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991.
Synthesis and characterization of the polyols by air oxidation of soybean oil and its effect on the morphology and dynamic mechanical properties of poly(vinyl chloride) blends 下载免费PDF全文
Pedro A. Ourique Jérôme M. L. Gril Gaëlle W. Guillaume Cesar H. Wanke Sergio G. Echeverrigaray Otávio Bianchi 《应用聚合物科学杂志》2015,132(24)
The use of natural additives, with low toxicity and good compatibility, for PVC is becoming increasingly attractive. In this study, soybean oil additives were prepared by air oxidation reactions and blending with PVC. The oxidation reaction produced a significant increase in the number of hydroxyl groups in soybean oil; however, this kind of reaction results in the formation of a heterogeneous structure due to free radical reactions in the medium. The oxidized soybean oil improved the compatibility with PVC due to an increase in the number of polar groups, such as hydroxyls, and thus a reduction in the amount of atactic polymer was observed. Furthermore, an increase in the molecular weight of the oxidized oil, as well as large amounts of polar groups contributes to reducing the migration of oil in the PVC. Regarding the crystallinity of PVC, the use of pure and oxidized soybean oil causes small changes in the crystalline phase of the polymer. Oxidized soybean oil has great potential for usage as a secondary plasticizer for PVC. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42102. 相似文献
992.
Plasticized poly(vinyl chloride) composites: Influence of different nanofillers as antimigration agents 下载免费PDF全文
In this study, plasticized poly(vinyl chloride) (PVC) composites with different nanofillers, including single‐walled carbon nanotubes (SWCNTs), organoclay, TiO2, and ZnO nanoparticles, were prepared, and their effects on plasticizer migration were investigated. Scanning electron micrographs revealed the dispersion quality of the nanofillers in the polymer matrix. It had a significant influence on the performance of the nanofillers in the process of plasticizer migration. Migration and exudation tests showed that the nanofillers could efficiently hinder plasticizer migration. On the basis of these results, we concluded that carbon nanotubes were the best antimigration agent in the plasticized system. This was ascribed to the high aspect ratio of the SWCNTs and the good interactions between them and the plasticizer. Also, TiO2 nanoparticles showed a better performance compared to the ZnO nanoparticles. This was due to the more homogeneous dispersion of the TiO2 in the polymer matrix and the higher surface area of the particles. The differential scanning calorimetry thermograms were in good agreement with the migration tests. The lowest change in the glass‐transition temperature was observed for the composite filled with SWCNTs. This indicated that a lower amount of the plasticizer migrated from PVC. The thermogravimetric analysis curves showed that the incorporation of the nanofillers improved the thermal stability of the PVC. The results could be useful for determining the efficiency of plasticized PVC in applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42559. 相似文献
993.
明胶由于其优异的生物学性能,近几十年来被广泛的应用于食品、保健品、化妆品、生物医药材料等行业。本文简要综述了明胶应用于医用材料的特性,列举了明胶在医用材料中的应用,展望了明胶应用于医用材料的前景。 相似文献
994.
缓释药物载体明胶微球酸水解影响因素的研究 总被引:1,自引:0,他引:1
采用乳化交联法制备明胶微球(GMS),以柠檬酸为水解促进剂,利用双缩脲法研究了反应时间、温度及pH值对GMS及明胶水解程度的影响。结果表明,GMS水解的速率随反应时间的增长或温度的增高而加快,随水解pH值的增高而减慢;同等条件下,相比于GMS,明胶的水解较为彻底,在酸性环境中不如GMS稳定;GMS水解过程的SEM图进一步表明,在酸液的作用下,GMS溶胀后表面光滑致密,药物只能通过骨架缓慢扩散或交联结构的水解而缓慢释放,避免了药物突释。优化反应条件为:在水解时间3 h,温度80℃,pH值2时,GMS的水解较为彻底。 相似文献
995.
