全文获取类型
收费全文 | 3750篇 |
免费 | 180篇 |
国内免费 | 25篇 |
专业分类
电工技术 | 55篇 |
综合类 | 5篇 |
化学工业 | 930篇 |
金属工艺 | 104篇 |
机械仪表 | 102篇 |
建筑科学 | 122篇 |
矿业工程 | 9篇 |
能源动力 | 463篇 |
轻工业 | 330篇 |
水利工程 | 22篇 |
石油天然气 | 63篇 |
无线电 | 309篇 |
一般工业技术 | 660篇 |
冶金工业 | 256篇 |
原子能技术 | 26篇 |
自动化技术 | 499篇 |
出版年
2023年 | 66篇 |
2022年 | 163篇 |
2021年 | 196篇 |
2020年 | 137篇 |
2019年 | 119篇 |
2018年 | 199篇 |
2017年 | 144篇 |
2016年 | 164篇 |
2015年 | 102篇 |
2014年 | 155篇 |
2013年 | 274篇 |
2012年 | 187篇 |
2011年 | 228篇 |
2010年 | 148篇 |
2009年 | 161篇 |
2008年 | 132篇 |
2007年 | 123篇 |
2006年 | 106篇 |
2005年 | 65篇 |
2004年 | 74篇 |
2003年 | 77篇 |
2002年 | 59篇 |
2001年 | 38篇 |
2000年 | 43篇 |
1999年 | 44篇 |
1998年 | 77篇 |
1997年 | 54篇 |
1996年 | 45篇 |
1995年 | 61篇 |
1994年 | 34篇 |
1993年 | 45篇 |
1992年 | 30篇 |
1991年 | 29篇 |
1990年 | 22篇 |
1989年 | 24篇 |
1988年 | 14篇 |
1987年 | 15篇 |
1986年 | 15篇 |
1985年 | 25篇 |
1984年 | 29篇 |
1983年 | 16篇 |
1982年 | 25篇 |
1981年 | 28篇 |
1980年 | 20篇 |
1979年 | 24篇 |
1978年 | 17篇 |
1977年 | 15篇 |
1976年 | 13篇 |
1975年 | 12篇 |
1973年 | 13篇 |
排序方式: 共有3955条查询结果,搜索用时 15 毫秒
61.
The concept of solubility parameter, developed by Hansen, has been applied to the determination of solubility diagram of polysulfone and sulfonated polysulfone. Data showing the effect of various parameters such as thermodynamic quality of the solvent, casting solution composition and viscosity, solvent evaporation period and precipitation bath composition, on membrane structure and performance have been presented. By adjusting these parameters a wide variety of sulfonated polysulfone membranes useful for both ultrafiltration and reverse osmosis applications could be obtained. 相似文献
62.
Julia A. King Ibrahim Miskioglu Debra D. Wright‐Charlesworth Charles D. Van Karsen 《应用聚合物科学杂志》2007,103(1):328-335
In a composite material, the degree of adhesion between the fiber and the matrix plays an important role in the overall performance of the material. Because the load between the fiber and the matrix is realized throughout the interphase region material, a lot of effort has gone into characterizing the strength of the interphase. In this study, nanoscratch tests on the composite samples were used to provide a relative measure of adhesion in different composite materials. Carbon‐filled nylon 6,6 and polycarbonate resins were evaluated with this method. The carbon fillers we used were polyacrylonitrile‐based carbon fibers sized and surface‐treated for the respective matrix and pitch‐based carbon fibers without any sizing or surface treatment. Tensile and X‐ray photoelectron spectroscopy data for the composites we considered are also presented to compare to the nanoscratch results. It is shown that nanoscratch testing on the composites, with the proposed data analysis, can be an effective tool for determining the relative degree of adhesion between different composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 328–335, 2007 相似文献
63.
