC) is an effective tool to deal with periodic unknown components. By using the backstepping procedures, an adaptive RLC law with periodic parameter estimation is designed. The overparameterization problem is overcome by postponing the parameter estimation to the last backstepping step, which could not be easily solved in robust adaptive control. It is shown that the proposed adaptive RLC law without overparameterization can guarantee the perfect tracking and boundedness of the states of the whole closed‐loop systems in presence of periodic uncertainties. In addition, the effectiveness of the developed controller is demonstrated by an implementation example on a single‐link flexible‐joint robot. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
42.
Wan‐Xia Wu 《Polymer International》2019,68(11):1848-1855
A series of novel aliphatic poly(β‐thioether ester)s with various methylene group contents were prepared by direct lipase‐catalyzed polycondensation of the monomer with an acid‐labile β‐thiopropionate group. The polycondensation reaction using immobilized lipase B from Candida antarctica was carried out in diphenyl ether at 90 °C. Poly(β‐thioether ester)s with high molecular weights of 20 500–57 000 Da and narrow polydispersities in the range 1.40–1.48 were obtained. Thermogravimetric analysis, differential scanning calorimetry and wide‐angle X‐ray diffraction were used to investigate the thermal properties and crystal structures of these polyesters. All the poly(β‐thioether ester)s were semicrystalline polymers and thermally stable up to at least 200 °C. In vitro degradation studies showed that they can rapidly degrade under acidic conditions by the hydrolysis of the β‐thiopropionate groups, suggesting their potential as acid‐degradable polymeric materials. © 2019 Society of Chemical Industry 相似文献
43.
Kang Zhang Rong‐rong Wang Kai‐rui Zhang Fei Cheng Yu Tian Yi Lin Mi Zhou Pu‐xin Zhu 《Polymer International》2020,69(3):274-279
A series of hyperbranched poly(citric polyethylene glycol) (PCPEG) materials with varied polyethylene glycol (PEG) chain lengths as plasticizers were mixed with maize starch (MS) via cooking and film‐forming. The structure, pasting property, plasticization, aging property, moisture absorption and compatibility of plasticized starches were studied by means of Fourier transform infrared spectroscopy, X‐ray diffraction, rapid viscosity analysis, tension testing, moisture absorption measurements and scanning electron microscopy. Compared with PEG and citric acid, PCPEG was more effective in promoting starch chain movement and inhibiting the retrogradation of starch film. Also, PCPEG/MS had smaller moisture content. The longer the plasticizer chain, the better were the aging resistance and moisture resistance of starch. But with an increase of PEG chain length, mechanical properties of PCPEG/MS deteriorated and the compatibility between PCPEG and MS decreased. The hyperbranched derivative of PEG with longer chain exhibited improved plasticization and compatibility with starch. © 2019 Society of Chemical Industry 相似文献
44.
45.
46.
47.
Jincy Joy Jessica Pereira Rachida Aid‐Launais Graciela Pavon‐Djavid Alok R Ray Didier Letourneur Anne Meddahi‐Pell Bhuvanesh Gupta 《Polymer International》2019,68(7):1367-1377
The work reported involved the fabrication of an electrospun tubular conduit of a gelatin and polycaprolactone (PCL) blend as an adventitia‐equivalent construct. Gelatin was included as the matrix for increased biocompatibility with the addition of PCL for durability. This is contrary to most of the literature available for biomaterials based on blends of gelatin and PCL where PCL is the major matrix. The work includes the assiduous selection of key electrospinning parameters to obtain smooth bead‐free fibres with a narrow distribution of pore size and fibre diameter. Few reports elucidate the optimization of all electrospinning parameters to fabricate tubular conduits with a focus on obtaining homogeneous pores and fibres. This stepwise investigation would be unique for the fabrication of gelatin–PCL electrospun tubular constructs. The fabricated microfibrous gelatin–PCL constructs had pores of size ca 50–100 μm reportedly conducive for cell infiltration. The measured value of surface roughness of 57.99 ± 17.4 nm is reported to be favourable for protein adhesion and cell adhesion. The elastic modulus was observed to be similar to that of the tunica adventitia of the native artery. Preliminary in vitro and in vivo biocompatibility tests suggest safe applicability as a biomaterial. Minimal cytotoxicity was observed using MTT assay. Subcutaneous implantation of the scaffold demonstrated acute inflammation which decreased by day 15. The findings of this study could enable the fabrication of smooth bead‐free microfibrous gelatin–PCL tubular construct as viable biomaterial which can be included in a bilayer or a trilayer scaffold for vascular tissue engineering. © 2019 Society of Chemical Industry 相似文献
48.
49.
50.