全文获取类型
收费全文 | 5791篇 |
免费 | 344篇 |
国内免费 | 124篇 |
专业分类
电工技术 | 20篇 |
综合类 | 273篇 |
化学工业 | 3813篇 |
金属工艺 | 46篇 |
机械仪表 | 48篇 |
建筑科学 | 73篇 |
矿业工程 | 31篇 |
能源动力 | 119篇 |
轻工业 | 582篇 |
水利工程 | 8篇 |
石油天然气 | 591篇 |
武器工业 | 9篇 |
无线电 | 54篇 |
一般工业技术 | 448篇 |
冶金工业 | 88篇 |
原子能技术 | 38篇 |
自动化技术 | 18篇 |
出版年
2024年 | 12篇 |
2023年 | 38篇 |
2022年 | 74篇 |
2021年 | 101篇 |
2020年 | 91篇 |
2019年 | 104篇 |
2018年 | 99篇 |
2017年 | 154篇 |
2016年 | 181篇 |
2015年 | 188篇 |
2014年 | 257篇 |
2013年 | 330篇 |
2012年 | 405篇 |
2011年 | 349篇 |
2010年 | 289篇 |
2009年 | 298篇 |
2008年 | 254篇 |
2007年 | 387篇 |
2006年 | 394篇 |
2005年 | 305篇 |
2004年 | 277篇 |
2003年 | 215篇 |
2002年 | 213篇 |
2001年 | 213篇 |
2000年 | 187篇 |
1999年 | 146篇 |
1998年 | 129篇 |
1997年 | 100篇 |
1996年 | 76篇 |
1995年 | 65篇 |
1994年 | 64篇 |
1993年 | 46篇 |
1992年 | 36篇 |
1991年 | 29篇 |
1990年 | 23篇 |
1989年 | 17篇 |
1988年 | 13篇 |
1987年 | 15篇 |
1986年 | 2篇 |
1985年 | 23篇 |
1984年 | 23篇 |
1983年 | 13篇 |
1982年 | 15篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1975年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有6259条查询结果,搜索用时 15 毫秒
991.
992.
993.
茉莉酸甲酯对鲜切苹果生理生化变化的影响 总被引:5,自引:0,他引:5
为研究茉莉酸甲酯(MeJA)对鲜切苹果生理生化变化的影响,将1cm3的鲜切富士苹果分别放入100、400、1600μmol/L的茉莉酸甲酯溶液中浸泡30min,包装后放入5℃冷库中贮藏。每2d测定各类酶活性以及与成熟衰老相关的指标等的变化。结果表明,经茉莉酸甲酯处理后,鲜切苹果的APX活性降低,但LOX、PAL、CAT、PPO、POD活性增加,相对电导率和丙二醛含量降低,说明茉莉酸甲酯处理启动了鲜切富士苹果的防御反应,导致相关防御反应的关键酶活性升高,从而降低机械伤害引发的自由基对细胞膜产生的伤害。研究认为,鲜切苹果贮前经适当浓度的茉莉酸甲酯溶液浸泡,可显著延长贮藏期和保持新鲜品质。 相似文献
994.
为探索鲜切果蔬保鲜的新途径,以鲜切水晶梨为试材,研究了不同浓度的茉莉酸甲酯对常温下贮藏的鲜切梨酶促褐变的影响。结果表明,梨经过鲜切后,相对电导率快速上升,多酚含量和PPO活性增加而发生酶促褐变,L^+值逐渐下降;而且切割伤害加剧了膜脂过氧化,进而诱导了POD、SOD、CAT活性的增加以清除过剩的自由基,提高果实的抗逆性。而茉莉酸甲酯处理保护了细胞膜结构,抑制了酚类物质外泄和PPO活性,减弱了酶促褐变的趋势;同时它也延缓了POD、SOD、CAT活性的上升以维持较长时间清除自由基的能力,从而推迟了膜脂过氧化的进程。尤其是1μmlol/L的茉莉酸甲酯处理更有效地保持了鲜切梨的贮藏品质,延迟了梨果实的衰老进程。 相似文献
995.
