全文获取类型
收费全文 | 1675篇 |
免费 | 102篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 37篇 |
综合类 | 3篇 |
化学工业 | 509篇 |
金属工艺 | 36篇 |
机械仪表 | 44篇 |
建筑科学 | 28篇 |
能源动力 | 128篇 |
轻工业 | 102篇 |
水利工程 | 16篇 |
石油天然气 | 1篇 |
无线电 | 136篇 |
一般工业技术 | 370篇 |
冶金工业 | 135篇 |
原子能技术 | 19篇 |
自动化技术 | 215篇 |
出版年
2024年 | 10篇 |
2023年 | 30篇 |
2022年 | 66篇 |
2021年 | 78篇 |
2020年 | 67篇 |
2019年 | 68篇 |
2018年 | 84篇 |
2017年 | 100篇 |
2016年 | 108篇 |
2015年 | 42篇 |
2014年 | 66篇 |
2013年 | 123篇 |
2012年 | 90篇 |
2011年 | 104篇 |
2010年 | 85篇 |
2009年 | 61篇 |
2008年 | 38篇 |
2007年 | 41篇 |
2006年 | 42篇 |
2005年 | 32篇 |
2004年 | 26篇 |
2003年 | 28篇 |
2002年 | 25篇 |
2001年 | 18篇 |
2000年 | 15篇 |
1999年 | 17篇 |
1998年 | 29篇 |
1997年 | 15篇 |
1996年 | 16篇 |
1995年 | 15篇 |
1994年 | 13篇 |
1993年 | 16篇 |
1992年 | 14篇 |
1991年 | 13篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 10篇 |
1987年 | 17篇 |
1986年 | 7篇 |
1985年 | 13篇 |
1984年 | 10篇 |
1983年 | 11篇 |
1982年 | 23篇 |
1981年 | 20篇 |
1980年 | 20篇 |
1979年 | 9篇 |
1977年 | 3篇 |
1976年 | 9篇 |
1973年 | 5篇 |
1972年 | 4篇 |
排序方式: 共有1779条查询结果,搜索用时 15 毫秒
1.
2.
Liangtao Yang Liang-Yin Kuo Juan Miguel López del Amo Prasant Kumar Nayak Katherine A. Mazzio Sebastian Maletti Daria Mikhailova Lars Giebeler Payam Kaghazchi Teófilo Rojo Philipp Adelhelm 《Advanced functional materials》2021,31(38):2102939
A known strategy for improving the properties of layered oxide electrodes in sodium-ion batteries is the partial substitution of transition metals by Li. Herein, the role of Li as a defect and its impact on sodium storage in P2-Na0.67Mn0.6Ni0.2Li0.2O2 is discussed. In tandem with electrochemical studies, the electronic and atomic structure are studied using solid-state NMR, operando XRD, and density functional theory (DFT). For the as-synthesized material, Li is located in comparable amounts within the sodium and the transition metal oxide (TMO) layers. Desodiation leads to a redistribution of Li ions within the crystal lattice. During charging, Li ions from the Na layer first migrate to the TMO layer before reversing their course at low Na contents. There is little change in the lattice parameters during charging/discharging, indicating stabilization of the P2 structure. This leads to a solid-solution type storage mechanism (sloping voltage profile) and hence excellent cycle life with a capacity of 110 mAh g-1 after 100 cycles. In contrast, the Li-free compositions Na0.67Mn0.6Ni0.4O2 and Na0.67Mn0.8Ni0.2O2 show phase transitions and a stair-case voltage profile. The capacity is found to originate from mainly Ni3+/Ni4+ and O2-/O2-δ redox processes by DFT, although a small contribution from Mn4+/Mn5+ to the capacity cannot be excluded. 相似文献
3.
Bibhuti Bhusan Nayak 《传热工程》2019,40(8):679-692
The thermo-fluidic transport characteristics of the fly ash–water slurry flow in a straight horizontal pipe are predicted by deploying two different multiphase modeling strategies, viz. the mixture and the Eulerian multiphase models. Comparisons between the two model predictions in terms of the pressure drop and heat transfer coefficient are done along with the comparisons between the single (water) and the two phase system (slurry). Spherical fly ash particles, with diameter of 13 µm for an average inflow velocity ranging from 1 to 5 m/s and particle concentrations within 0–40% by volume for each velocity are considered as the dispersed phase carried by the carrier phase water. Significant differences between the two model predictions can be observed both from the qualitative and quantitative perspectives. This finally leads to the appropriate choice of the multiphase model for predicting the thermo-fluidic transport characteristics in slurry flow. 相似文献
4.
A dynamic model for computer simulation and control of steelmaking has been developed. It is essentially based on multicomponent mixed transport control theory with the incorporation of energy balance calculations. The model is applicable to both steelmaking in electric furnaces as well as in oxygen steelmaking converters. The adjustable parameters of the model for simulation of oxygen steelmaking are gas evolution rate (Gco). oxygen flux factor (Fo) and emulsification factor (EM). These simulation parameters, when combined with on-line measurement of off-gas composition and temperature, enable complete dynamic control of the process. The model developed is applied, as an example, to an industrially produced heat in a top blown oxygen steelmaking converter and the results of simulation are discussed. 相似文献
5.
