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991.
This article presents the ternary phase diagram for methyl methacrylate (MMA), poly(methyl methacrylate) (PMMA), and n‐hexane system at 70°C. It was constructed by both theoretical calculations and online laser light scattering (LLS) technique. In situ polymerization of MMA in a nonpolar nonsolvent carried out in a LLS cell provides a new means for the accurate detection of the cloud points of highly viscous polymer mixtures, with polymer weight fractions over 0.6. The ternary phase diagram measured in this study can be used to design the reaction conditions for the precipitation and/or dispersion polymerization in a nonpolar nonsolvent medium where polymerization kinetics as well as polymer particle morphologies are strongly affected by thermodynamic phase separation phenomena. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
992.
Yiyoung Choi 《Polymer》2010,51(21):4713-4725
Supported hybrid catalysts using metallocenes and a nickel diimine catalyst were synthesized and used for ethylene slurry polymerization and ethylene/1-hexene copolymerization. Two types of metallocenes, together with a nickel diimine catalyst were supported onto SiO2 through chemical bonding, and a borate compound was physisorbed for the activation of the catalysts. These supported hybrid catalysts had high catalyst activities and made free-flowing polymer particles. The chemical composition distribution, molecular weight averages and distributions of resultant polymers were controlled by catalyst structure and polymerization conditions such as reaction temperature and the use of α-olefin. According to GPC-IR, 13C NMR and CEF characterization results of some polymers, more 1-hexene was incorporated in the high molecular weight region, short chain branches were generated by the chain walking mechanism in low molecular weight region. The morphologies of the resulting particles were investigated by SEM. 相似文献
993.
Hee Jung Kim Ji Eun Park Myung Gil Choi Sangdoo Ahn Suk-Kyu Chang 《Dyes and Pigments》2010,84(1):54-58
A novel, Hg2+-selective chemosensor was prepared via Mannich reaction of dichlorofluorescein with piperazinyl-coumarin moiety. The dichlorofluorescein–coumarin derivative exhibited well-defined Hg2+-selective chromogenic behavior, indicated by a green to pink colour change in solution, as well as fluorogenic signalling. Significant changes in fluorescence of the dichlorofluorescein subunit were analyzed in reference to the rather constant coumarin emission as an internal standard yielding Hg2+ selectivity. The Hg2+ selectivity of the chemosensor was not appreciably affected by the presence of common coexisting alkali, alkaline earth, and transition metal ions. The detection limit of the dichlorofluorescein–coumarin conjugate for the determination of Hg2+ ions was 4.3 × 10−6 mol L−1 and the conjugate dye could be used as a chemosensor for the analysis of Hg2+ ions in aqueous environments. 相似文献
994.
Dongho Seo Sangsun Park Yukwon Jeon Sung-Won Choi Yong-Gun Shul 《Korean Journal of Chemical Engineering》2010,27(1):104-109
The durability of PEMFCs is one of the most important issues for application in automotive vehicles with a repeated start-up
and shut-down system. The understanding of degradation phenomena such as causes, mechanisms and influence of working condition
is essential to improving the performance and lifetime of PEMFC. We conducted on/off cyclic operation in a single cell configuration
with ultra purity nitrogen gas to investigate the physical degradation of membrane electrode assembly (MEA). After on/off
cycle operation for 100,000 cycles under different humid condition, the characteristics of the MEAs were examined by in situ
and ex situ analyses techniques. The physical degradation of MEA by on/off cycling led to a change in the membrane-electrode
interfacial structure, which is mainly attributed to the loss of cell performance. 相似文献
995.
Bokkyu Choi 《Electrochimica acta》2010,55(28):8771-6701
Fuel cell/battery (FCB) systems are promising power generation/energy storage systems because of their bi-functionality as fuel cells and as secondary batteries. We investigated the required charging after the discharged manganese dioxide (MnOOH) by oxygen gas under the rest condition and during the fuel cell operation mode using manganese dioxide as a positive electrode for the FCB system. Electrochemical characterization was performed using cyclic voltammetry and galvanostatic measurements. Additionally, changes in the crystal structure and the chemical functional groups during the electrode reactions were monitored by X-ray diffractometry and Fourier transform infrared spectroscopy. The results indicated that MnOOH formed via the electrochemical discharge of manganese dioxide (MnO2) and that the oxyhydroxide can be chemically transformed back to MnO2 with gaseous oxygen (O2). The recharged MnO2 can be used as the cathode in a fuel cell with an O2 supply and it can also be electrochemically discharged without an O2 supply. In addition, we confirmed that MnO2 does not convert to Mn3O4 during the charge/discharge cycles if the redox reaction is maintained within a restricted range where a homogeneous process exists between MnO2 and MnOOH. The results in this study suggest that the FCB system can be constructed using MnO2 as the positive electrode and a metal hydride (MH) as the negative electrode, which can be rapidly charged to more than 70% of the theoretical capacity within 10 min using pressurized H2 and electrochemically discharged, in an alkaline electrolyte. This system possesses a high-power generation efficiency, a high-energy density and a high load-following capability. 相似文献
996.
