全文获取类型
收费全文 | 185366篇 |
免费 | 24399篇 |
国内免费 | 23247篇 |
专业分类
电工技术 | 18517篇 |
技术理论 | 8篇 |
综合类 | 13120篇 |
化学工业 | 38435篇 |
金属工艺 | 7579篇 |
机械仪表 | 12019篇 |
建筑科学 | 8495篇 |
矿业工程 | 2128篇 |
能源动力 | 5974篇 |
轻工业 | 13518篇 |
水利工程 | 2404篇 |
石油天然气 | 4109篇 |
武器工业 | 1934篇 |
无线电 | 28259篇 |
一般工业技术 | 20475篇 |
冶金工业 | 3947篇 |
原子能技术 | 3246篇 |
自动化技术 | 48845篇 |
出版年
2024年 | 514篇 |
2023年 | 2937篇 |
2022年 | 4961篇 |
2021年 | 6932篇 |
2020年 | 6424篇 |
2019年 | 5826篇 |
2018年 | 5366篇 |
2017年 | 7434篇 |
2016年 | 8212篇 |
2015年 | 9576篇 |
2014年 | 9255篇 |
2013年 | 12438篇 |
2012年 | 14314篇 |
2011年 | 16170篇 |
2010年 | 11642篇 |
2009年 | 11448篇 |
2008年 | 12697篇 |
2007年 | 14082篇 |
2006年 | 13463篇 |
2005年 | 11531篇 |
2004年 | 9743篇 |
2003年 | 7657篇 |
2002年 | 5846篇 |
2001年 | 4417篇 |
2000年 | 3674篇 |
1999年 | 3065篇 |
1998年 | 2550篇 |
1997年 | 2042篇 |
1996年 | 1536篇 |
1995年 | 1331篇 |
1994年 | 1182篇 |
1993年 | 884篇 |
1992年 | 709篇 |
1991年 | 577篇 |
1990年 | 488篇 |
1989年 | 359篇 |
1988年 | 277篇 |
1987年 | 173篇 |
1986年 | 168篇 |
1985年 | 224篇 |
1984年 | 194篇 |
1983年 | 141篇 |
1982年 | 193篇 |
1981年 | 94篇 |
1980年 | 95篇 |
1979年 | 23篇 |
1978年 | 15篇 |
1977年 | 23篇 |
1976年 | 14篇 |
1959年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 22 毫秒
991.
Yu. V. Raskovalov E. M. Tolstikova 《Power Technology and Engineering (formerly Hydrotechnical Construction)》2006,40(4):258-261
A set of measures that can be implemented by the Relay-Protection and Automated-Equipment Service for Centralized Dispatch
Regulation (CDR) in Siberia to determine the location of damage sustained by inter-system 550-and 220-kV transmission lines
maintained by the United Power System (UPS) of Siberia, and the methodology and technology of damage-location determination
(DLD) are described. The damage sustained by the 500-kV high-voltage lines (HL), and the accuracy of DLD relative to zero-sequence
emergency parameters are analyzed statically.
__________
Translated from élektricheskie Stantsii, No. 5, pp. 59–62, May, 2006. 相似文献
992.
993.
The photografting of methacrylic acid (MAA) on a linear low‐density polyethylene film (thickness = 30 μm) under air and nitrogen atmospheres was investigated at 60°C in mixed solvents consisting of water and an organic solvent, with xanthone as a photoinitiator. The organic solvents used were acetone, methanol, tetrahydrofuran, and dioxane. A maximum percentage of grafting occurred at a certain concentration of the organic solvent in the mixed solvent. This was observed for the systems under both air and nitrogen. The grafting reaction under air exhibited an induction period, but the rate of grafting after the period was greater than that under nitrogen. The formation of poly(ethylene peroxide)s by photoirradiation seemed to be a factor for the accelerated photografting under air. On the basis of attenuated total reflection infrared spectroscopy and scanning electron microscopy of the grafted film, the MAA‐grafted chains of the sample prepared under air tended to penetrate more deeply inside the film than those of the sample prepared under nitrogen. The resulting grafted films exhibited a pH‐responsive character: the grafted films shrank in an acidic medium but swelled in alkaline medium. This was evaluated from measurements of dimensional changes in the grafted films. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 992–998, 2003 相似文献
994.
本文介绍了差分光学吸收光谱法(DOAS)测量大气污染气体浓度的基本原理。DOAS方法就是利用氙灯发出的紫外—可见光,经望远镜准直后再经过一段距离的传输,由望远镜来接收.在传输中,由于各种不同的分子在不同的波段对光有不同的吸收特征,使光谱具有了污染物的特征,再通过与光源发出的光进行比较,反演这些气体在大气中浓度.我们将DOAS方法应用在监测有机物上,在分析光谱的过程中,应用多项式拟合和最小二乘法,从而精确地从测量光谱中来反演出大气中污染气体的浓度.文中用DOAS方法测量了苯和甲苯的样品,并分析了结果,结果和理论吻合.可为环境中有机污染物监测提供可靠的方法。 相似文献
995.
EPON技术具有大带宽、高性价比、结构简单和一定服务质量保证等特点,被业界普遍看好,成为 下一代接入网的最佳候选技术.本文主要介绍了EPON的工作原理、分层结构、接入控制和组帧方式,最后给出 了实现EPON的关键技术和难点以及EPON的发展近况. 相似文献
996.
We studied the rates of gelation and phase separation of poly(vinyl alcohol) (PVA) solutions in mixtures of dimethyl sulfoxide (DMSO) and water at 25 °C and found that both the rates show a maximum at a volume fraction of DMSO φDMSO=0.60 while gelation was not observed either in pure DMSO or pure water, suggesting that water-DMSO is a cononsolvent system for PVA. On the basis of the data by Cowie [Can J Chem 36 (1961) 2240] we concluded that the 1:2 stable complex between one DMSO molecule and two water molecules is the main cause of this cononsolvency. 相似文献
997.
采用两步溶胶–凝胶法制备出 ATO(掺锑氧化锡)-SiO_2复合抗静电薄膜。通过 DTA-TG、XRD、SEM 对 薄膜的结构和形貌进行了表征,结果表明:抗静电复合薄膜表面均匀致密。薄膜中 SiO_2为无定形结构,ATO 的衍射峰 与 SnO_2一致。研究了 SnO_2的含量对薄膜导电性能、结合强度和透过率的影响,发现随 SnO_2含量增加 ?(SnO_2/ SiO_2)从 5 至 12.5,薄膜的表面电阻降低(从 1010ù/□降低到 108ù/□),薄膜的结合强度下降,薄膜的透过率降低(从 89.0%降至 84.2%),结合三方面性能,得出最佳 SnO_2的配比为:?(SnO_2/ SiO_2)=10。 相似文献
998.
999.
Poly(ethylene oxide) (PEO) star polymers were prepared by anionic polymerization of methacryloyl chloride and glyceryl trimethacrylate with sec‐butyllithium in cyclohexane. The ensuing polymers were grafted with poly(ethylene glycol) of molecular weight 400. The final product was washed with methylene chloride and analyzed with infrared spectroscopy, differential scanning calorimetry, and thermogravimetry. Star polymers of PEO were also prepared by anionic polymerization of glycidol with sec‐butyllithium in cyclohexane. The initiator was chosen so as to yield a polymer of 10,000 molecular weight. The resulting polymers were analyzed by nuclear magnetic resonance, infrared spectroscopy, and thermogravimetry. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 322–327, 2003 相似文献
1000.