全文获取类型
收费全文 | 33052篇 |
免费 | 1753篇 |
国内免费 | 339篇 |
专业分类
电工技术 | 592篇 |
综合类 | 551篇 |
化学工业 | 6402篇 |
金属工艺 | 946篇 |
机械仪表 | 1294篇 |
建筑科学 | 1119篇 |
矿业工程 | 190篇 |
能源动力 | 949篇 |
轻工业 | 3214篇 |
水利工程 | 280篇 |
石油天然气 | 198篇 |
武器工业 | 27篇 |
无线电 | 3952篇 |
一般工业技术 | 5116篇 |
冶金工业 | 6131篇 |
原子能技术 | 298篇 |
自动化技术 | 3885篇 |
出版年
2023年 | 205篇 |
2022年 | 507篇 |
2021年 | 743篇 |
2020年 | 469篇 |
2019年 | 593篇 |
2018年 | 678篇 |
2017年 | 699篇 |
2016年 | 795篇 |
2015年 | 695篇 |
2014年 | 1019篇 |
2013年 | 1786篇 |
2012年 | 1446篇 |
2011年 | 1785篇 |
2010年 | 1334篇 |
2009年 | 1368篇 |
2008年 | 1352篇 |
2007年 | 1248篇 |
2006年 | 1053篇 |
2005年 | 926篇 |
2004年 | 996篇 |
2003年 | 1197篇 |
2002年 | 1445篇 |
2001年 | 1225篇 |
2000年 | 783篇 |
1999年 | 775篇 |
1998年 | 2136篇 |
1997年 | 1365篇 |
1996年 | 982篇 |
1995年 | 658篇 |
1994年 | 534篇 |
1993年 | 580篇 |
1992年 | 310篇 |
1991年 | 261篇 |
1990年 | 243篇 |
1989年 | 234篇 |
1988年 | 206篇 |
1987年 | 168篇 |
1986年 | 171篇 |
1985年 | 232篇 |
1984年 | 154篇 |
1983年 | 134篇 |
1982年 | 129篇 |
1981年 | 151篇 |
1980年 | 145篇 |
1979年 | 100篇 |
1978年 | 83篇 |
1977年 | 188篇 |
1976年 | 324篇 |
1975年 | 92篇 |
1973年 | 84篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
拉曼光谱特别是表面增强拉曼光谱(surface enhanced Raman scattering, SERS)是一种基于光的非弹性散射的光谱技术,具有实时、快速等特点,是一种很好的检测茶叶质量安全和品质分析的方法。本文介绍了拉曼光谱及SERS技术在茶叶农药残留、重金属和真菌毒素等质量安全检测方面的应用,以及在茶叶理化成分检测和茶叶种类分析等茶叶品质分析上的研究进展。 相似文献
992.
993.
Comparison and Characterization of Compounds with Antioxidant Activity in Lycium barbarum Using High‐Performance Thin Layer Chromatography Coupled with DPPH Bioautography and Tandem Mass Spectrometry 下载免费PDF全文
Shing‐Chung Lam Zhen Luo Ding‐Tao Wu Kit‐Leong Cheong De‐Jun Hu Zu‐Meng Xia Jing Zhao Shao‐Ping Li 《Journal of food science》2016,81(6):C1378-C1384
Methanol extracts from 50 batches of Lycium barbarum (L. barbarum, wolfberry) in China were compared and characterized using high‐performance thin‐layer chromatography coupled with 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) bioautography (HPTLC‐DPPH) and electrospray ionization quadrupole time‐of‐flight tandem mass spectrometry (ESI‐Q‐TOF‐MS/MS), respectively. Results showed that similar components occupying the major antioxidant activity existed in L. barbarum collected from different origins. However, the average antioxidant capacities of methanol extracts of L. barbarum collected in Ningxia were significantly higher than those of Qinghai, Xinjiang, Inner Mongolia, and Gansu, which may contribute to rational use of L. barbarum in China. Furthermore, the chemical structure of compound with the highest antioxidant capacity was tentatively identified as 2‐O‐β‐d ‐glucopyranosyl‐l ‐ascorbic acid using ESI‐Q‐TOF‐MS/MS analysis, which possessed high potentials to be used as an antioxidant biomarker for the quality control of L. barbarum. Results are helpful for the bioactivity‐based quality control of L. barbarum, and beneficial for the improvement of their performance in functional/health foods area, suggesting that HPTLC‐DPPH bioautography with ESI‐Q‐TOF‐MS/MS could be used as a routine approach for quality control of antioxidant components in L. barbarum. 相似文献
994.
