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71.
TS-1, Ti-beta and Ti-MCM-41 molecular sieves have been prepared by direct hydrothermal synthesis method and applied to the epoxidation of n-hexene and cyclohexene with H2O2 under mild conditions. Ti-beta with extremely low Al content was synthesized by using a seed method to suppress the formation of diol produced by Brønsted acid sites present in Ti-beta. It was also found that a large amount of by-products (1-ol and 1-one) formed over hydrophilic Ti-MCM-41. We further modified Ti-MCM-41 by silylation with bis(trimethylsilyl) trifluoroacetamide (BSTFA). Among these catalysts, the Ti-beta with low content of Al enhanced the yield of epoxide and suppressed the formation of diol markedly. The silylated Ti-MCM-41 reduced the formation of by-products and promoted the yields of epoxide significantly. Based on experimental results, a reaction mechanism with two parallel and competitive reactions was proposed. 相似文献
72.
Dong‐Seon Won Jin‐Hyang Kim Hyo Jin No You Jin Cho Ju‐Yeon Lee Bum Ku Rhee Hee‐Dok Choi 《Polymer International》2010,59(2):162-168
Stabilization of electrically induced dipole alignment is one of the important criteria in the development of nonlinear optical (NLO) polymers for electro‐optic device applications. Polyurethanes for NLO applications have attracted attention because of their high thermal stability due to hydrogen bonding. In the work reported here, we designed and synthesized a new type of NLO polyurethane, in which the pendant NLO chromophores are part of the polymer backbone. This mid‐type NLO polymer is expected to have the merits of both main‐chain and side‐chain NLO polymers, namely stable dipole alignment and good solubility. 1‐[3,4‐Di‐(2‐hydroxyethoxy)phenyl]‐2‐(2‐thienyl)ethene was prepared and condensed with 3,3′‐dimethoxy‐4,4′‐biphenylenediisocyanate to yield a polyurethane. This polyurethane was reacted with tetracyanoethylene to give a novel Y‐type polyurethane (7) containing 1‐(3,4‐dioxyphenyl)‐2‐[5‐(1,2,2‐tricyanovinyl)‐2‐thienyl]ethenes as NLO chromophores, which constitute part of the polymer backbone. Polyurethane 7 is soluble in common organic solvents such as N,N‐dimethylformamide and dimethylsulfoxide. It shows a thermal stability up to 280 °C from thermogravimetric analysis with a glass transition temperature obtained from differential scanning calorimetry of ca 162 °C. The second harmonic generation (SHG) coefficient (d33) of a poled polymer film of he polyurethane at 1560 nm fundamental wavelength is ca 1.11 × 10?18 C. Polymer 7 exhibits an enhanced thermal stability and no significant SHG decay is observed below 150 °C, which is acceptable for NLO device applications. Copyright © 2009 Society of Chemical Industry 相似文献
73.
Taek Ho Yang Young Jang Jeong Jun Han Joon Shick Rhee 《Journal of the American Oil Chemists' Society》2001,78(3):291-296
For the synthesis of low-calorie structured lipids (LCSL), transesterification between triacetin and stearic acid using immobilized lipase in a solvent-free system was investigated. Stearic acid, a long-chain saturated fatty acid, was incorporated mainly into the sn-1 and/or sn-3 positions of triacetin by lipase-catalyzed reaction. Three types of reactor systems (open, closed, and vacuum) were studied for the production of LCSL. The effects of various reaction variables such as water activity of substrates and lipase, molar ratio of substrates, stirring speed and reaction temperature were investigated. In the vacuum reactor system, a certain amount of water was added periodically to maintain the optimal water content of the reaction system. When a suitable amount of water (0.65 wt% of substrates) was added at every 1 h into the vacuum reactor system, more than 88% LCSL was obtained within 4 h using Chirazyme® L-2. 相似文献
74.
Contact-induced Damage in Ceramic Coatings on Compliant Substrates: Fracture Mechanics and Design 总被引:2,自引:0,他引:2
Young-Woo Rhee Hae-Won Kim Yan Deng Brian R. Lawn 《Journal of the American Ceramic Society》2001,84(5):1066-1072
Simple explicit relations are presented for the onset of competing fracture modes in ceramic coatings on compliant substrates from Hertzian-like contacts. Special attention is given to a deleterious mode of radial cracking that initiates at the lower coating surface beneath the contact, in addition to traditional cone cracking and quasiplasticity in the near-contact area. The critical load relations are expressed in terms of well-documented material parameters (elastic modulus, toughness, hardness, and strength) and geometrical parameters (coating thickness and sphere radius). Data from selected glass, Al2 O3 and ZrO2 coating materials on polycarbonate substrates are used to demonstrate the validity of the relations. The formulation provides a basis for designing ceramic coatings with optimum damage resistance. 相似文献
75.
Rheological characteristics of two pretreated petroleum pitches, during their transformation to mesophase, have been studied
by using rotalional viscometer. Simultaneously, the formation, growth, coalescence of mesuphase spheres, and the alignment
of coalesced mesophase were observed by Hot-Stage-Cinema-Microscope, discussed with the results of viscosity change and the
Q.I. content. It is found that both pretreated pitches were Newtonian fluids at low temperature, but behaved pseudoplastics
as increase of mesophase content above 390C. Shear thinning behaviour was also apparent in the shear rate range of 1.9–20
sec−1 at temperature above 390C. The apparent viscosity-temperature curves of this pyrolysed pitches were much affected by the
pretreatment conditions. 相似文献
76.
