全文获取类型
收费全文 | 117309篇 |
免费 | 10134篇 |
国内免费 | 5417篇 |
专业分类
电工技术 | 7069篇 |
技术理论 | 11篇 |
综合类 | 7793篇 |
化学工业 | 19361篇 |
金属工艺 | 6746篇 |
机械仪表 | 7566篇 |
建筑科学 | 9555篇 |
矿业工程 | 3564篇 |
能源动力 | 3514篇 |
轻工业 | 7788篇 |
水利工程 | 2298篇 |
石油天然气 | 7243篇 |
武器工业 | 1000篇 |
无线电 | 13021篇 |
一般工业技术 | 14219篇 |
冶金工业 | 5658篇 |
原子能技术 | 1495篇 |
自动化技术 | 14959篇 |
出版年
2024年 | 482篇 |
2023年 | 1943篇 |
2022年 | 3340篇 |
2021年 | 4705篇 |
2020年 | 3602篇 |
2019年 | 3135篇 |
2018年 | 3545篇 |
2017年 | 3915篇 |
2016年 | 3595篇 |
2015年 | 4618篇 |
2014年 | 6027篇 |
2013年 | 6933篇 |
2012年 | 7872篇 |
2011年 | 8375篇 |
2010年 | 7340篇 |
2009年 | 7023篇 |
2008年 | 6766篇 |
2007年 | 6473篇 |
2006年 | 6333篇 |
2005年 | 5441篇 |
2004年 | 3867篇 |
2003年 | 3498篇 |
2002年 | 3339篇 |
2001年 | 3080篇 |
2000年 | 2832篇 |
1999年 | 2902篇 |
1998年 | 2149篇 |
1997年 | 1786篇 |
1996年 | 1636篇 |
1995年 | 1443篇 |
1994年 | 1134篇 |
1993年 | 864篇 |
1992年 | 674篇 |
1991年 | 507篇 |
1990年 | 447篇 |
1989年 | 313篇 |
1988年 | 274篇 |
1987年 | 153篇 |
1986年 | 161篇 |
1985年 | 86篇 |
1984年 | 65篇 |
1983年 | 42篇 |
1982年 | 46篇 |
1981年 | 29篇 |
1980年 | 19篇 |
1979年 | 13篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1970年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
E. Q. Xie W. W. Wang N. Jiang D. Y. He Department of Physics Lanzhou University Lanzhou China 《金属学报(英文版)》2002,15(2):221-226
1. IntroductionThe transition metal silicides have attraeted much attention because of their potentialapplicatiOIl in very large scale integration (VLSI) de.ice[1]. Near-noble metal silicides canbe used as Schottky al1d ohn1ic col1tacts in silicon-based d… 相似文献
73.
合成4种标题配合物,用元素分析、红外和紫外光谱、摩尔电导、核磁共振氢谱、荧光光谱及X射线粉末衍射物相分析研究了它们的组成和性质及其结构。按结构将配合物分为两类,一是含氢键的离子缔合物;一是含金属—氧键的螯环型配合物。 相似文献
74.
本文阐述了新型酚醛玻璃钢风道的成型工艺、开发过程,并与传统玻璃钢风道作了比较,论述了新型酚醛玻璃钢风道的优点,并对其应用前景和对铁路客车的设计思路的影响进行了探讨。 相似文献
75.
Electron Emission from Barium Strontium Titanate Ceramics 总被引:1,自引:0,他引:1
Shutao Chen Xianlin Dong Shuxin Zheng Ziqiu Zhu Chuanxiang Tang 《Journal of the American Ceramic Society》2006,89(7):2118-2122
This paper focuses on understanding the influence of materials' properties on the ferroelectric electron emission. Ferroelectric ( x =1.0 and 0.8) and paraelectric ( x =0.67 and 0.5) compositions of barium strontium titanate (Ba x Sr(1− x ) TiO3 ) system were chosen for study based on their different ferroelectric and dielectric properties. Similar emission current waveforms were obtained from four compositions with negative triggering voltage applied to the rear electrode of the samples. It was difficult to explain the experimental results using the spontaneous polarization-switching model. The mechanism of electron emission from Ba x Sr(1− x ) TiO3 ceramics was ascertained to surface plasma emission. 相似文献
76.
