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621.
由11支团队、50名社会科学和生态学领域的研究人员共同推进的法国国家方案"城市绿色框架(Trame Verte Urbaine)",已经建立了一套城市绿色基础设施的评估体系,并为法国各地实施地方层面的绿色基础设施政策制定了参考。城市绿地主要具有提供持续生态系统服务的功能,为规划者和各地方政府进行相关工作提供了一定参考,例如,绿道可以被视为新城市文明指引下的一项兼具美学和生态价值的基础设施。本文研究了法国3座具有不同城市文化和环境背景的城市,具体包括巴黎(法国北部),马赛(法国南部)和斯特拉斯堡(法国东部)。 相似文献
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623.
Escherichia coli aspartate transcarbamylase (ATCase) catalyzes the first committed step in pyrimidine biosynthesis, the condensation of aspartate and carbamyl phosphate. ATCase is positively allosterically regulated by ATP and negatively regulated by CTP. We have used mild solvent perturbation to gain global molecular information about the mechanism of heterotropic allostery. The [NaCl], temperature, and osmotic pressure dependence of the enzymatic activity of ATCase has been examined in the presence and absence of allosteric effectors. The results indicate that: 1) Regulation of aspartate binding by CTP appears to involve a unique set of electrostatic interactions not involved in enzyme function in the presence of ATP or in the absence of effectors. 2) Aspartate binding is enthalpically driven in the presence and absence of allosteric effectors. 3) The apparent enthalpy and entropy of aspartate binding (delta H, delta S), and activation energy of catalysis (Ea) are substantially altered in the presence of CTP but not ATP. 4) The change in hydration of ATCase upon substrate binding is the same in the presence and absence of allosteric effectors. 5) The linkage between heterotropic and homotropic allostery is different for ATP and CTP. 相似文献
624.
Parfait Ramiandrasoa Philippe Guérin Jean Pierre Girault Philippe Bascou Amel Hammouda Sandrine Cammas Michel Vert 《Polymer Bulletin》1993,30(5):501-508
Summary The cycloaddition of ketene to methyl, ethyl, isopropyl and n-butyl glyoxylates resulting from the scission of corresponding tartrate diesters has been used to prepare racemic 4-alkyloxycarbonyl 2-oxetanones. The reaction was conducted in dichloromethane at low temperature in the presence of triethylamine as catalyst. The use of a chiral tertiary amine instead of triethylamine yielded an optically active -lactone as shown in the case of methyl glyoxylate. The maximum enantiomeric excess was about 70 per cent and the sign of the elected enantiomer depended on the chiral base. Racemic n-butyl malolactonate was homopolymerized and copolymerized with benzyl malolactonate. High molecular weight polymers resulting from the homopolymerization of n-butyl malolactonate or from the copolymerization of this monomer with benzyl malolactonate were characterized by SEC and NMR. The ketene route was also used to synthesize racemic 4-trichloroethyloxycarbonyl 2-oxetanone, a -substituted -lactone, which had never been synthesized by other routes. 相似文献
625.
When scanning, managers acquire and collect information about their environment to keep informed of its evolution, make decisions, and sometimes to anticipate changes. We attempted to understand this process and assess how French managers interpret scanning information to evaluate its importance. Our effort resulted in: (1) sixteen factors used by managers to make sense of the signs and signals they perceived when scanning; (2) a heuristic model of the process; and (3) two instances of the model. Our results suggested that ad hoc training should be provided and IT use should be fully investigated to enhance managers’ scanning skills if organizations wish to develop an ability to detect weak signs/signals, anticipate plausible change, and increase strategic decision effectiveness. 相似文献
626.
Layered double hydroxide (LDH) organo-modified by a surface-active monomer, 3-sulfopropyl methacrylate (SPMA) was used as filler for polystyrene (PS). Different nanocomposites SPMA/LDH:PS were prepared by bulk polymerization process using low amount of initiator. The two components, filler and polymer, as well as the degree dispersion of the reactive filler as a function of its loading in PS were characterized by a combination of several techniques: X-ray diffraction, high resolution 13C CP-MAS NMR, FTIR, UV-visible, thermal analysis, SEC and MET. The nanocomposites were submitted to UV-light exposures in the presence of oxygen. The oxidation photoproducts and the rates of oxidation were compared for the various samples. It was shown that the filler was not modifying the oxidation mechanism of the polymer, but had a slight effect on the oxidation rate. 相似文献
627.
The latest European Directive 98/83/CE (5 December 1998), concerning the quality of water intended for human consumption, has set a two-stage parametric value for bromate. Bromate concentration will comply with 25 μg/L after December 25, 2003, and with 10 μg/L after December 25, 2008. Bromate formation in water is generally due to bromide oxidation during the ozonation stage. Due to higher temperatures, this latter parametric value is often exceeded in summer. Minimizing bromate levels is thus a crucial problem for drinking water producers. A bromate-minimizing strategy consists of shortening the reaction time between ozone and water. This can be done by neutralizing dissolved ozone residual with bisulfite at the exit of the ozone reactor chamber and/or by managing the introduction of ozone in different chambers depending on the water flow rate. This is only possible if, in our case, the disinfection goal for ozone is respected toward bacteria and viruses. The CT value must comply with 1.6 mg/min/L. In our plants, this value could be very large due to high contact time in and after leaving the ozone reactors. 相似文献
628.
'Classical' real-time control (RTC) strategies in sewer systems are based on water level and flow measurements with the goal of activation of retention volume. The control system rule of 'clean (storm water) runoff into the receiving water - polluted runoff into the treatment plant' has been thwarted by rough operating conditions and lack of measurements. Due to the specific boundary conditions in the city of Wuppertal's separate sewer system (clean stream water is mixed with polluted storm water runoff) a more sophisticated--pollution-based--approach was needed. In addition the requirements to be met by the treatment of storm water runoff have become more stringent in recent years. To separate the highly-polluted storm water runoff during rain events from the cleaner stream flow a pollution-based real-time control (P-RTC) system was developed and installed. This paper describes the measurement and P-RTC equipment, the definition of total suspended solids as the pollution-indicating parameter, the serviceability of the system, and also gives a cost assessment. A sensitivity analysis and pollution load calculations have been carried out in order to improve the P-RTC algorithm. An examination of actual measurements clearly shows the ecological and economic advantages of the P-RTC strategy. 相似文献
629.
630.
I.?E.?dell’ErbaEmail author A.?Y.?Mansilla C.?E.?Hoppe R.?J.?J.?Williams 《Journal of Materials Science》2016,51(8):3817-3823
Stable dispersions of silver nanoparticles (Ag NPs) were synthesized employing glycerol as both a solvent and reducing agent, and 3-aminopropyl trimethoxysilane (APTMS) as a stabilizer. Average sizes varied between 13 and 55 nm, depending on the molar ratio of APTMS/Ag. Terminal alkoxysilanes reacted with OH groups of glycerol leading to the covalent bonding of glycerol moieties to the chain ends of the stabilizer. This produced extremely stable colloidal dispersions from which NPs could not be extracted with solvents immiscible with glycerol (as THF). Ag NPs were covalently bonded to the surface of a colloidal silica by hydrolysis/condensation of terminal Si–O–C bonds of the stabilizer with superficial SiOH bonds of silica. TEM images revealed the presence of individual NPs and small clusters of NPs attached to the silica surface. These clusters were presumably generated by intermolecular reactions among chain ends of the stabilizer producing Si–O–Si bonds. The antibacterial properties of the resulting powder were confirmed by conventional tests employing a culture of Escherichia Coli. 相似文献