全文获取类型
收费全文 | 3459篇 |
免费 | 100篇 |
国内免费 | 21篇 |
专业分类
电工技术 | 41篇 |
综合类 | 6篇 |
化学工业 | 868篇 |
金属工艺 | 124篇 |
机械仪表 | 80篇 |
建筑科学 | 48篇 |
矿业工程 | 3篇 |
能源动力 | 298篇 |
轻工业 | 184篇 |
水利工程 | 22篇 |
石油天然气 | 7篇 |
无线电 | 339篇 |
一般工业技术 | 801篇 |
冶金工业 | 470篇 |
原子能技术 | 25篇 |
自动化技术 | 264篇 |
出版年
2023年 | 37篇 |
2022年 | 74篇 |
2021年 | 107篇 |
2020年 | 86篇 |
2019年 | 85篇 |
2018年 | 142篇 |
2017年 | 77篇 |
2016年 | 83篇 |
2015年 | 77篇 |
2014年 | 112篇 |
2013年 | 217篇 |
2012年 | 159篇 |
2011年 | 195篇 |
2010年 | 157篇 |
2009年 | 143篇 |
2008年 | 121篇 |
2007年 | 117篇 |
2006年 | 93篇 |
2005年 | 78篇 |
2004年 | 67篇 |
2003年 | 81篇 |
2002年 | 50篇 |
2001年 | 46篇 |
2000年 | 38篇 |
1999年 | 68篇 |
1998年 | 154篇 |
1997年 | 99篇 |
1996年 | 93篇 |
1995年 | 50篇 |
1994年 | 53篇 |
1993年 | 53篇 |
1992年 | 36篇 |
1991年 | 40篇 |
1990年 | 34篇 |
1989年 | 34篇 |
1988年 | 27篇 |
1987年 | 38篇 |
1986年 | 39篇 |
1985年 | 28篇 |
1984年 | 36篇 |
1983年 | 41篇 |
1982年 | 24篇 |
1981年 | 19篇 |
1980年 | 23篇 |
1979年 | 32篇 |
1978年 | 22篇 |
1977年 | 16篇 |
1976年 | 23篇 |
1975年 | 9篇 |
1973年 | 11篇 |
排序方式: 共有3580条查询结果,搜索用时 46 毫秒
961.
B. P. Nethravathi K. Ramakrishna Reddy K. N. Mahendra 《Journal of Porous Materials》2014,21(3):285-291
Cobalt(II), copper(II) and zinc(II) complexes of 2-phenylbenzimidazole (PhBzlH) encapsulated in the supercages of zeolite-Y and ZSM-5 have been synthesized and characterized by spectroscopic studies (IR, UV/visible, EPR), elemental analyses, thermal studies and X-ray diffraction patterns. The catalytic activity of encapsulated complexes was investigated for the hydroxylation of phenol using 30 % H2O2 as an oxidant. Under optimized reaction conditions, the hydroxylation of phenol yielded catechol and hydroquinone as the major products. All catalysts show good selectivity for diphenol products. A maximum conversion of phenol was obtained with [Cu(PhBzlH)]-Y as the catalyst. The results showed that conversion of phenol varies in the order [Cu(PhBzlH)]-Y (53 %) > [Cu(PhBzlH)]-ZSM-5 > (49 %) > [Co(PhBzlH)]-ZSM-5 (47 %) > [Co(PhBzlH)]-Y (46 %) > [Zn(PhBzlH)]-Y (45 %) > [Zn(PhBzlH)]-ZSM-5 (41 %) after 6 h of reaction time. Test for the recyclability of the reaction was also carried out and the results indicate their recyclability. 相似文献
962.
Dr. Sebastian Müller Dr. Katta Laxmi‐Reddy Dr. Prakrit V. Jena Dr. Benoit Baptiste Dr. Zeyuan Dong Dr. Frédéric Godde Prof. Taekjip Ha Dr. Raphaël Rodriguez Prof. Shankar Balasubramanian Dr. Ivan Huc 《Chembiochem : a European journal of chemical biology》2014,15(17):2563-2570
We previously identified quinoline‐based oligoamide helical foldamers and a trimeric macrocycle as selective ligands of DNA quadruplexes. Their helical structures might permit targeting of the backbone loops and grooves of G‐quadruplexes instead of the G‐tetrads. Given the vast array of morphologies G‐quadruplex structures can adopt, this might be a way to achieve sequence selective binding. Here, we describe the design and synthesis of molecules based on macrocyclic and helically folded oligoamides. We tested their ability to interact with the human telomeric G‐quadruplex and an array of promoter G‐quadruplexes by using FRET melting assay and single‐molecule FRET. Our results show that they constitute very potent ligands—comparable to the best so far reported. Their modes of interaction differ from those of traditional tetrad binders, thus opening avenues for the development of molecules specific for certain G‐quadruplex conformations. 相似文献
963.
