全文获取类型
收费全文 | 620篇 |
免费 | 37篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 11篇 |
综合类 | 1篇 |
化学工业 | 146篇 |
金属工艺 | 17篇 |
机械仪表 | 14篇 |
建筑科学 | 20篇 |
能源动力 | 20篇 |
轻工业 | 90篇 |
水利工程 | 12篇 |
石油天然气 | 4篇 |
无线电 | 69篇 |
一般工业技术 | 149篇 |
冶金工业 | 25篇 |
原子能技术 | 8篇 |
自动化技术 | 74篇 |
出版年
2024年 | 3篇 |
2023年 | 16篇 |
2022年 | 57篇 |
2021年 | 67篇 |
2020年 | 33篇 |
2019年 | 38篇 |
2018年 | 56篇 |
2017年 | 38篇 |
2016年 | 37篇 |
2015年 | 26篇 |
2014年 | 32篇 |
2013年 | 53篇 |
2012年 | 28篇 |
2011年 | 17篇 |
2010年 | 20篇 |
2009年 | 12篇 |
2008年 | 14篇 |
2007年 | 16篇 |
2006年 | 12篇 |
2005年 | 5篇 |
2004年 | 5篇 |
2002年 | 4篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1970年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有660条查询结果,搜索用时 15 毫秒
641.
Hafsa Shahid Humaira Ashraf Hafsa Javed Mamoona Humayun Nz Jhanjhi Mohammed A. AlZain 《计算机、材料和连续体(英文)》2021,68(2):1967-1978
An IoT-based wireless sensor network (WSN) comprises many small sensors to collect the data and share it with the central repositories. These sensors are battery-driven and resource-restrained devices that consume most of the energy in sensing or collecting the data and transmitting it. During data sharing, security is an important concern in such networks as they are prone to many threats, of which the deadliest is the wormhole attack. These attacks are launched without acquiring the vital information of the network and they highly compromise the communication, security, and performance of the network. In the IoT-based network environment, its mitigation becomes more challenging because of the low resource availability in the sensing devices. We have performed an extensive literature study of the existing techniques against the wormhole attack and categorised them according to their methodology. The analysis of literature has motivated our research. In this paper, we developed the ESWI technique for detecting the wormhole attack while improving the performance and security. This algorithm has been designed to be simple and less complicated to avoid the overheads and the drainage of energy in its operation. The simulation results of our technique show competitive results for the detection rate and packet delivery ratio. It also gives an increased throughput, a decreased end-to-end delay, and a much-reduced consumption of energy. 相似文献
642.
Ramay Shahid M. Kassim Hamoud Mahmood Asif Siddig Abubaker A. Al Zayed Nasser Saleh 《Journal of Materials Science: Materials in Electronics》2022,33(18):14343-14355
Journal of Materials Science: Materials in Electronics - Because of the increasing demand for energy and the resulting environmental problems, it is necessary to look for an alternative energy... 相似文献
643.
Yang Li Liangyu Li Yunhe Zhao Canbin Deng Zhibin Yi Diwen Xiao Nauman Mubarak Mengyang Xu Jie Li Guangfu Luo Qing Chen Jang-Kyo Kim 《Small (Weinheim an der Bergstrasse, Germany)》2023,19(40):2303005
A Zn anode can offset the low energy density of a flow battery for a balanced approach toward electricity storage. Yet, when targeting inexpensive, long-duration storage, the battery demands a thick Zn deposit in a porous framework, whose heterogeneity triggers frequent dendrite formation and jeopardizes the stability of the battery. Here, Cu foam is transferred into a hierarchical nanoporous electrode to homogenize the deposition. It begins with alloying the foam with Zn to form Cu5Zn8, whose depth is controlled to retain the large pores for a hydraulic permeability ≈10−11 m2. Dealloying follows to create nanoscale pores and abundant fine pits below 10 nm, where Zn can nucleate preferentially due to the Gibbs–Thomson effect, as supported by a density functional theory simulation. Morphological evolution monitored by in situ microscopy confirms uniform Zn deposition. The electrode delivers 200 h of stable cycles in a Zn–I2 flow battery at 60 mAh cm−2 and 60 mA cm−2, performance that meets practical demands. 相似文献
644.
