全文获取类型
收费全文 | 83658篇 |
免费 | 9080篇 |
国内免费 | 3241篇 |
专业分类
电工技术 | 4993篇 |
技术理论 | 5篇 |
综合类 | 6548篇 |
化学工业 | 17551篇 |
金属工艺 | 7918篇 |
机械仪表 | 4280篇 |
建筑科学 | 9597篇 |
矿业工程 | 1418篇 |
能源动力 | 10907篇 |
轻工业 | 3487篇 |
水利工程 | 1233篇 |
石油天然气 | 3587篇 |
武器工业 | 611篇 |
无线电 | 4055篇 |
一般工业技术 | 9911篇 |
冶金工业 | 4553篇 |
原子能技术 | 1757篇 |
自动化技术 | 3568篇 |
出版年
2024年 | 280篇 |
2023年 | 1125篇 |
2022年 | 2149篇 |
2021年 | 2515篇 |
2020年 | 2624篇 |
2019年 | 2158篇 |
2018年 | 1979篇 |
2017年 | 2351篇 |
2016年 | 2738篇 |
2015年 | 2812篇 |
2014年 | 4847篇 |
2013年 | 5137篇 |
2012年 | 5780篇 |
2011年 | 6326篇 |
2010年 | 4689篇 |
2009年 | 4840篇 |
2008年 | 4117篇 |
2007年 | 5372篇 |
2006年 | 4927篇 |
2005年 | 4432篇 |
2004年 | 3675篇 |
2003年 | 3404篇 |
2002年 | 3027篇 |
2001年 | 2453篇 |
2000年 | 2136篇 |
1999年 | 1721篇 |
1998年 | 1451篇 |
1997年 | 1293篇 |
1996年 | 1044篇 |
1995年 | 874篇 |
1994年 | 689篇 |
1993年 | 588篇 |
1992年 | 508篇 |
1991年 | 356篇 |
1990年 | 300篇 |
1989年 | 280篇 |
1988年 | 193篇 |
1987年 | 146篇 |
1986年 | 118篇 |
1985年 | 87篇 |
1984年 | 110篇 |
1983年 | 80篇 |
1982年 | 71篇 |
1981年 | 22篇 |
1980年 | 27篇 |
1979年 | 11篇 |
1978年 | 7篇 |
1966年 | 7篇 |
1959年 | 35篇 |
1951年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
J. Pujara M. A. Siddiqui Z. Liu P. Bjegovic S. S. Takagaki P. Y. Li S. Ramaswamy 《Drying Technology》2008,26(3):341-348
This is part II of a study reported earlier on a method to characterize the air flow and water removal characteristics during vacuum dewatering. This article presents experimental data and analysis of results from the use of a cyclically actuated vacuum dewatering device for removing moisture from wetted porous materials such as paper with the intermittent application of vacuum and accompanying air flow though the material. Results presented include sheet moisture content as a function of residence time and hence water removal rate under a variety of process conditions. Also, experimental results on air flow through the wet porous structure and hence the role and importance of air flow during vacuum dewatering are presented. Vacuum dewatering process conditions include exit solids content between 11 and 20% solid under applied vacuum conditions of 13.5 to 67.7 kPa (4 to 20 in. Hg). Regression analysis indicated that the exit sheet moisture content exhibited a nonlinear relationship with residence time with exit solids reaching a plateau after a certain residence time. Final moisture content correlated linearly with the average overall flow rate of air through the paper sample and the basis weight of the material. 相似文献
133.
Marta Fernndez-García Pedro Francisco Caamero Jos Luis de la Fuente 《Reactive and Functional Polymers》2008,68(9):1384-1391
Epoxy-functional spontaneous gradient copolymers of glycidyl methacrylate (G) and n-butyl acrylate (B) were synthesized via atom transfer radical polymerization (ATRP). The copolymerization reactions were carried out in toluene solution at 70 °C, using methyl 2-bromopropionate (MBrP) as initiator and copper chloride with N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA) as the catalyst system. The kinetic behaviour of the statistical copolymerizations was studied in a wide composition interval with molar fractions of G ranging from 0.10 to 0.75. The synthesized copolymers were characterized by size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) spectroscopy. 1H NMR was employed to determine the copolymer composition, demonstrating the gradient character of the copolymers along the main chain in the whole monomer conversion interval. Apart from this, the sequence distribution and stereoregularity were analyzed. These microstructural experimental data agreed well with those calculated from Mayo-Lewis terminal model (MLTM) and a Bernoullian statistic with an isotacticity parameter of σG = 0.28 and a coisotacticity parameter of σ = 0.30. 相似文献
134.
