全文获取类型
收费全文 | 122774篇 |
免费 | 3080篇 |
国内免费 | 2067篇 |
专业分类
电工技术 | 2984篇 |
综合类 | 1496篇 |
化学工业 | 13963篇 |
金属工艺 | 6808篇 |
机械仪表 | 4335篇 |
建筑科学 | 3531篇 |
矿业工程 | 914篇 |
能源动力 | 3430篇 |
轻工业 | 7363篇 |
水利工程 | 1051篇 |
石油天然气 | 2155篇 |
武器工业 | 213篇 |
无线电 | 18010篇 |
一般工业技术 | 24309篇 |
冶金工业 | 26287篇 |
原子能技术 | 1564篇 |
自动化技术 | 9508篇 |
出版年
2023年 | 545篇 |
2022年 | 999篇 |
2021年 | 1558篇 |
2020年 | 1194篇 |
2019年 | 1242篇 |
2018年 | 1707篇 |
2017年 | 1777篇 |
2016年 | 1739篇 |
2015年 | 1770篇 |
2014年 | 2538篇 |
2013年 | 5812篇 |
2012年 | 3811篇 |
2011年 | 5270篇 |
2010年 | 4308篇 |
2009年 | 4892篇 |
2008年 | 4943篇 |
2007年 | 5236篇 |
2006年 | 4798篇 |
2005年 | 4275篇 |
2004年 | 3769篇 |
2003年 | 3544篇 |
2002年 | 3198篇 |
2001年 | 3423篇 |
2000年 | 3178篇 |
1999年 | 3599篇 |
1998年 | 9814篇 |
1997年 | 6497篇 |
1996年 | 5065篇 |
1995年 | 3446篇 |
1994年 | 3027篇 |
1993年 | 2887篇 |
1992年 | 1755篇 |
1991年 | 1670篇 |
1990年 | 1577篇 |
1989年 | 1368篇 |
1988年 | 1222篇 |
1987年 | 889篇 |
1986年 | 906篇 |
1985年 | 925篇 |
1984年 | 814篇 |
1983年 | 709篇 |
1982年 | 709篇 |
1981年 | 686篇 |
1980年 | 568篇 |
1979年 | 476篇 |
1978年 | 414篇 |
1977年 | 533篇 |
1976年 | 958篇 |
1975年 | 299篇 |
1974年 | 276篇 |
排序方式: 共有10000条查询结果,搜索用时 625 毫秒
991.
992.
Taking into consideration the knock-on cascade mechanism and the free volume theory, the cooling condition dependentR
s (ion etching rate) is investigated for a liquid-quenched Fe-10at%Si-15at%B alloy glass. A highR
s is found in a slow cooled glass. 相似文献
993.
Matan O. Baird H.S. Bromley J. Burges C.J.C. Denker J.S. Jackel L.D. Le Cun Y. Pednault E.P.D. Satterfield W.D. Stenard C.E. Thompson T.J. 《Computer》1992,25(7):59-63
A neural network algorithm-based system that reads handwritten ZIP codes appearing on real US mail is described. The system uses a recognition-based segmenter, that is a hybrid of connected-components analysis (CCA), vertical cuts, and a neural network recognizer. Connected components that are single digits are handled by CCA. CCs that are combined or dissected digits are handled by the vertical-cut segmenter. The four main stages of processing are preprocessing, in which noise is removed and the digits are deslanted, CCA segmentation and recognition, vertical-cut-point estimation and segmentation, and directly lookup. The system was trained and tested on approximately 10000 images, five- and nine-digit ZIP code fields taken from real mail 相似文献
994.
Kim S. Jeong S. Lee Y.T. Kim D.-H. Lim J.-S. Seo K.-S. Nam S. 《Electronics letters》2002,38(13):622-623
A new ultra-wideband, low-loss and small-size coplanar waveguide (CPW) to coplanar strip (CPS) transition which can be used from DC to 110 GHz is presented. The proposed transition connects CPW with CPS by the reformed air-bridge. Two ground planes of CPW are tied at their ends by a line and the centre of the line is connected to the ground strip of CPS by another line. Owing to the symmetry of the proposed structure, the currents of two ground planes of CPW are combined with the same phase and transferred to the ground strip of CPS. With height of 3 μm, the signal line of CPW passes over two connecting lines and is connected to the signal strip of CPS. For the back-to-back transition structure, insertion loss <1 dB and return loss >15 dB are obtained from 0.5 to 110 GHz 相似文献
995.