Pramod K. Singh B. Bhattacharya R.K. Nagarale Kang-Wook Kim Hee-Woo Rhee 《Synthetic Metals》2010,160(1-2):139-142
Biopolymer composite membranes based on chitosan doped with an ionic liquid (IL) 1-ethyl 3-methylimidazolium thiocyanate (EMImSCN) have been developed and characterized. The doped ionic liquid films show remarkable enhancement in ionic conductivity (σ). The Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM) and X-ray diffraction studies (XRD) affirmed the composite nature, good incorporation of ionic liquid and reduction in crystallinity of films, respectively. The interaction between ionic liquid, chitosan and iodide polymer electrolyte matrix was evaluated by cyclic voltammetry. The fabricated dye sensitized solar cell (DSSC) using this new biopolymer electrolyte membranes shows promising performance. 相似文献
77.
Seung Yong Cho Jin Won Lee Chul Rhee 《International Journal of Food Science & Technology》2010,45(5):1042-1049
Deep‐fried instant noodles were cooked in a microwave oven at 557 W (medium power) and 657 W (full power). The microwave cooking times were determined based on textural parameters and the qualities of microwave oven cooked noodles at medium power and full power were compared with those of products cooked using a conventional gas stove for 9.1 min (CON). Heating in the microwave increased the temperature of the noodle block faster than the cooking water, led to an increased degree of gelatinisation of instant noodles, and reduced the cooking times to 8.5 min (medium power) and to 7.5 min (full power). Cooking in the medium power microwave resulted in high water absorption and weak hardness values. Cooking in the full power microwave resulted in higher hardness and tensile strength than the medium power microwave and sensory evaluated organoleptic scores were comparable to the CON, despite having a significantly higher rancidity. 相似文献
78.
Tae-Hyun Kim Jin-Goo Kang Jeong-Soo Sohn Kang-In Rhee Seoung-Won Lee Shun-Myung Shin 《Metals and Materials International》2008,14(5):655-658
The treatment of spent zinc-carbon batteries for the recovery of valuable metals followed by conversion to Mn−Zn ferrite has
been conducted employing two-stage alkali and acid leaching and co-precipitation method. In the first stage, leaching process
was carried out with 4 M NaOH, which resulted in a recovery of 63.4 %Zn and 0.1% Mn. Electrowinning of alkali leaching solution
containing 12.75 g/L Zn at a current density of 0.2 A/cm2 produced Zn metal of 15 nm to 30 nm size and 99.9% purity. The second stage leaching of residue with 3 M H2SO4 and 6 vol.% H2O2 at a solid/liquid ratio of 1∶10 indicated the leaching efficiency of 98.0% Zn, 97.9% Mn and 55.2% Fe. The obtained leaching
solution was finally adjusted to suitable mole ratios of Mn∶Zn∶Fe (1∶1∶4) by the addition of Zn and Fe sulfate salts followed
by pH control to produce Mn−Zn ferrite powder. The characterization of the ferrite powder showed uniform nano-crystalline
particles of about 20 nm size with spinel structure. 相似文献
79.
Sung-Chan Kim Baek-Seok Ko Tae-Jong Baek Byeong-Ok Lim An D. Dong-Hoon Shin Jin-Koo Rhee 《Microwave and Wireless Components Letters, IEEE》2005,15(10):652-654
The hybrid ring coupler was designed and fabricated on a GaAs substrate using surface micromachining techniques, which adopted dielectric-supported air-gapped microstrip line (DAML) structure. The fabrication process of DAML is compatible with the standard monolithic microwave integrated circuit (MMIC) techniques, and the hybrid ring coupler can be simply integrated into a plane-structural MMIC. The fabricated hybrid ring coupler shows wideband characteristics of the coupling loss of 3.57 /spl plusmn/ 0.22dB and the transmission loss of 3.80 /spl plusmn/ 0.08dB across the measured frequency range of 85 to 105GHz. The isolation characteristics and output phase differences are -34dB and 180/spl plusmn/1/spl deg/, at 94GHz, respectively. 相似文献
80.
S. Nourbakhsh O. Sahin W. H. Rhee H. Margolin 《Metallurgical and Materials Transactions A》1991,22(12):3059-3064
A pressure-cast NiAl composite reinforced with polycrystalline alumina (PRD-166) fibers containing 0.2 weight fraction of
partially stabilized zirconia was examined by optical and transmission electron microscopy (TEM). Fibers in the preform used
for casting were forced into contact, and fiber bonding occurred in a number of instances. Fiber volume fraction was increased
from an initial value of 0.4 to 0.6 as a consequence of the applied pressure. An explanation is offered for the interaction
of applied pressure, wetting angle, and the rigidity of the fiber preform on the final volume fraction of the fibers in the
composite. At the fiber/matrix interface, the alumina was free of zirconia particles. It is proposed that alumina grain growth
forced the zirconia into the molten NiAl, where it dissolved. As solidification took place, the concentration of zirconium
in the molten NiAl increased to a point where zirconium reacted with alumina to form zirconia again. 相似文献