全文获取类型
收费全文 | 3529篇 |
免费 | 103篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 41篇 |
综合类 | 5篇 |
化学工业 | 539篇 |
金属工艺 | 57篇 |
机械仪表 | 55篇 |
建筑科学 | 137篇 |
矿业工程 | 22篇 |
能源动力 | 62篇 |
轻工业 | 326篇 |
水利工程 | 26篇 |
石油天然气 | 7篇 |
无线电 | 232篇 |
一般工业技术 | 601篇 |
冶金工业 | 1175篇 |
原子能技术 | 34篇 |
自动化技术 | 314篇 |
出版年
2022年 | 20篇 |
2021年 | 43篇 |
2020年 | 24篇 |
2019年 | 21篇 |
2018年 | 50篇 |
2017年 | 30篇 |
2016年 | 53篇 |
2015年 | 41篇 |
2014年 | 51篇 |
2013年 | 194篇 |
2012年 | 98篇 |
2011年 | 138篇 |
2010年 | 104篇 |
2009年 | 110篇 |
2008年 | 146篇 |
2007年 | 147篇 |
2006年 | 108篇 |
2005年 | 107篇 |
2004年 | 78篇 |
2003年 | 96篇 |
2002年 | 83篇 |
2001年 | 71篇 |
2000年 | 83篇 |
1999年 | 82篇 |
1998年 | 225篇 |
1997年 | 151篇 |
1996年 | 114篇 |
1995年 | 69篇 |
1994年 | 74篇 |
1993年 | 78篇 |
1992年 | 35篇 |
1991年 | 27篇 |
1990年 | 52篇 |
1989年 | 45篇 |
1988年 | 32篇 |
1987年 | 52篇 |
1986年 | 38篇 |
1985年 | 53篇 |
1984年 | 56篇 |
1983年 | 39篇 |
1982年 | 33篇 |
1981年 | 32篇 |
1980年 | 38篇 |
1979年 | 25篇 |
1978年 | 41篇 |
1977年 | 61篇 |
1976年 | 73篇 |
1975年 | 28篇 |
1974年 | 23篇 |
1969年 | 19篇 |
排序方式: 共有3633条查询结果,搜索用时 31 毫秒
71.
Bobby Russell 《Polymer》2005,46(3):785-798
In this paper, we consider the effect of cure conditions on the morphology and distribution of the rubber in a phase separated rubber-modified epoxy resin, which in effect is a two phase composite. Novel aspects of this study were measuring the elastic modulus of the dispersed rubber phase particles by atomic force microscopy (AFM) and verifying the presence of nano-dispersed rubber.The purpose of introducing dispersed rubber particles into the primary phase in these systems is to enhance their toughness. It is known that both the rubber particle size and volume fraction affect the degree to which the epoxy is toughened. It is not known, however, how the specific mechanical properties of the rubber phase itself affect the toughness.The objectives of this study were to: (1) use scanning electron microscopy (SEM) and atomic force microscopy (AFM) to determine the morphology and phase distribution of the rubber particles and (2) to measure the mechanical properties of the rubber particles using AFM. Ultimately, we would like to develop a clear understanding of how the changes in morphology and mechanical properties measured at the micro and nano-scales affect both the elastic modulus and fracture toughness of rubber-modified epoxy polymers.The epoxy system consisted of a diglycidyl ether of bisphenol-A, Epon 828, cured with piperidine and incorporating a liquid carboxyl-terminated acrlonitrile-butadiene rubber (CTBN). The carboxyl groups of the rubber are capable of reacting with the epoxy. The cure conditions considered were based on a statistically designed full factorial curing matrix, with the variables selected being cure temperature, initiator (piperidine) concentration, and rubber acrylonitrile concentration.Each of these primary variables was found to affect the phase distribution that resulted during cure. A statistical analysis of the effect of these variables on the phase morphology showed that the acrylonitrile content (%) of the rubber affected both the rubber particle size and volume fraction. The cure temperature strongly influenced the rubber particle volume fraction and modulus. Volume fractions of the rubber phase of up to 24% were obtained even though the amount of rubber added was only 12.5%. The rubber particle modulus varied from 6.20 to 7.16 MPa. Both the volume fraction and modulus of the rubber particles were found to influence the macroscopic mechanical properties of the composite. While larger volume fractions favor improved toughness, we note that that the toughness is greatest when the particle modulus values do not exceed ∼6.2 MPa. Thus, increased volume fraction by itself may not always result in increased toughness. The particles also must be sufficiently ‘soft’ in order to improve toughness. In the system of interest here, the processing conditions are a key factor in achieving the most appropriate material properties. By inference, this is likely to be the case as well in other rubber-modified thermosets. 相似文献
72.
