全文获取类型
收费全文 | 301篇 |
免费 | 9篇 |
专业分类
电工技术 | 11篇 |
化学工业 | 60篇 |
金属工艺 | 4篇 |
机械仪表 | 5篇 |
建筑科学 | 11篇 |
矿业工程 | 1篇 |
能源动力 | 9篇 |
轻工业 | 40篇 |
水利工程 | 1篇 |
无线电 | 42篇 |
一般工业技术 | 51篇 |
冶金工业 | 40篇 |
自动化技术 | 35篇 |
出版年
2024年 | 2篇 |
2023年 | 1篇 |
2022年 | 10篇 |
2021年 | 8篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 12篇 |
2017年 | 5篇 |
2016年 | 9篇 |
2015年 | 5篇 |
2014年 | 1篇 |
2013年 | 13篇 |
2012年 | 12篇 |
2011年 | 16篇 |
2010年 | 3篇 |
2009年 | 6篇 |
2008年 | 15篇 |
2007年 | 10篇 |
2006年 | 11篇 |
2005年 | 13篇 |
2004年 | 15篇 |
2003年 | 3篇 |
2002年 | 6篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 9篇 |
1998年 | 12篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 9篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有310条查询结果,搜索用时 78 毫秒
71.
Noncontiguous orthogonal frequency division multiplexing (NC-OFDM)-based cognitive radio (CR) systems achieve highly efficient spectrum utilization by transmitting unlicensed users' data on subcarriers of licensed users’ data when they are free. However, there are two disadvantages to the NC-OFDM system: out-of-band power (OBP) and a high peak-to-average power ratio (PAPR). OBP arises due to side lobes of an NC-OFDM signal in the frequency domain, and it interferes with the spectrum for unlicensed users. A high PAPR occurs due to the inverse fast Fourier transform (IFFT) block used in an NC-OFDM system, and it induces nonlinear effects in power amplifiers. In this study, we propose an algorithm called “Alternative Projections onto Convex and Non-Convex Sets” that reduces the OBP and PAPR simultaneously. The alternate projections are performed onto these sets to form an iteration, and it converges to the specified limits of in-band-power, peak amplitude, and OBP. Furthermore, simulations show that the bit error rate performance is not degraded while reducing OBP and PAPR. 相似文献
72.
Herein, the authors developed a new and potential semi‐interpenetrating polymer network (semi‐IPN) hydrogels of poly vinyl alcohol (PVA), acryl amide and diallyldimethyl ammonium chloride employing chemical cross‐linker N, N''‐methylene bisacrylamide (NNMBA) and ammonium persulphate as an initiator by radical polymerisation. To analyse the copolymer formation between two monomers and IPN cross‐linking reaction, the resulting hydrogel was characterised by Fourier transform infrared spectroscopy and the surface morphology was analysed using scanning electron microscopy. Differential scanning calorimetry and X‐ray diffraction studies were also carried out for investigating drug loading and distribution and swelling experiments were carried out for the uptake of water. In vitro release of ciprofloxacin hydrochloride from hydrogel was performed at intestinal conditions. The amount of PVA, NNMBA and total monomer concentration was found to strongly control the drug release behaviour from the hydrogels.Inspec keywords: hydrogels, polymer blends, biomedical materials, drug delivery systems, polymerisation, Fourier transform infrared spectra, surface morphology, scanning electron microscopy, differential scanning calorimetry, X‐ray diffraction, swelling, biological organs, ammonium compoundsOther keywords: PVA‐poly(acrylamide‐co‐diallyldimethyl ammonium chloride) semiIPN hydrogels, ciprofloxacin hydrochloride drug delivery, semiinterpenetrating polymer network hydrogels, polyvinyl alcohol, acryl amide, diallyldimethyl ammonium chloride, chemical crosslinker N,N''‐methylene bisacrylamide, ammonium persulphate, radical polymerisation initiator, NNMBA, copolymer formation, IPN crosslinking reaction, Fourier transform infrared spectroscopy, surface morphology, scanning electron microscopy, differential scanning calorimetry, X‐ray diffraction, drug loading, drug distribution, swelling, water uptake, in vitro ciprofloxacin hydrochloride release, intestinal conditions, total monomer concentration, drug release behaviour 相似文献
73.
