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81.
82.
《Journal of Sulfur Chemistry》2013,34(3):261-265
Stable crystalline phosphorus ylides were obtained in excellent yields from the 1:1:1 addition reaction between triphenylphosphine and dialkyl acetylenedicarboxylates in the presence of strong SH-acids, such as 2-mercapto-1-methylimidazole and 2-thiazoline-2-thiol. These stable ylides exist in solution as a mixture of two geometrical isomers as a result of restricted rotation around the carbon–carbon partial double bond resulting from conjugation of the ylide moiety with the adjacent carbonyl group. 相似文献
83.
《Journal of Sulfur Chemistry》2013,34(3):276-283
In this work, we have studied the reaction of substituted 2-thiocyanoacetophenone and hydrazine hydrate as a novel and simple pathway for the preparation of the substituted 1,4,5-thiodiazepine ring system. The mechanism of this reaction revealed that in the initial step condensation of hydrazine with carbonyl groups of substituted 2-thiocyanoacetophenons 2a–2f gives the corresponding substituted aromatic dithiocyano azide intermediates which in turn undergo cyclization to1,4,5-thiadiazepines in the presence of hydrazine. This cyclization is a novel method for the preparation of sulfide bond from the reaction of hydrazine and a dithiocyano intermediate. An account of the reaction mechanism is given. 相似文献
84.
甘氨酸席夫碱Ni(Ⅱ)复合物法不对称合成丝氨酸 总被引:1,自引:0,他引:1
采用甘氨酸席夫碱Ni(Ⅱ)复合物法不对称合成光学纯的D-和L-丝氨酸。以2-N-(N'-苄基)脯氨酰-氨基-二苯甲酮甘氨酸席夫碱Ni(Ⅱ)复合物与聚甲醛反应,生成2-N-(N'-苄基)脯氨酰-氨基-二苯甲酮丝氨酸席夫碱Ni(Ⅱ)复合物,经水解生成D-或L-丝氨酸,对映体过量值(e.e.)达到98%,重结晶后e.e.为99.5%,并对手性辅基2-N-(N;-苄基)脯氨酰-氨基-二苯甲酮进行了回收,回收率为85%~95%。 相似文献
85.
柠檬酸酯的合成及其在日化工业中的应用 总被引:5,自引:3,他引:5
重点综述了柠檬酸酯表面活性剂作为洗涤助剂、化妆品添加剂和食品添加剂等工业中的应用;讨论了柠檬酸酯合成中温度、时问、原料配比(物质的量比)、催化剂种类及用量等因素对产率的影响;特别指出了柠檬酸酯合成中生成的水去除的重要性以及产品的分离和纯化的复杂性;最后提出了柠檬酸酯的合成目前存在的问题、发展方向和应用前景等。 相似文献
87.
Enzymatic production of alkyl esters through alcoholysis: A critical evaluation of lipases and alcohols 总被引:3,自引:1,他引:3
Li?Deng Xuebing?XuEmail author Gudmundur?G.?Haraldsson Tianwei?Tan Fang?Wang 《Journal of the American Oil Chemists' Society》2005,82(5):341-347
This paper focuses on a detailed evaluation of commercially available immobilized lipases and simple monohydric alcohols for
the production of alkyl esters from sunflower oil by enzymatic alcoholysis. Six lipases were tested with seven alcohols, including
straight and branched-chain primary and secondary alcohols. The reactions were conducted in a batch stirred reaction vessel
using stoichiometric amounts of substrates under solvent-free conditions. Dramatic differences in alcoholysis performance
were observed among the different lipases. For most of the alcohols, Novozym 435 produced the highest yield of FA alkyl esters,
with yields well over 90% for methanol, absolute ethanol, and 1-propanol. Overall, 96% ethanol was the preferred alcohol for
all lipases except Novozym 435, and ethanolysis reactions reached the maximal conversion efficiency. Increasing the water
content in the system resulted in an increased degree of conversion for all lipases except Novozym 435. The secondary alcohol
2-propanol significantly reduced the alcoholysis reaction with all lipases; however, the branch-chain isobutanol was more
advantageous than linear 1-butanol for Novozym 435, Lipozyme RMIM, and Lipase PS-C. Many commercial immobilized lipases are
highly efficient and promising for the production of alkyl esters, offering high reaction yields and a simple operation process. 相似文献
88.
A half‐fraction, two‐level, four‐factor factorial experimental design was used to study the effects of the acetic anhydride concentration, reaction temperature, reaction time, and sulfuric acid concentration on the degree of substitution, intrinsic viscosity, and yield of oxidized cellulose acetate (OCA). Oxidized cellulose containing 20% (w/w) carboxylic acid was used as the starting material. The data were fitted by multiple regression analysis with SAS software. The correlation coefficients obtained from plots of the predicted and observed values for the degree of substitution, intrinsic viscosity, and yield were 0.985, 0.993, and 0.991, respectively. Residual normal plots of the regression models showed a linear relationship. Lenth and main‐factor‐effect plots revealed an increase in the degree of substitution of OCA with an increasing concentration of acetic anhydride. The latter had no effect on the intrinsic viscosity and yield of OCA. An increase in the reaction temperature led to an increase in the degree of substitution and a decrease in the intrinsic viscosity and yield of OCA. The influence of the reaction time on the degree of substitution and intrinsic viscosity followed a trend similar to that observed with the reaction temperature, but the yield of OCA was unaffected. Increasing the concentration of sulfuric acid reduced the degree of substitution, intrinsic viscosity, and yield of OCA. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 696–705, 2005 相似文献
89.
Torben?H.?Roenne Xuebing?Xu Tianwei?TanEmail author 《Journal of the American Oil Chemists' Society》2005,82(12):881-885
Enzymatic synthesis of esters of lactic acid and straight-chain alcohols with different chain lengths (C6–C18) were investigated in batch reactions with hexadecanol (C16) as the model alcohol. Cyclohexane was the best solvent for higher ester yields, and the best biocatalyst was the immobilized Candida antarctica lipase B (Novozym 435) as well as the textile-immobilized Candida sp. lipase. A method was established to obtain ester yields in the range of 71 to 82% for the different alcohols, and the most favorable conditions for the esterification reaction using Novozym 435 were an equimolar ratio of lactic acid to alcohol, each at a concentration of 120 mM each; a 50°C reaction temperature; 190 rpm shaking speed; and the addition of 100 mg molecular sieves (4 Å) for drying. The ester yield increased with increasing lipase load, and a yield of 79.2% could be obtained after 24 h of reaction at 20 wt% of Novozym 435. The immobilized Candida sp. lipase prepared in the laboratory also could be used to produce esters of lactic acid and straight-chain alcohols, but it had a much lower activity than Novozym 435 with a temperature optimum of 40°C. 相似文献
90.