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991.
Liang Liu Shaoqian Cao Yujuan Xu Mingwei Zhang Gengsheng Xiao Qianchun Deng Bijun Xie 《Food chemistry》2010
The degradation of flavanols had been studied both in the litchi pericarp during the storage and in the model system containing PPO and flavanols of litchi pericarp. The results showed that (−)-epicatechin was the optimal endogenous substrate of litchi pericarp PPO, and the procyanidins of litchi pericarp were oxidised very slowly when incubated alone with PPO. However, (−)-epicatechin could accelerate the oxidation of the other flavanols in litchi pericarp through a coupled oxidation pathway. The results obtained allowed us to draw a conclusion that the oxidation of (−)-epicatechin was a precursor of litchi pericarp browning. A pathway of enzymatic browning of litchi pericarp was proposed as follows: with the loss of cellular compartmentation, the litchi pericarp PPO and flavanols mixed and, then, (−)-epicatechin was oxidised by the PPO and o-quinones formed. The o-quinones reacted with other flavanols and anthocyanins, accelerating the oxidation of other polyphenols. Finally, the oxidation of (−)-epicatechin and other polyphenols led to the formation of the brown-coloured compounds, resulting in the enzymatic browning of litchi pericarp. 相似文献
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994.
蛋白质组分分析方法比较研究 总被引:2,自引:0,他引:2
采用蛋白质连续累进提取法与组分快速提取法测定了21个小麦面粉样品的蛋白质组分,以比较两种蛋白质组分分析方法的特点。连续累进提取法将小麦蛋白质分离成清蛋白、球蛋白、醇溶蛋白和谷蛋白;快速提取法将小麦蛋白质分离成单体蛋白、可溶性谷蛋白和不溶性谷蛋白。结果表明:单体蛋白与清蛋白、球蛋白、醇溶蛋白含量及清蛋白、球蛋白、谷蛋白之和均无关系;可溶性谷蛋白含量与清蛋白、弱化度呈负相关,与醇溶蛋白、谷蛋白、沉淀值呈极显著或显著正相关;不溶性谷蛋白与醇溶蛋白、谷蛋白、沉淀值、稳定时间、评价值、弱化度呈极显著或显著相关。连续累进提取法适合于小麦品质常规检测,快速提取法适用于小麦早代材料品质检测。两种方法对于预测小麦的加工品质有着相同的重要作用,应根据样品量及检测精度进行选择。 相似文献
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997.
Martin S. Pour Nikfardjam László Márk Péter Avar Mária Figler Robert Ohmacht 《Food chemistry》2006,98(3):453-462
Epidemiological data indicate that moderate red wine consumption leads to less coronary heart disease and shows anti-carcinogenic effects. Especially, red wine phenolics have been linked to these effects. Sixty-seven red wines from the Hungarian Villány region, of vintages from 1996 to 2003 were analysed for their polyphenolic and anthocyanin composition by means of RP-HPLC/UV–Vis. Varieties with generally high concentrations of polyphenols are Kékfrankos, Merlot and Zweigelt, while anthocyanin content was highest in Shiraz, Oportó, Kékfrankos and Zweigelt. In agreement with other authors, our results show that trans-resveratrol content is mainly dependent on variety and vintage year. Principal component analysis (PCA) revealed that flavan-3-ols and delphinidin- and petunidin-3-glucosides are mainly responsible for the separation of wines according to polyphenolic composition. We could not discriminate between varieties or wineries based on polyphenol content, but could for vintage years. 相似文献
998.
A new three-step fractionation scheme was applied to study the distribution of Al, As, Cd, Cr, Cu, Fe, Mn, Mo, Ni, Pb, S, Sb, Ti, V and Zn in fly ashes collected in the electrostatic precipitator of a thermal power plant in the city of San Nicolás (Argentina). Seven samples were collected during one week of operation in 2005. For the fractionation, the scheme applied consisted of extracting the elements in three fractions: (i) soluble and exchangeable elements, (ii) carbonates, oxides and reducible elements and (iii) residual elements. Metals and metalloids at μg g−1 level were determined in each fraction by plasma based techniques namely, inductively coupled plasma optical emission spectrometry (ICP OES) and inductively coupled plasma mass spectrometry (ICP-MS). For validation, a certified reference materials NIST SRM 2711 (Montana soil) was subject to the same chemical sequential extraction procedure. X-ray diffraction powder (XRD) analysis and scanning electron microscopy (SEM) were used to characterize the major minerals present in the matrix. The predominant phases found in the total samples were mullite, quartz, iron oxides and lime. Total analyte concentration varied (in μg g−1) from 1.54 for Cd to 30 600 for Al. The leachability of the 15 elements under study proved to be different. All the elements (except Cd and Pb) were detected in the soluble fraction in the order: Cu (0.10%) ∼ Mn (0.13%) < Ni (0.17%) ∼ Ti (0.19%) ∼ Fe (0.20%) ∼ As (0.21%) < Zn (0.86%) < Al (1.3%) < Cr (2.9%) < V (3.9%) < Sb (6.9%) < Mo (45.1%) < S (58.0%). Percentages higher than 20% of S (24.1%) < V (27.5%) < Mn (29.0%) were detected in the second fraction. Al, As, Cr, Cd, Cu, Fe, Ni, Pb, Sb and Zn were mostly associated to the residual fraction. Recoveries of the overall procedure varied between 106% (Mo) and 72% (Cr). 相似文献
999.
Shoyu is the Japanese name for soy sauce and the most popular liquid condiment (seasoning) used in Japanese cuisine as well as in cuisines of other oriental countries. Shoyu is prepared by digesting mold-cultured soybeans and wheat seeded with an aspergillus (koji in Japanese) in the presence of sodium chloride. Gyoshoyu is produced when the soybeans and wheat are replaced with fish. Both Shoyu and Gyoshoyu have high level of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity. Hydrogen peroxide is produced in green tea after exposure to air. To find a safe and economical method of preventing the production of H2O2 in green tea, effects of Shoyu and Gyoshoyu on H2O2 level in bottled green tea were examined. Both Shoyu and Gyoshoyu suppressed the production of H2O2. Gyoshoyu decomposed H2O2 possibly because of the presence of a thermostable catalase, while Shoyu did not. Some components of Shoyu and Gyoshoyu may be useful to suppress the production of H2O2 in green tea. 相似文献
1000.
Robert C. Soliva Pedro Elez Merc Sebastin Olga Martín 《Innovative Food Science and Emerging Technologies》2000,1(4)
The inhibition of enzymatic browning catalyzed by polyphenol oxidase is still an important challenge in food processing. The aim of this work was to evaluate the feasibility of using combined methods in reducing browning of avocado purée through the evolution of PPO activity and CIELab color parameters. Higher reductions of activity were achieved when EDTA was added as an antioxidant and stored under N2 conditions. Purées with greater activity decays were less sensitive to colour changes. These changes occurred in avocado, thus losing the original lightness and greenness of the pulp. The antioxidant utilised was the factor that most affected the initial color, EDTA being the more effective additive in order to avoid browning reactions. The combination of factors had to be taken into account to evaluate these changes. The influence of combined methods over PPO activity was also assessed. Greater activity inhibition was reflected in better color maintenance. 相似文献