全文获取类型
收费全文 | 1257篇 |
免费 | 52篇 |
国内免费 | 47篇 |
专业分类
化学 | 372篇 |
晶体学 | 12篇 |
力学 | 15篇 |
综合类 | 8篇 |
数学 | 1篇 |
物理学 | 92篇 |
综合类 | 856篇 |
出版年
2024年 | 6篇 |
2023年 | 10篇 |
2022年 | 28篇 |
2021年 | 18篇 |
2020年 | 30篇 |
2019年 | 31篇 |
2018年 | 33篇 |
2017年 | 40篇 |
2016年 | 44篇 |
2015年 | 55篇 |
2014年 | 47篇 |
2013年 | 64篇 |
2012年 | 65篇 |
2011年 | 68篇 |
2010年 | 62篇 |
2009年 | 69篇 |
2008年 | 70篇 |
2007年 | 88篇 |
2006年 | 77篇 |
2005年 | 67篇 |
2004年 | 63篇 |
2003年 | 53篇 |
2002年 | 45篇 |
2001年 | 29篇 |
2000年 | 26篇 |
1999年 | 31篇 |
1998年 | 25篇 |
1997年 | 20篇 |
1996年 | 24篇 |
1995年 | 6篇 |
1994年 | 8篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 5篇 |
1990年 | 7篇 |
1989年 | 10篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1985年 | 1篇 |
1983年 | 1篇 |
排序方式: 共有1356条查询结果,搜索用时 640 毫秒
51.
Natalia CZUMA Wojciech FRANUS Pawe BARAN WIK Agnieszka Katarzyna ZARBSKA 《Turkish Journal of Chemistry》2020,44(1):155
In the presented study, the sulfur dioxide sorption properties of fly ash zeolite X were investigated. Sorption tests were performed on fly ash zeolite samples that were not prepared specially for sorption, in addition to dried samples and samples in the presence of water vapor. The samples saturated with water vapor showed the highest sorption capacity. The sorption capacity of the samples additionally dried prior to the sorption experiment was higher than that of the samples that were not specially prepared for the sorption test. Regeneration tests indicated relatively good regeneration properties. The obtained results were described with the use of Langmuir, Sips, and Dubinin–Astakhov models, with the Dubinin–Astakhov model providing the best fit. 相似文献
52.
不同年龄栓皮栎的灰分含量、干质量热值和去灰分热值是栓皮栎能源开发利用的重要基础。通过对5个年龄栓皮栎不同器官热值、灰分含量的分析,得出:平均灰分含量从高到低时的树龄依次为46、36、17、57、27 a;枝或干的灰分含量低于叶或皮。平均干质量热值从高到低的树龄依次为27、57、36、17、46 a;树叶、树皮、树干的干质量热值与灰分含量均呈不显著负相关,树枝的干质量热值与灰分含量间为极显著线性负相关,平均干质量热值与灰分含量呈显著线性负相关;枝或干的干质量热值均低于叶或皮。平均去灰分热值从高到低时的树龄依次为57、27、36、17、46 a;枝或干的去灰分热值均低于叶或皮。从热值与栓皮栎能源林的经营成本考虑,17、27、36、46、57 a的5个栓皮栎年龄段中,27 a可为栓皮栎能源林的理想经营年龄。 相似文献
53.
研究两种不同特性工业废渣铁尾矿、粉煤灰对海泥烧结多孔砖样品泛霜程度的影响及机理.结果表明:铁尾矿减轻海泥烧结砖泛霜程度的有利因素多,粉煤灰提高海泥烧结砖泛霜程度的不利因素多.此外,掺加外加剂可以在某种程度上降低海泥烧结砖的泛霜等级;当掺量达到某一范围时,能够较大幅度减少砖坯成型用水量,烧成中产生液相的非瘠性工业废渣-铁... 相似文献
54.
将废玻璃破碎人工级配作集料、粉煤灰作填料、碳纤维作增强材料与环氧树脂胶粘剂结合,成功配制出7 d抗压强度达到51.23 MPa、抗折强度达到21.68 MPa的树脂混凝土.采用均匀试验设计安排试验方案,利用SPSS技术处理试验数据并建立强度回归方程,用MATLAB技术得到树脂混凝土的配合比优化范围.该项目吃"渣"大,废玻璃、粉煤灰取代天然砂石占树脂混凝土总质量88%以上,研究成果对固体废弃物的治理有重要的现实意义. 相似文献
55.
Maropeng V. Raletsena Samukelisiwe Mdlalose Olusola S. Bodede Hailemariam A. Assress Adugna A. Woldesemayat David M. Modise 《Molecules (Basel, Switzerland)》2022,27(4)
1H NMR and LC-MS, commonly used metabolomics analytical platforms, were used to annotate the metabolites found in potato (Solanum tuberosum L.) irrigated with four different treatments based on FA to AMD ratios, namely: control (0% AMD; tap water), 1:1 (50% AMD), 3:1 (75% AMD is 75% FA: AMD), and 100% AMD (untreated). The effects of stress on plants were illustrated by the primary metabolite shifts in the region from δH 0.0 to δH 4.0 and secondary metabolites peaks were prominent in the region ranging from δH 4.5 to δH 8.0. The 1:3 irrigation treatment enabled, in two potato cultivars, the production of significantly high concentrations of secondary metabolites due to the 75% FA: AMD content in the irrigation mixture, which induced stress. The findings suggested that 1:1 irrigation treatment induced production of lower amounts of secondary metabolites in all crops compared to crops irrigated with untreated acid mine drainage treatment and with other FA-treated AMD solutions. 相似文献
56.
