全文获取类型
收费全文 | 8719篇 |
免费 | 769篇 |
国内免费 | 39篇 |
专业分类
电工技术 | 131篇 |
综合类 | 38篇 |
化学工业 | 2397篇 |
金属工艺 | 272篇 |
机械仪表 | 557篇 |
建筑科学 | 174篇 |
矿业工程 | 8篇 |
能源动力 | 344篇 |
轻工业 | 814篇 |
水利工程 | 26篇 |
石油天然气 | 15篇 |
无线电 | 1456篇 |
一般工业技术 | 1880篇 |
冶金工业 | 427篇 |
原子能技术 | 123篇 |
自动化技术 | 865篇 |
出版年
2024年 | 11篇 |
2023年 | 115篇 |
2022年 | 195篇 |
2021年 | 311篇 |
2020年 | 256篇 |
2019年 | 306篇 |
2018年 | 291篇 |
2017年 | 335篇 |
2016年 | 353篇 |
2015年 | 329篇 |
2014年 | 417篇 |
2013年 | 566篇 |
2012年 | 647篇 |
2011年 | 724篇 |
2010年 | 540篇 |
2009年 | 489篇 |
2008年 | 484篇 |
2007年 | 348篇 |
2006年 | 335篇 |
2005年 | 284篇 |
2004年 | 256篇 |
2003年 | 256篇 |
2002年 | 235篇 |
2001年 | 199篇 |
2000年 | 148篇 |
1999年 | 168篇 |
1998年 | 206篇 |
1997年 | 147篇 |
1996年 | 111篇 |
1995年 | 78篇 |
1994年 | 61篇 |
1993年 | 42篇 |
1992年 | 53篇 |
1991年 | 38篇 |
1990年 | 30篇 |
1989年 | 35篇 |
1988年 | 27篇 |
1987年 | 24篇 |
1986年 | 15篇 |
1985年 | 15篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 4篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1977年 | 3篇 |
1976年 | 12篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1914年 | 2篇 |
排序方式: 共有9527条查询结果,搜索用时 0 毫秒
61.
We determined the optimal reaction conditions to minimize the energy cost and the quantities of by‐products for a poly(ethylene terephthalate) process by using the iterative dynamic programming (IDP) algorithm. Here, we employed a sequence of three reactor models: the semibatch transesterification reactor model, the semibatch prepolymerization reactor model, and the rotating‐disc‐type polycondensation reactor model. We selectively chose or developed the reactor models by incorporating experimentally verified kinetic models reported in the literature. We established the model for the entire reactor system by connecting the three reactor models in series and by resolving some joint problems arising when different types of reactor models were interconnected. On the basis of the simulation results of the reactor system, we scrutinized the cause and effect between the reaction conditions and the final quality of the polymer product. Here, we set up the optimization strategy by using IDP on the basis of the integrated reactor model, and the process variables with significant influence on the properties of polymer were selected as control variables with the help of a simulation study. With this method, we could refine the reaction conditions at the end of each iteration step by contracting the spectra of control regions, and the iteration process finally stopped when the profile of the optimal trajectory converged. We also took the constraints on the control variables into account to guarantee polymer quality and to suppress side reactions. Constituting six different strategies by setting weighting vectors differently, we examined the differences in optimal trajectories, the trend of optimality, and the quality of the final polymer product. For each of the strategies, we conducted the optimization to examine whether the number‐average degree of polymerization approached the desired value. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 993–1008, 2002 相似文献
62.
Jae Ryong Kim Do-Hyeong Kim Chong Hee Kim 《Journal of the American Ceramic Society》1990,73(8):2567-2569
The effects of ZrO2 and Y2 O3 on the densification of hotpressed Si3 N4 -Zr(Y)O2 composites have been studied. High density could not be obtained by the addition of pure or 3-mol%-Y2 O3 -doped ZrO2 in this composite; however, nearly full density (>97%) could be obtained in Si3 N4 using 6- and 8-mol%-Y2 O3 -doped ZrO2 . It is concluded that Y2 O3 diffusing out from the added Zr(Y)O2 promoted the densification and that ZrO2 also had some role in the formation of an oxynitride glass. 相似文献
63.
High‐performance shape‐memory polyurethane block copolymers, prepared with two types of poly(tetramethylene glycol) (PTMG) used as soft segments, were investigated for their mechanical properties. Copolymers with a random or block soft‐segment arrangement had higher stresses at break and elongations at break than those with only one kind of PTMG. Random copolymers with fewer interchain interactions showed higher elongation than block copolymers. All the copolymers had shape‐recovery ratios higher than 80%. In dynamic mechanical testing, the glass‐transition behavior clearly depended on the soft‐segment arrangement: random copolymers had only one glass‐transition peak, whereas block copolymers showed two separate glass‐transition peaks. Overall, the control of the soft‐segment arrangement plays a vital role in the development of high‐performance shape‐memory polyurethane. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2410–2415, 2004 相似文献
64.
