全文获取类型
收费全文 | 149054篇 |
免费 | 18518篇 |
国内免费 | 9499篇 |
专业分类
电工技术 | 20518篇 |
技术理论 | 8篇 |
综合类 | 13405篇 |
化学工业 | 14776篇 |
金属工艺 | 11631篇 |
机械仪表 | 10421篇 |
建筑科学 | 10254篇 |
矿业工程 | 7425篇 |
能源动力 | 4310篇 |
轻工业 | 8182篇 |
水利工程 | 3685篇 |
石油天然气 | 10890篇 |
武器工业 | 1928篇 |
无线电 | 21239篇 |
一般工业技术 | 16100篇 |
冶金工业 | 8288篇 |
原子能技术 | 2047篇 |
自动化技术 | 11964篇 |
出版年
2024年 | 332篇 |
2023年 | 2199篇 |
2022年 | 3867篇 |
2021年 | 4853篇 |
2020年 | 5151篇 |
2019年 | 4388篇 |
2018年 | 4193篇 |
2017年 | 5406篇 |
2016年 | 6001篇 |
2015年 | 6404篇 |
2014年 | 9328篇 |
2013年 | 8685篇 |
2012年 | 11347篇 |
2011年 | 11819篇 |
2010年 | 8598篇 |
2009年 | 8769篇 |
2008年 | 8094篇 |
2007年 | 10297篇 |
2006年 | 9331篇 |
2005年 | 7893篇 |
2004年 | 6501篇 |
2003年 | 5964篇 |
2002年 | 4883篇 |
2001年 | 4195篇 |
2000年 | 3562篇 |
1999年 | 2984篇 |
1998年 | 2246篇 |
1997年 | 1845篇 |
1996年 | 1656篇 |
1995年 | 1326篇 |
1994年 | 1129篇 |
1993年 | 795篇 |
1992年 | 624篇 |
1991年 | 501篇 |
1990年 | 409篇 |
1989年 | 370篇 |
1988年 | 243篇 |
1987年 | 161篇 |
1986年 | 110篇 |
1985年 | 104篇 |
1984年 | 97篇 |
1983年 | 47篇 |
1982年 | 74篇 |
1981年 | 45篇 |
1980年 | 49篇 |
1979年 | 23篇 |
1975年 | 14篇 |
1964年 | 13篇 |
1959年 | 23篇 |
1951年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
31.
为解决电镀砂轮磨削加工中容屑空间不足的问题,采用点胶微粘接的方法制备了磨料有序排布的电镀砂轮,分析了磨料粘接效果和镀层力学性能。通过SEM分析了磨料/镀层/导电胶的结合界面,并进行了干磨削试验。研究结果表明,直径约为磨料粒径40%的胶点可粘接住磨料,单个胶点上粘接多颗磨料的占比小于6%;双脉冲电镀工艺制备的镀层显微硬度大于500HV,表层残余应力小于100MPa,磨料/镀层/导电胶之间的界面贴合紧密,无明显缺陷;砂轮在磨削时没有出现磨料脱落现象。 相似文献
32.
Alison Willette Benjamin Fallen Hem Bhandari Carl Sams Feng Chen Virginia Sykes Chris Smallwood Kristin Bilyeu Zenglu Li Vincent Pantalone 《Journal of the American Oil Chemists' Society》2021,98(8):861-869
Soybean oil hydrogenation alters the linolenic acid molecule to prevent the oil from becoming rancid, however, health reports have indicated trans-fat caused by hydrogenation, is not generally regarded as safe. Typical soybeans contain approximately 80 g kg−1 to 120 g kg−1 linolenic acid and 240 g kg−1 of oleic acid. In an effort to accommodate the need for high-quality oil, the United Soybean Board introduced an industry standard for a high oleic acid greater than 750 g kg−1 and linolenic acid less than 30 g kg−1 oil. By combing mutations in the soybean plant at four loci, FAD2-1A and FAD2-1B, oleate desaturase genes and FAD3A and FAD3C, linoleate desaturase genes, and seed oil will not require hydrogenation to prevent oxidation and produce high-quality oil. In 2017 and 2018, a study comparing four near-isogenic lines across multiple Tennessee locations was performed to identify agronomic traits associated with mutations in FAD3A and FAD3C loci, while holding FAD2-1A and FAD2-1B constant in the mutant (high oleic) state. Soybean lines were assessed for yield and oil quality based on mutations at FAD2-1 and FAD3 loci. Variations of wild-type and mutant genotypes were compared at FAD3A and FAD3C loci. Analysis using a generalized linear mixed model in SAS 9.4, indicated no yield drag or other negative agronomic traits associated with the high oleic and low linolenic acid genotype. All four mutations of fad2-1A, fad2-1B, fad3A, and fad3C were determined as necessary to produce a soybean with the new industry standard (>750 g kg−1 oleic and <30 g kg−1 linolenic acid) in a maturity group-IV-Late cultivar for Tennessee growers. 相似文献
33.