Lightweight distributed geographical: a lightweight distributed protocol for virtual clustering in geographical forwarding cognitive radio sensor networks 下载免费PDF全文
Suleiman Zubair Norsheila Fisal Mohammed B. Abazeed Bala Alhaji Salihu Adnan Shahid Khan 《International Journal of Communication Systems》2015,28(1):1-18
Recent literature characterizes future wireless sensor networks (WSN) with dynamic spectrum capabilities. When cognitive radio is introduced as a main component of a network, a network management protocol is needed to ensure network connectivity and stability especially in highly dynamic environments. Implementing such protocols in WSN opens more challenges because of the resource constraints in sensor networks. We propose a distributed lightweight solution that fulfills this need for WSN. With this protocol, a node in a multichannel environment is quickly able to establish a control channel with neighboring nodes. Lightweight distributed geographical either increases or reduces the coverage area of the control channel based on perceived interference and adequately takes care of intersecting nodes with minimal overhead. By identifying local minima nodes, it also has the potentiality of reducing route failure by 70% further reducing the time and energy overhead incurred by switching to angle routing or maximum power transmission schemes usually used to solve the local minima issue. The work shows best operating values in terms of duty cycle and signal to noise ratio threshold frequencies and the lightweight nature of lightweight distributed geographical in terms of energy and communication overhead, which suits network management protocols for cognitive radio sensor networks. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
645.
Abdul Wadood Khan Sabna Kotta Shahid Husain Ansari Rakesh Kumar Sharma 《Drug development and industrial pharmacy》2015,41(5):772-779
Context: Naringenin (NRG), the aglycone flavonoid present in grapefruits, possesses anti-inflammatory, anti-carcinogenic, anti-lipid peroxidation and hepato-protective effects. However, it is poorly soluble in water and exhibits slow dissolution after oral ingestion, thus restricting its therapeutic efficacy.Objective: With the aim to enhance the dissolution rate and oral bioavailability of NRG, solid dispersion technique has been applied using Soluplus® as carrier.Methods: Solid dispersions of NRG were prepared by solvent evaporation and kneading methods using various ratios (1:4, 3:7, 2:3 and 1:1) of NRG:Carrier. Characterization of the optimized formulations was performed using Fourier transform infrared spectroscopy, differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis. The in vivo behavior of the optimized formulations was also investigated in Wistar Albino rats.Results: NRG solid dispersion showed a significantly higher solubility and drug dissolution rate than pure NRG (p?0.001) and it followed the Higuchi model. Among the different methods employed for the preparation of solid dispersions, solvent evaporation showed better drug release profile. DSC analysis indicated reduced crystallinity of NRG as no discrete peaks of NRG were observed. This was further substantiated by XRD analysis. Furthermore, area under the drug concentration time-curve (AUC) of NRG from solid dispersion revealed a significant increase in NRG absorption compared to NRG alone.Conclusion: Based on these results, it was concluded that solid dispersion technique markedly enhances the in vitro drug release and in vivo behavior of the grapefruit flavonoid NRG. 相似文献
646.
Thieno[3,2‐b]thiophene Flanked Isoindigo Polymers for High Performance Ambipolar OFET Applications 下载免费PDF全文
Iain Meager Mark Nikolka Bob C. Schroeder Christian B. Nielsen Miquel Planells Hugo Bronstein Joseph W. Rumer David Ian James Raja Shahid Ashraf Aditya Sadhanala Pascal Hayoz Jean‐Charles Flores Henning Sirringhaus Iain McCulloch 《Advanced functional materials》2014,24(45):7109-7115
The synthesis of a new thieno[3,2‐b]thiophene isoindigo (iITT) based monomer unit, and its subsequent incorporation into a series of alternating copolymers is reported. Copolymerisation with benzothiadiazole, bithiophene and thiophene comonomer units by palladium catalysed cross coupling gives three new narrow band gap semiconducting polymers for OFET applications. Extending the fused nature of the isoindigo core serves to further enhance molecular orbital overlap along the polymer backbones and facilitate good charge transport characteristics thus demonstrating the potential of extending the fused ring system that is attached to the isoindigo core. When used as the semiconducting channel in top‐gate/bottom‐contact OFET devices, good ambipolar properties are observed, with hole and electron mobilities up to 0.4 cm2/Vs and 0.7 cm2/Vs respectively. The three new polymers show good stability, with high temperature annealing showing an increase in the crystallinity of the polymers which corresponds directly to charge carrier mobility improvement as shown by X‐ray diffraction, atomic force microscopy and photothermal deflection spectroscopy. 相似文献
647.