Erhan Kilinc Anthony M. T. Bell Paul A. Bingham Russell J. Hand 《Journal of the American Ceramic Society》2021,104(8):3921-3946
Crystallization, mechanical properties, and workability are all important for the commercialization and optimization of silicate glass compositions. However, the inter-relations of these properties as a function of glass composition have received little investigation. Soda-lime-silica glasses with Na2O-MgO-CaO-Al2O3-SiO2 compositions relevant to commercial glass manufacture were experimentally studied and multiple liquidus temperature and viscosity models were used to complement the experimental results. Liquidus temperatures of the fabricated glasses were measured by the temperature gradient technique, and Rietveld refinements were applied to X-Ray powder diffraction (XRD) data for devitrified glasses, enabling quantitative determination of the crystalline and amorphous fractions and the nature of the crystals. Structural properties were investigated by Raman spectroscopy. Acoustic echography, micro-Vicker's indentation, and single-edge-notched bend testing methods were used to measure Young's moduli, hardness, and fracture toughness, respectively. It is shown that it is possible to design lower-melting soda-lime-silica glass compositions without compromising their mechanical and crystallization properties. Unlike Young's modulus, brittleness is highly responsive to the composition in soda-lime-silica glasses, and notably low brittleness values can be obtained in glasses with compositions in the wollastonite primary phase field: an effect that is more pronounced in the silica primary phase field. The measured bulk crystal fractions of the glasses subjected to devitrification at the lowest possible industrial conditioning temperatures indicate that soda-lime-silica glass melts can be conditioned close to their liquidus temperatures within the compositional ranges of the primary phase fields of cristobalite, wollastonite, or their combinations. 相似文献
73.
The supremacy of online white supremacists – an analysis of online discussions by white supremacists
A content analysis was conducted on five different white supremacist online forums to observe the discourse and types of activities occurring within. In addition, web link analysis was conducted on the forums to identify the presence of external links being posted and discussed by members. We found that members used the forums primarily for information provision, recruitment and networking. Based on these results, we discuss the implications that online hate speech have within offline settings, and the affects these activities have on Canadian citizens in light of the recent repeal of section 13 of the Canadian Human Rights Act (1985), the primary tool in Canada with which to deal with hate speech and other activities observed. The insights extracted from this research have provided novel insight into the sentiments and activities of the white supremacist movement online, a relatively unexplored venue of hate speech and propaganda online. 相似文献
74.
75.
Chi-Hoon Lee Osmar R. Zaïane Ho-Hyun Park Jiayuan Huang Russell Greiner 《Information Sciences》2008,178(23):4501-4511
There is no doubt that clustering is one of the most studied data mining tasks. Nevertheless, it remains a challenging problem to solve despite the many proposed clustering approaches. Graph-based approaches solve the clustering task as a global optimization problem, while many other works are based on local methods. In this paper, we propose a novel graph-based algorithm “GBR” that relaxes some well-defined method even as improving the accuracy whilst keeping it simple. The primary motivation of our relaxation of the objective is to allow the reformulated objective to find well distributed cluster indicators for complicated data instances. This relaxation results in an analytical solution that avoids the approximated iterative methods that have been adopted in many other graph-based approaches. The experiments on synthetic and real data sets show that our relaxation accomplishes excellent clustering results. Our key contributions are: (1) we provide an analytical solution to solve the global clustering task as opposed to approximated iterative approaches; (2) a very simple implementation using existing optimization packages; (3) an algorithm with relatively less computation time over the number of data instances to cluster than other well defined methods in the literature. 相似文献
76.
77.
Memory-based collaborative filtering (CF) recommender systems have emerged as an effective technique for information filtering. CF recommenders are being widely adopted for e-commerce applications to assist users in finding and selecting items of interest. As a result, the scalability of CF recommenders presents a significant challenge; one that is particularly resilient because the volume of data these systems utilize will continue to increase over time. This paper examines the impact of discrete wavelet transformation (DWT) as an approach to enhance the scalability of memory-based collaborative filtering recommender systems. In particular, a wavelet transformation methodology is proposed and applied to both synthetic and real-world recommender ratings. For experimental purposes, the DWT methodology’s effect on predictive accuracy and calculation speed is evaluated to compare recommendation quality and performance. 相似文献
78.
Farrugia Russell Portelli Barnaby Grech Ivan Camilleri Duncan Casha Owen Micallef Joseph Gatt Edward 《Microsystem Technologies》2022,28(6):1451-1465
Microsystem Technologies - The maximum scan angle amplitude of resonating micro-mirrors, intended for micro-projection display applications is limited by air damping. Three-dimensional transient... 相似文献
79.
80.
Shuhua Zhang Muhammad Naeem Shah Feng Liu Zhongqiang Zhang Qin Hu Thomas P.Russell Minmin Shi Chang-Zhi Li Hongzheng Chen 《Nano Research》2017,(11):3765-3774
The ternary strategy for incorporating multiple photon-sensitive components into a single junction has emerged as an effective method for optimizing the nanoscale morphology and improving the device performance of organic solar cells (OSCs).In this study,efficient and stable ternary OSCs were achieved by introducing the small-molecule dye (5E,5'E)-5,5'-(4',4″-(1,2-diphenylethene-1,2-diyl)bis(biphenyl-4',4-diyl))bis(methan-1-yl-1-ylidene)bis(3-ethyl-2-thioxothia zolidin-4-one) (BTPERn) into poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiopheneco-3-fluorothieno[3,4-b]thiophene-2-carboxylate] (PTB7-Th):[6,6]-phenyl C71 butyric acid methyl ester (PC71BM) blend films processed using a 1,8-diiodooctane (DIO)-free solvent.The incorporation of BTPE-Rn enhanced the short-circuit current density and fill factor of the ternary OSCs compared with those of binary OSCs.An investigation of the optical,electronic,and morphological properties of the ternary blends indicated that the third component of BTPE-Rn not only promoted the photon utilization of blends through the energy-transfer process but also improved the electron mobility of the blends owing to the fullerene-rich nanophase optimization.More importantly,this ternary strategy of utilizing a small-molecule dye to replace the photounstable DIO additive enhanced the operational stability of the OSCs. 相似文献