全文获取类型
收费全文 | 90857篇 |
免费 | 4006篇 |
国内免费 | 4269篇 |
专业分类
电工技术 | 4100篇 |
技术理论 | 5篇 |
综合类 | 8537篇 |
化学工业 | 13178篇 |
金属工艺 | 5759篇 |
机械仪表 | 3091篇 |
建筑科学 | 4373篇 |
矿业工程 | 1265篇 |
能源动力 | 2781篇 |
轻工业 | 6488篇 |
水利工程 | 1946篇 |
石油天然气 | 4125篇 |
武器工业 | 689篇 |
无线电 | 6804篇 |
一般工业技术 | 14112篇 |
冶金工业 | 2571篇 |
原子能技术 | 2205篇 |
自动化技术 | 17103篇 |
出版年
2024年 | 158篇 |
2023年 | 310篇 |
2022年 | 566篇 |
2021年 | 644篇 |
2020年 | 1054篇 |
2019年 | 985篇 |
2018年 | 1092篇 |
2017年 | 1047篇 |
2016年 | 1578篇 |
2015年 | 2214篇 |
2014年 | 4027篇 |
2013年 | 4785篇 |
2012年 | 4071篇 |
2011年 | 4693篇 |
2010年 | 3937篇 |
2009年 | 5319篇 |
2008年 | 5320篇 |
2007年 | 5699篇 |
2006年 | 5221篇 |
2005年 | 4385篇 |
2004年 | 3760篇 |
2003年 | 3690篇 |
2002年 | 3752篇 |
2001年 | 2784篇 |
2000年 | 3176篇 |
1999年 | 2966篇 |
1998年 | 2493篇 |
1997年 | 2384篇 |
1996年 | 2558篇 |
1995年 | 2656篇 |
1994年 | 2417篇 |
1993年 | 1471篇 |
1992年 | 1491篇 |
1991年 | 1031篇 |
1990年 | 750篇 |
1989年 | 668篇 |
1988年 | 635篇 |
1987年 | 375篇 |
1986年 | 224篇 |
1985年 | 376篇 |
1984年 | 415篇 |
1983年 | 430篇 |
1982年 | 330篇 |
1981年 | 407篇 |
1980年 | 271篇 |
1979年 | 114篇 |
1978年 | 114篇 |
1977年 | 70篇 |
1976年 | 43篇 |
1975年 | 56篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Dysprosium-doped bismuth sodium titanate ceramics were prepared using the conventional mixed-oxide method. The amount of dysprosium used was varied from 0 to 2 at.%. The mixed powders were calcined at 800 °C and checked for phase purity using X-ray diffraction technique. The calcined powders were then cold-pressed into pellets and sintered at 1050 °C for the time ranging from 2 to 48 h. The ceramics were checked for phases and microstructures using an X-ray diffractometer and a scanning electron microscope, respectively. The analysis showed that undoped BNT ceramics sintered at longer time exhibited a significant grain growth with non-uniform grain size distribution and shape. The Dy-doped BNT however showed a much more limited grain growth behavior, resulting in smaller grain size and more equiaxed grain shape. It was also found that all Dy-doped BNT ceramics sintered at 48 h possessed lower porosity than those sintered for shorter time. 相似文献
102.
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
103.
Oxide films were deposited on different substrates by laser molecular beam epitaxy. Reflection high-energy electron diffraction was performed to in situ investigate the change of growth mode and the lattice relaxation during the growth. An asymmetrical phenomenon was found in the two kinds of strain states, compressive stress and tensile stress of heterostructures with different lattice mismatch. In the case of BaTiO3/SrTiO3 (2.2%), 2D layer-by-layer growth mode without lattice relaxation can be maintained for a longer period for BTO films on STO with compressive stress, comparing to STO films on BTO with tensile stress. When MgO films were deposited on SrTiO3 with a large mismatch of 7.8%, compressive stress leads to rapid lattice relaxation with a very thin wet layer, and 3D strained island were observed. As a comparison, SrTiO3 films on MgO with tensile stress were configured. No RHEED patterns can be observed duo to a large tensile stress. 相似文献
104.