A new graphical estimation technique is proposed for the determination of the kinetic parameters describing an autocatalytic reaction. A differential scanning calorimeter was used to monitor the reaction kinetics of an epoxy-based vinyl ester resin. The method utilizes information from a zero initial reaction rate, conversation at vitrification, the ratio of reaction rate constants under different isothermal conditions, and characteristics of the phenomenological kinetic model with assumptions being made about the overall reaction order. By fitting data to the integrated reaction rate equation with adjustments for the isothermal conditions, the kinetic parameters are estimated without using a linear or nonlinear regression method. Different kinetic parameters can be estimated from data before and after the gel point which was obtained from the relationship between the glass transition temperature and the degree of cure. 相似文献
65.
The dynamical behavior of polymers with molecular weight distribution is analyzed from the standpoint of reptation and tube
renewal. In a binary blend where the entanglements between longer chains are prominent, the shorter chain relaxes only by
reptation, whereas the longer chain shows more complex behavior, i.e., reptation in the original tube, short-range tube renewal
causing the tube enlargement, and thereafter reptation again in the expanded tube. Dynamic moduli data from literature are
used for determining the compositional dependence of the relaxation times. Also on the basis of the relaxation mechanism considered
here, the critical composition due to the onset of entanglements between different longer chains is proposed as a function
of their component molecular weighl ratio. 相似文献
66.
Summary A confined stiff chain model is suggested for the prediction of the rotational diffusion coefficient of a rigid rodlike polymer with a slight flexibility above the region of dilute solution (c1/L3). It shows a fairly good agreement with the experimental data of various polymers. Among them, PBLG and PBT with more rigidity are more consistent with the model when the log-jamming effect is considered. The predicted rotational diffusivity shows approximately the inverse seventh-power of length, which is less than 9 of Doi-Edwards tube model, but larger than the experimental value 5.7 of M-virus, while it shows the inverse power of concentration is a little larger than the value 2 of tube model except for the rodlike virus M-13. 相似文献
67.
A heating process for obtaining free-standing carbon nanotube emitters is presented with the aim of improving field-emission properties from the screen-printed multiwalled carbon nanotube (MWCNT) films. Using an atmosphere with an optimum combination of nitrogen and air for heat treatment of CNT films, the CNT emitters can be made to protrude from the surface. This allows for a high emission current and the formation of very uniform emission sites without special surface treatment. The morphological change of the CNT film by this technique has eliminated additional processing steps, such as surface treatment which may result in secondary contamination and damage to the film. Despite its simplicity the process provides a high reproducibility in emission current density which makes the films suitable for practical applications. 相似文献
68.
Bo Hyun Ryu Sang Yup Lee Dong Hyun Lee Gui Young Han Tae-Jin Lee Ki June Yoon 《Catalysis Today》2007,123(1-4):303-309
Carbon black has recently been reported to act as an effective catalyst for methane decomposition and to exhibit stable catalytic behavior despite carbon deposition, and thus it can be used for CO2-free production of hydrogen from natural gas. In this work, various carbon blacks with different primary particle size were investigated with respect to methane decomposition under atmospheric pressure from 1123 to 1223 K. Catalytic characteristics, such as activity, activation energy and reaction order, were investigated and compared. It was observed that with decreasing primary particle size (or increasing specific surface area), the specific activity increased and the activation energy decreased. The reaction orders for various pelletized, rubber-reinforcing carbon blacks were 0.6–0.7, about the same regardless of the primary particle size, while they were near 1 for fluffy carbon blacks. Fluffy carbon black showed higher activity and activation energy than the pelletized carbon black of the same primary particle size. Changes of the surface morphology during carbon deposition were observed by TEM. Variations of the number of active sites were discussed in regard of the primary particle size, carbon deposition and binder. The presence of different types of active sites was also suggested. 相似文献
69.
Polypropylene (PP)/layered silicate nanocomposites were prepared via simple melt mixing of three components, PP, layered silicates modified with octadecylamine (C18-MMT) and antioxidant, to investigate the role of antioxidant. TEM and X-ray scattering results confirmed the intercalated state of silicates in PP/layered silicate nanocomposites with antioxidant. In rheological and mechanical study, the nanocomposites with antioxidant showed higher properties than those of the unfilled PP. The nanocomposite with 5 wt% C18-MMT and 0.5 phr antioxidant exhibited about 1.4 times higher tensile modulus and 1.3 times higher storage modulus than the unfilled PP. However, PP/C18-MMT without antioxidant showed lower rheological values owing to the thermal decomposition of PP and the poor compatibility between PP and C18-MMT. It could be concluded that antioxidants played an important role in enhancing the compatibility between PP and C18-MMT. According to the real time X-ray diffraction, the nanocomposite showed the weak ordering of PP crystals than the unfilled PP in the load-extension plateau region of elongation. 相似文献
70.
Zirconia-rich subsolidus phase relationships in the ZrO2 –Sc2 O3 and ZrO2 –In2 O3 systems were investigated. Phase inconsistencies in the ZrO2 –Sc2 O3 system resulted from a diffusionless cubic-to-tetragonal ( t' ) phase transformation not being recognized in the past. Through three different measuring techniques, along with microstructural observations, the solubility limits of the tetragonal and cubic phases were determined. 相似文献