全文获取类型
收费全文 | 925篇 |
免费 | 90篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 1篇 |
综合类 | 18篇 |
化学工业 | 217篇 |
金属工艺 | 9篇 |
机械仪表 | 4篇 |
建筑科学 | 3篇 |
矿业工程 | 5篇 |
能源动力 | 2篇 |
轻工业 | 715篇 |
水利工程 | 5篇 |
石油天然气 | 17篇 |
无线电 | 2篇 |
一般工业技术 | 16篇 |
冶金工业 | 3篇 |
原子能技术 | 4篇 |
自动化技术 | 5篇 |
出版年
2024年 | 6篇 |
2023年 | 13篇 |
2022年 | 27篇 |
2021年 | 50篇 |
2020年 | 33篇 |
2019年 | 48篇 |
2018年 | 29篇 |
2017年 | 36篇 |
2016年 | 41篇 |
2015年 | 25篇 |
2014年 | 55篇 |
2013年 | 90篇 |
2012年 | 64篇 |
2011年 | 82篇 |
2010年 | 45篇 |
2009年 | 41篇 |
2008年 | 47篇 |
2007年 | 69篇 |
2006年 | 54篇 |
2005年 | 18篇 |
2004年 | 16篇 |
2003年 | 32篇 |
2002年 | 18篇 |
2001年 | 18篇 |
2000年 | 9篇 |
1999年 | 8篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有1026条查询结果,搜索用时 328 毫秒
11.
S. Chevolleau J. F. Mallet E. Ucciani J. Gamisans M. Gruber 《Journal of the American Oil Chemists' Society》1992,69(12):1269-1271
Hexane and methanol leaf extracts of sixteen Mediterranean plant species were obtained by percolation. Higher yields were
observed for methanol (16.4–47.8%) than for hexane extracts (1.3–13%). Antioxidant activity of these extracts was determined
by a rapid spectrophotometric method involving the combined oxidation of beta-carotene and linoleic acid. Leaf extracts were
thus characterized by an Antioxidant Activity Coefficient (AAC) ranging from 0 to 1000. Hexane extracts gave much higher AAC
values than the corresponding methanol extracts. In both cases, myrtle (Myrtus communis) showed the best antioxidant effectiveness. 相似文献
12.
Identification of organochlorines and organobromines in coals 总被引:1,自引:0,他引:1
Xian-Yong Wei Xiao-Hua Wang Zhi-Min Zong Zhong-Hai Ni Li-Fang Zhang Ya-Fei Ji Ke-Chang Xie Chul Wee Lee Zhen-Xue Liu Nai-Bo Chu Jiao-Ying Cui 《Fuel》2004,83(17-18):2435-2438
Four Chinese bituminous coals were extracted with CS2, n-hexane, benzene, methanol, acetone, tetrahydrofuran (THF) and THF/methanol (1: 3 vol/vol) mixed solvent sequentially. The resulting 28 extracts were analyzed with GC/MS. Six organochlorines (OCs) and two organobromines (OBs) were identified in eight extracts from the coals. Our experiments provide, for the first time, the information on the molecular structure of OCs and OBs in coals. 相似文献
13.
14.
15.
16.
虎杖根提取物及分离组分对黄瓜白粉病的作用效果 总被引:1,自引:0,他引:1
在实验室内进行了虎杖(Polygonum cuspidatum Sieb.etZucc.)根提取物及其活性组分分离研究,并且对黄瓜白粉病进行了活性测定及温室小区试验。结果表明,无论提取率还是作用效果,乙醇较适合于做为虎杖根提取物的提取溶剂。虎杖根乙醇提取物和乙醚提取物对黄瓜白粉病的EC90值分别为537.85、35.38mg/L,而乙醚提取后残留物的活性很弱,说明乙醇提取物中具有杀菌作用的成分主要存在于乙醚提取物中。用pH梯度分离法对乙醚提取物进行分离,得到3个不同组分,其中以氢氧化钠分离得到的组分对黄瓜白粉病显示了极高的杀菌活性。在温室条件下虎杖乙醇提取物在800~1600mg/L下对黄瓜白粉病的防效相当或优于对照药剂三唑酮。 相似文献
17.