Qiang Wang Ji Hyang Sohn So Ye Park Jin Seong Choi Joo Young Lee Jong Shik Chung 《Journal of Industrial and Engineering Chemistry》2010,16(1):68-73
Pure phase K4Zr5O12 is synthesized via solid state method in the present work. Various K/Zr ratios and temperatures are applied, and the synthesis process is investigated in detail by means of X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. Its catalytic activity for soot oxidation is studied by temperature programmed oxidation with different types of soot/catalyst contacts. It is revealed that K4Zr5O12 is very active in the presence of 2–10% O2 for both tight and loose contacts (Tp(tight) = 335 °C, Tp(ethanol) = 355 °C and Tp(shaking) = 370 °C). Thermal stability study shows that K4Zr5O12 is highly stable up to at least 900 °C. 相似文献
997.
Jae‐hong Choi Oh‐tak Kwon Hyun‐young Lee Andrew D Towns Chun Yoon 《Coloration Technology》2010,126(4):237-242
The synthesis and spectroscopic properties of monoazo dye series, whose members consist of N‐alkylphthalimide diazo components combined with a coupling component containing two ester groups, are reported. Such colourants are potentially alkali‐clearable as a consequence not only of the presence of diester functionality on the coupler, but also through use of the base‐sensitive phthalimide system. Shortening the N‐alkyl group by removing one or two methylene units from a butyl chain made little difference to absorption properties, as would be expected given the relatively minor differences in inductive character produced. Shifts in the absorption maximum of the dyes associated with dibromination of the phthalimidylazo motif and its subsequent cyanodehalogenation were in agreement with theory and literature data for related series. Diester substitution on the coupling component brought about hypsochromism and hypochromism. 相似文献
998.
Myung Lee Rui Zhang Chunhui Zhu Tae Rim Park Chang-Sub Shin Young-Ae Jeon Seong-Hee Lee Sang-Sung Choi Yong Liu Sung-Woo Park 《Communications Magazine, IEEE》2010,48(1):54-61
This article presents an overview of the IEEE project 802.15.5 that targets providing mesh capabilities to both high-rate and low-rate wireless personal area networks. Low-rate mesh is built on IEEE 802.15.4 MAC, while high-rate mesh utilizes IEEE 802.15.3 MAC. We seek to share our insights and motivations of the approach adopted in the major components of the standard instead of presenting a la carte items drawn in the specification. We hope this article helps readers of the 802.15.5 standard to better understand the rationale and intent of the protocol design. 相似文献
999.
Myoung-Ha Kim Il-Soo Kim Yong-Hee Park Tae-Eon Park Jung H. Shin Heon-Jin Choi 《Nanoscale research letters》2010,5(2):286-290
We report the optical activation of erbium coated silicon nanowires (Er–SiNWs) grown with the assist of platinum (Pt) and
gold (Au), respectively. The NWs were grown on Si substrates by using a chemical vapor transport process using SiCl4 and ErCl4 as precursors. Pt as well as Au worked successfully as vapor–liquid–solid (VLS) catalysts for growing SiNWs with diameters
of ~100 nm and length of several micrometers, respectively. The SiNWs have core–shell structures where the Er-crystalline
layer is sandwiched between silica layers. Photoluminescence spectra analyses showed the optical activity of SiNWs from both
Pt and Au. A stronger Er3+ luminescence of 1,534 nm was observed from the SiNWs with Pt at room- and low-temperature (25 K) using the 488- and/or 477-nm
line of an Ar laser that may be due to the uniform incorporation of more Er ions into NWs with the exclusion of the formation
of catalyst-induced deep levels in the band-gap. Pt would be used as a VLS catalyst for high performance optically active
Er–SiNWs. 相似文献
1000.