全文获取类型
收费全文 | 8844篇 |
免费 | 499篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 172篇 |
综合类 | 23篇 |
化学工业 | 1867篇 |
金属工艺 | 259篇 |
机械仪表 | 457篇 |
建筑科学 | 181篇 |
矿业工程 | 6篇 |
能源动力 | 333篇 |
轻工业 | 707篇 |
水利工程 | 44篇 |
石油天然气 | 21篇 |
无线电 | 1684篇 |
一般工业技术 | 1595篇 |
冶金工业 | 743篇 |
原子能技术 | 103篇 |
自动化技术 | 1165篇 |
出版年
2024年 | 7篇 |
2023年 | 72篇 |
2022年 | 106篇 |
2021年 | 157篇 |
2020年 | 142篇 |
2019年 | 163篇 |
2018年 | 212篇 |
2017年 | 189篇 |
2016年 | 278篇 |
2015年 | 236篇 |
2014年 | 371篇 |
2013年 | 628篇 |
2012年 | 514篇 |
2011年 | 574篇 |
2010年 | 420篇 |
2009年 | 492篇 |
2008年 | 412篇 |
2007年 | 362篇 |
2006年 | 369篇 |
2005年 | 317篇 |
2004年 | 308篇 |
2003年 | 286篇 |
2002年 | 301篇 |
2001年 | 231篇 |
2000年 | 199篇 |
1999年 | 195篇 |
1998年 | 385篇 |
1997年 | 241篇 |
1996年 | 176篇 |
1995年 | 153篇 |
1994年 | 126篇 |
1993年 | 119篇 |
1992年 | 62篇 |
1991年 | 77篇 |
1990年 | 57篇 |
1989年 | 61篇 |
1988年 | 41篇 |
1987年 | 46篇 |
1986年 | 42篇 |
1985年 | 33篇 |
1984年 | 29篇 |
1983年 | 21篇 |
1982年 | 14篇 |
1981年 | 23篇 |
1980年 | 16篇 |
1979年 | 9篇 |
1978年 | 15篇 |
1977年 | 17篇 |
1976年 | 21篇 |
1973年 | 8篇 |
排序方式: 共有9360条查询结果,搜索用时 15 毫秒
21.
22.
We have studied the CO2/CH4 mixed gas permeation through hollow fiber membranes in a permeator. An approach to characterize the true separation performance of hollow fiber membranes for binary gas mixtures was provided based on experiments and simulations. Experiments were carried out to measure the retentate and permeate flow rates and compositions at each outlet. The influences of pressure drop within the hollow fibers, non-ideal gas behavior in the mixture and concentration polarization were taken into consideration in the mathematics model. The calculation results indicate that the net influence of the non-ideal gas behavior, competitive sorption and plasticization yields the calculated CO2 permeance in a mixed gas permeator close to that obtained in pure gas tests. Whereas the CH4 permeance is higher in the mixed gas tests than that in the pure gas tests, as the plasticization caused by CO2 dominates the permeation process. As a result, the CO2/CH4 mixed gas selectivity is smaller than those obtained in pure gas tests at equivalent pressures.The calculated membrane performance shows little changes with stage cut if the effect of concentration polarization is accounted for in the calculation. The integration method developed in this study could provide more accurate characterizations of mixed gas permeance of hollow membranes than other estimation methods, as our model considers the roles of non-ideal gas behavior and concentration polarization properly. 相似文献
23.
Core–shell type nanoparticles of poly(L ‐lactide)/poly(ethylene glycol) (LE) diblock copolymer were prepared by a dialysis technique. Their size was confirmed as 40–70 nm using photon correlation spectroscopy. The 1H‐NMR analysis confirmed the formation of core–shell type nanoparticles and drug loading. The particle size, drug loading, and drug release rate of the LE nanoparticles were slightly changed by the initial solvents that were used. The drug release behavior of LE core–shell type nanoparticles showed an initial burst during the first 12 h and then a sustained release until 100 h. The degradation behavior of LE block copolymer nanoparticles was divided into three phases: the initial rapid degradation phase, the stationary phase, and the rapid degradation phase until complete degradation. It was suggested that lidocaine release kinetics were predominantly governed by the diffusion mechanism in the initial burst phase and after that by both of the diffusion and degradation mechanisms. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2625–2634, 2002 相似文献
24.
25.
GaN buffer and main layers were grown by the conventional hydride vapor phase epitaxy technique using GaCl3 consecutively. The deposited buffer layers were investigated by atomic force microscopy and X-ray analysis. To examine the behavior of the buffer layers at main layer growth temperature, heat treatment was conducted at 900°C. Based on the results of the buffer layer study, GaN thick films were grown at 1050°C. Optimum deposition conditions of buffer layer from the buffer and main layer studies generally coincided. On the φ scanning pattern, the GaN films grown on (0001) Al2 O3 were single-crystalline. Band-edge emission dominated photoluminescence was observed at room temperature. 相似文献
26.
27.
Chengcai YaoB.T.F Chung G.-X Wang 《International Journal of Heat and Mass Transfer》2002,45(11):2397-2405
Equilibrium solidification in a semitransparent planar layer is studied using an isothermal mushy zone model. The layer is made up of a pure material being emitting, absorbing and isotropically scattering and is subject to radiative and convective cooling. The model involves solving simultaneously the transient energy equation and the radiation transport equation. An implicit finite volume scheme is employed to solve the energy equation, with the discrete ordinate method being used to deal with the radiation transport. A systematical parametric study is performed and the effects of various materials optical properties and processing conditions are investigated. It is found that decreasing the optical thickness and increasing the scattering albedo both lead to a wider mushy zone and a slower rate of solidification. 相似文献
28.
A systematic study of wall effects on the shear viscosity of short glass fiber-filled polypropylene and polystyrene is presented. The dependence of these effects on capillary radius, shear rate, temperature, and polymer matrix is examined. The “true” viscosity curves of these materials (free from wall effects) can be obtained by an extrapolation procedure. Breakage of glass fibers in the high shear-rate processes of extrusion and injection molding lead to an appreciable reduction of the viscosity of these materials and is probably the more important effect to take into account in these processes. 相似文献
29.
Proton-exchanged planar waveguides were demonstrated in Z-cut LiNBO/sub 3/ using toluic acid as a new organic proton source. These waveguides exhibit a propagation loss of around 1 dB/cm, and a step refractive index profile with an index increase of 0.124 measured at 0.663 mu m. The diffusion rate was found to be lower than those obtained using the popular benzoic and phosphoric acids.<> 相似文献
30.
Shye Lin Wu Chung Len Lee Tan Fu Lei Chen C.F. Chen L.J. Ho K.Z. Ling Y.C. 《Electron Device Letters, IEEE》1994,15(4):120-122
In this study, it is demonstrated that the incorporation of fluorine can enhance poly-Si/Si interfacial oxide break-up in the poly-Si emitter contacted p+-n shallow junction formation. The annealing temperature for breaking up the poly-Si/Si interfacial oxide has been found to be as low as 900°C. As a result, the junction depth of the BF2-implanted device is much larger than that of the boron-implanted device 相似文献