全文获取类型
收费全文 | 1916篇 |
免费 | 98篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 14篇 |
综合类 | 1篇 |
化学工业 | 446篇 |
金属工艺 | 44篇 |
机械仪表 | 51篇 |
建筑科学 | 47篇 |
矿业工程 | 3篇 |
能源动力 | 83篇 |
轻工业 | 176篇 |
水利工程 | 11篇 |
石油天然气 | 19篇 |
无线电 | 179篇 |
一般工业技术 | 301篇 |
冶金工业 | 355篇 |
原子能技术 | 34篇 |
自动化技术 | 253篇 |
出版年
2024年 | 12篇 |
2023年 | 18篇 |
2022年 | 70篇 |
2021年 | 85篇 |
2020年 | 62篇 |
2019年 | 63篇 |
2018年 | 57篇 |
2017年 | 61篇 |
2016年 | 62篇 |
2015年 | 45篇 |
2014年 | 50篇 |
2013年 | 95篇 |
2012年 | 81篇 |
2011年 | 94篇 |
2010年 | 65篇 |
2009年 | 74篇 |
2008年 | 72篇 |
2007年 | 65篇 |
2006年 | 53篇 |
2005年 | 62篇 |
2004年 | 44篇 |
2003年 | 22篇 |
2002年 | 25篇 |
2001年 | 26篇 |
2000年 | 41篇 |
1999年 | 33篇 |
1998年 | 105篇 |
1997年 | 77篇 |
1996年 | 49篇 |
1995年 | 36篇 |
1994年 | 25篇 |
1993年 | 36篇 |
1992年 | 14篇 |
1991年 | 18篇 |
1990年 | 12篇 |
1988年 | 16篇 |
1987年 | 15篇 |
1986年 | 9篇 |
1985年 | 17篇 |
1983年 | 12篇 |
1982年 | 8篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 14篇 |
1977年 | 15篇 |
1976年 | 17篇 |
1973年 | 6篇 |
1972年 | 6篇 |
1969年 | 6篇 |
排序方式: 共有2017条查询结果,搜索用时 0 毫秒
71.
Polyacrylamide homopolymers and graft copolymers of poly(acrylamide-g-ethylene oxide) and poly(acrylamide-g-propylene oxide) were synthesized, characterized by SEC, FTIR and 13C-NMR and the behavior of their aqueous solutions was evaluated by surface tension measurements. By using the macromonomer
technique, it is more difficult to incorporate poly(propylene oxide) branches than poly(ethylene oxide) branches. Graft copolymers
of polyacrylamide and poly(propylene oxide) showed higher reduction of surface tension than poly(acrylamide-g-ethylene oxide) since they present a structure made up of hydrophilic and hydrophobic segments. Poly(acrylamide-g-propylene oxide) exhibits surfactant behavior, and the surface tension of its aqueous solution depends on the poly(propylene
oxide) graft chain length and amount.
Received: 9 December 1996/Revised: 15 May 1997/Accepted: 23 May 1997 相似文献
72.
Susan J. Altman Richard P. Jensen Malynda A. Cappelle Andres L. Sanchez Randy L. Everett Howard L. Anderson Lucas K. McGrath 《Desalination》2012
A pilot study was conducted to determine whether membrane treatment on a side stream of recirculating cooling-tower water could reduce overall water usage and discharge. The treated permeate was returned to the cooling tower while the concentrate was discharged to the sanitary sewer. Flow rates, pressures and water chemistry were monitored. The pilot demonstrated potential substantial water savings. Maximum make-up water and discharge reduction were 16% and 49%, respectively. As high as possible permeate recovery is needed to maximize water conservation. Silica scaling on the membranes limited water savings in this pilot. Development of membranes with a solute-rejection capacity less than the 92% average of the membranes used in the pilot would assist in optimizing water savings. Decreased water outlays compensated for the additional energy used by membrane treatment. Scaling control is critical for economic operation. 相似文献
73.
Lize M. S. L. Oliveira Rita C. P. Nunes Larissa M. B. Pessoa Leidiane G. Reis Luciana S. Spinelli Elizabete Fernandes Lucas 《应用聚合物科学杂志》2020,137(33):48969
One of the methods to prevent wax precipitation, during petroleum production, transport, and refining, is the use of polymer additives that can reduce the oil pour point. However, no single additive work for all types of crude oil and this relation is not yet well known. In this study, a family of polymers based on poly(ethylene-co-vinyl acetate), containing hydroxyl groups and long pendant hydrocarbon chains (from C6 to C18), were synthesized and characterized by H1 nuclear magnetic resonance and solubility test. Four crude oil samples containing different amounts and size distribution of the wax were used. The additive's action is favored by higher contents of iso + cycloalkanes and lower contents of n-paraffins with larger chain sizes. The presence of the CH3COO group in the copolymers promoted the lowering of the pour point, supported by a low OH concentration and the presence of a long pendant hydrocarbon chain: the best results were obtained with C10 and C12 chain lengths. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48969. 相似文献
74.
