全文获取类型
收费全文 | 1402篇 |
免费 | 78篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 20篇 |
综合类 | 2篇 |
化学工业 | 328篇 |
金属工艺 | 28篇 |
机械仪表 | 37篇 |
建筑科学 | 55篇 |
矿业工程 | 1篇 |
能源动力 | 100篇 |
轻工业 | 121篇 |
水利工程 | 22篇 |
石油天然气 | 19篇 |
无线电 | 171篇 |
一般工业技术 | 282篇 |
冶金工业 | 28篇 |
原子能技术 | 3篇 |
自动化技术 | 273篇 |
出版年
2024年 | 5篇 |
2023年 | 36篇 |
2022年 | 83篇 |
2021年 | 125篇 |
2020年 | 67篇 |
2019年 | 80篇 |
2018年 | 89篇 |
2017年 | 71篇 |
2016年 | 55篇 |
2015年 | 48篇 |
2014年 | 58篇 |
2013年 | 126篇 |
2012年 | 66篇 |
2011年 | 83篇 |
2010年 | 63篇 |
2009年 | 53篇 |
2008年 | 43篇 |
2007年 | 32篇 |
2006年 | 24篇 |
2005年 | 18篇 |
2004年 | 20篇 |
2003年 | 20篇 |
2002年 | 21篇 |
2001年 | 17篇 |
2000年 | 15篇 |
1999年 | 12篇 |
1998年 | 13篇 |
1997年 | 13篇 |
1996年 | 16篇 |
1995年 | 10篇 |
1994年 | 5篇 |
1993年 | 12篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1985年 | 3篇 |
1984年 | 10篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1978年 | 2篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1972年 | 2篇 |
排序方式: 共有1490条查询结果,搜索用时 15 毫秒
71.
Social media usage among organizations is growing tremendously. Organizations are now building and maintaining social media public pages to improve their social network salience, enhance interest in their organizations, and build relationships with the online public. The majority of the studies on social media usage are based on the individual perspective while some are from the organizational perspective. However, not many studies have investigated the actual impact of social media usage on organizational performance. Therefore, using the qualitative approach, this study investigates the various purposes of social media usage and its impact on organizational performance. This study however, focuses only on the social media managers’ views. The senior managers of six organizations that are using social media are interviewed from which we find that social media is used for various purposes in organizations, such as advertising and promotion, branding, information search, building customer relations and many more. The results also show that social media has a greater impact on the performance of organizations in terms of enhancement in customer relations and customer service activities, improvement in information accessibility and cost reduction in terms of marketing and customer service. 相似文献
72.
Natural Palm Olein Polyol as a Replacement for Polyether Polyols in Viscoelastic Polyurethane Foam
下载免费PDF全文
![点击此处可从《Journal of the American Oil Chemists](/ch/ext_images/free.gif)
H. Nurul ‘Ain T. I. Tuan Noor Maznee M. N. Norhayati M. A. Mohd Noor S. Adnan P. P. Kosheela Devi S. Mohd Norhisham S. K. Yeong A. H. Hazimah Irma Campara Vahid Sendijarevic Ibrahim Sendijarevic 《Journal of the American Oil Chemists' Society》2016,93(7):983-993
The impact of replacing three polyether polyols with different levels of a single palm olein‐based natural oil polyol (NOP) was systematically correlated with the changes in foaming reactivity, cell structure, physico‐mechanical properties, and morphology of viscoelastic (VE) foams. The data show that replacing the polyether polyols with the NOP slightly increased the rate of the foaming reactivity. Increasing the NOP content resulted in increased cell size and cells remained fully open. Increased NOP content contributed to higher load bearing properties of VE foam, which can be attributed to higher functionality of NOP compared to polyether polyols. Addition of the NOP slightly increased the resilience of the foams, however, the hysteresis which is the measure of energy absorption remained mostly unaffected. Age properties, characterized by dry and humid compression sets, were mostly unaffected by the replacement of the polyether polyol with the NOP. The addition of NOP did not impact the morphology of the VE foam polymer matrix, which appears to retain a low degree of hard and soft segment domain separation. Overall, the results demonstrate a feasibility that the NOP can be used to partially replace the polyether polyols in VE polyurethane foams without significant impact on the functional performance. 相似文献
73.