77.
A series of phosphorus‐containing, wholly aromatic thermotropic copolyesters from acetylated 2‐(6‐oxide‐6H‐dibenz〈c,e〉〈1,2〉oxa phosphorin‐6‐yl)‐1,4‐dihydroxy phenylene, p‐acetoxybenzoic acid, terephthalic acid, and isophthalic acid were prepared by melting polycondensation. The structure and basic properties of the polymers, such as the glass‐transition temperature (Tg), melting temperature (Tm), thermal stability, crystallinity, and liquid crystallinity, were investigated with Fourier transform infrared, elemental analysis, differential scanning calorimetry (DSC), thermogravimetric analysis, wide‐angle X‐ray diffraction, and hot‐stage polarizing optical microscopy. The copolyesters had relatively high Tg values ranging from 183 to 192°C. The Tm values obtained from DSC curves for samples P‐20 and P‐25 were 290 and 287°C, respectively (where the number in the sample name indicates the molar fraction of the phosphorus‐containing monomer in the reactants). The initial flow temperatures of other samples observed with hot‐stage polarizing microscopy were 271–290°C. The 5% degradation temperatures in nitrogen ranged from 431 to 462°C, and the char yields at 640°C were 41–52%. All the copolyesters, except P‐40, were thermotropic and nematic. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1278–1284, 2002 相似文献
78.
Rui-Hong Liang Xian-Lin Dong Ying Chen Fei Cao Yong-Ling Wang 《Journal of the American Ceramic Society》2006,89(10):3273-3276
Ba0.55 Sr0.45 TiO3 /MgO composites were successfully prepared by the heterogeneous precipitation method and their structural, surface morphological, tunable properties, and dielectric properties at microwave frequency were systemically investigated. Compared with the sample prepared by the traditional solid-state method, the sample prepared by the heterogeneous precipitation method exhibits a smaller grain size, more uniform microstructure, higher tunability, and lower microwave loss, and these properties are very beneficial to the development of the microwave tunable devices application. Moreover, the effects of La2 O3 doping on the dielectric and tunable properties of BST/MgO composites are investigated. The result shows that the La3+ -doped sample has higher tunability and lower microwave loss than the undoped one. 相似文献
79.
Behavioral cues to deception are instrumental in detecting deception. As one of the primary sources of deception behavior, text has been analyzed at the level of sub-sentence or message but not the discourse of interaction. Additionally, empirical studies on cues to deception in the case of multiple receivers remain nonexistent. To fill these voids, we propose a discourse framework and six hypotheses about deception behaviors in a multi-receiver environment. The deception behaviors are operationalized by discourse features based on an analysis of real-world data. The results of statistical analysis validate the efficacy of discourse features in discriminating deceivers from truth-tellers. 相似文献
80.
Poly(vinyl chloride)/wood fiber (flour) composites are currently experiencing a dramatic increase in use. Most of them are used to produce window/door profiles, decking, railing, and siding by using conical counterrotating intermeshing twin‐screw extruders. Heat stabilizers, processing aids, impact modifiers, lubricants, and pigments are still important for PVC/wood composite formulations. Poly[methylene(polyphenyl isocyanate)] (PMPPIC), γ‐aminopropyltriethoxysilane, maleated polypropylene (MAPP), and copper metallic complex have proved to be effective coupling agents for this composite system. Mechanical properties of PVC/wood composites can be enhanced by combining wood with mica or glass fibers to form hybrid reinforcements. Ultraviolet light resistance and weathering dimensional stabilities of PVC/wood composites are superior to those of natural wood. Density reduction can be achieved through the microcellular foaming technique by using chemical blowing agents, such as azodicarbonamide and sodium bicarbonate, or physical blowing agents, such as carbon dioxide. J. Vinyl Addit. Technol. 10:59–69, 2004. © 2004 Society of Plastics Engineers. 相似文献