全文获取类型
收费全文 | 39551篇 |
免费 | 4941篇 |
国内免费 | 1952篇 |
专业分类
电工技术 | 1221篇 |
技术理论 | 8篇 |
综合类 | 2317篇 |
化学工业 | 14948篇 |
金属工艺 | 2810篇 |
机械仪表 | 915篇 |
建筑科学 | 2287篇 |
矿业工程 | 833篇 |
能源动力 | 2406篇 |
轻工业 | 2130篇 |
水利工程 | 290篇 |
石油天然气 | 2185篇 |
武器工业 | 152篇 |
无线电 | 1902篇 |
一般工业技术 | 8350篇 |
冶金工业 | 2798篇 |
原子能技术 | 360篇 |
自动化技术 | 532篇 |
出版年
2024年 | 240篇 |
2023年 | 1025篇 |
2022年 | 1438篇 |
2021年 | 1495篇 |
2020年 | 1591篇 |
2019年 | 1497篇 |
2018年 | 1379篇 |
2017年 | 1565篇 |
2016年 | 1660篇 |
2015年 | 1530篇 |
2014年 | 2270篇 |
2013年 | 2429篇 |
2012年 | 2889篇 |
2011年 | 3132篇 |
2010年 | 2308篇 |
2009年 | 2351篇 |
2008年 | 1836篇 |
2007年 | 2325篇 |
2006年 | 2282篇 |
2005年 | 1911篇 |
2004年 | 1612篇 |
2003年 | 1465篇 |
2002年 | 1159篇 |
2001年 | 879篇 |
2000年 | 803篇 |
1999年 | 609篇 |
1998年 | 541篇 |
1997年 | 381篇 |
1996年 | 339篇 |
1995年 | 281篇 |
1994年 | 251篇 |
1993年 | 183篇 |
1992年 | 150篇 |
1991年 | 117篇 |
1990年 | 107篇 |
1989年 | 62篇 |
1988年 | 44篇 |
1987年 | 48篇 |
1986年 | 32篇 |
1985年 | 57篇 |
1984年 | 46篇 |
1983年 | 45篇 |
1982年 | 25篇 |
1981年 | 4篇 |
1980年 | 13篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1963年 | 1篇 |
1959年 | 5篇 |
1951年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
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
82.
Asbestos fibres, of the chrysotile variety, and chopped carbon fibres were pretreated by an in-situ polycondensation technique eventually resulting in a polyamide coating on the fibre surface. Ionomer based composites containing either carbon or asbestos fibres in random in plane fibre orientation were prepared, and the influence of this coating process on the tensile properties was investigated. It was found that for the asbestos-filled composites the presence of the nylon 6,6 interlayer improves the tensile performance, especially at moderate polyamide depositions. This is not the case with the pretreated carbon-filled composites for which carbon fibres with higher polyamide contents are preferred. Combinations of the treated asbestos fibres with carbon and/or aramid fibres may be used to reduce the asbestos content in asbestos-only based engineering plastics. 相似文献
83.
The effect of heat treatment on microstructure of a plain-weave carbon fabric reinforced carbon-carbon composite with phenolformaldehyde-derived carbon matrix was investigated by X-ray diffraction. The diffraction patterns were analysed by the least-square fitting program Carbonxs. After heat treatment from 1000 to 2800 °C the interplanar distance of (002) planes decreased from 3.488 to 3.420 Å and the lattice parameter in basal plane increased from 2.440 to 2.464 Å, respectively. Simultaneously, the coherent block size in the basal plane directions increased from 18 to 54 Å, which was accompanied by an increase of the fraction of organised carbon atoms from 0.50 to 0.85. The 002 diffraction profile of the composite was much narrower than the sum of peaks of the matrix and fabric alone. This can probably be caused by a better crystallographic ordering (or by a partial graphitisation) of the matrix in the composite. On the other hand, the composite Young’s modulus slightly decreased with the treatment temperature increasing from 2200 to 2800 °C in spite of the established strong improvement of fibre crystallinity and, therefore, fibre modulus. The mechanisms diminishing the modulus of composite (e.g. partial matrix graphitisation at the fibre/matrix interface and decreasing fibre/matrix contact area) probably prevailed over the increasing contribution of the fibre modulus. 相似文献
84.
85.
Activated nanostructured-carbon cloths with a high ratio of surface area to volume are used as electrode for capacitive deionization. The electrochemical properties on capacitive deionization for NaCl solution have been investigated to improve efficiency of capacitive deionization properties from aqueous solution, employing chemical surface-modification by etching in alkaline and acidic solution. The removal efficiency of inorganic salts of activated carbon cloths by chemical modification significantly increased. Specially the carbon cloth surface modified in HNO3 showed an effect of improvement in the CDI efficiency due to not only ion adsorption by an electric double layer, but also electron transfer by Faradaic reaction. 相似文献
86.
