全文获取类型
收费全文 | 3047篇 |
免费 | 100篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 63篇 |
综合类 | 4篇 |
化学工业 | 1020篇 |
金属工艺 | 70篇 |
机械仪表 | 34篇 |
建筑科学 | 198篇 |
矿业工程 | 30篇 |
能源动力 | 34篇 |
轻工业 | 380篇 |
水利工程 | 11篇 |
石油天然气 | 3篇 |
无线电 | 161篇 |
一般工业技术 | 422篇 |
冶金工业 | 281篇 |
原子能技术 | 28篇 |
自动化技术 | 409篇 |
出版年
2022年 | 27篇 |
2021年 | 37篇 |
2020年 | 32篇 |
2019年 | 29篇 |
2018年 | 42篇 |
2017年 | 43篇 |
2016年 | 68篇 |
2015年 | 91篇 |
2014年 | 78篇 |
2013年 | 116篇 |
2012年 | 113篇 |
2011年 | 155篇 |
2010年 | 110篇 |
2009年 | 113篇 |
2008年 | 118篇 |
2007年 | 136篇 |
2006年 | 116篇 |
2005年 | 110篇 |
2004年 | 103篇 |
2003年 | 72篇 |
2002年 | 68篇 |
2001年 | 57篇 |
2000年 | 55篇 |
1999年 | 54篇 |
1998年 | 89篇 |
1997年 | 62篇 |
1996年 | 62篇 |
1995年 | 60篇 |
1994年 | 74篇 |
1993年 | 44篇 |
1992年 | 48篇 |
1991年 | 41篇 |
1990年 | 26篇 |
1989年 | 37篇 |
1988年 | 22篇 |
1987年 | 31篇 |
1986年 | 34篇 |
1985年 | 39篇 |
1984年 | 38篇 |
1983年 | 36篇 |
1982年 | 33篇 |
1981年 | 31篇 |
1980年 | 27篇 |
1978年 | 26篇 |
1977年 | 35篇 |
1976年 | 35篇 |
1975年 | 43篇 |
1974年 | 23篇 |
1973年 | 23篇 |
1970年 | 30篇 |
排序方式: 共有3148条查询结果,搜索用时 31 毫秒
111.
Private investment subsidies are a key instrument for regional policy making to foster the economic development in lagging regions. In this paper, we analyze their effect on labor productivity growth for German labor market regions for the period from 1994 to 2006. A spatially augmented multiplicative interaction model based on neoclassical growth theory is used, which allows us to assess the marginal effect of regional policy proxied by overall payments of the main German regional development program on the region’s convergence speed conditional on its initial income position as well as policy-related spillovers from its spatial neighborhood. Our results show a statistically significant positive effect of regional policy on labor productivity growth, which increases, the further away the supported region is from its steady-state income level, and the more grants are provided to its geographical neighborhood. The latter effect highlights the existence of positive spatial spillover effects from regional policy in Germany, which enhance the attractiveness of the whole macro region for private sector investments. The additional growth stimulus provided by a 1 % increase in the region’s funding volume is thereby related to an up to 0.3 % gain in terms of labor productivity growth. For regions with the highest initial gaps to steady-state income in the sample distribution, the regional policy stimulus accounts for almost 8 % of the regions’ productivity growth performance. 相似文献
112.
Chalissery Jaime M. Gries Regine Alamsetti Santosh K. Ardiel Madison J. Gries Gerhard 《Journal of chemical ecology》2022,48(3):302-311
Journal of Chemical Ecology - Four species of Tetramorium pavement ants are known to guide foraging activities of nestmates via trail pheromones secreted from the poison gland of worker ants, but... 相似文献
113.
