全文获取类型
收费全文 | 102440篇 |
免费 | 9807篇 |
国内免费 | 7034篇 |
专业分类
电工技术 | 3434篇 |
技术理论 | 2篇 |
综合类 | 6056篇 |
化学工业 | 24504篇 |
金属工艺 | 7746篇 |
机械仪表 | 6123篇 |
建筑科学 | 3482篇 |
矿业工程 | 2465篇 |
能源动力 | 2380篇 |
轻工业 | 6143篇 |
水利工程 | 1365篇 |
石油天然气 | 3635篇 |
武器工业 | 847篇 |
无线电 | 14767篇 |
一般工业技术 | 17722篇 |
冶金工业 | 3543篇 |
原子能技术 | 1646篇 |
自动化技术 | 13421篇 |
出版年
2024年 | 402篇 |
2023年 | 2080篇 |
2022年 | 3258篇 |
2021年 | 3942篇 |
2020年 | 3523篇 |
2019年 | 3244篇 |
2018年 | 2973篇 |
2017年 | 3575篇 |
2016年 | 3912篇 |
2015年 | 4108篇 |
2014年 | 5536篇 |
2013年 | 5814篇 |
2012年 | 6493篇 |
2011年 | 8391篇 |
2010年 | 6266篇 |
2009年 | 6927篇 |
2008年 | 6021篇 |
2007年 | 6694篇 |
2006年 | 5852篇 |
2005年 | 5158篇 |
2004年 | 4294篇 |
2003年 | 3836篇 |
2002年 | 3285篇 |
2001年 | 2172篇 |
2000年 | 2108篇 |
1999年 | 1725篇 |
1998年 | 1358篇 |
1997年 | 1103篇 |
1996年 | 1040篇 |
1995年 | 762篇 |
1994年 | 742篇 |
1993年 | 555篇 |
1992年 | 432篇 |
1991年 | 355篇 |
1990年 | 265篇 |
1989年 | 230篇 |
1988年 | 143篇 |
1987年 | 120篇 |
1986年 | 134篇 |
1985年 | 78篇 |
1984年 | 55篇 |
1983年 | 55篇 |
1982年 | 54篇 |
1981年 | 35篇 |
1980年 | 44篇 |
1979年 | 33篇 |
1978年 | 12篇 |
1977年 | 18篇 |
1976年 | 17篇 |
1974年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
LiFePO4 is a potential candidate for the cathode material of the lithium secondary batteries. A co-precipitation method was adopted to prepare LiFePO4 because it is simple and cheap. Nitrogen gas was needed to prevent oxidation of Fe2+ in the aqueous solution. The co-precipitated precursor shows the high reactivity with the reductive gas, and the single phase of LiFePO4 is successfully synthesized with the aid of carbon under less reductive conditions. LiFePO4 fine powder prepared by co-precipitation method shows high rate capability, impressive specific capacity and cycle property. 相似文献
42.
The effects of gallia additions on the sintering behavior of gadolinia-doped ceria were systematically investigated from the following aspects: the variation in sintered density, the variation in grain size, and the existing forms of Ga2O3 in CeO2.Sintered density increased with increasing Ga2O3 content up to 5 mol.% and then it decreased with further addition of Ga2O3. Grain size also increased with increasing Ga2O3 content up to 5 mol.% and then decreased with further addition of Ga2O3. Decrease in grain size was caused by a pinning effect of Ga2O3 precipitation at grain boundaries. Lattice constant decreased with increasing Ga2O3 content up to 5 mol.%. This decrease will be due to the substitution of smaller Ga3+ ions for Ce4+ ions in the CeO2 structure. According to the results obtained from scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses, the solubility limit of Ga2O3 in Ce0.8Gd0.2O1.9 ceramics can be estimated to be nearly 5 mol.%. The addition of Ga2O3 up to the solubility limit was found to promote the sintering properties of Gd2O3-doped CeO2. 相似文献
43.
The thick film of Zn-Sb-O was prepared by coating the paste of nanoparticles mixture (Sb2O3:ZnO=1:3) on the alumina substrate, followed by sintering at 500-900 °C for 2 h in air. The electrical resistance and gas-sensing properties to benzene, alcohol and acetone of Zn-Sb-O films were found to be dependent on the change of phase structure caused by sintering temperature. 相似文献
44.