Material Crystallinity as a Determinant of Triplet Dynamics and Oxygen Quenching in Donor Polymers for Organic Photovoltaic Devices 下载免费PDF全文
Ying W. Soon Safa Shoaee Raja Shahid Ashraf Hugo Bronstein Bob C. Schroeder Weimin Zhang Zhuping Fei Martin Heeney Iain McCulloch James R. Durrant 《Advanced functional materials》2014,24(10):1474-1482
This paper is concerned with the photophysics of triplet excitons in conjugated donor polymers, and their quenching by molecular oxygen. These photophysics are assayed by transient absorption spectroscopy, and correlated with X‐ray diffraction measurements of relative material crystallinity. Eleven different donor polymers are considered, including representatives from several classes of donor polymers recently developed for organic solar cell applications. Triplet lifetimes in an inert (nitrogen) environment range from <100 ns to 5 μs. A remarkably quantitative correlation is observed between these triplet lifetimes and polymer XRD strength, with more crystalline polymers exhibiting shorter triplet lifetimes. Given the broad range of polymers considered, this correlation indicates that material crystallinity is the dominant factor determining triplet lifetime for the polymers studied herein. The rate constant for oxygen quenching of these triplet states, determined from a comparison of transient absorption data under inert and oxygen environments, also show a correlation with material crystallinity. Overall these dependencies result in the yield of oxygen quenching of polymer triplet states increasing strongly as the crystallinity of the polymer is reduced. These photophysical data are compared with photochemical stability of these donor polymers, assayed by photobleaching studies of polymer films under continuous light exposure in an oxygen environment. A partial correlation is observed, with the most stable polymers being the most crystalline, exhibiting negligible oxygen quenching yields. These results are discussed in terms of the likely origins of the correlations between material crystallinity and photophysics, and in terms of their implications for the environmental stability of such donor polymers in optoelectronic devices. 相似文献
648.
649.
650.
Hassan Alhweij Ida Amura Jannis Wenk Emma Anna Carolina Emanuelsson Salman Shahid 《应用聚合物科学杂志》2021,138(31):50756
Membranes heavily rely on chlorination to diminish (bio)fouling, but chlorination can also lead to membrane degradation. We developed sulfonated polyaniline (S-PANI) ultrafiltration (UF) membranes with improved chlorine resistance and intrinsic antifouling properties. The S-PANI membranes were synthesized through Non-solvent Induced Phase Separation (NIPS). Membrane performance was evaluated under harsh chlorine conditions (250 ppm sodium hypochlorite for 3 days under different pH conditions). The S-PANI membranes showed improved chlorine resistance including a stable performance without changes in model foulant BSA rejection. In contrast, PANI membranes suffered critical structural damage with complete leakage and commercial PES membranes showed a 76% increase in pure water flux and a noticeable change in BSA rejection. Small changes in S-PANI membrane performance could be linked to membrane structural changes with pH, as confirmed by SEM, IR spectroscopy, and contact angle measurements. Additionally, the S-PANI membranes showed better antifouling properties with a high flux recovery ratio in comparison to PANI membranes using alginic acid, humic acid, and BSA model foulants. Chemical cleaning by sodium hypochlorite re-instated the transport properties to its initial condition. Overall, the developed S-PANI membranes have a high chlorine tolerance and enhanced antifouling properties making them promising for a range of UF membrane applications. 相似文献