We have performed selective area epitaxy (SAE) of CdTe layers grown by molecular beam epitaxy using a shadow mask technique.
This technique was chosen over other SAE techniques due to its simplicity and its compatibility with multiple SAE patterning
steps. Features as small as 50 microns × 50 microns were obtained with sharp, abrupt side walls and flat mesa tops. Separations
between mesas as small as 20 microns were also obtained. Shadowing effects due to the finite thickness of the mask were reduced
by placing the CdTe source in a near normal incidence position. Intimate contact between the mask and the substrate was essential
in order to achieve good pattern definition. 相似文献
996.
We generated plasmid expression vectors encoding ubiquitin and beta-galactosidase (beta-gal) with different intervening amino acids, allowing for the production of processed protein products that have either stabilizing or destabilizing residues at their N-termini. P815 cells transfected with plasmids encoding beta-gal with a destabilizing N-terminus did not have detectable expression beta-gal unless they were treated with inhibitors specific for the proteasome. Inhibitors of other proteolysis pathways had no such effect. Nevertheless, transfectants expressing beta-gal with different amino acid residues were equally sensitive to cytolysis by a CTL clone specific for a beta-gal peptide presented in the context of H-2Ld. In contrast to vectors encoding native beta-gal, plasmid vectors encoding beta-gal with a destabilizing residue did not induce detectable anti-beta-gal Abs when injected into skeletal muscle of BALB/c mice. However, such vectors were significantly more effective than vectors encoding native beta-gal or beta-gal with a stabilizing residue in stimulating CTL specific for P13.2, a lacZ transfectant of P815. We conclude that incorporation of strategies that enhance proteasome-dependent degradation may generate DNA vaccines that are more effective in inducing cellular immunity against targeted Ags. 相似文献
997.
Courteville A. Gharbi T. Cornu J.Y. 《IEEE transactions on bio-medical engineering》1998,45(2):145-150
A high-sensitivity human muscle-vibration measurement (MMG) sensor adapted to clinical use is presented. The muscle vibration phenomenon is modeled and investigated to optimize the measurement technique. The sensor uses an acoustic impedance adaptation technique to convert the skin surface vibration in terms of acoustic pressure, which is sensed by a microphone. The device is calibrated and gives the real amplitude of the vibration. It is also well fitted to measure other physiological vibrations in the 2 Hz-1 kHz range 相似文献
998.
Y. Itoh Y. Mitsunaka K. Sakamoto T. Nagashima 《Journal of Infrared, Millimeter and Terahertz Waves》1992,13(9):1353-1359
An experiment was carried out for transforming the 120 GHz-TE12.2 whispering-gallery mode (WGM) into a circularly polarized hollow radiation beam. A hollow beam was formed by reflecting the WGM, which was radiated from a 16 mm radius circular waveguide cut, with an annular mirror having suitable local normal vectors. The experimentally observed field intensity profiles of the reflected wave were in good agreement with calculated results. 相似文献
999.
1000.
Measurements of the thermal diffusivity of thin films on substrate have been performed by the photoacoustic method. In order to examine the method we have built a new apparatus and proposed (1) a system calibration procedure using optically and thermally thick reference samples and (2) a data analysis procedure based on the RG (Rosencwaig and Gersho) theory. As a result of using a transparent photoacoustic cell, the systematic errors which are caused by stray light have been reduced. With this apparatus, measurements have been performed on platinum, titanium, and stainless steel (SUS304) thin foils (thickness form 50 to 100 µm) with three different liquid backing materials (water, glycerol, and ethyl alcohol). The reproducibility was within ±7% regardless of film thickness and substrate materials. 相似文献