Shinsook Yoon Mi-Kyoung Kim In-Young Lee Mikyung Yun Jeong E. Nam Shin 《Journal of Industrial and Engineering Chemistry》2008,14(6):759-764
We have developed a mutant strain derived from Agrobacterium sp. ATCC 31750, which produces a water-soluble polysaccharide having potential utility to the food, feed, pharmaceutical and cosmetic industries. A high concentration of product (15 g/L) is obtained by 48 h cultivation of the mutant strain under optimized fermentation conditions. The water-soluble polysaccharide obtained from cultures of the mutant strain beta82 has Glc:Man:Gal in approximate molar ratios of 5.8:6.7:1.0. The molecular weight of the polysaccharide was determined to be approximately 1000 kDa by HPSEC analysis. Linkage analysis contained 3-Glcp, 3-Manp, terminal Glcp and terminal Manp, as well as a small proportion of 3- and 3,4-Galp, and 4,6-Manp residues. Based on analyses using FT-IR and 13C NMR spectrometers, most glycosidic bonds joining these sugar residues are of the α-type, and acetyl groups are apparently attached to the polymer chain at random. 相似文献
105.
BBN (BaBi2Nb2O9) is very interesting and promising lead free material with relaxor properties in capacitors, sensors and actuators. 相似文献
106.
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
107.
A self-assembled monolayer (SAM) of p-hydroxymethylbenzene HOCH2C6H4 - (HOMB) moiety adsorbed on iron by the formation of a covalent bond between carbon and iron atoms was prepared by electrochemical derivatization of an iron electrode with p-hydroxymethylbenzenediazonium tetrafluoroborate HOCH2C6H4N2BF4. The electrode covered with the HOMB SAM was modified with alkyltriethoxysilanes CnH2n+1Si(OC2H5)3 (CnTES, n = 8 or 18) to prepare a film of one-dimensional polymer. The protective ability of the polymer film was determined by polarization measurement of the covered electrode in an aerated 0.5 M NaCl solution. The ability was enhanced by modification of the HOMB SAM with CnTES markedly. The iron surface coated with the one-dimensional polymer film of the HOMB SAM modified with C8TES was characterized by contact angle measurement and FTIR reflection and X-ray photoelectron spectroscopies. The persistence in the protective ability of the polymer film against iron corrosion in 0.5 M NaCl may be associated with the strong adsorption via the covalent bond, revealed by electron-probe microanalysis. 相似文献
108.
Recent advances in isotropic conductive adhesives for electronics packaging applications 总被引:4,自引:0,他引:4
Isotropic conductive adhesives (ICAs) have recently received a lot of focus and attention from the researchers in electronics industry as a potential substitute to lead-bearing solders. Numerous studies have shown that ICAs possess many advantages over conventional soldering such as environmental friendliness, finer pitch printing, lower temperature processing and more flexible and simpler processing. However, complete replacement of soldering by ICAs is yet not possible owing to several limitations of ICAs which are mainly related to reliability aspects like limited impact resistance, unstable contact resistance, low adhesion and conductivity etc. Continued efforts for last 15 years have resulted in development of ICAs with improved properties. This review article is aimed at providing a better understanding of ICAs, their principles, performance and significant research and development work addressing the technological utility of ICAs. 相似文献
109.
No authorship indicated 《Canadian Metallurgical Quarterly》2005,41(1):291
Presents a brief tribute to Irving B. Harris upon his passing. Harris played a central role in launching the Harris School of Public Policy Studies and the Center for Human Potential and Public Policy at the University of Chicago. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
110.
陆建明 《数字社区&智能家居》2005,(17)
本文利用Windows的API函数将VB窗体前置,避免教师在CAI过程中频繁切换活动窗口,并通过VB控件将各种不同的电子文档内容在窗体中显示出来。 相似文献