全文获取类型
收费全文 | 51533篇 |
免费 | 4829篇 |
国内免费 | 2255篇 |
专业分类
电工技术 | 693篇 |
技术理论 | 3篇 |
综合类 | 3315篇 |
化学工业 | 24376篇 |
金属工艺 | 1685篇 |
机械仪表 | 1001篇 |
建筑科学 | 1480篇 |
矿业工程 | 598篇 |
能源动力 | 1230篇 |
轻工业 | 3252篇 |
水利工程 | 238篇 |
石油天然气 | 3154篇 |
武器工业 | 572篇 |
无线电 | 4789篇 |
一般工业技术 | 8702篇 |
冶金工业 | 1038篇 |
原子能技术 | 243篇 |
自动化技术 | 2248篇 |
出版年
2024年 | 175篇 |
2023年 | 942篇 |
2022年 | 1004篇 |
2021年 | 1508篇 |
2020年 | 1551篇 |
2019年 | 1469篇 |
2018年 | 1379篇 |
2017年 | 1603篇 |
2016年 | 1804篇 |
2015年 | 1791篇 |
2014年 | 2832篇 |
2013年 | 2801篇 |
2012年 | 3359篇 |
2011年 | 3895篇 |
2010年 | 2914篇 |
2009年 | 3137篇 |
2008年 | 2645篇 |
2007年 | 3475篇 |
2006年 | 3190篇 |
2005年 | 2855篇 |
2004年 | 2333篇 |
2003年 | 2144篇 |
2002年 | 1839篇 |
2001年 | 1547篇 |
2000年 | 1343篇 |
1999年 | 1027篇 |
1998年 | 820篇 |
1997年 | 625篇 |
1996年 | 511篇 |
1995年 | 433篇 |
1994年 | 399篇 |
1993年 | 291篇 |
1992年 | 228篇 |
1991年 | 163篇 |
1990年 | 132篇 |
1989年 | 78篇 |
1988年 | 58篇 |
1987年 | 53篇 |
1986年 | 33篇 |
1985年 | 45篇 |
1984年 | 38篇 |
1983年 | 28篇 |
1982年 | 24篇 |
1981年 | 15篇 |
1980年 | 14篇 |
1979年 | 19篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1974年 | 3篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
33.
N. Leclerc A. Michaud K. Sirois J.‐F. Morin M. Leclerc 《Advanced functional materials》2006,16(13):1694-1704
New electroactive and photoactive conjugated copolymers consisting of alternating 2,7‐carbazole and oligothiophene moieties linked by vinylene groups have been developed. Different oligothiophene units have been introduced to study the relationship between the polymer structure and the electronic properties. The resulting copolymers are characterized by UV‐vis spectroscopy, size‐exclusion chromatography, and thermal and electrochemical analyses. Bulk heterojunction photovoltaic cells from different copolymers and a soluble fullerene derivative, [6,6]‐phenyl‐C61 butyric acid methyl ester, have been fabricated, and promising preliminary results are obtained. For instance, non‐optimized devices using poly(N‐(4‐octyloxyphenyl)‐2,7‐carbazolenevinylene‐alt‐3″,4″‐dihexyl‐2,2′;5′,2″;5″,2″′;5″′,2″″‐quinquethiophenevinylene 1″,1″‐dioxide) as an absorbing and hole‐carrier semiconductor exhibit power conversion efficiency up to 0.8 % under air mass (AM) 1.5 illumination. These features make 2,7‐carbazolenevinylene‐based and related polymers attractive candidates for solar‐cell applications. 相似文献
34.
