全文获取类型
收费全文 | 53236篇 |
免费 | 4195篇 |
国内免费 | 2078篇 |
专业分类
电工技术 | 1790篇 |
技术理论 | 1篇 |
综合类 | 2589篇 |
化学工业 | 12867篇 |
金属工艺 | 977篇 |
机械仪表 | 2620篇 |
建筑科学 | 775篇 |
矿业工程 | 869篇 |
能源动力 | 2144篇 |
轻工业 | 11899篇 |
水利工程 | 267篇 |
石油天然气 | 19486篇 |
武器工业 | 65篇 |
无线电 | 318篇 |
一般工业技术 | 1325篇 |
冶金工业 | 813篇 |
原子能技术 | 54篇 |
自动化技术 | 650篇 |
出版年
2024年 | 216篇 |
2023年 | 666篇 |
2022年 | 1303篇 |
2021年 | 1658篇 |
2020年 | 1745篇 |
2019年 | 1792篇 |
2018年 | 1469篇 |
2017年 | 1827篇 |
2016年 | 1991篇 |
2015年 | 1801篇 |
2014年 | 2921篇 |
2013年 | 3256篇 |
2012年 | 3587篇 |
2011年 | 3726篇 |
2010年 | 2631篇 |
2009年 | 2445篇 |
2008年 | 2163篇 |
2007年 | 2824篇 |
2006年 | 3105篇 |
2005年 | 2721篇 |
2004年 | 2409篇 |
2003年 | 2246篇 |
2002年 | 1967篇 |
2001年 | 1655篇 |
2000年 | 1469篇 |
1999年 | 1216篇 |
1998年 | 995篇 |
1997年 | 849篇 |
1996年 | 673篇 |
1995年 | 517篇 |
1994年 | 402篇 |
1993年 | 267篇 |
1992年 | 237篇 |
1991年 | 191篇 |
1990年 | 132篇 |
1989年 | 91篇 |
1988年 | 52篇 |
1987年 | 46篇 |
1986年 | 23篇 |
1985年 | 61篇 |
1984年 | 56篇 |
1983年 | 39篇 |
1982年 | 26篇 |
1981年 | 8篇 |
1980年 | 16篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1976年 | 4篇 |
1951年 | 5篇 |
1944年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Francesco Di Girolamo Andrea Masotti Isabella Lante Margherita Scapaticci Cosima Damiana Calvano Carlo Zambonin Maurizio Muraca Lorenza Putignani 《International journal of molecular sciences》2015,16(9):20896-20912
Extra virgin olive oil (EVOO) with its nutraceutical characteristics substantially contributes as a major nutrient to the health benefit of the Mediterranean diet. Unfortunately, the adulteration of EVOO with less expensive oils (e.g., peanut and corn oils), has become one of the biggest source of agricultural fraud in the European Union, with important health implications for consumers, mainly due to the introduction of seed oil-derived allergens causing, especially in children, severe food allergy phenomena. In this regard, revealing adulterations of EVOO is of fundamental importance for health care and prevention reasons, especially in children. To this aim, effective analytical methods to assess EVOO purity are necessary. Here, we propose a simple, rapid, robust and very sensitive method for non-specialized mass spectrometric laboratory, based on the matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS) coupled to unsupervised hierarchical clustering (UHC), principal component (PCA) and Pearson’s correlation analyses, to reveal corn oil (CO) adulterations in EVOO at very low levels (down to 0.5%). 相似文献
32.
33.
Effect of Different Cosolvents on Transesterification of Waste Cooking Oil in a Microreactor 下载免费PDF全文
Biodiesel was prepared from waste cooking oil combined with methanol. The process was performed via transesterification in a microreactor using kettle limescale as a heterogeneous catalyst and various cosolvents under different conditions. n‐Hexane and tetrahydrofuran were selected as cosolvents to investigate fatty acid methyl esters (FAMEs). To optimize the reaction conditions, the main parameters affecting FAME% including reaction temperature, catalyst concentration, oil‐to‐methanol volumetric ratio, and cosolvent‐to‐methanol volumetric ratio were studied via response surface methodology. Under optimal reaction conditions and in the presence of the cosolvents n‐hexane and tetrahydrofuran, high FAME purities were achieved. Considering the experimental results, the limescale catalyst is a unique material, and the cosolvent method can reduce significantly the reaction time and biodiesel production cost. 相似文献
34.
