全文获取类型
收费全文 | 51402篇 |
免费 | 1298篇 |
国内免费 | 186篇 |
专业分类
电工技术 | 638篇 |
综合类 | 635篇 |
化学工业 | 6433篇 |
金属工艺 | 690篇 |
机械仪表 | 1108篇 |
建筑科学 | 1123篇 |
矿业工程 | 407篇 |
能源动力 | 738篇 |
轻工业 | 3411篇 |
水利工程 | 697篇 |
石油天然气 | 88篇 |
武器工业 | 6篇 |
无线电 | 2195篇 |
一般工业技术 | 4398篇 |
冶金工业 | 23354篇 |
原子能技术 | 241篇 |
自动化技术 | 6724篇 |
出版年
2024年 | 81篇 |
2023年 | 265篇 |
2022年 | 386篇 |
2021年 | 459篇 |
2020年 | 236篇 |
2019年 | 292篇 |
2018年 | 744篇 |
2017年 | 983篇 |
2016年 | 1379篇 |
2015年 | 987篇 |
2014年 | 709篇 |
2013年 | 1010篇 |
2012年 | 2539篇 |
2011年 | 2978篇 |
2010年 | 1048篇 |
2009年 | 1179篇 |
2008年 | 955篇 |
2007年 | 917篇 |
2006年 | 814篇 |
2005年 | 3490篇 |
2004年 | 2700篇 |
2003年 | 2181篇 |
2002年 | 966篇 |
2001年 | 822篇 |
2000年 | 366篇 |
1999年 | 750篇 |
1998年 | 6785篇 |
1997年 | 4183篇 |
1996年 | 2770篇 |
1995年 | 1585篇 |
1994年 | 1195篇 |
1993年 | 1242篇 |
1992年 | 276篇 |
1991年 | 334篇 |
1990年 | 342篇 |
1989年 | 312篇 |
1988年 | 322篇 |
1987年 | 244篇 |
1986年 | 228篇 |
1985年 | 195篇 |
1984年 | 88篇 |
1983年 | 104篇 |
1982年 | 143篇 |
1981年 | 198篇 |
1980年 | 214篇 |
1979年 | 67篇 |
1978年 | 106篇 |
1977年 | 678篇 |
1976年 | 1446篇 |
1975年 | 107篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
33.
34.
35.
Utilities in the sky?: 《Refocus》2002,3(6):54-57
Could huge arrays of space-based solar power systems one day supply utility scale electricity to the electric power grid on earth? How realistic a possibility is this option for alternative energy supply at the moment? Finley R. Shapiro, USA compares space-based and terrestrial solar power systems. 相似文献
36.
37.
Larissa Canilha Walter Carvalho Marco Giulietti Maria Das Graças Almeida Felipe João Batista Almeida E Silva 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(5):715-721
BACKGROUND: Xylitol bioproduction from lignocellulosic residues comprises hydrolysis of the hemicellulose, detoxification of the hydrolysate, bioconversion of the xylose, and recovery of xylitol from the fermented hydrolysate. There are relatively few reports on xylitol recovery from fermented media. In the present study, ion‐exchange resins were used to clarify a fermented wheat straw hemicellulosic hydrolysate, which was then vacuum‐concentrated and submitted to cooling in the presence of ethanol for xylitol crystallization. RESULTS: Sequential adsorption into two anion‐exchange resins (A‐860S and A‐500PS) promoted considerable reductions in the content of soluble by‐products (up to 97.5%) and in medium coloration (99.5%). Vacuum concentration led to a dark‐colored viscous solution that inhibited xylitol crystallization. This inhibition could be overcome by mixing the concentrated medium with a commercial xylitol solution. Such a strategy led to xylitol crystals with up to 95.9% purity. The crystallization yield (43.5%) was close to that observed when using commercial xylitol solution (51.4%). CONCLUSION: The experimental data demonstrate the feasibility of using ion‐exchange resins followed by cooling in the presence of ethanol as a strategy to promote the fast recovery and purification of xylitol from hemicellulose‐derived fermentation media. Copyright © 2008 Society of Chemical Industry 相似文献
38.
There are some foods that contain mutagenic or carcinogenic agents, some of which occur naturally and others that may be formed during preparation or cooking. Several foods such as legumes, also contain natural antimutagens and/or anticarcinogens. Lupine is one such legume that contains high amounts of protein (40%) and oils (14%). About 90 species of lupine have been reported throughout Mexico. However, the use of this crop as a source of food has been limited by the presence of antinutritional agents such as phenolic compounds (PC), carbohydrates (CH) and quinolizidinic alkaloids (Qas). It has also been suggested that consuming these compounds can affect human health and may even reduce the risk of disease. The objective of this work was to determine the effect of PC, CH and Qas, isolated and quantified from Lupinus campestris on the mutagenicity of 1-nitropyrene (1-NP) as a model mutagen and we used the Salmonella typhimurium tester strain YG1024 by the Kado microsuspension method. The results indicate that L. campestris seeds have 11 mg (+)catechin equivalent g(-1) seed coat; 120.3 mg g(-1) seeds and 2.13 mg g(-1) seeds of PC, CH and Qas, respectively. 1-NP mutagenicity was inhibited by 86% for PC, 76% for CH and 75% for Qas at concentrations of 200, 512 and 13.6 microg/tube, respectively. 相似文献
39.
E St?lberg S St?lberg M Melander K Arimura 《Computer methods and programs in biomedicine》1991,34(2-3):219-227
Programs for rule based electromyography (EMG) interpretation and reporting are described. A number of parameters are obtained during an EMG investigation. The combination of these data leads to a neurophysiological conclusion. Knowledge from the literature, research and experience is the basis for rule development. Rules have been developed for 14 of the most commonly used classifications of an EMG. The syntax is relatively easy and the user may change the rules, add rules or apply the system for other types of data. The results are displayed in a new graphical way. The system presented here is part of an integrated EMG laboratory with administrative routines, distributed databases for storage of results and routines for automatic report generation. 相似文献
40.