The graft copolymerization of methyl methacrylate onto natural rubber (NR) was carried out varying the concentration of monomer, initiator, thiourea, and silver nitrate over a wide range. The grafting reaction was temperature-dependent. From the Arrhenius plot, the overall energy of activation was computed. A suitable reaction scheme and rate expression for the rate of polymerization was suggested. 相似文献
6.
This paper presents a quantum protocol that demonstrates that weak coin flipping with bias ≈0.239, less than 1/4, is possible. A bias of 1/4 was the smallest known, and followed from the strong coin flipping protocol of Ambainis in [33rd STOC, 2001] (also proposed by Spekkens and Rudolph [Phys. Rev. A 65 (2002) 012310]). Protocols with yet smaller bias ≈0.207 have independently been discovered by Ambainis (2001) and Spekkens and Rudolph [Phys. Rev. Lett. 89 (2002) 227901]. We also present an alternative strong coin flipping protocol with bias 1/4 with analysis simpler than that of Ambainis [33rd STOC, 2001]. 相似文献
7.
Factors affecting the performance of antacids F-MA 11, dihydroxy aluminum aminoacetate, magaldrate and magnesium hydroxide were studied in vitro using Schaub's acid neutralization test, a modified Reheis reaction velocity test and the USP test. From the results obtained it was evident that type and combination of antacid, the adjuvants and formulation techniques used in preparation of antacids affect their performance. The USP preliminary antacid test and acid neutralization test are not optimal in vitro tests to evaluate in vitro onset and duration of action of antacids. 相似文献
8.
Siba Prasada Panigrahi Santanu Kumar Nayak Sasmita Kumari Padhy 《International Journal of Adaptive Control and Signal Processing》2008,22(7):705-716
This paper presents a neuro‐fuzzy network (NFN) where all its parameters can be tuned simultaneously using genetic algorithms (GAs). The approach combines the merits of fuzzy logic theory, neural networks and GAs. The proposed NFN does not require a priori knowledge about the system and eliminates the need for complicated design steps such as manual tuning of input–output membership functions, and selection of fuzzy rule base. Although, only conventional GAs have been used, convergence results are very encouraging. A well‐known numerical example derived from literature is used to evaluate and compare the performance of the network with other equalizing approaches. Simulation results show that the proposed neuro‐fuzzy controller, all parameters of which have been tuned simultaneously using GAs, offers advantages over existing equalizers and has improved performance. From the perspective of application and implementation, this paper is very interesting as it provides a new method for performing blind equalization. The main contribution of this paper is the use of learning algorithms to train a feed‐forward neural network for M‐ary QAM and PSK signals. This paper also provides a platform for researchers of the area for further development. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
9.
Present paper deals with the electro-osmotic flow in a infinitely extended cylindrical micro- and nano-channel. The channel height is considered to be much less than the channel length. We consider a mixture of water or another neutral solvent and a salt compound such as sodium chloride for which the ionic species are entirely dissociated. We have developed a two-dimensional numerical model to analyze the flow characteristics and concentration distributions of a electro-osmotic flow without using the Debye-Hückel approximation. The governing system of equations consist of the mole fractions of ions, the potential and the fluid flow equations. Results are produced for the case, where the channel height is much greater than the width of the electric double layer (EDL) (micro-channel) and for the case where the channel height is of the order of the width of the EDL (nano-channel). For various values of mole fraction, we studied the electro-osmotic flow profiles and the potential distribution along the channel at different channel heights. In this case of steady flow the velocity field and the potential are identical. The electro-osmotic flow produces a uniform ‘plug profile’ at channel heights greater than 20 nm, which results in reduced sample species dispersion as compared to the velocity gradients associated with the pressure driven flows. Asymptotic solutions are obtained when the flow in a micro-channel is considered. 相似文献
10.
Bera L.K. Ray S.K. Mukhopadhyay M. Nayak D.K. Usami N. Shiraki Y. Maiti C.K. 《Electron Device Letters, IEEE》1998,19(8):273-275
Growth of ultrathin (<100 Å) oxynitride on strained-Si using microwave N2O and NH3 plasma is reported. X-ray photoelectron spectroscopy (XPS) results indicate a nitrogen-rich layer at the strained-Si/SiO2 interface. The electrical properties of oxynitrides have been characterized using a metal-insulator-semiconductor (MIS) structure. A moderately low value of insulator charge density (6.1×1010 cm-2) has been obtained for NH3 plasma treated N2O oxide sample. Nitrided oxide shows a larger breakdown voltage and an improved charge trapping properties under Fowler-Nordheim (F-N) constant current stress 相似文献