全文获取类型
收费全文 | 127029篇 |
免费 | 23405篇 |
国内免费 | 5583篇 |
专业分类
电工技术 | 8149篇 |
技术理论 | 5篇 |
综合类 | 7334篇 |
化学工业 | 29729篇 |
金属工艺 | 5527篇 |
机械仪表 | 6864篇 |
建筑科学 | 9938篇 |
矿业工程 | 2482篇 |
能源动力 | 3397篇 |
轻工业 | 14008篇 |
水利工程 | 2309篇 |
石油天然气 | 4073篇 |
武器工业 | 928篇 |
无线电 | 17733篇 |
一般工业技术 | 20882篇 |
冶金工业 | 3857篇 |
原子能技术 | 1225篇 |
自动化技术 | 17577篇 |
出版年
2024年 | 518篇 |
2023年 | 1648篇 |
2022年 | 3189篇 |
2021年 | 4580篇 |
2020年 | 4580篇 |
2019年 | 5493篇 |
2018年 | 5547篇 |
2017年 | 6281篇 |
2016年 | 6491篇 |
2015年 | 7589篇 |
2014年 | 8519篇 |
2013年 | 10368篇 |
2012年 | 9211篇 |
2011年 | 9167篇 |
2010年 | 8839篇 |
2009年 | 8552篇 |
2008年 | 8010篇 |
2007年 | 7349篇 |
2006年 | 6827篇 |
2005年 | 5589篇 |
2004年 | 4274篇 |
2003年 | 3926篇 |
2002年 | 4153篇 |
2001年 | 3699篇 |
2000年 | 3119篇 |
1999年 | 2134篇 |
1998年 | 1166篇 |
1997年 | 1036篇 |
1996年 | 914篇 |
1995年 | 734篇 |
1994年 | 597篇 |
1993年 | 410篇 |
1992年 | 337篇 |
1991年 | 246篇 |
1990年 | 177篇 |
1989年 | 160篇 |
1988年 | 121篇 |
1987年 | 91篇 |
1986年 | 64篇 |
1985年 | 49篇 |
1984年 | 29篇 |
1983年 | 24篇 |
1982年 | 26篇 |
1981年 | 19篇 |
1980年 | 25篇 |
1979年 | 16篇 |
1962年 | 42篇 |
1961年 | 39篇 |
1960年 | 16篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A study to evaluate the tensile mechanical properties of sulfonated poly(ether ether ketone) (SPEEK) and BPO4/SPEEK composite membranes has been carried out. It is aimed to give an assessment of these materials for applications in proton exchange membrane fuel cells. The stress–strain response of the membranes was measured as a function of the degree of sulfonation (DS) and the filler–matrix ratio. In addition, the effects of immersion in water at various temperatures were explored in situ by means of a homemade testing chamber fitted to the tensile analyzer. The results indicate that the DS has an important influence on the final mechanical behavior of the membranes. The introduction of the BPO4 solid filler leads to deterioration in mechanical performance compared to unfilled SPEEK. A general picture of the microstructural features influencing the mechanical properties of SPEEK and BPO4/SPEEK membranes is proposed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2380–2393, 2005 相似文献
992.
HN型催化剂催化α——蒎烯制苎烯的初步研究 总被引:2,自引:0,他引:2
本文用HN型催化剂低温催化α-蒎烯异构化制苎烯,考察了反应温度、反应时间、催化剂种类对反应结果的影响。实验结果表明在70℃、反应4h以上,苎烯的选择性仍保持在35%以上。 相似文献
993.
994.
光引发剂噻吨酮ITX的合成研究 总被引:2,自引:0,他引:2
以二硫代二苯甲酸(DTSA)经过酰氯化、氯代、然后与异丙苯在三氧化铝催化下缩合成为光引发剂。研究了反应时间、反应温度、配料比对反应的影响,得到了最佳反应条件。 相似文献
995.
996.
997.
