全文获取类型
收费全文 | 2990篇 |
免费 | 81篇 |
国内免费 | 175篇 |
专业分类
电工技术 | 7篇 |
综合类 | 149篇 |
化学工业 | 989篇 |
金属工艺 | 112篇 |
机械仪表 | 62篇 |
建筑科学 | 47篇 |
矿业工程 | 14篇 |
能源动力 | 31篇 |
轻工业 | 1201篇 |
水利工程 | 3篇 |
石油天然气 | 88篇 |
武器工业 | 5篇 |
无线电 | 68篇 |
一般工业技术 | 301篇 |
冶金工业 | 51篇 |
原子能技术 | 63篇 |
自动化技术 | 55篇 |
出版年
2024年 | 14篇 |
2023年 | 82篇 |
2022年 | 121篇 |
2021年 | 146篇 |
2020年 | 152篇 |
2019年 | 154篇 |
2018年 | 88篇 |
2017年 | 142篇 |
2016年 | 124篇 |
2015年 | 102篇 |
2014年 | 183篇 |
2013年 | 358篇 |
2012年 | 360篇 |
2011年 | 318篇 |
2010年 | 159篇 |
2009年 | 143篇 |
2008年 | 116篇 |
2007年 | 107篇 |
2006年 | 79篇 |
2005年 | 63篇 |
2004年 | 74篇 |
2003年 | 36篇 |
2002年 | 23篇 |
2001年 | 19篇 |
2000年 | 11篇 |
1999年 | 4篇 |
1998年 | 17篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1975年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有3246条查询结果,搜索用时 0 毫秒
71.
《Ceramics International》2022,48(11):15791-15799
With the aim to understand electric polarization mechanisms of β-tricalcium phosphate as an advanced biomaterial, Na ion-substituted β-Ca3(PO4)2 (Na-β-TCPs) ceramics with controlled lattice vacancies were synthesized and structural refinement was performed by the Rietveld method. The Rietveld analysis revealed that Ca and vacancies at Ca(4) sites in the β-TCP structure decreased with an increase in Na substitution. Electrical measurements by the complex impedance method revealed that the conductivity and the activation energy calculated from Cole-Cole plots rapidly decreased to a constant value with an increase in Na substitution and decrease in vacancies. The thermally stimulated depolarization current (TSDC) curve of the electrically polarized Na-β-TCP showed one large peak at 530–610 °C. However, the accumulated charge decreased with an increase in Na ions and decrease in vacancies up to 2.37 mol%, after which it became constant. These results are consistent with the presumed formation of a dipole moment between aligned Ca2+ ions and their vacancies along the direction of the external polarization field applied at high temperature. We conclude that the large amount of stored charge in β-TCP caused by electrical polarization is due to the low site occupancy of calcium ions and vacancies at Ca(4) sites in the β-TCP structure, which is not the case for hydroxyapatite (HAp), as previously reported. 相似文献
72.
为深入了解美拉德反应与其伴生危害物之间的关系,以色氨酸、葡萄糖和肌酐为反应底物建立β-咔啉类杂环胺美拉德反应模型体系,在160、180、200℃条件下分别反应不同时间,分析各体系β-咔啉类杂环胺及理化指标的变化规律并对其进行相关性分析.结果 表明:随着反应时间延长和反应温度升高,β-咔啉类杂环胺Norharman和Ha... 相似文献
73.
《Journal of Industrial and Engineering Chemistry》2014,20(4):1741-1751
This study investigates the adsorption of As(III) on β-cyclodextrin modified hydrous ferric oxide (HCC). This is characterized by XRD, FESEM, AFM, XPS, BET, surface site concentration and FTIR. The modification of hydrous ferric oxide (HFO) surface by β-cyclodextrin provides ample OH groups which in turn increase As(III) adsorption on HCC compared to HFO. The adsorption remains almost constant in pH range 3–8 which decreases at higher pH (>8) and followed monolayer and pseudo first order kinetics. It is spontaneous at 303 K with increasing entropy and decreasing enthalpy. Thus HCC is found to be more efficient adsorbent than HFO. 相似文献
74.