Can Ercan S. Esra Safran Artuğ Türkmenoğlu Uğur Karabakal 《Journal of surfactants and detergents》2021,24(1):139-147
Garzan oil field is located at the south east of Turkey. It is a mature oil field and the reservoir is fractured carbonate reservoir. After producing about 1% original oil in place (OOIP) reservoir pressure started to decline. Waterflooding was started in order to support reservoir pressure and also to enhance oil production in 1960. Waterflooding improved the oil recovery but after years of flooding water breakthrough at the production wells was observed. This increased the water/oil ratio at the production wells. In order to enhance oil recovery again different techniques were investigated. Chemical enhanced oil recovery (EOR) methods are gaining attention all over the world for oil recovery. Surfactant injection is an effective way for interfacial tension (IFT) reduction and wettability reversal. In this study, 31 different types of chemicals were studied to specify the effects on oil production. This paper presents solubility of surfactants in brine, IFT and contact angle measurements, imbibition tests, and lastly core flooding experiments. Most of the chemicals were incompatible with Garzan formation water, which has high divalent ion concentration. In this case, the usage of 2-propanol as co-surfactant yielded successful results for stability of the selected chemical solutions. The results of the wettability test indicated that both tested cationic and anionic surfactants altered the wettability of the carbonate rock from oil-wet to intermediate-wet. The maximum oil recovery by imbibition test was reached when core was exposed 1-ethly ionic liquid after imbibition in formation water. Also, after core flooding test, it is concluded that considerable amount of oil can be recovered from Garzan reservoir by waterflooding alone if adverse effects of natural fractures could be eliminated. 相似文献
34.
《Ceramics International》2022,48(14):20062-20069
Photocatalytic N2 fixation is a promising and sustainable manufacturing process of ammonia (NH3); however, the NH3 production rate by this method is very low, thus severely restricting further application of this sustainable technology. Therefore, developing an efficient photocatalyst for N2 fixation under mild conditions is urgently required. Herein, ferroelectric Bi2WO6 materials with different surface oxygen defects were prepared, and the concentration of corresponding defects was controlled by adjusting the thermal reduction time. The abundant oxygen defects in Bi2WO6 can provide more reactive sites to promote the effective adsorption of N2, and the photogenerated charge carrier can be efficiently separated benefiting from the internal electric field. These would weaken the N2 triple bond and reduce the activation energy barrier for the conversion of N2 to NH3 under mild conditions. In the absence of sacrificial agents and cocatalysts, the optimized Bi2WO6 with oxygen defects shows an indigenous NH3 yield of 132.175 μmol·g-1·L-1·h-1, which is more than two times higher than that of the original Bi2WO6. Surprisingly, the Bi2WO6 with oxygen defects produced more than eight times NH3 (471.13 μmol·g-1·L-1·h-1) than that of the original Bi2WO6 when assisted by an external magnetic field, thus providing a new perspective for further enhancing the N2 fixation performance. 相似文献
35.
Grace Lara Chieko Takahashi Miku Nagaya Kunihiko Uemura 《International Journal of Food Science & Technology》2022,57(6):3251-3262
The present study aimed to investigate the influence of radio frequency (RF) heating at 70 and 80 °C, in comparison with the traditional conventional heating. The RF heating technology was applied for maintaining the colour and textural quality as well as inactivating the enzymatic activity of polyphenol oxidase (PPO) and reducing the Escherichia coli growth in packaged fresh-cut peach samples. To evaluate this, 120 g of freshly cut peach fruit was placed in heat-resistant plastic bags, and 50 mL of sugar solution (12°Brix) was added to each bag and vacuum-packed for conventional heating and radio frequency (RF) heating. Our results demonstrated that the RF heating process could reduce the heating time by up to 83% at 70 and 80 °C as compared to conventional heating. Moreover, RF heating at 70 and 80 °C reduced the PPO enzymatic activity, which caused enzymatic browning, up to 85.46% and 93.5%, respectively, as compared to 40.86% reduction only for conventional heating. Furthermore, RF heating completely inhibited E. coli growth. Collectively, we demonstrated that RF heating is an emerging and promising technology for improving the quality of fresh-cut fruits such as peach during various storage conditions. The present study provides relatively novel information on the effectiveness of RF heating in maintaining the quality of fresh-cut peaches. In the future, we would like to investigate the effectiveness of RF heating on other agricultural products. 相似文献
36.
通过对广西2021年度推广种植的野香优、广粮香2号、百香、丝香四个主要品种系列的早晚籼优质稻谷品种进行采样,按照《优质稻谷》《中国好粮油 稻谷》《广西好粮油 广西香米》标准中规定质量品质指标进行检测,并依据检测数据对四个主要稻谷品种在不同季节、不同种植区域以及同一种植区域不同种植季节品质变化情况进行对比分析研究,寻找优质稻因品种、产地、种植季节不同对其品质的影响规律,为优质稻谷品种的选育和推广种植工作提供科学依据和数据支持,促进广西优质粮食产业和“广西香米”产业进一步发展。 相似文献
37.