The effect of adding 330–4930 ppm hydrogen to a reaction mixture of NO and CO (2000 ppm each) over platinum and rhodium catalysts has been investigated at temperatures around 200–250°C. Hydrogen causes large increases in the conversion of NO and, surprisingly, also of CO. Oxygen atoms from the additional NO converted are eventually combined with CO to give CO2 rather than react with hydrogen to form water. This reaction is described by CO + NO +3/2H2 CO2 + NH3 and accounts for 50–100% of the CO2 formed with Pt/Al2O3 and 20–50% with Rh/Al2O3. With the latter catalyst a substantial amount of NO converted produces nitrous oxide. Comparison with a known study of unsupported noble metals suggests that isocyanic acid (HNCO) might be an important intermediate in a reaction system with NO, CO and H2 present. 相似文献
64.
The conventional pad-dry-cure method was used for effecting crosslinking of cotton with N-methylol finishing agents under different conditions. Factors studied include nature and concentration of finishing agent and softener, type and concentration of catalyst, and curing temperatures. Variation of soiling and soil release characteristics of crosslinked cotton with these factors were investigated. The effect of finishing agent on aqueous soiling followed the order: Carbamate reactant-fabric > Dimethylolethylene urea-fabric > Dimethyloldihydroxyethylene urea-fabric > Untreated fabric > Modified triazinone-fabric ≥ Modified ethylene urea-fabric. On the other hand, the effect of these finishing agents was to enhance the susceptibility of the fabric to oily soiling. Nevertheless, nature of the finishing agent governed the magnitude of this enhancement. Aqueous and oily soil release depended also upon the nature of finishing agent, soiling increased and soil release decreased by increasing finishing agent concentration. Type of catalyst exerted a considerable influence on aqueous and oily soil release without significantly affecting the degree of soiling. For aqueous soil release, the following order was found: Al2(SO4)3 · 18H2O > MgCl2 · 6H2O > urea nitrate > ZnCl2 · 6H2O > Zn(NO3)2 · 6H2O > urea phosphate > urea oxalate > NH4 · H2PO4 ≥ NH4Cl. A reverse order held good for oily soil release. Both aqueous and oily soil release were impaired by increasing catalyst concentration. Similarly, nature and concentration of the softener had no striking effect on soiling while they did on soil release. Raising the curing temperature from 80 to 140°C caused substantial reduction in case of soil removal of urea salts catalyzed-crosslinked cotton samples while having the degree of soiling practically intact. 相似文献
65.
Ibrahim R. Shimi Nabila A. Maroun Mamdouh Y. Kamel Hemmat H. Ragheb Mohga M. Badran 《Lipids》1974,9(6):368-373
Gas liquid chromatographic analysis of the fatty acid methyl esters from eggs ofDermacentor andersoni Stiles (Ixodidae) revealed the presence of significant quantities (15% total fatty acids) of an unidentified component with a retention time between C18∶3−C22∶0 fatty acids. Smaller amounts of the unidentified component (ca. 5% total fatty acid) also were detected in host rabbit serum. Purified, the unidentified component's methyl ester collected from the tick eggs by preparative gas liquid chromatography was partially identified and characterized by chemical and spectroscopic analyses. The evidence suggests that the unidentified component is a methyl branched C15 tricarboxylic acid containing two vicinal carboxylic acid groups. Biosynthesis of the unidentified component by the tick is under investigation. 相似文献
66.
Claude Leger Lucie Fremont Didier Marion Ibrahim Nassour Marie-Françoise Desfarges 《Lipids》1981,16(8):593-600
This paper describes evidence of (n−3) and particularly of 22∶6 (n−3) fatty acid enrichment in trout lipoproteins as well
as in vitellogenin, egg lipovitellin and oil globule. Among the lipoproteins, HDL and LDL were the main forms of blood lipid
transport, whereas phospholipids and cholesteryl esters are the preferential chemical carriers for (n−3) fatty acid transport.