964.
A film of 1-octadecyl-1H-1,2,4-triazole (OTA) was formed on a fresh copper surface by self-assembly technique. The optimum concentration of OTA and immersion time for the formation of a protective OTA film have been established using electrochemical impedance spectroscopy (EIS). These are (i) 15 mM concentration of OTA in methanol and (ii) immersion period of 48 h. X-ray photoelectron spectroscopy (XPS), reflection absorption FTIR spectroscopy, atomic force microscopy (AFM), and contact angle measurements have been used to characterize the OTA film on copper surface. The efficiency of OTA film to protect copper from corrosion in aqueous NaCl environment has been investigated using EIS, potentiodynamic polarization studies, cyclic voltammetry and weight-loss studies. All these studies showed that the OTA film affords excellent protection against corrosion of copper. 相似文献
965.
Reddy Damavarapu ThomasM. Klaptke Jrg Stierstorfer KarinaR. Tarantik 《Propellants, Explosives, Pyrotechnics》2010,35(4):395-406
The compounds barium tetrazolate ( 6 ), barium 5‐aminotetrazolate tetrahydrate ( 7 ), barium 5‐nitriminotetrazolate dihydrate ( 8 ), barium bis(1H‐5‐nitriminotetrazolate) tetrahydrate ( 9 ), barium 1‐methyl‐5‐nitriminotetrazolate monohydrate ( 10 ), and barium 2‐methyl‐5‐nitriminotetrazolate dihydrate ( 11 ) were synthesized by the reactions of barium hydroxide octahydrate and 1H‐tetrazole ( 1 ), 5‐aminotetrazole ( 2 ), 1,4H‐5‐nitriminotetrazole ( 3 ), 1‐methyl‐5‐nitriminotetrazole ( 4 ), and 2‐methyl‐5‐nitraminotetrazole ( 5 ), respectively. The compounds were characterized using multi‐nuclear NMR spectroscopy, vibrational (IR and Raman) spectroscopy, elemental analysis, and differential scanning calorimetry. The solid‐state structures of 7 – 11 were determined using low temperature X‐ray diffraction and a comprehensive characterization is given. In addition, the sensitivities (impact, friction, electrical discharge) of 6 – 11 were investigated and bomb calorimetric measurements were carried out. 相似文献
966.
Whole hop bines (HBs), the peeled outer bark (OB) of HBs, and fibers chemically extracted from hop bark (HFs) were used as reinforcements to make lightweight composites with polypropylene (PP) webs or fibers as the matrix materials. Using discarded HBs for composites not only increases the value of hop crops but also provides a green, sustainable, and biodegradable material for the composite industry. Lightweight composites are preferred, especially for automotive applications because of the potential energy savings. In this research, the effects of the processing parameters on the properties of PP composites reinforced with HBs were studied. The composites reinforced with OB without any chemical treatment showed better properties than the composites reinforced with HFs or HBs. Compared with jute–PP composites of the same density (0.47 g/cm3), composites reinforced with OB had 43% higher flexural strength, 46% higher impact resistance, 56% higher Young's modulus, similar modulus of elasticity, 33% lower tensile strength, and better sound‐absorption properties. OB–PP composites with optimized properties have the potential to be used in industrial applications such as support layers in automotive interiors, ceiling tiles, and office panels. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
967.