Urethane‐forming reaction kinetics and catalysis of model palm olein polyols: Quantified impact of primary and secondary hydroxyls
下载免费PDF全文
![点击此处可从《应用聚合物科学杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Tuan Noor Maznee Tuan Ismail Kosheela Devi Poo Palam Zailan Bin Abu Bakar Hoong Seng Soi Yeong Shoot Kian Hazimah Abu Hassan Christi Schiffman Aisa Sendijarevic Vahid Sendijarevic Ibrahim Sendijarevic 《应用聚合物科学杂志》2016,133(5)
Model palm olein natural oil polyols (NOPs) with varying ratios of primary to secondary hydroxyls were synthesized, characterized, and evaluated in reaction kinetics study with isocyanate in formation of polyurethanes. Reaction rate constants and activation energies associated with primary and secondary hydroxyls of NOPs were quantified. The kinetic study in toluene shows that the NOP containing primary hydroxyls have three times higher reaction rate constants in noncatalyzed reaction with 4,4′‐diphenylmethane diisocyanate (4,4′‐MDI) compared to the model NOP containing only secondary hydroxyls, which is associated with higher activation energy of secondary hydroxyls. However, the difference in reaction rate constants of primary and secondary hydroxyls in NOPs diminished in the reactions catalyzed with dibutyltin dilaurate. Bulk polymerization reaction confirms the kinetics results in toluene, showing that the model NOP containing primary hydroxyls reached gel time at a faster rate. Evaluation of elastomers from bulk polymerization shows low degree of phase separation of hard and soft segments for elastomers based on the model NOPs. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42955. 相似文献
74.
Farman Muhammad Nawaz Fahim Majeed Sadia Javeed Hafiz Muhammad Rashad Ahsan Muhammad Ahmad Khawaja Shafique Aurangzaib Muhammad Bukhari Muhammad Adnan Shehzad Muhammad Asif Hussain Muhammad Baqir 《SILICON》2022,14(13):7901-7917
Silicon - The present study evaluated the effect of silicon (Si) seed priming and sulfur (S) foliar spray on drought tolerance of two contrasting maize hybrids viz. drought tolerant Hi-Corn 11 and... 相似文献
75.
Siliu Lyu Muhammad Adnan Younis Zhibin Liu Libin Zeng Xianyun Peng Bin Yang Zhongjian Li Lecheng Lei Yang Hou 《Frontiers of Chemical Science and Engineering》2022,16(6):777
As an eco-friendly, efficient, and low-cost technique, photoelectrochemical water splitting has attracted growing interest in the production of clean and sustainable hydrogen by the conversion of abundant solar energy. In the photoelectrochemical system, the photoelectrode plays a vital role in absorbing the energy of sunlight to trigger the water splitting process and the overall efficiency depends largely on the integration and design of photoelectrochemical devices. In recent years, the optimization of photoelectrodes and photoelectrochemical devices to achieve highly efficient hydrogen production has been extensively investigated. In this paper, a concise review of recent advances in the modification of nanostructured photoelectrodes and the design of photoelectrochemical devices is presented. Meanwhile, the general principles of structural and morphological factors in altering the photoelectrochemical performance of photoelectrodes are discussed. Furthermore, the performance indicators and first principles to describe the behaviors of charge carriers are analyzed, which will be of profound guiding significance to increasing the overall efficiency of the photoelectrochemical water splitting system. Finally, current challenges and prospects for an in-depth understanding of reaction mechanisms using advanced characterization technologies and potential strategies for developing novel photoelectrodes and advanced photoelectrochemical water splitting devices are demonstrated. 相似文献
76.
Dwivedi Pooja Siddiquee Arshad Noor Maheshwari Sachin 《Russian Journal of Non-Ferrous Metals》2021,62(2):212-225
Russian Journal of Non-Ferrous Metals - Aluminum alloys have always been the material of choice for the aircraft industry owing to their versatile attributes, such as excellent strength to weight... 相似文献
77.
