首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   64354篇
  免费   5572篇
  国内免费   3288篇
电工技术   2465篇
技术理论   1篇
综合类   3670篇
化学工业   13702篇
金属工艺   1183篇
机械仪表   3163篇
建筑科学   1094篇
矿业工程   1103篇
能源动力   2297篇
轻工业   13069篇
水利工程   406篇
石油天然气   19998篇
武器工业   219篇
无线电   1444篇
一般工业技术   1832篇
冶金工业   968篇
原子能技术   173篇
自动化技术   6427篇
  2024年   342篇
  2023年   872篇
  2022年   1656篇
  2021年   1985篇
  2020年   2170篇
  2019年   2113篇
  2018年   1840篇
  2017年   2296篇
  2016年   2482篇
  2015年   2322篇
  2014年   3623篇
  2013年   4011篇
  2012年   4442篇
  2011年   4586篇
  2010年   3311篇
  2009年   3226篇
  2008年   2962篇
  2007年   3697篇
  2006年   3737篇
  2005年   3334篇
  2004年   2853篇
  2003年   2634篇
  2002年   2269篇
  2001年   1870篇
  2000年   1673篇
  1999年   1373篇
  1998年   1105篇
  1997年   941篇
  1996年   763篇
  1995年   599篇
  1994年   472篇
  1993年   317篇
  1992年   301篇
  1991年   229篇
  1990年   177篇
  1989年   120篇
  1988年   64篇
  1987年   64篇
  1986年   35篇
  1985年   78篇
  1984年   71篇
  1983年   54篇
  1982年   41篇
  1981年   19篇
  1980年   27篇
  1979年   9篇
  1978年   8篇
  1977年   8篇
  1976年   10篇
  1975年   8篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
31.
32.
Oil degradation caused by the number of fryings performed and the effect of oil degradation on the color of fried battered squid rings were studied. Spectrophotometric techniques with absorbance in the UV and visible ranges, and iodine, peroxide, and acid values were used to determine oil degradation. Determination of various CIELAB parameters in order to study the external color of the fried battered squid rings revealed no differences in color due to the number of fryings. A study of the color of the battered squid rings at various frying times and temperatures showed significant differences for both variables. Although there was some degradation in the oil after 20 fryings, appearing as a slight darkening, it did not affect the final color of the fried, battered squid rings.  相似文献   
33.
Bleached and unbleached forms of a rosemary oleoresin (RO) in stripped and nonstripped soybean oil behave both as antioxidant and prooxidant in a light-induced oxidative system. At 0.02 and 0.05% levels, RO had the greatest antioxidant activity, while at 0.01 and 0.5% levels it had the highest prooxidant activity in both stripped and nonstripped soybean oil. Treatment of both soybean oil systems with tertiary butylhydroquinone controlled light-induced oxidation of the oil better than did the oleoresin treatments. The prooxidant activity of the 0.5% RO level was probably due to an excess of prooxidant components being carried into the oil at that level, whereas the reduced antioxidant activity at 0.01% was probably due to the low initial level of active antioxidant components being added to the oil. Published as Journal Series No. 10072, Nebraska Agricultural Research Division, Department of Food Science and Technology, University of Nebraska, Lincoln, NE 68583-0919.  相似文献   
34.
A brown coal, peat and oil shale were subjected to a rapid pyrolysis process and medium-heat-value gases together with tar were collected. The char residue was of high activity and suitable for gasification to create a two-stage gasification system. The coal-tar is used for manufacturing liquid fuels and chemicals.  相似文献   
35.
A monitoring program was performed to investigate heavy metal content alteration due to exploratory drilling for oil using non-aqueous fluids (NAFs) in Brazilian offshore, 900 m deep. Fourteen elements were monitored in 54 sites and it was verified that after drilling activities the average Ba concentration was remarkably increased with respect to background level, even 1 year after the activity. A minor increase in Mn and a moderate increase in Al concentrations were verified. The Cd, Cr, Ni, As, Co, Cu, Pb, V, and Zn concentrations were at the background levels, ca. 1 year after the NAFs drilling materials deposition on the seafloor. The Al, Ba, Cd, Cr, Cu, Ni and Zn mean concentrations were significantly different (P<0.05) between the three sampling operations (cruises) performed, while As, Cd, Fe and Pb presented different mean values according to the distance of the oil well, independent of the sampling operation. Interaction between sampling operation and distance was observed for Mn. In all sediment samples the Hg concentration was below the detection limit (0.07 μg g−1).  相似文献   
36.