Roberta K. Rodrigues Lucas A. S. Silva Gabriel G. Vargas Bruno V. Loureiro 《Journal of surfactants and detergents》2020,23(1):21-40
This study describes the effects of wormlike micelles formed by the commercial surfactants tallowalkylamidopropyl dimethylamine oxide (Aromox APA-TW) and oleyl methyl bis(2-hydroxyethyl) ammonium chloride (Ethoquad O/12) as drag reducers. Ethoquad O/12 is immune to degradation by heat and microorganisms. Conversely, Aromox APA-TW is biodegradable in the environment, and its susceptibility to heat-induced degradation was previously assessed. This work considers the effects of temperature, salt, and time on the drag-reduction capacity (in different Reynolds number) of wormlike micelles of these two surfactants. Wormlike micelles formed by Aromox APA-TW are able to reduce drag at higher temperatures compared to wormlike micelles formed by Ethoquad O/12. However, Aromox APA-TW can degrade after being heated to 80 °C and also after storage of the wormlike micelle solutions. Ethoquad O/12 does not undergo degradation after being heated or stored. These surfactants have the potential to be used as additives in industrial operations, as the wormlike micelles formed are able to reduce drag in systems with long pumping distances or recirculation, even in solutions with high salt concentrations (brine) and high temperatures. 相似文献
75.
Lucas Jégo Daniel Milési Jean-Jacques Robin Christine Joly-Duhamel 《Polymer Engineering and Science》2020,60(1):95-103
The photocrosslinking of thick samples of 5-ethylidene-2-norbornene–ethylene propylene diene monomer (ENB-EPDM) under air at room temperature was investigated. First, a model study was carried out on low-molecular weight oligomers: squalene, 1,2-polybutadiene, and 1,4-polybutadiene. Several crosslinking agents (meth(acrylics), bismaleimide, and thiol) combined with various photoinitiators were tested to improve the reactivity of these oligomers under UV irradiation. Gel contents, crosslinking densities, viscosities, and viscoelastic properties were measured in order to characterize the extent of crosslinking. Acrylate-based crosslinking agents appeared to be the most reactive species and these results were then applied to a low-molecular weight EPDM. Several photoinitiators were tested and benzophenone turned out to be the most efficient photoinitiator when combined with trimethylolpropane triacrylate. Finally, a commercial EPDM was subsequently photocrosslinked and high gel content and crosslinking density were obtained after only 2 min of irradiation. POLYM. ENG. SCI., 60:95–103, 2020. © 2019 Society of Plastics Engineers 相似文献
76.
Wax crystallization can cause serious damage to petroleum flow because as the viscosity increases, there is organic deposition in the pipe lines, which causes oil production reduction. Ethylene–vinyl acetate copolymers (EVA) are used as an alternative to prevent such problems. The influence of EVA copolymers on the properties of wax synthetic systems, composed of a solvent mixture and paraffin and petroleum asphalt residue (PAR), was evaluated in this work. The performance of EVA as a wax inhibitor depends on the molecular weight and vinyl acetate content of the copolymer and on the presence of the asphalt fraction. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1337–1348, 2002 相似文献
77.
Jean-Pierre Guin Tanguy Rouxel Jean-Christophe Sanglebuf Isabelle Melscoët Jacques Lucas 《Journal of the American Ceramic Society》2002,85(6):1545-1552
Ge–Se chalcogenide glasses are characterized by relatively low hardness (0.39–2.35 GPa) and low fracture toughness (0.1–0.28 MPa·m1/2 ). Actually, the hardness of chalcogen-rich glasses is low enough so that the brittleness parameter, B = H / K c , is lower than that of silicate glasses. Whereas hardness and Young's modulus increase with increasing germanium contents, fracture toughness follows a trend similar to that of the density and exhibits a maximum for the Ge20 Se80 composition, which corresponds to the rigidity percolation threshold. Optical microscopy and atomic force microscopy observations suggest that the indentation deformation proceeds by a localized shear deformation phenomenon. Glasses in the chalcogen-rich region behave viscoelastically at room temperature. As a consequence, an increase of the loading time results in a decrease of hardness and toughness. 相似文献
78.