Ha Youn Song Suk Young Lee Seung Jun Choi Kyung Mi Kim Jin Sook Kim Gui Jung Han Tae Wha Moon 《Food science and biotechnology》2014,23(1):23-31
The effects of annealing on the digestibility, morphology, and physicochemical characteristics of four types of granular sweet potato starches [Yulmi (YM), Yeonwhangmi (YHM), sweet potato starch from Samyang Genex (SSPS), and commercial sweet potato starch (CSPS)] were investigated. Annealing was performed at 55°C and 90% moisture content for 72 h. Morphology, the branched chain distribution of amylopectin, and the X-ray diffraction pattern remained unchanged during the annealing process. The slowly digestible starch content in annealed YM, YHM, and SSPS starches increased, but did not change in annealed CSPS. The gelatinization temperatures increased, but the gelatinization temperature range decreased with annealing. The swelling factor and amylose leaching decreased, while the close packing concentration increased. Rapid Visco Analyser analysis revealed that annealed starches possessed thermal stability and higher pasting temperatures. It is suggested that the enhanced packing arrangement formed during annealing impacts the digestibility and physicochemical properties of sweet potato starches. 相似文献
995.
996.
DNA barcoding as a new tool for food traceability 总被引:1,自引:0,他引:1
Andrea Galimberti Fabrizio De Mattia Alessia Losa Ilaria Bruni Silvia Federici Maurizio Casiraghi Stefano Martellos Massimo Labra 《Food research international (Ottawa, Ont.)》2013,50(1):55-63
Food safety and quality are nowadays a major concern. Any case of food alteration, especially when reported by the media, has a great impact on public opinion. There is an increasing demand for the improvement of quality controls, hence addressing scientific research towards the development of reliable molecular tools for food analysis. DNA barcoding is a widely used molecular-based system, which can identify biological specimens, and is used for the identification of both raw materials and processed food. In this review the results of several researches are critically analyzed, in order to exploit the effectiveness of DNA barcoding in food traceability, and to delineate some best practices in the application of DNA barcoding throughout the industrial pipeline. The use of DNA barcoding for food safety and in the identification of commercial fraud is also discussed. 相似文献
997.
Covaci A Gerecke AC Law RJ Voorspoels S Kohler M Heeb NV Leslie H Allchin CR De Boer J 《Environmental science & technology》2006,40(12):3679-3688
Hexabromocyclododecanes (HBCDs) are brominated aliphatic cyclic hydrocarbons used as flame retardants in thermal insulation building materials, upholstery textiles, and electronics. As a result of their widespread use and their physical and chemical properties, HBCDs are now ubiquitous contaminants in the environment and humans. This review summarizes HBCD concentrations in several environmental compartments and analyzes these data in terms of point sources versus diffuse sources, biomagnification potential, stereoisomer profiles, time trends, and global distribution. Generally, higher concentrations were measured in samples (air, sediment, and fish) collected near point sources (plants producing or processing HBCDs), while lower concentrations were recorded in samples from locations with no obvious sources of HBCDs. High concentrations were measured in top predators, such as marine mammals and birds of prey (up to 9600 and 19 200 ng/g lipid weight, respectively), suggesting a biomagnification potential for HBCDs. Relatively low HBCD concentrations were reported in the few human studies conducted to date (median values varied between 0.35 and 1.1 ng/g lipid weight). HBCD levels in biota are increasing slowly and seem to reflect the local market demand. One important observation is the shiftfrom the high percentage of the gamma-HBCD stereoisomer in the technical products to a dominance of the alpha-HBCD stereoisomer in biological samples. A combination of factors such as variations in solubility, partitioning behavior, uptake, and, possibly, selective metabolism of individual isomers may explain the observed changes in stereoisomer patterns. Recommendations for further work include research on how HBCDs are transferred from products into the environment upon production, use, and disposal. Time trends need to be analyzed more in detail, including HBCD stereoisomers, and more data on terrestrial organisms are needed, especially for humans. Whenever possible, HBCDs should be analyzed as individual stereoisomers in order to address their fate and effects. 相似文献
998.
