全文获取类型
收费全文 | 31175篇 |
免费 | 3403篇 |
国内免费 | 2405篇 |
专业分类
电工技术 | 372篇 |
技术理论 | 1篇 |
综合类 | 1925篇 |
化学工业 | 14643篇 |
金属工艺 | 459篇 |
机械仪表 | 2201篇 |
建筑科学 | 2544篇 |
矿业工程 | 809篇 |
能源动力 | 947篇 |
轻工业 | 4609篇 |
水利工程 | 690篇 |
石油天然气 | 1518篇 |
武器工业 | 152篇 |
无线电 | 650篇 |
一般工业技术 | 3309篇 |
冶金工业 | 785篇 |
原子能技术 | 539篇 |
自动化技术 | 830篇 |
出版年
2024年 | 106篇 |
2023年 | 411篇 |
2022年 | 839篇 |
2021年 | 1279篇 |
2020年 | 1112篇 |
2019年 | 1179篇 |
2018年 | 1064篇 |
2017年 | 1059篇 |
2016年 | 1181篇 |
2015年 | 1126篇 |
2014年 | 1691篇 |
2013年 | 2050篇 |
2012年 | 2019篇 |
2011年 | 2174篇 |
2010年 | 1635篇 |
2009年 | 1681篇 |
2008年 | 1569篇 |
2007年 | 1986篇 |
2006年 | 1920篇 |
2005年 | 1701篇 |
2004年 | 1432篇 |
2003年 | 1306篇 |
2002年 | 1006篇 |
2001年 | 861篇 |
2000年 | 684篇 |
1999年 | 671篇 |
1998年 | 553篇 |
1997年 | 504篇 |
1996年 | 343篇 |
1995年 | 317篇 |
1994年 | 276篇 |
1993年 | 271篇 |
1992年 | 200篇 |
1991年 | 144篇 |
1990年 | 92篇 |
1989年 | 92篇 |
1988年 | 61篇 |
1987年 | 48篇 |
1986年 | 44篇 |
1985年 | 45篇 |
1984年 | 57篇 |
1983年 | 39篇 |
1982年 | 36篇 |
1981年 | 51篇 |
1980年 | 22篇 |
1979年 | 7篇 |
1961年 | 2篇 |
1959年 | 2篇 |
1955年 | 3篇 |
1951年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
81.
82.
This paper presents the mass transfer results from an impinging liquid jet to a rotating disk. The mass transfer coefficients were measured using the electrochemical limiting diffusion current technique (ELDCT). Rotational Reynolds number (Rer) in the range of 3.4 × 104–1.2 × 105, jet Reynolds number (Rej) 1.7 × 104–5.3 × 104 and non-dimensional jet-to-disk spacing (H/d) 2–8 were taken into consideration as parameters. It was found that the jet impingement resulted in a substantial enhancement in the mass transfer compared to the case of the rotating disk without jet. 相似文献
83.
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
84.
高层地下室底板混凝土施工的裂缝控制 总被引:1,自引:0,他引:1
以德益花园写字公寓楼地下室底板205m厚混凝土的施工工程为例,坚持预防为主的原则,采取了一系列温控技术措施,有效地防止或控制了温度裂缝(收缩裂缝)的产生,确保了混凝土的施工质量。 相似文献
85.
For the first time, order-order and order-disorder transitions were detected and characterized in a model diblock copolymer of poly(butadiene-1,3) and poly(dimethylsiloxane) (PB-b-PDMS). This model PB-b-PDMS copolymer was synthesized by the sequential anionic polymerization (high vacuum techniques) of butadiene 1,3 (B) and hexamethylciclotrisiloxane (D3), and subsequently characterized by nuclear magnetic resonance (1H and 13C NMR), size exclusion chromatography (SEC), Fourier Transform infrared spectroscopy (FTIR), Small-Angle X-ray scattering (SAXS) and rheology. SAXS combined with rheological experiments shows that the order-order and order-disorder transitions are thermoreversible. This fact indicates that the copolymer has sufficient mobility at the timescale and at the temperatures of interest to reach their equilibrium morphologies. 相似文献
86.
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
87.
Ring‐opening polymerization of D,L ‐lactide (LA) has been successfully carried out by using rare earth 2,6‐dimethylaryloxide (Ln(ODMP)3) as single component catalyst or initiator for the first time. The effects of different rare earth elements, solvents, monomers and catalyst concentration as well as polymerization temperature and time on the polymerization were investigated. The results show that La(ODMP)3 exhibits higher activity to prepare poly(D,L ‐lactide) (PLA) with a viscosity molecular weight of 4.5 × 104 g mol?1 and the conversion of 97 % at 100 °C in 45 min. The catalytic activity of Ln(ODMP)3 has following sequence: La > Nd > Sm > Gd > Er > Y. A kinetic study has indicated that the polymerization is first order with respect to both monomer and catalyst concentration. The apparent activation energy of the polymerization of LA with La(ODMP)3 is 69.6 kJ mol?1. The analyses of polymer ends indicate that the LA polymerization proceeds according to ‘coordination–insertion’ mechanism with selective cleavage of the acyl–oxygen bond of the monomer. Copyright © 2004 Society of Chemical Industry 相似文献
88.
London Resin (LR) White is a commonly used resin for embedding specimens to be used for immuno- and/or cytochemical studies. In some instances, due to either the properties of the specimen or the availability of various reagents and equipment, it becomes necessary and/or more convenient to polymerize LR White using heat rather than chemical accelerators or UV light. It is known, however, that heat can reduce or even eliminate the anti genicity of the tissue being embedded. It is therefore desirable to polymerize specimens at the lowest temperature possible and to remove the specimens from the oven as soon as polymerization is complete. We have developed a technique that provides a visual marker that allows the exothermic polymerization of LR White to be monitored, thus minimizing the amount of time a specimen must stay in the oven while excluding oxygen from capsules of polymerizing LR White. 相似文献
89.
文章以上海富华大厦工程为例,对在高温季节如何针对大体积混凝土基础施工的裂缝进行控制,提出了相关措施,达到了控制裂缝的预期目标。 相似文献
90.
结合大同铁路分局中心医院直线加速器室工程实际,介绍了大体积防射线混凝土的特点及施工中应注意的事项,并阐述了具体的施工技术。 相似文献