Amna Youssef Ramzy Ahmed Mohammed Moneeb El‐Sabbagh Leif Steuernagel Gerhard Ziegmann Dieter Meiners 《应用聚合物科学杂志》2014,131(3)
The presented study investigates the flow length and the corresponding fiber content distribution in the injection‐moulded natural fiber reinforced thermoplastics and its relation to fiber type and processing parameters such as injection pressure, temperature, injection rate and mould tempering by increasing die temperature. In this research, polypropylene compounds with nominally 30 wt % hemp and sisal fibers are investigated. The influence of the injection pressure (500 and 1000 bar), melt temperature (180°C, 200°C, and 220°C), and die temperature (23°C and 80°C) on the fiber content distribution all over the sample is investigated. An increasing linear trend of fiber content along the spiral length is observed as an evidence of a fiber/polymer multiflow system. A pattern for fiber content distribution with respect to the fiber length along the injected spiral can be distinguished, where the longer fibers are usually found at the end of the injected part and the shorter fibers remain near mould entrance point. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39861. 相似文献
114.
Turning wine (waste) into water: Toward technological advances in the use of constructed wetlands for winery effluent treatment 下载免费PDF全文
Craig Sheridan Diane Hildebrand David Glasser 《American Institute of Chemical Engineers》2014,60(2):420-431
The research presented in this article describes an investigation into the use of vegetated submerged reedbeds (VSR) as a practicable alternative for effluent treatment for small‐scale wine producers. In this study, we found that the hydraulic processes occurring within the VSR display significantly nonideal behavior. If the feed to the VSR was located on the surface the dead volume accounted for approximately 25% of the nonideal behavior of the system and bypass accounted for a further 6%. A preferential flow pattern was found within the VSR with the greatest flow occurring closest the surface and in the center, and the least at the sidewalls. We propose that the flow profile can be conceptualized as being hull shaped and found that this profile was the same for irregularly shaped gravel and for spherically shaped gelatinous beads. We, therefore, hypothesize that it is not dependent on the geometry of the VSR or the packing medium. © 2013 American Institute of Chemical Engineers AIChE J 60: 420–431, 2014 相似文献
115.
Jalal Poostforooshan Stephan Rennecke Manuel Gensch Sabine Beuermann Gabriella-Paula Brunotte Gerhard Ziegmann 《Aerosol science and technology》2014,48(10):1111-1122
This article presents a novel method to encapsulate gas-borne nanoparticles with a polymeric shell. This method implies heterogeneous condensation of monomer vapor around the surface of nanoparticles as nuclei and polymerization is then subsequently started by addition of NH3 as aerosol initiator. Ag and SiO2 nanoparticles were generated as inorganic core by spark discharge and nebulization, respectively, and glycidyl methacrylate (GMA) was used as organic monomer. The effect of several parameters, including vapor pressure of monomer and properties of inorganic core such as morphology, material, particle size, and production method on the thickness of polymeric shell and morphology of resulting nanocomposites has been investigated. The particle size distribution and morphology of the resulting core-shell nanoparticles have been studied via scanning mobility particle sizer (SMPS) and transmission electron microscope (TEM). Finally, the coating efficiency was determined by aerosol photoemission (APE) and the results show that monomer and polymer coating efficiency are 99% and 60%, respectively.
Copyright 2014 American Association for Aerosol Research 相似文献
116.
Gerhard Heise Andreas Brner Marcel Dickmann Marina Englmaier Andreas Heiss Matthias Kemnitzer Jan Konrad Regina Moser Jrg Palm Helmut Vogt Heinz P. Huber 《Progress in Photovoltaics: Research and Applications》2015,23(10):1291-1304
In this paper, we present the selective structuring of all three patterns (P1, P2 and P3) of a monolithic interconnection of CIS (Cu(In,Ga)(S,Se)2) thin film solar cells by picosecond laser pulses at a wavelength of 1064 nm. We show results for single pulse ablation threshold values and line scribing of molybdenum films on glass (P1), CIS on molybdenum (P2) and zinc oxide on CIS (P3). The purposes of these processes are the p‐type isolation (P1), cell interconnect (P2) and n‐type isolation (P3), which are required for complete cell architecture. The half micron thick molybdenum back electrode can be structured with a process speed of more than 15 m/s at about 15 W average power without detectable residues and damage by direct induced laser ablation from the back side (P1). The CIS layer can be structured selectively down to the molybdenum at process speeds up to 1 m/s at about 15 W average power, due to the precision of direct laser ablation in the ultrashort pulse regime (P2). The ZnO front electrode layer is separated by clean trenches with straight side walls at process speeds of up to 15 m/s at about 10 W average power, as a result of indirect induced laser ablation (P3). A validation of functionality of all processes is demonstrated on CIS solar cell modules (30 × 30 cm2). By replacing one state‐of‐the‐art process by a picosecond laser process at a time, solar efficiencies could be increased for P1 and P2 and stayed on a similar level for P3. After an optimization of the patterning processes in the R&D pilot line of AVANCIS, we achieved a new record efficiency for an all‐laser‐patterned CIS solar module: 14.7% as best value for the aperture area efficiency of a 30 × 30 cm2 sized CIS module was reached. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
117.