The electro-deoxidation of porous titanium dioxide precursors in molten calcium chloride under cathodic potential control 总被引:1,自引:0,他引:1
A study on the electro-deoxidation of porous titanium dioxide precursors in molten calcium chloride is reported. Experiments were performed with a three-terminal electrochemical cell, comprising a molten salt electrolyte of calcium chloride with additions of calcium oxide, a cathode of compact titanium dioxide with a significant degree of open porosity, as well as a graphite anode and a graphite pseudo-reference electrode. Reductions were carried out under cathodic potential control and at different applied potentials. The results reveal that the formation of titanium metal occurs at electrode potentials significantly more positive than that of calcium deposition, whilst the realisation of very low residual oxygen contents requires potentials around that of calcium deposition. It is demonstrated that oxygen contents in the titanium metal prepared of below 5000 ppm by mass may be achieved reproducibly within processing times of 16 h and at current efficiencies between 10 and 40%. The kinetic pathway is investigated, by analysing the compositions of samples prepared at different cathode potentials, and compared against the results from foregoing studies. It is found that the presence of calcium oxide in the calcium chloride accelerates the overall rate of electro-deoxidation, and that the temporary occurrence in the cathode of the calcium-containing compounds calcium titanate, CaTiO3, and calcium titanite, CaTi2O4, are inherent features of the reaction path. The overpotential at the anode is shown to be of significant magnitude. 相似文献
996.
997.
通常,人们利用微波进行化学合成,如果反应温度控制在低于溶剂的沸点温度,反应体系一旦达到所设定温度,自动控温系统就会自动切断加热电源,停止加热。对于微波反应来说,也就停止了微波的连续作用,而系统仅仅是保持在恒温状态。如果系统的保温效果很好的话,微波的作用可能就比较少,而仅仅是热效应对化学反应作用,没有体现出微波的持续作用。该研究选择特定的溶剂体系,采用在溶剂沸点温度下进行微波有机合成反应,以保证微波始终持续作用。结合题示表面活性剂的合成,探讨了微波合成反应的动力学参数,分析了微波作用原理。分别在微波作用以及传统加热两种方式下,考察了十二烷基甲基二羟乙基溴化铵合成动力学,获得了两种方式下的反应动力学参数,结果表明,微波的作用没有改变反应级数,两种情况下都是一级反应。微波作用下的活化能为ΔH=33.59 kJ/mol;而传统加热的活化能为ΔH=55.83 kJ/mol。该文提出以单位时间单位容积内、微波作用下反应物的变化量减去相同温度条件下传统加热时的变化量,作为微波对反应速率的贡献量Δ(-rA)的概念。实验结果表明,在同一温度条件下,反应时间越短,即反应物浓度越高,微波对反应速率的贡献量Δ(-rA)就越大;在其他条件相同时,反应温度越低,微波对反应速率的贡献量Δ(-rA)就越大。 相似文献
998.
999.
The pitting behaviour of type 321 stainless steel in sulfide-containing chloride aqueous environments was studied using cyclic potentiodynamic polarization. A well-established correlation between H2S and Na2S2O3 in the study of corrosion was applied, that is, H2S was simulated by Na2S2O3. The major factors affecting the pitting corrosion of type 321 stainless steel are the Cl- concentration, solution pH and temperature. The results clearly indicate that both Epit and E
pp decrease with increasing Cl- concentration and temperature, while I
pass is more sensitive to temperature variation. E
pit decreased with decreasing pH in the range 2 < pH < 7.5. The surface morphology and chemistry of the corroded type 321 stainless steel resulting from anodic polarization in 0.01 M S2O
3
2-
-containing Cl- solution were analysed by XRD, SEM and EPMA. A higher concentration of sulfur was found in the pits, and the dark surface film was mainly composed of FeS and -Fe2O3. The results describe the pitting behaviour of type 321 stainless steel in sulfide-containing Cl- aqueous environments. 相似文献
1000.
硝酸铈铵在有机合成中的应用 总被引:3,自引:0,他引:3
就近10年来硝酸铈铵在硝化及硝酸酯化,氧化和催化氧化,引发加成和聚合等方面进行的应用进行了综述。 相似文献