Izabella Jackowska Monika Bojanowska Monika Staszowska-Karkut Monika Sachadyn-Król 《International Journal of Food Science & Technology》2019,54(12):3175-3184
Ozonation is an innovative way to preserve high quality of seed during storage and it is an alternative to harmful organophosphorus agents. Disclosure of changes in the rapeseed oil under the influence of oxidative action of ozone on the seeds was the aim of the work and is presented for the first time. Two ozone concentrations and different length of ozonation were applied. The changes in tocopherols, phenolics, flavonoids contents, antiradical activity and oxidative stability were examined. The average vitamin E concentration was 33 mg per 100 g of oil before and 31.7 after ozonation of seeds. The average content of phenolic compounds was 14.3 mg of sinapic acid g−1 and 16.9 after the ozone treatment. Changes in the flavonoids content and antioxidant activity were observed too. Ozonation caused a decrease in the vitamin E concentration which resulted also in reducing the quenching of free radicals and reduction of oil induction time. 相似文献
35.
Samia Mokh Khaled El Hawari Haifa Abdul Rahim Mohamad Al Iskandarani 《Food Additives and Contaminants: Part B: Surveillance Communications》2020,13(2):121-129
ABSTRACT The treatment of animals with antimicrobial products may lead to the contamination of edible tissues by their residues, which may represent a risk to human health. Therefore, this study aimed to determine the level of antimicrobial residues in food-producing animals (chicken, beef, and milk) in Lebanon. A total of 310 samples were collected and analysed using an LC-MS/MS for the determination of 48 compounds belonging to different families in order to map their compliance according to the European Commission decision 2002/657/EC. Results show that 60% of the analysed samples were not contaminated by any residue, while 12% presented a concentration higher than the MRLs for tetracyclines, sulphonamides, quinolones, and macrolides. Results revealed that chicken were the most contaminated by antimicrobial residues, when compared to beef and milk. The obtained results demonstrate the uncontrolled use of antimicrobials in some Lebanese farms and claim for better management of livestock. 相似文献
36.
37.
Shailesh J. Patil 《Chemical Engineering Communications》2019,206(5):605-618
Jatropha oil is a promising nonedible feedstock for producing renewable diesel. In this work, the hydrotreatment processing of jatropha oil was investigated. Instead of using conventional alumina-supported Co–Mo, Ni–Mo, and Ni–W catalysts that need sulfidation pretreatment, noble metals such as Pd and Ru were chosen. Trials were performed in an isothermal trickle-bed reactor and the reaction conditions were as follows: temperature 603–663?K, weight hourly space velocity (WHSV) 1 to 4/h, pressure 1.5–3?MPa, and H2/oil ratio 200–800 (v/v). Yield of n-C15 to n-C18 hydrocarbons was maximized (70.3 and 43.8% for Pd/Al2O3 and Ru/Al2O3, respectively) at the following conditions: T?=?663 K, WHSV?=?2/h, P?=?3?MPa, and H2/oil ratio?=?600 (v/v). Since Ru favored cracking reactions to a larger extent than Pd, the yield of C15 to C18 hydrocarbons over Ru/Al2O3 was lowered. Using simple first-order plots for oil conversion, activation energies for the hydrotreating process over Pd/Al2O3 and Ru/Al2O3 were found and they were equal to 109 and 121?kJ/mol, correspondingly. 相似文献
38.
