全文获取类型
收费全文 | 2570篇 |
免费 | 185篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 43篇 |
综合类 | 2篇 |
化学工业 | 701篇 |
金属工艺 | 85篇 |
机械仪表 | 81篇 |
建筑科学 | 63篇 |
矿业工程 | 9篇 |
能源动力 | 94篇 |
轻工业 | 486篇 |
水利工程 | 14篇 |
石油天然气 | 31篇 |
无线电 | 153篇 |
一般工业技术 | 363篇 |
冶金工业 | 276篇 |
原子能技术 | 16篇 |
自动化技术 | 341篇 |
出版年
2024年 | 15篇 |
2023年 | 29篇 |
2022年 | 76篇 |
2021年 | 143篇 |
2020年 | 79篇 |
2019年 | 97篇 |
2018年 | 131篇 |
2017年 | 123篇 |
2016年 | 106篇 |
2015年 | 68篇 |
2014年 | 98篇 |
2013年 | 200篇 |
2012年 | 152篇 |
2011年 | 162篇 |
2010年 | 146篇 |
2009年 | 148篇 |
2008年 | 112篇 |
2007年 | 93篇 |
2006年 | 65篇 |
2005年 | 67篇 |
2004年 | 44篇 |
2003年 | 38篇 |
2002年 | 39篇 |
2001年 | 30篇 |
2000年 | 43篇 |
1999年 | 38篇 |
1998年 | 76篇 |
1997年 | 70篇 |
1996年 | 50篇 |
1995年 | 37篇 |
1994年 | 23篇 |
1993年 | 33篇 |
1992年 | 12篇 |
1991年 | 18篇 |
1990年 | 10篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1982年 | 5篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 11篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1973年 | 2篇 |
排序方式: 共有2758条查询结果,搜索用时 15 毫秒
31.
dos Santos Tiago G. Silva Antonio O. S. Pedrosa Anne M. G. Araujo Antonio S. Souza Marcelo J. B. 《Journal of Porous Materials》2021,28(3):919-928
Journal of Porous Materials - Catalysts of AlMCM-48 with different Si/Al molar rations were synthesized by modified hydrothermal method with respect to previous works. As a consequence, the... 相似文献
32.
Liu Chu Jiajia Shi Yue Yu Eduardo Souza De Cursi 《International journal of molecular sciences》2021,22(9)
With the distinguished properties in electronics, thermal conductivity, optical transparence and mechanics, graphene has a powerful potential in nanosensors, nano-resonators, supercapacitors, batteries, etc. The resonant frequency of graphene is an important factor in its application and working environment. However, the random dispersed porosities in graphene evidently change the lattice structure and destroy the integrity and geometrical periodicity. This paper focuses on the effects of random porosities in resonant frequencies of graphene. Monte Carlo simulation is applied to propagate the porosities in the finite element model of pristine graphene. The statistical results and probability density distribution of porous graphene with atomic vacancy defects are computed based on the Monte Carlo finite element model. The results of porous graphene with atomic vacancy defects are compared and discussed with the results of graphene with bond vacancy defects. The enhancement effects of atomic vacancy defects are confirmed in porous graphene. The influences of atomic vacancy defects on displacement and rotation vector sums of porous graphene are more concentrated in local places. 相似文献
33.
Rodriguez J. S. Duran J. F. Aguilar Y. Alcazar G. A. Perez Souza R. M. Zambrano O. A. 《Metallurgical and Materials Transactions A》2022,53(8):2961-2976
Metallurgical and Materials Transactions A - In the present work, the dynamic recrystallization and microstructural evolution of the family of advanced high-strength steels Fe18MnxAl0.74C are... 相似文献
34.
Joo Batista A. Silva Regina C. M. de Paula Judith P. A. Feitosa Eduardo Diogo Gurgel‐Filho Claudio Maniglia‐Ferreira Francisco Jose de Souza Filho 《应用聚合物科学杂志》2006,100(5):4082-4088
Gutta‐percha cone is the most widely used material for root canal filling. The in vivo aging of this cone focus on the degradation of its main organic component, trans‐1,4‐polyisoprene, was studied. Aged cones (25 samples) from 2 to 30 years of root canal filling were extracted from different patients in the occasion of retreatment by mechanical way. The information about the aging time was given by the patients. Gel‐permeation chromatography (GPC) and infrared spectroscopy (FTIR) were the analytical techniques used. Polyisoprene degrades with time of aging, but in a slow process. Decrease in polymer molar mass from 5.7 × 105 to 1.7 × 105 g/mol was observed in polyisoprene from cone after 30 years of root canal filling and inside a noninfected tooth. In tooth with caries and periodontal infection, the decrease in molar mass is higher (4.6 × 104 g/mol in cone with 10 years of aging). The production of carbonyl and hydroxyl groups in the aged material indicates that the process is oxidative, even in closed teeth. In these cases, the oxygen could be provided from tissue fluid. The degradation mechanism is complex and depends on many factors, besides time of root canal filling. The dental problem caused by the aging could be the production and migration of cytotoxic substances to periodontal ligament and the reduction on the canal sealing property due to the polymer weight loss. Both of them could contribute to the root canal treatment failure. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100:4082–4088, 2006 相似文献
35.