R. Wongmaneerung W. Chaisan O. Khamman R. Yimnirun S. Ananta 《Ceramics International》2008,34(4):813-817
The potential of the vibro-milling technique as a simple method to obtain usable quantities of single-phase electroceramic powders with nanosized particles was examined. A detailed study considering the role of both milling time and firing condition on phase formation and particle size of the final product was performed. The calcination temperature for the formation of the desired phase was lower when longer milling times have been applied. More importantly, by employing an appropriate choice of the milling time and calcination condition, high purity electroceramic nanopowders have been successfully prepared with a simple solid-state reaction method. 相似文献
45.
Takayuki Honma Yuichiro Kuroki Tomoichiro Okamoto Masasuke Takata Yukihiro Kanechika Masanobu Azuma Hitofumi Taniguchi 《Ceramics International》2008,34(4):943-946
Aluminum nitride ceramics were prepared by sintering with 0–4.8 mass% of Ca3Al2O6 (C3A) as a sintering additive. The transmittance in the range of 260–550 nm increased with increasing amount of C3A. The cathodoluminescence intensity attributed to oxygen-induced defects decreased with increasing amount of C3A. From the results, the increase of the transmittance in the range of 260–550 nm was considered to be related to the decrease of the oxygen-induced defect density. 相似文献
46.
MIMO (Multiple-Input Multiple-Output)的显著优点就是在不增加带宽的情况下,能够成倍地提高通信系统容量和频谱利用率,是未来移动通信与个人通信系统实现高速率数据传输,提高高传输质量的重要途径,也是未来移动通信系统广泛采用的关键技术.文中简要介绍了MIMO系统及其一种新的MIMO系统中的应用技术,即PARC(Per-antenna Rate Control)技术. 相似文献
47.
K. Uchiyama T. Shiosaki T. Kosaka A. Kasamatsu M. Echizen 《Ceramics International》2008,34(4):979-983
Advanced sol–gel methods using a secondary solvent addition into (Pb, La)(Zr, Ti)O3 (PLZT) sol–gel solution and a methanol pre-treatment of sapphire substrates are demonstrated. For the secondary solvent addition, the additive affected the crystallinity and electro-optic (EO) property of PLZT films and only methanol addition can improve them. In addition, the methanol pre-treatment is also appeared to be effective to improve film characteristics.
Through these optimizations, epitaxially grown PLZT thin films on r-cut sapphire are obtained and a high Pockels coefficient which is comparable to those of bulk PLZTs is achieved. It is believed that these PLZT thin films are applicable for integrated EO devices and open the door for the future data communication systems. 相似文献
48.
文章通过对五口井的现场应用介绍,阐述了快速色谱分析技术在油气层识别和解释方面的准确性,探讨了该技术在薄油气层的发现和评价、快速钻进条件下油气层的发现、对油气层全烃组份变化的统一、水平井的地质导向以及排除钻井液添加荆对油气显示的影响五个方面的优势,从而论证了快速色谱分析技术在油气勘探中的应用价值。 相似文献
49.
J. L. Barron R. E. Mercer X. Chen P. Joe 《International journal of imaging systems and technology》2005,15(3):189-198
We present local least squares and regularization frameworks for computing 3D velocity (3D optical flow) from 3D radial velocity measured by a Doppler radar. We demonstrate the performance of our algorithms quantitatively on synthetic radial velocity data and qualitatively on real radial velocity data, obtained from the Doppler radar at Kurnell Radar station, Botany Bay, New South Wales, Australia. Radial velocity can be used to predict the future positions of storms in sequences of Doppler radar datasets.© 2005 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 15, 189–198, 2005 相似文献
50.
Ring‐opening polymerization of D,L ‐lactide (LA) has been successfully carried out by using rare earth 2,6‐dimethylaryloxide (Ln(ODMP)3) as single component catalyst or initiator for the first time. The effects of different rare earth elements, solvents, monomers and catalyst concentration as well as polymerization temperature and time on the polymerization were investigated. The results show that La(ODMP)3 exhibits higher activity to prepare poly(D,L ‐lactide) (PLA) with a viscosity molecular weight of 4.5 × 104 g mol?1 and the conversion of 97 % at 100 °C in 45 min. The catalytic activity of Ln(ODMP)3 has following sequence: La > Nd > Sm > Gd > Er > Y. A kinetic study has indicated that the polymerization is first order with respect to both monomer and catalyst concentration. The apparent activation energy of the polymerization of LA with La(ODMP)3 is 69.6 kJ mol?1. The analyses of polymer ends indicate that the LA polymerization proceeds according to ‘coordination–insertion’ mechanism with selective cleavage of the acyl–oxygen bond of the monomer. Copyright © 2004 Society of Chemical Industry 相似文献