《Ceramics International》2022,48(3):3833-3840
Ca-doped Ni–Mg–Mn spinel ferrites with compositions of Ni0·5Mg0·3Mn0.2CaxFe2-xO4 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) were prepared via sol-gel auto-ignition technique. TGA/DTA, FTIR, XRD, FESEM, and VSM were employed to evaluate the thermal, spectral, structural, morphological, and magnetic features of Ca-doped Ni–Mg–Mn spinel ferrites. TGA/DTA curves show the weight loss in the sample. This weight loss was attributed to the oxidation and decomposition of the sample contents at a temperature of 500 °C. XRD reveals a single-phase structure of the Ni–Mg–Mn nano ferrites. A single-phase orthorhombic structure was confirmed for Ca-doped Ni–Mg–Mn ferrites. Structural parameters such as lattice parameter, ‘da’, ‘db’, ‘dc’, and ‘dv’ were evaluated using unit cell software. The absorption peaks at 427 to 538 cm?1 confirmed the spinel structure, which was evaluated using FTIR. FESEM analyses showed that the agglomerations increased with the doping of Ca in Ni–Mg–Mn ferrites. Remanence, Y–K angles, saturation, coercive force, magnetic squareness, magnetic moment, and anisotropy constant were determined for Ca-doped Ni–Mg–Mn spinel ferrite samples. It is noticed that saturation increases from 29.157 to 51.322 emu/g, whereas remanence increased from 5.34 to 9.40 emu/g, respectively. The permeability, anisotropy constant, and magnetic moments were also found to increase with Ca doping. However, the Y–K angles increased with Ca concentration in Ni–Mg–Mn nano ferrites. In addition, the switching field distribution (SFD) and high-frequency response of all the Ca-doped Ni–Mg–Mn samples were also evaluated. Ca-doped Ni–Mg–Mn samples are suggested to be suitable for switching, filters, inductors, and microwave absorption applications because of the superparamagnetic nature of the prepared spinel ferrites. 相似文献
38.
Kai Han Xin‐Yang Li Ye‐Qi Zhang Yong‐Lin He Rui Hu Xiu‐Li Lu Qi‐Jiu Li Jing Hui 《European Journal of Lipid Science and Technology》2020,122(4)
Hyperlipidemia is a common cardiovascular disease. At present, the influence of high fat diet (HFD) on this is being explored. Recently, vegetable oils rich in omega‐3 have been reported that can treat hyperlipidemia caused by HFD. However, the effects of chia seed oil (CSO) on HFD‐induced hyperlipidemia and oxidative stress are poorly studied. Hence, in this study, the effects of CSO on hyperlipidemia and oxidative stress induced by HFD in mice are analyzed by various commercial kits, section staining, and protein expression. The results show that CSO decreases body weight and organ index. Meanwhile, CSO reduces serum lipid levels of total cholesterol, triglyceride, and low‐density lipoprotein cholesterol. It can also elevate superoxide dismutase and glutathione peroxidase activities and reduce malondialdehyde content in serum and liver. The results of histopathological analysis prove that CSO improves hepatic steatosis and reduces lipid deposition. Further, the results of western blot demonstrate that CSO upregulates the expression of peroxisome proliferator‐activated receptor alpha and carnitine palmitoyltransferase 1a in the liver. As a result, CSO may be a potential lipid‐lowering oil to prevent and treat HFD‐induced hyperlipidemia and oxidative stress. Practical Applications CSO, as a byproduct of chia seed processing, is a rich source of α‐linolenic acid. This study investigates the effects of CSO on HFD‐induced hyperlipidemia and oxidative stress in mice. It is concluded that dietary CSO can improve the hyperlipidemia in HFD‐induced mice via analysis of lipid parameters, histopathology study of the liver, and lipid metabolism related genes. In addition, supplementation of CSO also can improve the oxidative stress in mice. Therefore, CSO can be used for the prevention of hyperlipidemia and oxidative stress. This research provides a theoretical basis for the comprehensive development and utilization of functional chia seed oil. 相似文献
39.
Rongli Xu Da Bian Yongwu Zhao Xiaoyan Xu Yaxuan Liu Wenlei Zhou 《International Journal of Applied Ceramic Technology》2020,17(3):1010-1016
To improve the wear resistance of the chemically bonded phosphate ceramic coatings, MWCNTs are selected as the reinforcement after the modification. The high temperature wear experiment is carried out to investigate the wear behavior of the coatings with different temperatures. The results suggest that, when the temperature is below 500℃, MWCNTs can decrease friction coefficient, and the lowest friction coefficient is about 0.28, but MWCNTs lose the lubricant function at 500℃ and the friction coefficient keeps at the level of ~ 0.68. In addition, the wear resistance of coatings is improved with the introduction of MWCNTs at 100℃ and 300℃ (the wear rate is below 15X10-3mm3/Nm), but keeps similar level at 500℃ (the wear rate is ~ 22 × 10−3mm3/Nm). Besides, the wear mechanism of the coatings reinforced by MWCNTs is also investigated based on the wear behavior and microstructural characterizations. MWCNTs improve the fracture toughness by preventing the crack generation and forming the bridge when crack occurs, which leads to smooth wear tracks and good wear resistance of coatings. The coatings with MWCNTs achieve poor wear resistance at 500℃ because MWCNTs lose their strength and resistance to fatigue by oxidizing. 相似文献
40.