Taha Mahdi Arshad Ahmad Adnan Ripin Mohamed Mahmoud Nasef 《Korean Journal of Chemical Engineering》2014,31(5):875-880
A vapor-liquid equilibrium (VLE) study was conducted on ethanol/ethylacetate mixture as a preliminary step towards developing an ultrasonic-assisted distillation process for separating azeotropic mixtures. The influence of ultrasonic intensity and frequency on the vapor-liquid equilibrium (VLE) of the mixture was examined using a combination of four ultrasonic intensities in range of 100–400W/cm2 and three frequencies ranging from 25–68 kHz. The sonication was found to have significant impacts on the VLE of the system as it alters both the relative volatility and azeotrope point, with preference to lower frequency operation. A maximum relative volatility of 2.32 was obtained at an intensity of 300 W/cm2 and a frequency of 25 kHz coupled with complete elimination of ethanol-ethyl acetate azeotrope. Results from this work were also congruent with some experimental and theoretical works presented in the literature. These findings set a good beginning towards the development of an ultrasonic assisted distillation that is currently in progress. 相似文献
78.
Waste expanded polystyrene (EPS) represents a source of valuable chemical products like styrene and other aromatics. The catalytic degradation was carried out in a batch reactor with a mixture of polystyrene (PS) and catalyst at 450 °C for 30 min in case of Mg and at 400 °C for 2 h both for MgO and MgCO3 catalysts. At optimum degradation conditions, EPS was degraded into 82.20±3.80 wt%, 91.60±0.20 wt% and 81.80±0.53 wt% liquid with Mg, MgO and MgCO3 catalysts, respectively. The liquid products obtained were separated into different fractions by fractional distillation. The liquid fractions obtained with three catalysts were compared, and characterized using GC-MS. Maximum conversion of EPS into styrene monomer (66.6 wt%) was achieved with Mg catalyst, and an increase in selectivity of compounds was also observed. The major fraction at 145 °C showed the properties of styrene monomer. The results showed that among the catalysts used, Mg was found to be the most effective catalyst for selective conversion into styrene monomer as value added product. 相似文献
79.
Noor Faeizah Amat Andanastuti Muchtar Mariyam Jameelah Ghazali Norziha Yahaya 《Ceramics International》2014
The stability of nano-zirconia 3YSZ powder in suspension was extensively studied by the colloidal method, and the optimum sintering temperature of the green sample fabricated through slip casting was determined. Zirconia suspensions with 10 vol% powder loading were prepared with distilled water, and HNO3 was used to adjust the pH of the suspension to pH 1–6. All of the suspensions were subjected to sedimentation test, and the results showed that the suspensions adjusted to pH 2 had the lowest sediment volume. This finding indicates that a suspension with pH 2 produces higher packing density. Viscosity test was carried out for the suspensions added with dispersant ranging from 0.3 wt% to 0.7 wt% polyethyleneimine (PEI) with and without pH adjustment. The suspension containing 0.5 wt% PEI with pH 2 adjustment produced the lowest viscosity because of interparticle bond breakage in the aggregates, thus forming colloidally stable suspensions. The zirconia suspension containing 0.5 wt% PEI and whose pH was adjusted to pH 2 was chosen to be slip casted into cylindrical shape. Green samples were sintered at various sintering temperatures that ranged from 1100 °C to 1500 °C through a two-step sintering method. The sample sintered at 1500 °C was found to be porosite-free, and its highest relative density was 99.6% of the theoretical density. Morphological studies detected pores in the microstructure of the samples sintered at low sintering temperatures (1100 and 1200 °C). By contrast, the samples sintered at 1400 and 1500 °C were fully densified. However, the grain size of the sample sintered at 1500 °C was 230 nm, which indicated excessive grain growth. The Vickers hardness of the sample sintered at 1400 °C was found to be highest (12.9 GPa) and comparable to results found in the literature. 相似文献
80.
CAD-oriented analytic formulas are presented for calculating the quasistatic TEM parameters of the overlayed supported asymmetric coplanar waveguides (OSACPW). The effect of the thicknesses and the dielectric constants of the overlaying and supporting materials on the quasistatic parameters has been investigated by using the expressions derived by the conformal mapping techniques. Comparisons have also been made between this article's results and the results available in the literature for the conventional coplanar waveguide (CPW) and the asymmetric coplanar waveguide (ACPW). It has been shown that the present formulas can also be used for calculating the quasistatic TEM parameters of the line structures such as the open, the open supported, and the overlayed supported CPW or ACPW. © 1996 John Wiley & Sons, Inc. 相似文献