Pyrylium Compounds. 31. Reaction of 3-Alkyl-2,4,6-triarylpyrylium Salts with 1,3-Diketonates: A Method for the Preparation of 3-Acylsubstituted Benzophenones Reaction of 3-alkyl-2,4,6-triarylpyrylium salts with 1,3-diketones in the presence of one equivalent of triethylamine or potassium tert-butoxide does not lead — as originally suspected — to the primary adducts of 2H-pyran structure 6 , but to the open-chain valence isomers 7 . Treatment of the latter with one equivalent of tert-butoxide in tert-butyl alcohol gives the same 3-alkyl-2,4,6-triarylacetophenones 9 which are obtained directly from 5 , 1,3-diketones and two equivalents of potassium tert-butoxide. However, on treating 7 with aqueous ethanolic sodium hydroxide 3-acylsubstituted benzophenones 10 are formed in good yields. The reaction sequence 5→7→10 can also be performed through a one-pot-procedure. — The i.r., u.v., n.m.r. and mass spectroscopic data of the novel products 7, 9 , and 10 are reported. 相似文献
118.
Pyrylium Compounds. 37. Arylbenzenes from 2,4,6-Triarylpyrylium Salts and Carboxylic Acid Anhydrides Refluxing 2,4,6-triarylpyrylium salts 1 with excess carboxylic acid anhydrides (RCH2CO)2O ( 2a : R = H, 2b : R = Me) in the presence of condensing agents like sodium or potassium acetate, sodium carbonate or methoxide, triethylamine or pyridine results in 1,3,5-triarylbenzenes 3 (R = H, Me). Under similar conditions, phenylacetic acid anhydride ( 2c ), generated in situ from sodium phenylacetate and excess 2a or 2b , yields 1,2,3,5-tetraarylbenzenes 3 (R = Ph). Thus, the reaction 1 + 2 → 3 represents a new and simple method for replacing the pyrylium heteroatom =O⊕– by the =CR– moiety (R = H, Me, Ph). The structure of the arylbenzenes 3 was proved by spectroscopic methods, by comparison with literature data or by independent synthesis. As by-products 2-acyloxy-benzophenones 10 are formed. Reaction of 3,5-dimethyl-2,4,6-triphenyl-pyrylium perchlorate ( 11 ) with acetic acid anhydride/sodium acetate (or sodium phenylacetate) takes another course leading to 2-acetoxy-3,5-dimethyl-4,6-diphenyl-benzophenone ( 15 ), whereas treatment of 11 with propionic acid anhydride/sodium acetate follows the reaction scheme 1 + 2 → 3 giving 1,3,5-trimethyl-2,4,6-triphenylbenzene ( 16 ). The mechanisms of the different pyrylium ring transformations are discussed. 相似文献
119.
Hans-Rainer Sagaster Gerhard Rbisch Achim Mehlhorn 《Advanced Synthesis \u0026amp; Catalysis》1987,329(6):1045-1051
Investigations on the Tautomerism of o,o'-Dihydroxy Azo Dyes of the Eriochrome Type Investigation of the u.v.-vis-, 1H- and 13C-n.m.r. spectra of the title substances and the isomers 3 and 3p at different pH-values and in different solvent mixtures as well as of O,O'-dimethyl derivatives of 2 and 3 show that in aqueous solution as well the monoanions as the trianions exist in the azo forms only. The dianions exist in dependence on the solvents as mixtures of tautomers. The results of PPP calculations for different prototropic structures are in good accordance with the experimental results. 相似文献
120.