T. Damodara Venkata Appala Naidu B. K. Madhavi K. Lal Kishore 《Analog Integrated Circuits and Signal Processing》2017,93(1):41-47
This paper presents the design of low noise amplifier and mixer (LIXER) circuit for wireless receiver front ends using 65 nm CMOS technology. The circuit is implemented with CMOS transistors and uses 65 nm CMOS process. Proposed LIXER circuit achieves a maximum gain of 25 dB and DSB noise figure of 3.5 dB. In the given circuit, current shunt paths had created by using LC tank circuit with transistors Q5 and Q6. By using the creative current recycle technique circuit consumes 3.6 mW power with 1.2 V power supply. The operating frequency of the proposed structure is 2.4 GHz with 25 dB conversion gain and ?13 dBm IIP3. The operating of the receiver front end is 2.4 GHz is used for IEEE 802.11a WLAN, Bluetooth, and ZigBee applications. 相似文献
74.
75.
K. S. V. Krishna Rao M. C. S. Subha B. Vijaya Kumar Naidu M. Sairam N. N. Mallikarjuna T. M. Aminabhavi 《应用聚合物科学杂志》2006,102(6):5708-5718
Controlled release of diclofenac sodium (DS) and ibuprofen (IB) drugs through sodium alginate (NaAlg)‐hydroxy ethyl cellulose (HEC) blend polymeric beads has been investigated. Beads were prepared by precipitating the viscous solution of NaAlg and HEC blend in alcohol followed by crosslinking with calcium chloride. Different formulations were developed in bead form by varying the amount of HEC, crosslinking agent, and drug concentration. Swelling studies in water, percent encapsulation of drugs, and release studies were carried out. The DS‐loaded beads have shown better release performance than the IB‐loaded beads. Diffusion parameters were evaluated from the Fickian diffusion theory. Mathematical modeling studies and drug release characteristics through bead matrices were studied by solving Fick's diffusion equation. The results are discussed in terms of drug release patterns and theoretical concentration profiles generated through matrices, considering spherical geometry of the beads. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5708–5718, 2006 相似文献
76.
In general polymers are used in the form of composites (fiber reinforced, solid lubricated or both) in tribo-applications,
where they may encounter more than one type of wear situations or mechanisms to different extents. The area of investigating
the optimum concentration of fillers for best combination of tribo-performance in different wear modes and mechanical strength
is sparingly researched. In this paper, research findings on the influence of the contents of short carbon fibers (CF) and
PTFE (particulate form) in Polyamide (PA) 12 on friction and wear behavior in two wear modes (adhesive and fretting) have
been reported. With increase in contents of CF up to 30% (vol) most of the mechanical properties and tribo-performance improved
in adhesive and fretting wear modes. With a view to enhance it further, PTFE was added step by step in the best performing
composite (PA+30% CF). This boosted the tribo-performance further, however, at the cost of strength properties. With increase
in PTFE percentage (10, 15 and 20% by vol), specific wear rate (K
o) and friction coefficient (μ) both decreased appreciably in adhesive as well as fretting wear modes. The composite consisting of 30% CF and 20% PTFE showed
lowest values for μ and K
o rendering it the best tribo-combination for all practical purposes. The abrasive wear behavior of composites was also investigated.
However, wear performance in this mode showed exactly opposite trends. Inclusion of fibers or combination of fibers and PTFE
proved detrimental.
相似文献
J. BijweEmail: |
77.
Wireless Networks - Heterogeneous networks assist in enhancing the data rates. In this context, heterogeneous networks comprising eNodeB, Femtocell and Wi-Fi Access Point (AP) operate conjointly to... 相似文献
78.
Wireless Networks - In this paper, an innovative technique is given to reduce the implementation time taken for doing the seamless communication in heterogeneous networks. When a new user arrives... 相似文献
79.