Abstract A regional study of Selenium (Se) speciation in surface waters, groundwaters, and saturation extracts from Soan-Sakesar valley Salt-Range, Pakistan was started in March 1994 and completed in October 1996. Groundwaters, streams, and springs had median concentrations of: total Se 48, 404.5, and 82 μg/l; Se+VI 40, 350 and 51 μg/l; Se+IV 8, 48 and 29 μg/l; Se-II 0, 6.5 and 2.0 μg/l, respectively. The concentration of Se exceeded the recommended water quality guidelines for drinking and irrigation water of 10 and 20 μg/l, respectively. In saturation extracts, median total Se, Se+VI, Se+IV and Se-II were 190, 146, 37 and 7.0 μg/l, respectively. Uchhali, Khabbaki and Jahlar lake water samples had the mean concentration of: total Se 2103, 670 and 297 μg/l; Se+VI 1777, 470, and 233 μg/l; Se+IV 291, 166 and 39 μg/l; Se-II 35, 34 and 25 μg/l, respectively. The Sakesar limestone Formation of Eocene age rich in shales and fossils (median Se concentration 7.2 μg/kg) are considered to be the source of selenium that have enriched soils of Soan-Sakesar valley. Selenim speciation results show the abundance of selenate in all the environmental samples. A linear relationship between Se+VI and pH (R2= 0.84, 0.58, 0.88, 0.82, and 0.91; significant at the 0.05 level) for groundwater, saturation extract, stream, spring, and lake waters were noted, suggesting that the Se+VI in the samples is highly associated with pH. Linear relationships were established between Se+VI and Mg, NO3, and SO4 for groundwater (R2= 0.24, 0.16, and 0.64; significant at the 0.01 level) and surface water (R2= 0.96, 0.14, and 0.91; significant at the 0.001 level). This suggests the high concentrations of Mg, NO3 and SO4, which strongly adsorb and compete with selenium for surface site, increases the Se+VI fraction. The results show that the higher percentage of selenate on other species in the analyzed samples is favored by higher pH and oxidizing environments of the valley. 相似文献
18.
Nazish Jahan Saba Aslam Khalil ur Rahman Tuba Fazal Fareeha Anwar Rubab Saher 《Journal of Experimental Nanoscience》2016,11(1):72-80
Nanotechnology is a promising technique to increase the bioavailability of herbal medicines. This paper presents the nanosuspension approach for increasing the aqueous solubility and thereby bioactivity of important herbal extracts. Nanosuspensions of the seeds of three plants extract (Silybum marianum, Elettaria cardamomum and Coriandrum sativum) were prepared by using polyvinyl alcohol (1.5% w/v) as a stabiliser. Prepared nanoparticles were characterised by scanning electron microscope. Activity of nanosuspension formulation was assessed by using four in vitro antioxidant assays. S. marianum, E. cardamomum and C. sativum particle size was observed to fall in range of 446.1 ± 112.6, 456.63 ± 339.2 and 432.1 ± 172.8 nm, respectively, most of the particles were having spherical shape and smooth topology. These synthesised nanoparticles were found to be more effective against quenching free radical than their crude extracts and standards [butylated hydroxyl toluene and ascorbic acid]. C. sativum nanosuspension showed most free radical scavenging potential against 2,2-diphenyl-1-picrylhdrazyl (DPPH) and superoxide free radical scavenging assays (IC50 0.59 ± 0.01 and 0.81 ± 0.11 mg/ml). S. marianum nanosuspension was found to be most effective against DPPH radicals scavenging (IC50 0.34 ± 0.02 mg/ml). It was concluded that nanosuspension of herbal medicines potentiates the antioxidant potential. 相似文献
19.
20.