Beatriz O. Hincapie Luis J. Garces Sinue Gomez Ruma Ghosh Steven L. Suib 《Catalysis Today》2005,110(3-4):323
Copper containing faujasite has been successfully prepared for the first time using a direct synthesis method. Faujasite type zeolite can be prepared in the presence of copper species by tuning the synthesis conditions. Ammonium hydroxide was used to form a copper complex that was later mixed with the reacting gel. Sodium is required to obtain copper faujasite. The complete elimination of sodium ions from the starting gel produces amorphous material. Crystallization took place at 358 K for 11 days. Crystallization temperature of 373 K produces ANA type zeolite as an impurity. Increasing by two times the amount of copper complex added to the reacting gel increases the crystallization time of Cu-FAU from 11 to 20 days (the crystallization rate decreases). The copper containing faujasite obtained was characterized by XRD, FESEM, EDX, EPR, FT-IR, TPR, and BET. According to the XRD pattern only FAU type zeolite was obtained. According to TPR experiments, the reduction temperature for Cu2+ ions present in Cu-FAU prepared by direct synthesis was 70 K more than for Cu-FAU prepared by ion-exchange. This difference can be due to the different location of the copper ions in the supercages or in the sodalite cages of the faujasite. 相似文献
35.
KS Atia AI El‐Batal 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(7):805-811
Glucose oxidase (EC 1.1.3.4) was immobilized on different polymeric materials using different immobilization techniques (entrapping by γ‐irradiation, and covalent binding using epichlorohydrin). Studies were carried out to increase the thermal stability of glucose oxidase (GOD) for different applications. The activity and stability of the resulting biopolymers have been compared with those of free GOD. The effect of different polyvinyl alcohol/polyacrylamide (PVA/PAAm) compositions of the copolymer carrier on the enzymatic activity of the immobilized GOD was studied. The maximum enzymatic activity was obtained with the composition ratio of PVA/PAAm of 60:40. The behaviour of the free and immobilized enzyme was analysed as a function of pH. A broadening in the pH profile (5.5–8) was observed for immobilized preparations. The activity and stability of the resulting biopolymers produced by immobilization of GOD onto different carriers have been compared, in both aqueous and organic media, with those of the free GOD. The enzyme's tolerance toward both heat and organic solvent was enhanced by immobilization onto polymers. The addition of different concentrations of organic solvents (10–50%, v/v) to the enzyme at higher temperature (60 °C) was found to stabilize the enzyme molecule. The strongest stabilizing effect on the enzymatic activity was achieved at a concentration of 10%. Copyright © 2005 Society of Chemical Industry 相似文献
36.
氯化铁催化合成富马酸二甲酯 总被引:9,自引:0,他引:9
氯化铁可代替硫酸催化酯化反应,探讨了氯化铁催化合成富马酸二甲酯的条件,操作简便,反应温和,无腐蚀,减少了污染与产品纯化。 相似文献
37.
有机地球化学和有机岩石学研究结果表明,新疆三塘湖盆地侏罗系煤中富集孢子体和角质体(3.0%~6.0%,全岩体积百分比),对煤中氯仿沥青“A”组成中较高的总烃馏分(30%~50%)和饱芳比(0.6~3.0)产生了影响。煤的聚集环境是影响煤的显微组分组成及生油特性的关键因素。三塘湖盆地侏罗系煤属于“晚生晚排”叠加有“早生早排”类型的烃源岩。 相似文献
38.
SHS法陶瓷衬管的研究现状及应用前景 总被引:2,自引:0,他引:2
回顾了自蔓延高温合成陶瓷衬管的发展历史,对国内外的研究现状进行归纳总结,介绍了离心SHS法生产陶瓷衬管的工艺特点及产品性能,展望了离心SHS陶瓷衬管的应用前景。 相似文献
39.
相转移催化合成芳基烷基醚 总被引:7,自引:0,他引:7
报道了以四丁基溴化铵为相转移催化剂,简便地合成了10个芳基烷基醚,反应几乎是定量地快速进行。 相似文献
40.
二苯并-18-冠-6的合成条件的优化 总被引:3,自引:0,他引:3
通过改变溶剂的极性、离子性、离去基团的活性及反应温度等方法,对传统的Pedersen冠醚合成法进行了优化,使目标产物的最高产率达到71%以上.产物通过IR、1H NMR及元素分析等方法进行结构表征. 相似文献