Yang Y Kapalavavi B Gujjar L Hadrous S Marple R Gamsky C 《International journal of cosmetic science》2012,34(5):466-476
Several high-temperature liquid chromatography (HTLC) and subcritical water chromatography (SBWC) methods have been successfully developed in this study for separation and analysis of preservatives contained in Olay skincare creams. Efficient separation and quantitative analysis of preservatives have been achieved on four commercially available ZirChrom and Waters XBridge columns at temperatures ranging from 100 to 200°C. The quantification results obtained by both HTLC and SBWC methods developed for preservatives analysis are accurate and reproducible. A large number of replicate HTLC and SBWC runs also indicate no significant system building-up or interference for skincare cream analysis. Compared with traditional HPLC separation carried out at ambient temperature, the HTLC methods can save up to 90% methanol required in the HPLC mobile phase. However, the SBWC methods developed in this project completely eliminated the use of toxic organic solvents required in the HPLC mobile phase, thus saving a significant amount of money and making the environment greener. Although both homemade and commercial systems can accomplish SBWC separations, the SBWC methods using the commercial system for preservative analysis are recommended for industrial applications because they can be directly applied in industrial plant settings. 相似文献
996.
Multiwalled carbon nanotube network (MWCNT‐N)/poly(methyl methacrylate) (PMMA ) composite is prepared by solution radical polymerization. The entangled multiwall carbon nanotube network (MWCNT‐N) is obtained by vacuum filtration and functionalized by allyl isocyanate to form polymerizable vinyl groups on a nanotube surface. The solution polymerization binds PMMA covalently to these groups and yields MWCNT‐N/PMMA composite manifesting electrical conduction and selective chemical vapor sensing. The latter property is evaluated in terms of affinity of organic solvent vapor and PMMA polarities. It is found that the affinity of acetone polarity with polarity of PMMA improves significantly the sensitivity of the composite to this solvent while the sensitivity to methanol is the same and to iso‐pentane even decreased in comparison with the corresponding property of MWCNT‐N. The composite selective response is favorable for a possible composite use as a sensing element and/or vapor switch. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
997.
An improved suspension polymerization method for preparation of the magnetic poly(methyl acrylate) microspheres (mPMA‐DVB) was investigated. Through subsequent reaction with methyl acrylate (MA) and ethylenediamine (EDA), the magnetic poly(methyl acrylate) microspheres with dendron surface was obtained, and the magnetic poly(methyl acrylate) microspheres with dendron surface reacted with carbon bisulfide and sodium hydroxide to create sodium dithiocarbamate. Following, the resultant magnetic microspheres with dendron surface modification were used to adsorb Au(III) from aqueous solution. The result showed that the capacity of amino groups on the surface of the mPMA microspheres increased from 1.67 mmol/g for the magnetic polymer microspheres with G0 dendron to 4.35 mmol/g with G3 dendron, and the adsorption capacity rose from 0.1981 g/g with G0 dendron to 0.7853 g/g with G3 dendron. The effects of solution pH, the adsorption temperature, the adsorption time, and the initial concentration of Au(III) on the adsorption of Au(III) were studied, the optimum pH for Au(III) adsorption was found at pH = 1, the adsorption capacity achieved the maximum in 60 min, and the adsorption process was endothermic reaction and conformed to pseudo‐second‐order kinetic models. Furthermore, the adsorption process was in accordance with the Langmuir model. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
998.
999.
1000.
把壳聚糖和羟丙甲基纤维素溶液相混合,通过相转化法成膜工艺制备壳聚糖和羟丙甲基纤维素共混膜,以猪大肠为黏附对象,考察在不同工艺条件下制得的CS/HPMC共混膜对猪大肠的黏附特征,研究结果表明:在越高温度下成膜,生物黏附性能越差;甘油的加入会使共混膜的生物黏附性能下降,当用量增加到0.2g时,生物黏附性能下降变得平缓;制膜液的浓度越高,所成膜的生物黏附性能越好;随着HPMC用量的增加,共混膜的生物黏附性能增强。并阐明CS/HPMC共混膜的生物黏附性能与在不同条件下成膜所得到的膜片材料结构和表面形态之间的关系。扫描电镜照片显示CS/HPMC共混膜的微观形貌呈多孔结构,这种结构对其生物黏附性能有影响。 相似文献