Summary A synthetic approach for the preparation of poly(aryl ether amides) has been developed where the generation of an aryl ether
linkage was the polymer-forming reaction. The amide moiety was found to be sufficiently electron withdrawing to activate halosubstituents,
towards nucleophilic aromatic substitution polymerizations, analogous to conventional activating groups (i.e, sulfone, ketone
etc.). Several new A-B monomers, 4-fluoro-N-(4-hydroxyphenyl)benzamide, 1, and 4-fluoro-N-(3-hydroxyphenyl)benzamide, 2, which contain both an amide-activated fluoro group and a phenol group were prepared and their self polymerization studied.
Compounds 1 and 2 were prepared by the condensation of 4-fluorobenzoyl chloride with either 4-or 3-aminophenol, respectively. The polymerizations
were carried out in an N-methyl-2-pyrrolidone (NMP)/N-cyclohexyl-2-pyrrolidone (CHP) solvent mixture in the presence of potassium
carbonate. Several new high molecular weight poly(aryl ethers) were prepared by this route with Tg's in the 225 °C range. 相似文献
79.
A.?de?Lucas J.?Rincón I.?GraciaEmail author 《Journal of the American Oil Chemists' Society》2003,80(2):181-188
Supercritical CO2 extraction is a viable alternative process for the extraction of high-quality oil from olive husk (also known as olive pomace),
a residue obtained in the production of olive oil. We analyzed the effect of pressure (100–300 bar), temperature (40–60°C),
solvent flow (1–1.5 L/min), and particle size (0.30–0.55 mm) on four important quality parameters of the oil extracted with
CO2: tocopherol concentration, extinction coefficients at 232 and 270 nm, and saponification value. Response surface methodology
was used to obtain mathematical expressions related to the operating variables and parameters studied. Results from these
experiments were also used to design a three-step sequential CO2 extraction procedure to obtain a higher-quality extract. The optimal operational sequence consisted of a first extraction
step at 75 bar for 1 h using 1% (vol/vol) ethanol modifier, followed by a second extraction stage at 350 bar for 2.5 h without
ethanol and a third step, also at 350 bar, for 2.5 h but using ethanol. These extraction conditions obtained an intermediate
fraction of oil with 64% yield and all normal parameters according to European Commission food legislation. This fraction
is suitable without any further refining. On the contrary, the oils obtained by hexane extraction and by conventional supercritical
CO2 extraction at optimal conditions are suitable for human consumption after further refining. This last finding may result
in improved economics of the sequential CO2 extraction process compared to the conventional extraction method with hexane. 相似文献
80.
Trang Vu Ye Xue Trinh Vuong Matthew Erbe Christopher Bennet Ben Palazzo Lucas Popielski Nelson Rodriguez Xiao Hu 《International journal of molecular sciences》2016,17(9)
This study reports the formation of biocompatible hydrogels using protein polymers from natural silk cocoon fibroins and sheep wool keratins. Silk fibroin protein contains β-sheet secondary structures, allowing for the formation of physical cross-linkers in the hydrogels. Comparative studies were performed on two groups of samples. In the first group, ultrasonication was used to induce a quick gelation of a protein aqueous solution, enhancing the ability of Bombyx mori silk fibroin chains to quickly entrap the wool keratin protein molecules homogenously. In the second group, silk/keratin mixtures were left at room temperature for days, resulting in naturally-assembled gelled solutions. It was found that silk/wool blended solutions can form hydrogels at different mixing ratios, with perfectly interconnected gel structure when the wool content was less than 30 weight percent (wt %) for the first group (ultrasonication), and 10 wt % for the second group (natural gel). Differential scanning calorimetry (DSC) and temperature modulated DSC (TMDSC) were used to confirm that the fibroin/keratin hydrogel system was well-blended without phase separation. Fourier transform infrared spectroscopy (FTIR) was used to investigate the secondary structures of blended protein gels. It was found that intermolecular β-sheet contents significantly increase as the system contains more silk for both groups of samples, resulting in stable crystalline cross-linkers in the blended hydrogel structures. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to analyze the samples’ characteristic morphology on both micro- and nanoscales, which showed that ultrasonic waves can significantly enhance the cross-linker formation and avoid phase separation between silk and keratin molecules in the blended systems. With the ability to form cross-linkages non-chemically, these silk/wool hydrogels may be economically useful for various biomedical applications, thanks to the good biocompatibility of protein molecules and the various characteristics of hydrogel systems. 相似文献