The temperature-dependent resistance changing characteristics (thermistor behaviors) of a poly(3,4-ethylenedioxythophene):poly(4-styrenesulfonate) (PEDOT:PSS) thin film are investigated in the 30–100 °C range using Greek-cross and bar patterns. The PEDOT:PSS film was spin-coated onto a Si wafer passivated with a SiO2 layer, and a conventional dry etching technique was used to pattern the PEDOT:PSS film in conjunction with a nitride etch mask layer. Cr/Au was used for the electrode material. It was found that the characteristic temperature (T0) and resistivity of the PEDOT:PSS film have an inversely proportional relationship with the number of coatings and the number of interfaces between multiply coated PEDOT:PSS layers. It was also found that as the number of coatings and the number of the interfaces increase, lower temperature-dependent resistance changes are observed. The temperature coefficient of resistance (TCR) value of 60 nm thick PEDOT:PSS film was slightly larger than or comparable to that of a conventional metal (Au or Pt) thermistor. The possibility of utilizing the PEDOT:PSS thin film in thermistor applications is discussed. 相似文献
999.
Jae Young Cho Eun Hye Choi Jung Il Kang Changsun Choi Hyang Sook Chun 《Food science and biotechnology》2013,22(3):859-864
The objective of this study was to investigate the possible protective effects of maca (Lepidium meyenii) extract (MLE) by supercritical fluid extraction on dextran sodium sulfate (DSS)-induced colitis. Experimental colitis was induced by giving male BALB/c mice 3% DSS in drinking water, and MLE (30 mg/kg BW), sulfasalazine (100 mg/kg BW) or vehicle were administered orally. DSS challenge caused significant body weight loss, rectal bleeding, diarrhea, shortened colon length, histological changes, and increased myeloperoxidase (MPO) activity in DSS-treated mice. Oral administration of MLE significantly relieved the symptoms of diarrhea and rectal bleeding, and reduced colonic MPO activity (p<0.05). MLE treatment inhibited expression of several colonic proteins related to inflammatory responses, such as interleukin (IL)-1β, tumor necrosis factor-α, IL-6, and S100 calcium-binding protein A8, whose expressions were increased significantly by DSS treatment. These results suggest that MLE can alleviate DSS-induced colitis in mice by modulating colonic inflammatory mediators. 相似文献
1000.
利用原子吸收光谱测定了有代表性的几种针叶木和阔叶木原料中金属元素分布及含量,并利用扫描电镜—能谱仪分析了原料的不同部位中金属离子的分布规律。结果发现在实验范围内,各种木材原料中都存在由多种金属离子构成的复杂体系;不同种原料中金属离子的含量和成分存在着很大差异;针叶木Fe、Mn 含量显著,高于阔叶木;同种原料中,边材金属离子含量一般高于心材;不同生长环境会导致木材金属离子分布出现差异。纸浆中的金属离子主要来源于原料本身,因此对金属离子含量不同的原料,纸浆漂前的除过渡金属离子预处理条件应该不同。 相似文献