Sobha Rani Tenkayala Marata Chinna Subbarao Subha Venkata Reddy Gorla Yong Ha Kim Chowdoji Rao Kashayi Venkata Prasad Chalapati 《应用聚合物科学杂志》2010,117(6):3533-3538
A new class of materials based on inorganic and organic species combined at a nanoscale level has received large attention recently. In this work the idea of producing hybrid materials with controllable properties is applied to obtain foams to be used as catalyst supporting. Hybrids were synthesized by reacting poly(vinyl alcohol) in acidic solution with water glass. The inorganic phase was also modified by incorporating a hexamethyldisiloxane as precursor. The hybrid aerogel powder was analyzed by scanning electron microscopy, TG‐DTA, Nitrogen adsorption–desorption, X‐ray diffraction and fourier transform infrared spectroscopy (FTIR) spectroscopy. The powder obtained had a higher porosity varying from 65 to 90% and the nanopore diameter ranged from 17 to 20 nm. The surface area and nanopore volume decreased as polymer content increased in the hybrids. The sharp decline in the weight observed at around 500°C accompanied an exothermic peak of the DTA curve. The sharp peak was observed around 211°C represents the DTA curve of Poly vinyl alcohol constituent in nano hybrids. The peak at 1638 cm?1 in the FTIR indicated the formation of Si? O? PVA? O? Si bridge in aerogel powder. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
968.
C. Venkata Prasad K. Chowdoji Rao G.Venkata Reddy Yong‐Ha Kim T. Shobha Rani M. C. S. Subha 《应用聚合物科学杂志》2010,115(5):2806-2812
A naturally occurring fabric belonging to the species Hardwikia binata was extracted from the sheath of stem, bark, and branches of the tree. The fabric specimens were treated with sodium hydroxide and poly (vinyl alcohol). The morphology of the fabric specimens before and after NaOH treatment was studied using scanning electron microscopy technique. Ligno‐cellulosic properties of fabric were analyzed by XRD, FTIR, and thermo gravimetric methods before and after NaOH treatment. Tensile strength and percentage of elongation at break of the fabric were also studied by using a universal testing machine (model AGS‐10kNG). The results showed that the poly (vinyl alcohol)‐treated fabric specimens showed higher tensile strength than sodium hydroxide‐treated fabric specimens. The Binata fabric has good thermal resistance and was also found to increase by alkali treatment. The FTIR method indicates lowering the hemi cellulose and lignin content by alkali treatment in the fabric. Further, the X‐ray diffraction studies revealed an increase in crystallinity of the fabric by alkali treatment. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
969.
S.T. Reddy A.E. Lewis G.J. Witkamp H.J.M. Kramer J. van Spronsen 《Chemical Engineering Research and Design》2010
The increasing amount of waste water and effluent from South Africa's mining industry forms a growing problem, which processing requires sustainable solutions in which both the water and the dissolved component can be re-used. Eutectic freeze crystallisation (EFC) has been identified as a key technology that is not only energy efficient, but also produces ice and salt products of high quality. Unlike reverse osmosis membrane systems, EFC can treat both dilute and concentrated systems minimising waste water volumes. In this paper it is shown that freeze and eutectic freeze crystallisation can be used for the processing of a reverse osmosis retentate stream containing 4% NaSO4 and a number of impurities (F, Cl, K, Li, Mg, Ca, NO3 and NH4), producing both pure water and NaSO4·10H2O crystals. The influence of the impurities on the eutectic point and on the crystal structure of mirabilite was investigated using EFC technology investigated for a pure binary system, for a synthetic reverse osmosis retentate as well as for a concentrated NaCl system. In addition, investigations into the recovery and purity of mirabilite for these streams were conducted. 相似文献
970.
Natesan Kapilan T. P. Ashok Babu Rana Pratap Reddy 《European Journal of Lipid Science and Technology》2010,112(2):180-187
Biodiesel derived from non‐edible Madhuca Indica oil (MIO) seems to be a better alternative to diesel oil in India. In the present work, effects of reaction variables such as mass ratio of methanol to oil, catalyst concentration, reaction time and reaction temperature on biodiesel yield were studied. The acid value of the commercially available MIO is high, and hence a two‐step process was used to produce biodiesel from MIO. In the first step, the acid value of the MIO was reduced to less than 1 mg KOH/g, using acid‐catalyzed transesterification. In the second step, the pretreated MIO was converted to biodiesel using alkaline‐catalyzed transesterification. From the experimental results, it is observed that the optimized conditions for biodiesel production are a 1 : 4 mass ratio of methanol to oil, 55 °C reaction temperature, 120 min of reaction time, and 1% sodium hydroxide catalyst. The properties of the MIO biodiesel were found to be within the biodiesel limits of the European Union. Hence, the MIO biodiesel can be used as a substitute for diesel for the sustainable development of rural areas and as a renewable fuel. 相似文献