L. deMan V. D’Souza J. M. deMan B. Blackman 《Journal of the American Oil Chemists' Society》1992,69(3):246-250
A number of North American vegetable and animal fat shortenings, which had been analyzed previously for their physical and
textural characteristics, were analyzed also for their chemical composition. The fatty acid and triglyceride composition of
the solids were calculated by analyzing the composition of the original product and the liquid phase, and by determination
of the solid fat content (SFC) of the fat. The solids were also isolated by isopropanol (IP) separation, and the high melting
glycerides (HMG) by acetone crystallization at 15°C. There was not much difference in total saturates andtrans content between vegetable and animal fat shortenings. Changing formulations from soy-palm to soy-cottonseed does not change
the total saturates plustrans content. The solids of the vegetable shortenings in the β form contained about 20% of 16:0, those in the β′ form 30% or more.
The animal fat shortenings were mainly in the β form, their solids contained 30% or more of 16:0. C54 triglyceride content
of the solids of β vegetable shortenings (calculated and IP-separated) was >45%, that of all animal fats was <25%. Solids
of animal fat shortenings contain high levels of C52. The C54 triglycerides are β-tending and should be kept low in vegetable
shortening. In the HMG the C54 should not exceed 30%. This can only be achieved by incorporation of a β′ hard fat, preferably
palm hard fat. Animal fat, especially lard, crystallizes in the β form because the palmitic acid in the glyceride molecule
is located in the 2-position, whereas those of vegetable fats are in the 1- and 3-position. 相似文献
36.
Marsaro AL Souza RC Della Lucia TM Fernandes JB Silva MF Vieira PC 《Journal of chemical ecology》2004,30(9):1771-1780
The response of Atta sexdens rubropilosa Forel workers to essential oils, epicuticular wax and hexane, dichloromethane, ethyl acetate, and methanol extracts of Eucalyptus maculata was evaluated. Hexane extracts of E. maculata interfered with the recognition mechanism among workers. The main active compounds identified from this plant were the sesquiterpenes elemol and beta-eudesmol. These compounds may be responsible for the resistance of this species to ant attack. 相似文献
37.
The catalytic hydrogenation of acrylonitrile‐butadiene copolymer (nitrile rubber, NBR) using Pd(OAc)2 or RuCl2(PPh3)3 catalysts has been investigated in order to produce a totally saturated nitrile rubber. The hydrogenation of NBR is effective with both catalysts and achieved total conversion under the appropriate reaction conditions. In the case of palladium the effects of reaction parameters such as reaction temperature, pressure, time, catalyst concentration, and NBR concentration have been investigated. Even though both ruthenium‐ and palladium‐based catalysts are effective in the production of HNBR, the former requires harsh reaction conditions and has the drawback of gel formation under high conversion, motivating the migration to RuCl2 (PPh3)3 as an alternative catalyst. The degree of hydrogenation was determined by IR and NMR spectroscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 相似文献
38.
39.
Rafael Prikladnicki Alexander Boden Gabriela Avram Cleidson R. B. de Souza Volker Wulf 《Empirical Software Engineering》2014,19(4):822-856
Global Software Engineering has become a standard in today’s software industry. Research in distributed software development poses severe challenges that are due to the spatial and temporal distribution of the actors, as well as to language, intercultural and organizational aspects. These challenges occur in addition to “traditional” challenges of the domain itself in large-scale software projects, like coordination and communication issues, requirements volatily, lack of domain knowledge, among others. While several authors have reported empirical studies of global software development projects, the methodological difficulties and challenges of this type of studies have not been sufficiently discussed. In this paper, we share our experiences of collecting and analysing qualitative data in the context of Global Software Engineering projects. We discuss strategies for gaining access to field sites, building trust and documenting distributed and complex work practices in the context of several research projects we have conducted in the past 9 years. The experiences described in this paper illustrate the need to deal with fundamental problems, such as understanding local languages and different cultures, observing synchronous interaction, or dealing with barriers imposed by political conflicts between the sites. Based on our findings, we discuss some practical implications and strategies that can be used by other researchers and provide some recommendations for future research in methodological aspects of Global Software Engineering. 相似文献
40.
Jairton Dupont Paulo A.Z. Suarez Alexandre P. Umpierre Roberto F. de Souza 《Catalysis Letters》2001,73(2-4):211-213
The combination of 1-n-butyl-3-methylimidazolium chloride with ZnCl2 affords ionic mixtures with different melting point temperatures depending on the zinc molar fraction. RuCl2(PPh3)3 immobilised in the low melting mixture (60°C) promotes the 1-hexene hydrogenation (turnover frequencies up to 44 min–1) and the recovered solid catalyst phase can be reused several times. 相似文献