米文瑜 《华北科技学院学报》2007,4(3):52-54
建筑材料检验是保证工程质量的重要措施.本文针对目前施工现场建筑材料在取样方面存在的问题,就如何规范建材取样,确保工程质量提出了建议. 相似文献
57.
江静 《华北科技学院学报》2006,3(3):85-89
煤质监测系统由Delphi 6.0编制,运行于选煤厂内部的局域网中,是基于对兖矿集团济宁三号选煤厂在线测灰仪实时监测、查询系统进行的研究设计,主要实现煤质数据的网络发布和共享.系统采用友好的图形用户界面:查询信息由用户从键盘输入,结果以表格输出,历史数据以图形曲线输出.该系统已投入运行.实践证明不但可以为选煤厂提供准确、完整的煤质检测和化验信息,而且有力地推动选煤厂的信息化工作. 相似文献
58.
Samar Beaino Peter El Hage Rodolphe Sonnier Sylvain Seif Roland El Hage 《Molecules (Basel, Switzerland)》2022,27(2)
This study highlights the synthesis of a new thermal insulating geopolymer based on the alkaline activation of fly ashes. A porous geopolymer material can be prepared without the addition of a foaming agent, using high ratio solution/ashes (activating solutions used are water, sodium or potassium hydroxide). In order to increase the porosity of the material and to make it more ecological, rice husks are incorporated into the formulation. The geopolymer materials were prepared at room temperature and dried at moderate temperature (105 °C) by a simple procedure. The microstructural characteristics of these new porous geopolymers were assessed by optical microscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA) and X-ray fluorescence (XRF). Infrared spectroscopy (FTIR) was used to confirm the geopolymerisation. The effect of the ratio solution/ashes and the percentage of the rice husk addition on thermal and mechanical analysis was evaluated. An insulating material for a solution/ashes ratio of 0.9 and a rice husk content of 15% having a λ value of 0.087 W/(m·K), a porosity of 61.4% and an Rc value of 0.1 MPa was successfully prepared. 相似文献
59.
用扫描电子显微镜/能量色散谱(SEM/EDS),超级场发射电子显微镜(Super FE-S叫)研究了H2SO4与粉煤灰的固相反应.常温反应后,单个粉煤灰表面微区有明显的溶解点,粉煤灰在一定程度上出现粘结、结块现象.反应前后粉煤灰的组成变化不大,表明固相反应仅在粉煤灰表面进行,未渗入到颗粒内部.反应后所得水溶物主要是Al2(SO4)3、Fe 2(S04),.当反应温度达到200℃时,扫描电镜可观察到粉煤灰表面产生块状Al2(SO4)3、Fe 2(SO4)3结晶.250℃下反应产生的结晶物明显多于200℃,且导电性明显提高.热力学计算和表面纳米观测技术都表明,粉煤灰表面的铝、铁氧化物转化成可溶性的硫酸盐,氧化硅未参与化学反应. 相似文献
60.
Angelika Macior Izabela Zaborniak Pawe Chmielarz Joanna Smenda Karol Wolski Ewa Ciszkowicz Katarzyna Lecka-Szlachta 《Molecules (Basel, Switzerland)》2022,27(3)
The article presents the modification of ash wood via surface initiated activators regenerated by electron transfer atom transfer radical polymerization mediated by elemental silver (Ag0 SI-ARGET ATRP) at a diminished catalyst concentration. Ash wood is functionalized with poly(methyl methacrylate) (PMMA) and poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) to yield wood grafted with PMMA-b-PDMAEMA-Br copolymers with hydrophobic and antibacterial properties. Fourier transform infrared (FT-IR) spectroscopy confirmed the covalent incorporation of functional ATRP initiation sites and polymer chains into the wood structure. The polymerization kinetics was followed by the analysis of the polymer grown in solution from the sacrificial initiator by proton nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC). The polymer layer covalently attached to the wood surface was observed by scanning electron microscopy (SEM). The hydrophobic properties of hybrid materials were confirmed by water contact angle measurements. Water and sodium chloride salt aqueous solution uptake tests confirmed a significant improvement in resistance to the absorption of wood samples after modification with polymers. Antibacterial tests revealed that wood-QPDMAEMA-Br, as well as wood-PMMA-b-QPDMAEMA-Br, exhibited higher antibacterial activity against Gram-positive bacteria (Staphylococcus aureus) in comparison with Gram-negative bacteria (Escherichia coli). The paper presents an economic concept with ecological aspects of improving wood properties, which gives great opportunities to use the proposed approach in the production of functional hybrid materials for industry and high quality sports equipment, and in furniture production. 相似文献