K. C. Cole C. Depecker M. Jutigny J.‐M. Lefebvre P. Krawczak 《Polymer Engineering and Science》2004,44(2):231-240
Infrared spectroscopy was used to study the evolution of structure in films of polyamide‐6 drawn on a Cellier tenter frame laboratory tester under conditions of simultaneous equibiaxial stretching and planar uniaxial stretching. The “tilted film” method was used to obtain trichroic spectra corresponding to the machine, transverse, and normal directions, as well the “structural factor” spectrum. From these it was possible to obtain information on the molecular orientation and the evolution of the crystalline structure. The starting films, prepared by melt casting from an extruder on a chilled roll, contained predominantly the mesomorphic β form. The structural factor spectra confirmed that strain‐induced transformation into the α form occurred upon drawing, and that the amount of α form increased with the extent of drawing. The trichroic spectra showed that the molecular orientation was localized mainly, but not exclusively, in the α form. Orientation functions could be determined for both the molecular chain axis and the normal to the hydrogen‐bonded sheets. For both the equibiaxial and planar uniaxial films, these sheets were found to be strongly oriented parallel to the plane of the film, with the degree of orientation increasing with overall draw ratio. For the biaxial samples, the molecular chain orientation was found to be equibiaxial, as expected. Mechanical test results indicated that the chains are evenly distributed in the film plane rather than showing a preference for the two orthogonal draw directions. For the planar uniaxial samples, the chain orientation was predominantly in the draw direction, but some degree of orientation in the transverse direction was also observed. The variation of orientation functions with draw ratio suggested that the α structure evolves in two stages, the first involving chain orientation in the draw direction and the second involving rotation of the sheets into the plane of the film. 相似文献
998.
Preparation of fluoroacrylate nanocopolymer by miniemulsion polymerization used in textile finishing
Latex based on fluoroacrylate (TAN) and other comonomers was prepared via miniemulsion polymerization in the presence of stearyl trimethyl ammonium chloride (STAC) and 2, 2′‐azobis (2‐amidinopropane) dihydrochloride (ABAP) as a water soluble initiator. Light transmittance studies demonstrated that the light transmittance of prepared emulsions increases with the amount of TAN, STAC, cosolvent DPM, and hydrophobe DM. Given suitable reaction temperature and quantities of TAN, STAC, DPM, and DM, a copolymer emulsion of fluoroacylate with a particle size of 50 nm was produced. The water repellency tested on polyester fabrics displayed greater effectiveness than that of commercial products with higher fluorine content. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1466–1472, 2004 相似文献
999.
介绍了以山西运城南风自产芒硝为原料生产精制元明粉的几种工艺,以及国内外精制元明粉的市场及生产状况.精制工艺包括化学除杂法、原料优选法、重结晶法.结果表明,精制元明粉的生产过程实质是一个除杂、提纯过程:对于钙离子含量高的原料,可采用化学除杂法;对于氯离子含量高的原料,可采用氯离子富集法、冷冻法或洗涤法;镁离子较难去除,可采用水硝洗涤、冷冻法. 相似文献
1000.
低截留分子质量新型聚芳醚腈酮超滤膜的研制 总被引:7,自引:0,他引:7
以新型聚芳醚腈酮为膜材料 ,以N -甲基 - 2 -吡咯烷酮 (NMP)为溶剂 ,研究了聚合物浓度、添加剂种类及含量、凝胶浴温度等对超滤膜性能的影响。结果表明 ,聚合物质量分数以 1 2 %~ 1 3 %为合适的制膜浓度 ,以聚乙二醇PEG - 4 0 0为添加剂时获得了高截留率和高水通量的超滤膜。随着凝胶浴温度的升高 ,水通量明显增大 ,而截留率有所下降 ,而共聚物的浓度增加则有相反的效果。制得的超滤膜具有较低的截留分子量 (PEG- 2 0 0 0 ) ,将制得的超滤膜用于达旦黄、黄X-G等染料的分离 ,截留率均达 90 %以上 相似文献