However, cholesteryl esters were less important as esterified fatty acid carriers than in man. Taken together with the data
obtained in mammals, our results suggest that there may be a relationship between EFA activity and the distribution of the
EFA among the lipoprotein lipid fractions in vertebrates, irrespective of the EFA series. Administration of an (n−3) fatty
acid deficient diet for three months prior to trout spawning produced a significant increase in egg lipid content, primarily
as a result of the increase of the oil globule composed almost exclusively of triacylglycerols. This diet decreased the 22∶6
(n−3), as well as the (n−3) fatty acid contents of lipoproteins, lipovitellin, vitellogenin and the oil globule. In contrast,
the (n−3) fatty acid level was always higher in lipoproteins and lipovitellin than in the vitellogenin and the oil globule.
Moreover, the relative levels of 22∶6 (n−3) and total (n−3) fatty acids were quite similar in lipoproteins and lipovitellin
on the one hand, and in vitellogenin and the oil globule on the other. These findings suggest a direct relationship between
the two forms of plasma lipid transport and the two egg compartments. During ovogenesis, dietary lipids seemed to be diverted
from the adipose tissue and essentially deposited in the egg. 相似文献
67.
Sayeda M. Ibrahim 《应用聚合物科学杂志》2003,89(2):349-354
This work reports on the characterization and uses of gamma radiation‐crosslinked poly(vinyl alcohol) (PVA) films as absorbents for different classes of dyestuffs normally released from textile factors. Dyestuffs were selected from different producers. These dyestuffs were Remacryl Blue (basic dye), Remazol Golden Orange (reactive dye), Solar Orange (direct dye), and Sandolan (acid dye). The percentage dye sorption by PVA was determined by spectroscopic analysis and color‐strength measurements of the PVA films after absorbing the different dyestuffs. The results showed that the concentration of dimethylbisacrylamide as a crosslinking agent has a great effect on the gel fraction and percentage swelling in water of the PVA polymer. In general, crosslinked PVA showed a low tendency to absorb the different dyestuffs under investigation at room temperature. This tendency was shown to increase with an increasing temperature of the dye solution from room temperature to 70°C. Meanwhile, the highest percentage of dye sorption was found in the case of the basic dye and the lowest one in the case of the reactive dye depending on the active groups on the dyes. Moreover, the percentage dye sorption by PVA was slightly higher in the acid medium rather than in the alkaline one. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 349–354, 2003 相似文献
68.
The dynamics of a gas‐solid fluidized bed containing Geldart Group D particles mixed with a small proportion of Geldart Group B particles are investigated using pressure fluctuations data. Time series analysis, using a variety of nonlinear dynamics tools, shows that the slugging present with Group D particles can be suppressed by the addition of a small proportion of Group B particles. The power spectra and the auto‐correlation function are used for a preliminary evaluation of dominant slug frequencies. It is shown that the bed fluidized with the mixture of Group D and B particles behaves in a less periodic manner and is dominated by more random bubble motion. On the other hand, the correlation integral is used to analyze the chaotic behaviour of the flow, through evaluation of the fractal structure of the reconstructed attractors. It is shown that the bed fluidized with Group D particles is characterized by a combination of steady slug motion and irregular particles motion. The behaviour of the fluidized bed of Group D/B particles mixture is characterized by a single correlation dimension for a wide range of fluidization velocities. 相似文献
69.
70.
Jan Brinker Halil Ibrahim Gündüz 《The International Journal of Advanced Manufacturing Technology》2016,87(5-8):2259-2268
The determining of efficient packaging sizes is a key factor in saving material and transportation costs and also in reducing packaging waste. By analyzing the range of items and their contribution to sales-relevant order structures of a globally operating mail order company, a simplified packing algorithm is proposed. In combination with well-known methodologies, this heuristic provides near optimal solutions improving current packaging of eCommerce companies. It is shown that simple, practical heuristics are sufficient to achieve average material savings of more than 10 %. In order to find efficient packaging sizes, a set of them is generated by discretization of packaging dimensions. Given the set of orders and the set of packaging sizes, a p-median approach is applied to find a specified number of optimal, demand-related packaging sizes. 相似文献