Özge Seçmeler Özlem Güçlü Üstündağ 《International Journal of Food Science & Technology》2019,54(5):1609-1616
The partitioning of predominant lipophilic olive bioactives (squalene, β-sitosterol and α-tocopherol) in olive oil processing was studied for the first time using common integrated olive milling plant. 7% of the oil and 5% of the squalene present in the olives was lost in the last pomace. β-sitosterol and α-tocopherol, which are mainly concentrated in the seed of the olive fruit, was recovered in virgin olive oil to a lesser extent (66%, 67%) while 10% were lost in last pomace. Thus, the loss of β-sitosterol and α-tocopherol was higher than that of squalene and oil, due to nonrecovered bound forms. 19% of the α-tocopherol and 21% of the β-sitosterol loss was unaccounted for, which can be attributed to degradation of α-tocopherol and incomplete recovery of sterols from the olive and pomace matrices. This study provides a basis for process development studies. 相似文献
39.
Zohal Safaei Mahmoudabadi Alimorad Rashidi Mohammad Panahi 《International Journal of Hydrogen Energy》2021,46(7):5270-5285
Highly active ReS2 nanocatalysts were prepared by CVD method and characterized by XRD, BET -BJH, Raman spectroscopy, XPS, TPR, NH3-TPD, SEM, and HRTEM techniques. Catalytic activities were used in upgrading heavy crude oil using methane as hydrogen source. The results showed a significant increase in API and decrease in sulfur and nitrogen content of crude oil. RSM technique was used to investigate the interactive effects of temperature (200–400 °C), pressure (20–40 bar) and dosage of nanocatalyst (0.5–2 wt. %) on the performance of HDS reaction. The results represent that the maximum predicted HDS activity (74.375%) was estimated under the optimal conditions (400 °C, 20 bars, and 2 wt % of nanocatalyst). Also, the effect of reaction temperature, pressure and dosage of ReS2 nanorods catalyst on HDN of heavy crude oil was investigated and highest efficiency in the HDN process (93%) occurred at 400 °C and 40 bar using 2 wt % ReS2. 相似文献
40.
Geochemical investigation of Paleogene oils from the onshore Yufutsu oil- and gasfield, southern Hokkaido, and from two nearby offshore wells, revealed the presence of numerous biomarkers of higher plant origin. Biomarkers in the oils belong to different groups of both angiosperm and gymnosperm origin; they include bicyclic sesquiterpanes, diterpanes, and triterpanes and their aromatized counterparts, which suggests a terrestrial origin for the oils. The oils were characterized as having a high wax content, a low content of organosulphur compounds, a high pristane/phytane ratio, and a low C27 /(C27 +C29 ) sterane ratio.
Although the oils from on- and offshore Southern Hokkaido are similar in their geochemical composition, notable differences were observed in the biomarker signature of both saturate and aromatic fractions. The oils from the offshore wells appeared to have a greater abundance of higher plant biomarkers compared to those from the Yufutsu field, suggesting an enrichment in higher plant components. Differences in biomarker fingerprint could not be linked to the maturity effect, since the oils appeared to be of similar maturity levels, corresponding to the late stage of the oil window (0.9–1.2%, Rc). The differences in the biomarker signatures between the oils from the Yufutsu field and the offshore wells are likely to be due to facies variations in source organic matter, resulting from differences in the quantity and quality of land plant input. 相似文献
Although the oils from on- and offshore Southern Hokkaido are similar in their geochemical composition, notable differences were observed in the biomarker signature of both saturate and aromatic fractions. The oils from the offshore wells appeared to have a greater abundance of higher plant biomarkers compared to those from the Yufutsu field, suggesting an enrichment in higher plant components. Differences in biomarker fingerprint could not be linked to the maturity effect, since the oils appeared to be of similar maturity levels, corresponding to the late stage of the oil window (0.9–1.2%, Rc). The differences in the biomarker signatures between the oils from the Yufutsu field and the offshore wells are likely to be due to facies variations in source organic matter, resulting from differences in the quantity and quality of land plant input. 相似文献