The kinetics of the chlorination reaction of molybdenum trioxide with gaseous carbon tetrachloride has been studied at temperatures between 713 and 753 K. The effects of temperature, reaction time, residence time and gaseous reactant concentration on conversion were studied throughout the reaction. In all cases, there was an increase in conversion when the above operating variables were increased. The kinetic model proposed is consistent with and correlates the experimental data. In the range studied for the different variables, the step that controls the rate of reaction is the surface chemical reaction. Values of the rate constant and the activation energy were estimated. 相似文献
87.
The solubilities of ethyl palmitate, ethyl oleate, ethyl eicosapentaenoate (EPA) and ethyl docosahexaenoate (DHA) in supercritical
carbon dioxide were determined by a continuous flow method. The solubilities of fatty acid ethyl esters increased with pressure
and decreased as the temperature was increased. An empirical equation, similar to Chrastil's equation, was used to describe
the relationship between solute solubility and the density of carbon dioxide. The empirical equation was further used to qualitatively
estimate the separation efficiency of isolating EPA and DHA ethyl esters from fatty acid esters. The operating conditions
yielding high solubility gave fast extraction rate but resulted in low separation efficiency. Experiments were conducted to
separate ethyl EPA and ethyl DHA from a model mixture containing four fatty acid ethyl esters and from esterified squid visceral
oil. The experimental data compared closely with the calculated values. 相似文献
88.
东营凹陷古近系烃源岩超压特征及分布规律 总被引:26,自引:1,他引:25
统计分析1307口探井实测压力系数和83l口探井使用的钻井液密度数据,发现东营凹陷古近系沙三段、沙四段普遍存在异常超压,超压(压力系数1.1-1.5)主要出现在2100-3500m深度,强超压(压力系数大于1.5)主要出现在2800-3500m深度。东营凹陷沙三段、沙四段主力烃源岩超压平面分布具有北高南低、东高西低的总体特点,超压主要分布在洼陷带、断裂构造带和中央背斜带上。烃源岩压力系数等值线北部陡坡带比较密集,南部缓坡带相对稀疏。生油洼陷中心附近异常高压带的分布与生油洼陷基本一致,洼陷深陷区压力系数很大,向周围斜坡和构造高部位呈辐射状逐渐减小至正常,压力分布带与洼陷、边缘斜坡和构造较高部位的欠压实与压实带发育、分布规律的一致性很好。图3表l参9 相似文献
89.
M.A Lillo-Ródenas 《Carbon》2003,41(2):267-275
Direct mixing of an anthracite with hydroxides (KOH or NaOH) and heat treatment up to 730 °C has shown to be a very good activation procedure to obtain activated carbons with very high surface areas and high micropore volumes. The reactions involved during the heat treatment of these hydroxide/anthracite mixtures have been analysed to deep into the fundamental of the knowledge of this chemical activation process, that has not been studied before. For this purpose, the present paper analyses the drying process, the atmosphere during the carbonisation, the chemical state of the activating agents (NaOH, KOH and Na2CO3) and the chemical reactions occurring during the heat treatment which have been followed by FTIR and TPD. The analysis of our results allows us to conclude that steam is a good atmosphere for the carbonisation process, alone or joined with nitrogen, but not as good as pure nitrogen. On the other hand, during the activation process, the presence of CO2 should be avoided because it does not develop porosity. The reactions, and chemical changes, involved during this chemical process are discussed both from a thermodynamical point of view as well as identifying the reaction products (H2 by TPD and Na2CO3 by FTIR). As a result, this paper helps to cover the present lack of understanding of the fundamentals of the reactions of an anthracite with hydroxides which are necessary to understand the activation of the material. 相似文献
90.
F Javier Álvarez‐Hornos Carmen Gabaldón Vicente Martínez‐Soria Paula Marzal Josep‐Manuel Penya‐roja 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(5):643-653
BACKGROUND: Two peat biofilters were used for the removal of toluene from air for one year. One biofilter was fed with pure toluene and the other received 1:1 (by weight) ethyl acetate:toluene mixture. RESULTS: The biofilters were operated under continuous loading: the toluene inlet load (IL) at which 80% removal occurred was 116 g m?3 h?1 at 57 s gas residence time. Maximum elimination capacity of 360 g m?3 h?1 was obtained at an IL of 745 g m?3 h?1. The elimination of toluene was inhibited by the presence of ethyl acetate. Intermittent loading, with pollutants supplied for 16 h/day, 5 days/week, did not significantly affect the removal efficiency (RE). Biomass was fully activated in 2 h after night closures, but 6 h were required to recover RE after weekend closures. Live cell density remained relatively constant over the operational period, while the dead cell fraction increased. Finally, a 15 day starvation period was applied and operation then re‐started. Performance was restored with similar re‐acclimatization period to that after weekend closures, and a reduction in dead cell fraction was observed. CONCLUSION: This study demonstrates the capacity of the system to handle intermittent loading conditions that are common in industrial practices, including long‐term starvation. Copyright © 2008 Society of Chemical Industry 相似文献