全文获取类型
收费全文 | 50157篇 |
免费 | 6370篇 |
国内免费 | 3913篇 |
专业分类
电工技术 | 2497篇 |
技术理论 | 6篇 |
综合类 | 4181篇 |
化学工业 | 12634篇 |
金属工艺 | 1502篇 |
机械仪表 | 3743篇 |
建筑科学 | 4942篇 |
矿业工程 | 1168篇 |
能源动力 | 5181篇 |
轻工业 | 5253篇 |
水利工程 | 1378篇 |
石油天然气 | 1562篇 |
武器工业 | 360篇 |
无线电 | 3144篇 |
一般工业技术 | 5831篇 |
冶金工业 | 1993篇 |
原子能技术 | 1215篇 |
自动化技术 | 3850篇 |
出版年
2024年 | 266篇 |
2023年 | 925篇 |
2022年 | 1708篇 |
2021年 | 2138篇 |
2020年 | 2035篇 |
2019年 | 2000篇 |
2018年 | 1803篇 |
2017年 | 1821篇 |
2016年 | 2010篇 |
2015年 | 1948篇 |
2014年 | 2852篇 |
2013年 | 3524篇 |
2012年 | 3172篇 |
2011年 | 3652篇 |
2010年 | 2689篇 |
2009年 | 2674篇 |
2008年 | 2554篇 |
2007年 | 3102篇 |
2006年 | 2791篇 |
2005年 | 2612篇 |
2004年 | 2118篇 |
2003年 | 1965篇 |
2002年 | 1567篇 |
2001年 | 1278篇 |
2000年 | 1055篇 |
1999年 | 878篇 |
1998年 | 835篇 |
1997年 | 727篇 |
1996年 | 607篇 |
1995年 | 553篇 |
1994年 | 422篇 |
1993年 | 371篇 |
1992年 | 324篇 |
1991年 | 235篇 |
1990年 | 217篇 |
1989年 | 185篇 |
1988年 | 140篇 |
1987年 | 108篇 |
1986年 | 98篇 |
1985年 | 74篇 |
1984年 | 93篇 |
1983年 | 56篇 |
1982年 | 43篇 |
1981年 | 63篇 |
1980年 | 28篇 |
1979年 | 12篇 |
1977年 | 7篇 |
1966年 | 8篇 |
1959年 | 17篇 |
1951年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
T. A. Hall 《Journal of microscopy》1991,164(1):67-79
When a microregion in a thin section of frozen-dried and embedded tissue is analysed by the conventional electron-probe X-ray continuum-normalization method, the measured quantity is in mmol of element per kg of embedded specimen. As each microregion contains an unknown amount of embedding medium, this quantity generally lies indeterminately somewhere within the wide range between mmol of element per kg of hydrated tissue and mmol of element per kg of dehydrated tissue. However, if a ‘tag’ element is incorporated in the embedding medium, the contribution of the medium to the local continuum count in each probed field should be measurable, and the X-ray data may then unambiguously yield mmol of element per kg of dehydrated tissue. This result should not be affected by shrinkage on freeze-drying or by incomplete replacement of water by embedding medium. The same X-ray data can additionally provide estimates of mmol of element per unit volume, mmol of element per kg of hydrated tissue and local dry-mass fraction. However, these estimates are subject to errors due to tissue shrinkage, incomplete replacement of water and beam damage. 相似文献
43.
Technology can take many forms from the development of sophisticated electronics to the application of basic procedural principles. Technology transfer can also take several forms, however, in this case, it is the transfer of technological principles between application domains that is of primary interest. This paper presents a framework (the Five ‘M’s framework) that can be used to consider the likely success of technology transfer. The framework is based upon a sociotechnical system approach. The framework is illustrated with an evaluation of the introduction of intelligent cruise control into motor vehicles. It is argued that this is a technological concept first developed as an aerospace application in the form of the autopilot. In this case, it is argued that the transfer of this technology in its current form may potentially compromise safety. 相似文献
44.
我国风机盘管技术现状分析 总被引:2,自引:2,他引:0
介绍了近年来我国在风机盘管技术领域的最新成果,在结构形式、强化传热、提高室内空气品质、降低噪音和提高自动控制水平等方面的技术进展情况,分析了目前风机盘管中存在的问题,并对今后的发展方向进行了展望。 相似文献
45.
Sirisha Nerella Debendra K. Das Godwin A. Chukwu Abhijit Y. Dandekar Santanu Khataniar Shirish L. Patil 《Petroleum Science and Technology》2003,21(7):1275-1294
Gas-to-liquids (GTL) technology involves the conversion of natural gas to liquid hydrocarbons. In this article, theoretical studies have been presented to determine the feasibility of transporting GTL products through the Trans-Alaska Pipeline System (TAPS). To successfully transport GTL through TAPS, heat loss along the route must be carefully determined. This study presents heat transfer and fluid dynamic calculations to evaluate this feasibility. Because of heat loss, the fluid temperature decreases in the direction of flow and this affects the fluid properties, which in turn influence convection coefficient and pumping power requirements. The temperature and heat loss distribution along the pipeline at different locations have been calculated. Fairly good agreement with measured oil temperatures is observed. The powers required to pump crude oil and GTL individually, against various losses have been calculated. Two GTL transportation modes have been considered; one as a pure stream of GTL and the second as a commingled mixture with crude oil. These results show that the pumping power and heat loss for GTL are less than that of the crude oil for the same volumetric flow rate. Therefore, GTL can be transported through TAPS using existing equipment at pump stations. 相似文献
46.
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
47.
F Javier Benítez Ana I Leal Francisco J Real Juan L Acero Gloria Roldán 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(3):309-316
BACKGROUND: The first stage of the cork industrial process generates great volumes of wastewater with moderate to high organic pollutant content that must be purified using different procedures, such as filtration by membranes. RESULTS: The tangential filtration of these wastewaters was studied using two different laboratory equipments. In the first one, three ultrafiltration (UF) membranes were tested, with molecular weight cut‐off (MWCO) 100 kDa and 30 kDa, and two operating modes were used: total recycling of permeate and retentate streams, and in continuous mode, without recycling both streams. In the total recycling UF experiments, the influence of the operating variables on the permeate flux was first established. The effectiveness of the different membranes was determined by evaluating the rejection coefficients for several parameters that measure the global pollutant content of the effluent. The values found for these rejection coefficients were in the following order: ellagic acid and color > absorbance at 254 nm > tannic content > COD (chemical oxygen demand). In the continuous mode experiments, the fouling mechanism for each membrane was established by fitting the experimental data to various filtration fouling models given in the literature. The operating mode in the second equipment was batch concentration, and additional experiments were carried out with an UF membrane (2 kDa), and with a NF membrane (with MWCO in the range 150–300 Da). CONCLUSIONS: The three operating modes tested provided different rejection levels of organic matter; among them, the most effective procedure tested was batch concentration mode using a NF membrane. Copyright © 2007 Society of Chemical Industry 相似文献
48.
49.
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
50.
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