Giulio Croce Paola Dagaro Carlo Nonino 《International Journal of Heat and Mass Transfer》2007,50(25-26):5249-5259
135.
This study develops a mathematical model for coupled heat and mass transfer in an unsaturated porous slab exposed to a flowing hot gas. Effects of the initial saturation conditions on associated variables, i.e., total pressure, temperature, moisture content, and multiphase flow, are studied. The Newton-Raphson method based on a finite volume technique is applied. This study emphasizes the influence of initial saturation level and gravitational effect in heat and multiphase flow phenomena associated with this system. Gravity enhances the downward flow of liquid within the porous slab. Pressure buildup occurs near the interface between the wet and the dry zone. However, it appears that the order of magnitude to the total pressure is small. This study explains the fundamental mechanism of multiphase flow that involves heat and mass transfer in a heated unsaturated porous slab. 相似文献
136.
In office buildings, the use of passive cooling techniques combined with a reduced cooling load may result in a good thermal summer comfort and therefore save cooling energy consumption. This is shown in the low-energy office building ‘SD Worx’ in Kortrijk (Belgium), in which natural night ventilation and an earth-to-air heat exchanger are applied. In winter, the supply air is successively heated by the earth-to-air heat exchanger and the regenerative heat exchanger, which recovers the heat from the exhaust air. In summer, the earth-to-air heat exchanger cools the ventilation air by day. In addition, natural night ventilation cools down the exposed structure which has accumulated the heat of the previous day. In this article the overall thermal comfort in the office building is evaluated by means of measuring and simulation results. Measurements of summer 2002 are discussed and compared to simulations with a coupled thermal and ventilation simulation model TRNSYS-COMIS. The simulations are used to estimate the relative importance of the different techniques. The evaluation shows that passive cooling has an important impact on the thermal summer comfort in the building. Furthermore, natural night ventilation appears to be much more effective than an earth-to-air heat exchanger to improve comfort. 相似文献
137.
The main components of thermophotovoltaic (TPV) devices are the primary lens (or mirror), the absorber, the PV cell, and a photon recuperator system. A theory integrating all these components is used in this paper to analyse a particular type of TPV device (plane disk absorber and PV cell). The TPV efficiency is maximized by using three optimization parameters, namely absorber, PV cell temperatures, and cell voltage. Almost ideal operation conditions are envisaged and upper bounds are obtained for the TPV efficiency. They are strongly dependent on PV cell bandgap and radiation concentration. Preliminary results suggest the existence of an optimum solar radiation concentration ratio. The improvement in thermal design quality allows the usage of PV cells based on wide bandgap semiconductors. 相似文献
138.
本文探讨了60Si2Mn合金钢发蓝原理,针对其膜层泛红问题,分析了热处理、表面前处理、发蓝及浸油等过程对发蓝质量的影响,由此采取了相应的技术措施,生产实践证明发蓝质量稳定,生产效率明显提高。 相似文献
139.
In this work, the kinetics and mechanism of free-radical polymerisation of glycidyl methacrylate (GMA) using potassium peroxydisulphate
(PDS) as water soluble initiator in the presence of synthesized 1, 4-Bis (tributyl methyl ammonium) benzene dichloride (TBMABDC)
as multi-site phase transfer catalyst (MPTC) was studied. The polymerisation reactions were carried out under inert and unstirred
conditions at constant temperature of 60 ± 1°C in cyclohexane/water biphase media. The role of concentrations of monomer,
initiator, catalyst and volume fraction of aqueous phase, solvent polarity and temperature on the rate of polymerisation (Rp)
was ascertained. The order with respect to monomer and initiator was found to be unity. The order with respect to catalyst
was found to be 0.51. The rate of polymerisation is independent of ionic strength and pH of the medium. However, an increase
in the polarity of solvent has slightly increased the Rp value. Based on the results obtained, a suitable kinetic scheme has
been proposed to account for the experimental observations and its significance discussed. 相似文献
140.
裂齿矩形翅片板翅式换热器优化设计的分析 总被引:2,自引:0,他引:2
对裂齿矩形翅片板翅式换热器中的裂齿矩形翅片的传热效率作了分析,并以单位质量材耗的换热能力最大为目标函数,分析研究了在不同雷诺数(Re)的操作条件下裂齿矩形翅片间角度、翅片厚、长度、宽度及极厚之间的关系。结果表明:在气体换热的场合下,当Re在某一范围时翅片可有效地起到强化传热的作用。当板厚为5mm,翅片厚为3mm,翅片间夹角为45°~70°,Re为2×10~3~8×10~3,最佳翅片纵向间距与翅片长度和翅片厚度乘积的平方根的比为1.5~2.5,最佳翅片尺寸系数为3~5时,传热强化效果较好。 相似文献