全文获取类型
收费全文 | 18456篇 |
免费 | 1784篇 |
国内免费 | 917篇 |
专业分类
电工技术 | 305篇 |
技术理论 | 2篇 |
综合类 | 1734篇 |
化学工业 | 5526篇 |
金属工艺 | 628篇 |
机械仪表 | 476篇 |
建筑科学 | 4118篇 |
矿业工程 | 882篇 |
能源动力 | 396篇 |
轻工业 | 1433篇 |
水利工程 | 230篇 |
石油天然气 | 1629篇 |
武器工业 | 48篇 |
无线电 | 1065篇 |
一般工业技术 | 996篇 |
冶金工业 | 534篇 |
原子能技术 | 373篇 |
自动化技术 | 782篇 |
出版年
2024年 | 62篇 |
2023年 | 239篇 |
2022年 | 470篇 |
2021年 | 586篇 |
2020年 | 546篇 |
2019年 | 501篇 |
2018年 | 439篇 |
2017年 | 583篇 |
2016年 | 628篇 |
2015年 | 689篇 |
2014年 | 1155篇 |
2013年 | 1278篇 |
2012年 | 1465篇 |
2011年 | 1437篇 |
2010年 | 1027篇 |
2009年 | 997篇 |
2008年 | 886篇 |
2007年 | 1106篇 |
2006年 | 1078篇 |
2005年 | 883篇 |
2004年 | 796篇 |
2003年 | 699篇 |
2002年 | 567篇 |
2001年 | 515篇 |
2000年 | 445篇 |
1999年 | 360篇 |
1998年 | 287篇 |
1997年 | 359篇 |
1996年 | 196篇 |
1995年 | 180篇 |
1994年 | 123篇 |
1993年 | 99篇 |
1992年 | 101篇 |
1991年 | 81篇 |
1990年 | 64篇 |
1989年 | 63篇 |
1988年 | 48篇 |
1987年 | 33篇 |
1986年 | 14篇 |
1985年 | 8篇 |
1984年 | 11篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 19篇 |
1979年 | 9篇 |
1974年 | 1篇 |
1963年 | 1篇 |
1959年 | 1篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Claudio Arbib Fabrizio Marinelli 《International Journal of Flexible Manufacturing Systems》2003,15(4):333-354
A cook has to prepare n cakes using an oven with two racks. According to the recipe, the i-th cake has to be baked for exactly a
i minutes. Cakes to be cooked are taken from a table and carried to the oven, and once cooked are carried back to the table by means of a trolley that can carry two cakes at a time. What is the minimum number q
* of round trips required of the cook? This problem has application to the operation scheduling of transportation systems and to material cutting. A different problem arises according to whether the cook accepts or not to stay near the oven for awhile with the trolley. If the trolley cannot be idle at the oven, an optimum schedule with no oven idle-time always exists: consequently, the trolley schedule is trivial, and the problem is transformed into a set packing. For this case, we propose and test a heuristic method which generates all of the promising columns of the set packing, and solves the resulting problem by branch-and-bound. Instead, if the trolley can be idle at the oven for a limited amount of time, a problem arises to find an optimal schedule of the trolley: in this case we show how to use a scaling technique in order to obtain a very good feasible solution by the method above. 相似文献
32.
活性炭单柱提取肌苷新技术研究 总被引:1,自引:0,他引:1
活性炭单柱提取肌苷新技术研究李永泉,张进,姚恕,郑莲英,俞峰(杭州大学生物系杭州310028)(浙江大学化工系杭州310027)关键词:肌苷,提取技术,活性炭单柱1前言目前,国内肌苷发酵后处理工艺落后,在分离提取工序中肌苷损失严重,收率一般只有50%... 相似文献
33.
Auguste Commeyras Hlne Collet Laurent Boiteau Jacques Taillades Odile Vandenabeele‐Trambouze Herv Cottet Jean‐Philippe Biron Raphaël Plasson Louis Mion Olivier Lagrille Herv Martin Franck Selsis Michel Dobrijevic 《Polymer International》2002,51(7):661-665
Addressing the still open question of the prebiotic origin of sequential macromolecules (peptides, nucleic acids) on the primitive Earth, we describe a molecular engine (the primary pump), which works at ambient temperature and continuously generates, elongates and complexifies sequential peptides. This new scenario is based on a cyclic reaction sequence, whose keystep is the activation of amino acids into their N‐carboxyanhydrides (NCA) through nitrosation by NOx. This process could have taken place on tidal beaches; it requires a buffered ocean, emerged land and a nitrosating atmosphere. With the help of geochemical studies and computer simulations of atmosphere photochemistry, we show that the primitive Earth during the Hadean may have satisfied all these requirements. © 2001 Society of Chemical Industry. 相似文献
34.