丁锦萍 《山西化工》2002,22(1):31-33
介绍了国外利用天然气生产油口的生产工艺,探讨了山西省利用丰富的煤层气资源发展合成油的可能性和优势,并提出了相应的发展建议。  相似文献   
37.
Adsorption isotherms of sesame oil in a concentrated miscella system   总被引:2,自引:0,他引:2  
The adsorption of peroxides, unsaturated carbonyls, free fatty acids and carotenoids from unrefined sesame oil on vegetable carbon (5%, w/w) in a miscella system was studied. Three different solvent conditions (hexane/ethanol, 100:0, 95:5 and 75:25, vol/vol), combined in a factorial design with five levels of solvent (0, 10, 20, 30 and 40%, w/w), were used to develop the miscella. Equilibrium adsorption was not achieved during the 100 min of adsorption, mainly because the oil components were involved in oxidation reactions during the adsorption process. However, for a given solvent concentration, adsorption of the oil components showed a significant linear regression on their respective initial concentration in the miscella (Ci). Peroxides and carbonyls showed, at all solvent levels investigated, an affinity for the carbon more independent of their Ci than free fatty acids and carotenoids. In general, at the same Ci, a higher adsorption was achieved as solvent concentration increased. The results indicated that free fatty acid adsorption may depend on competitive adsorption based on molecule hydrophobicity. However, in spite of the higher hydrophobicity of carotenoids, compared with free fatty acids, they might not be competing for the same adsorbing sites. Ethanol showed a prooxidant effect that increased peroxide production during adsorption but did not affect the reaction involved in carbonyl production.  相似文献   
38.
Changes in the content of aliphatic waxes during industrial deodorization and/or physical refining of bleached olive oil were studied in an experimental discontinuous pilot plant of 250 kg deodorizer using nitrogen as stripping gas in place of steam. The kinetic constants for the decomposition of waxes during the deodorization process were determined. The reaction orders studied are zero (or can be considered zero) within the working interval. The values of rate constants, activation energy, frequency factor, increment of activation Gibbs free energy, activation enthalpy, and activation entropy are established.  相似文献   
39.
Phase transitions of canola oil sediment   总被引:3,自引:0,他引:3  
Canola sediment was obtained from an industrial filter cake by solvent extraction. When heated in the differential scanning calorimeter (DSC) (5–100°C), the sediment exhibited a single narrow melting peak at around 74.8°C. No solid-state polymorphic transformation of the material could be detected over this temperature range. The X-ray powder diffraction pattern of canola sediment resembled waxes from other sources with an orthorhombic unit cell. The phase transition behavior of canola sediment in oil was studied by both DSC and polarizing microscopy. With increasing ratio of oil/sediment, a reduction in both melting temperature and transition enthalpy was observed. The shape of the supercooling curve resembled that of the melting curve. The induction time was determined by spectrophotometry and was used to calculate the interfacial free energyσ between sediment and oil; σ=4.71 erg/cm2. The effect of temperature and sediment concentration on the clouding time of canola oil was studied; the clouding time was the shortest at 5°C.  相似文献   
40.
杜昭辉 《辽宁化工》2004,33(10):559-561
对不饱和聚酯树脂 (UPR)废料裂解制原料油技术进行了研究 ,系统地考察了催化裂解反应工艺条件。试验结果表明 ,催化裂解所需反应温度为 40 0~ 45 0℃ ,反应时间为 70~ 80min ;剂油比 1∶5 ;试验对 4种催化剂的催化性能进行了评价 ,研究表明单独使用YB -2催化剂 ,液相产品收率为 5 8.2 2%~ 5 9.1 4% ;YB -1和YB -2混合使用 ,最高液相产品收率为 68.76%。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号