全文获取类型
收费全文 | 408849篇 |
免费 | 39762篇 |
国内免费 | 15418篇 |
专业分类
电工技术 | 21940篇 |
技术理论 | 58篇 |
综合类 | 23462篇 |
化学工业 | 77330篇 |
金属工艺 | 21075篇 |
机械仪表 | 24387篇 |
建筑科学 | 30994篇 |
矿业工程 | 12275篇 |
能源动力 | 11698篇 |
轻工业 | 28881篇 |
水利工程 | 6724篇 |
石油天然气 | 24779篇 |
武器工业 | 2989篇 |
无线电 | 47484篇 |
一般工业技术 | 53429篇 |
冶金工业 | 20459篇 |
原子能技术 | 3852篇 |
自动化技术 | 52213篇 |
出版年
2024年 | 1601篇 |
2023年 | 6088篇 |
2022年 | 10605篇 |
2021年 | 15074篇 |
2020年 | 12568篇 |
2019年 | 11888篇 |
2018年 | 13128篇 |
2017年 | 14845篇 |
2016年 | 13929篇 |
2015年 | 17465篇 |
2014年 | 21585篇 |
2013年 | 26154篇 |
2012年 | 25367篇 |
2011年 | 27558篇 |
2010年 | 24221篇 |
2009年 | 23132篇 |
2008年 | 22251篇 |
2007年 | 21420篇 |
2006年 | 21969篇 |
2005年 | 19142篇 |
2004年 | 12990篇 |
2003年 | 11765篇 |
2002年 | 10975篇 |
2001年 | 9900篇 |
2000年 | 9902篇 |
1999年 | 10823篇 |
1998年 | 8682篇 |
1997年 | 7172篇 |
1996年 | 6695篇 |
1995年 | 5582篇 |
1994年 | 4615篇 |
1993年 | 3263篇 |
1992年 | 2629篇 |
1991年 | 2082篇 |
1990年 | 1604篇 |
1989年 | 1303篇 |
1988年 | 1085篇 |
1987年 | 714篇 |
1986年 | 573篇 |
1985年 | 358篇 |
1984年 | 258篇 |
1983年 | 216篇 |
1982年 | 209篇 |
1981年 | 138篇 |
1980年 | 144篇 |
1979年 | 81篇 |
1978年 | 42篇 |
1977年 | 42篇 |
1976年 | 61篇 |
1975年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Shufang Wang Yuanhui Ma Yanji Wang Wei Xue Xinqiang Zhao 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(11):1466-1471
BACKGROUND: A single‐step conversion of nitrobenzene (NB) to p‐aminophenol (PAP) through catalytic hydrogenation is a widely used synthesis route for PAP. The main shortcoming of this route is the use of sulfuric acid for rearrangement of the phenylhydroxylamine (PHA) intermediate. In this paper, S2O82?/ZrO2 (PSZ) solid acid and Pt‐S2O82?/ZrO2 (Pt‐PSZ) bifunctional catalysts were prepared for the synthesis of PAP in non‐acid medium. RESULTS: Calcination temperature has a substantial effect on the acidity, structure and activity for PHA rearrangement of PSZ. The highest PAP yield was 33.8% over PSZ calcined at 823 K when the reaction was carried out in water at 423 K. A high PAP yield of 23.9% was achieved by a single‐step reaction of nitrobenzene over Pt‐PSZ bifunctional catalysts. CONCLUSION: PSZ solid acid exhibits high activity for PHA rearrangement. Perfect tetragonal ZrO2 and much stronger acid sites play important roles in catalytic activity. Inhibiting the hydrogenation activity by reducing the amount of Pt loading on Pt‐PSZ can improve the competition of PHA rearrangement on acid sites with hydrogenation of PHA on metal active sites, resulting in better selectivity to PAP. Copyright © 2008 Society of Chemical Industry 相似文献
992.
993.