The influence of NaCl and CO2 on the atmospheric corrosion of magnesium alloy AZ91 is studied in the laboratory. Samples were exposed under carefully controlled air and flow conditions; the relative humidity was 95%, the temperature was 22.0°C and the concentration of CO2 was < 1 ppm or 350 ppm. Different amounts of sodium chloride (0–70 μg/cm2) were added before exposure. The corrosion products were analyzed by gravimetry, ion chromatography, X‐ray diffraction and scanning electron microscopy. Mass gain and metal loss results are reported. The combination of high humidity and NaCl is very corrosive towards AZ91. However, the NaCl‐induced corrosion is inhibited by ambient concentrations of CO2. Exposure in the absence of CO2 gives rise to heavy pitting, with brucite, Mg(OH)2, being the dominant corrosion product. In the presence of CO2 a layer of hydrated magnesium hydroxy carbonate, Mg5(CO3)4(OH)2 · 5 H2O forms. A tentative corrosion mechanism is presented that explains the behavior in the two environments. 相似文献
35.
在辽宁省工业城市进行 A3钢大气暴露试验。两年后测出不同地点腐蚀率。依据所记录的各试验点的气象数据和污染数据,讨论了 A3钢的大气腐蚀规律。 相似文献
36.
灭蚊窗涂剂的毛细管柱气相色谱分析 总被引:2,自引:2,他引:0
介绍了用AT-101毛细管柱,以邻苯二甲酸二正戊酯为内标,对灭蚊窗涂剂中3种有效成分残杀威、氯菊酯、氯氰菊酯同柱同条件下定量分析的方法。该方法的分析时间短,准确度、精密度高,重现性好。 相似文献
37.
从120号溶剂油中提取正庚烷并回收甲基环己烷的研究 总被引:1,自引:0,他引:1
总结了国内外正庚烷的生产状况和市场行情,分析了中小型石化企业生产正庚烷的可行件,提出采用萃取精馏分离正庚烷的方法.在间歇精馏塔塔顶温度为91-101℃、塔釜为103-110℃的条件下,可以得到58%以上正庚烷和甲基环己烷的混合液.根据物质相关性质,初步确定有关萃取溶剂,利用单级循环汽液平衡釜对初选的萃取剂进行实验研究,选定乙二醇作为萃取剂,为进一步实验研究提供依据. 相似文献
38.
Narendra Singh Shah & Nirankar Nath 《International Journal of Food Science & Technology》2006,41(9):1073-1081
Litchi (Litchi chinensis Sonn.) fruits are very susceptible to pericarp browning which adversely affects consumer acceptability even though the aril portion remains in excellent condition. Litchi arils (litchis) were treated with a solution containing 0–2% (w/v) calcium lactate (CL), 0–0.02% (w/v) 4‐hexyl resorcinol (4‐HR) and 1% potassium sorbate. The pH of solution was adjusted to 4.0 with citric acid. Treated litchis were packed in polystyrene trays, over‐wrapped with polypropylene film, vacuum‐packed (0, 47409.3, 94831.9 Pa) and stored at 4 ± 2 °C. Drip losses, pH, total soluble solids (TSS), sensory attributes and microbiological quality of stored samples were estimated. A four‐factor, three‐level experimental design (D6 Hokes design) with 19 experiments was chosen. Mathematical models were developed to analyse and predict the effect of CL, 4‐HR, in‐package vacuum and storage time on the responses. TSS, pH and sensory scores decreased significantly (P 0.01), whereas drip losses and microbial count increased significantly (P 0.01) with time. Drip loss was significantly (P 0.1) reduced by addition of CL. 4‐HR prevented browning and changes in colour score during storage were significantly less. Vacuum in packages exerted significant (P 0.01) effect over pH, TSS, sensory and microbiological qualities of minimally processed litchis. 相似文献
39.
双氧水冷漂助剂液中的润滑剂——烷基硫酸钠可以在四级氧化铝柱上用氯仿和乙醇—水的淋洗体系进行分离而获得纯品;用NMR和GC法进行结构分析;两相滴定法测定其含量。 相似文献
40.
The surface of polyethyleneterephthalate (PET) nonwoven fabric was modified by He/O2 atmospheric pressure plasma treatment, varying plasma exposure time. The plasma treated PET surfaces have been analyzed to investigate the chemical nature and morphology of surface by X‐ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively. The change of wettability was measured depending on plasma exposure time. XPS results indicated the presence of oxygen‐based functional groups on the PET nonwoven fabric surface after plasma treatment and oxygen content increased as exposure time increased. The mean roughness increased after 30 s exposure and further increase in exposure to 60 s led to decrease of the roughness and then again increase. The root mean square roughness followed the similar trend to mean roughness. The average difference in height, Rz, increased after plasma exposure for 30 s, while it slightly decreased after 60 s exposure. Despite of redeposition, the Rz of 90 s exposed sample increased more than two times compared with those of 30 and 60 s exposed. Wettability increased progressively up to 10 times after 90 s exposure compared with the untreated. It is attributed to the increases of hydrophilicity and surface roughness. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献