Suwajee SaencomNaphaporn Chiewchan Sakamon Devahastin 《Food and Bioproducts Processing》2011,89(4):414-421
Ivy gourd (Coccinia grandis) has recently been recognized as a rich source of β-carotene. To add value to the fresh leaves a process to produce dried ivy gourd sheet as a health snack was the aim of this study. The effects of pretreatment, i.e., blanching in NaCl solution (0-3% w/v), and drying methods, i.e., hot air drying and vacuum drying at 60-80 °C, on the drying characteristics and quality, viz. colour, texture and β-carotene content of dried ivy gourd sheet were investigated. The results showed that dried sheet pretreated by brine blanching and vacuum drying resulted in better retention of colour and β-carotene as well as texture of the dried sheet as compared to the dried untreated and dried water blanched samples. Higher drying temperature also resulted in higher β-carotene retention due to shorter drying time. 相似文献
75.
J. Prasad RaoKurt E. Geckeler 《Progress in Polymer Science》2011,36(7):887-913
76.
This review outlines the new developments on chitosan-based bioapplications. Over the last decade, functional biomaterials research has developed new drug delivery systems and improved scaffolds for regenerative medicine that is currently one of the most rapidly growing fields in the life sciences. The aim is to restore or replace damaged body parts or lost organs by transplanting supportive scaffolds with appropriate cells that in combination with biomolecules generate new tissue. This is a highly interdisciplinary field that encompasses polymer synthesis and modification, cell culturing, gene therapy, stem cell research, therapeutic cloning and tissue engineering. In this regard, chitosan, as a biopolymer derived macromolecular compound, has a major involvement. Chitosan is a polyelectrolyte with reactive functional groups, gel-forming capability, high adsorption capacity and biodegradability. In addition, it is innately biocompatible and non-toxic to living tissues as well as having antibacterial, antifungal and antitumor activity. These features highlight the suitability and extensive applications that chitosan has in medicine. Micro/nanoparticles and hydrogels are widely used in the design of chitosan-based therapeuticsystems. The chemical structure and relevant biological properties of chitosan for regenerative medicine have been summarized as well as the methods for the preparation of controlled drug release devices and their applications. 相似文献
77.
SiAlON ceramics with high hardness and high toughness can be made through designing α/β-SiAlON composites. An important advantage of α-SiAlON phase is that the amount of intergranular phase is reduced by the transient liquid phase being absorbed into the matrix of α-SiAlON phase during sintering. But, the thermal stability of the α-SiAlON phase is an important concern for α/β-SiAlON composites especially at high temperatures. The use of different types of single or multiple cations during fabrication directly affects resultant microstructures and mechanical behavior of α/β-SiAlON composites. In this study, the creep behavior of a multi-cation (Y, Sm and Ca) doped α/β-SiAlON composite, in which aluminum-containing nitrogen melilite solid solution phase was designed as intergranular phase, was investigated by four-point bending creep tests under stresses from 50 to 150 MPa and at temperatures from 1300 °C to 1400 °C in air. The stress exponent was determined to be 1.6 ± 0.13 at 1400 °C and the creep activation energy was calculated to be 692 ± 37 kJ/mol−1. Grain boundary sliding coupled with diffusion was identified as the rate-controlling creep mechanism for the α/β-SiAlON composite. 相似文献
78.
79.
80.
Poly(β-amino ester) networks are being explored for biomedical applications, but they may lack the mechanical properties necessary for long term implantation. The objective of this study is to evaluate the effect of adding methyl methacrylate on networks’ mechanical properties under simulated physiological conditions. The networks were synthesized in two parts: (1) a biodegradable crosslinker was formed from a diacrylate and amine, (2) and then varying concentrations of methyl methacrylate were added prior to photopolymerizing the network. Degradation rate, mechanical properties, and glass transition temperature were studied as a function of methyl methacrylate composition. The crosslinking density played a limited role on mechanical properties for these networks, but increasing methyl methacrylate concentration improved the toughness by several orders of magnitude. Under simulated physiological conditions, networks showed increasing toughness or sustained toughness as degradation occurred. This work establishes a method of creating degradable networks with tailorable toughness while undergoing partial degradation. 相似文献