Xinsheng Zhu Hansong Xu Jianmei Lu Juying Wang Shunhua Zhou 《Journal of Polymer Research》2008,15(4):295-300
Poly(ethylene terephthalate) (PET) is of excellent mechanical properties and melt processability and is widely used as raw
material for textile fibers. However, the flame retardant properties of PET were rather poor, and both reactive and additive
phosphorus- and halogen-containing compounds have been employed to enhance the reaction-to-fire properties while the meltdripping
behaviour during burning hasn’t been handled properly with the flame retardants. In this work, fluoropolymer was blended with
both pure PET (pPET) and reactive phosphorus-containing flame retarded copolyester (fPET), and the flame retardance and char
formation and mechanical properties of the resulted pPET and fPET blends were investigated. The tensile strengths of modified
pPET samples were worsen whereas those of modified fPET samples were improved at low concentrations. The initial thermal degradation
in nitrogen was accelerated remarkably for the two polyesters with fluoropolymer. The oxygen indices of the all modified samples
were reduced while char formation and meltdripping suppression were encouraged. The apparent melt viscosity and elasticity
for the two polyesters were gained much with antidripping agent. Therefore, fluoropolymer improved char formation of the two
polyesters based on the gaseous phase mechanism while the partial suppression of meltdripping behavior and the decrease of
mechanical properties mainly originated from the increase of melt viscosity via fibrillation for pPET. 相似文献
994.
995.
Ying‐Hung So 《Polymer International》2006,55(2):127-138
Poly(2,4‐dimethyl‐1,4‐phenylene oxide) (PPO), poly(benzo[1,2‐d:5,4‐d′]bisoxazole‐2,6‐diyl‐1,4‐phenylene) (PBO) and poly(benzo[1,2‐d:4,5‐d′]bisthiazole‐2,6‐diyl‐1,4‐phenylene) (PBZT), which are polymers with extended conjugated structures, undergo a self‐sensitized photo‐induced electron‐transfer reaction. A second component is not required. This article presents many similar observations on these polymers when they are exposed to light and evidence to support the proposed photo‐induced electron‐transfer mechanism. Methods to stabilize these polymers against photo‐oxidation are also described. Workers investigating other conjugated polymeric systems may find the experimental methods, observations and polymer stabilization approaches discussed in this review useful. Copyright © 2005 Society of Chemical Industry 相似文献
996.
997.
稠油热采注汽管道由于长期在高温、高压下运行,极易发生各种损伤,如腐蚀、裂纹、材料退化等,极易造成管道承压能力降低,发生失效事故。如何检测出潜在危险性缺陷,判断注汽管道能否继续使用,是保证注汽管道安全运行的关键问题。探讨了高温压力管道在线检测技术发展现状及其应用范围。 相似文献
998.
后浇带质量控制的措施 总被引:1,自引:0,他引:1
后浇带起着超长建筑的温度伸缩、高层建筑高层部分与裙房间沉降缝的作用,已普遍采用,但有些工程由于施工不当,设了后浇带起不到应有作用,本文就施工中如何采取有效措施,对后浇带的质量进行控制,作了探讨,以期能真正发挥后浇带的作用。 相似文献
999.
Kum‐Il Lee Yong‐Sik Yim Sang‐Wook Chung Jiaqiu Wei Jong Il Rhee 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(9):1036-1045
A two‐dimensional (2D) spectrofluorometer was used to monitor various fermentation processes with recombinant E coli for the production of 5‐aminolevulinic acid (ALA). The whole fluorescence spectral data obtained during a process were analyzed using artificial neural networks, ie self‐organizing map (SOM) and feedforward backpropagation neural network (BPNN). The SOM‐based classification of the whole spectral data has made it possible to qualitatively associate some process parameters with the normalized weights and variances, and to select some useful combinations of excitation and emission wavelengths. Based on the classified fluorescence spectra a supervised BPNN algorithm was used to predict some of the process parameters. It was also shown that the BPNN models could elucidate some sections of the process's performance, eg forecasting the process's performance. Copyright © 2005 Society of Chemical Industry 相似文献
1000.
The simultaneous contrast effect is investigated in this article. A total of 174 and 154 test/induction combinations were studied for CRT and surface colours respectively. Each combination was assessed by nine observers using a matching technique. The test and induction colours used for CRT colours were similar to surface colours using fabric samples. The results indicated a strong lightness contrast effect for both CRT and surface media; that is, the lightness of a test colour surrounded by a lighter induction colour was reduced for both CRT and surface colours. However, the effect in CRT medium was more pronounced than in the surface medium. © 2004 Wiley Periodicals, Inc. Col Res Appl, 30, 13–20, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20074 相似文献