全文获取类型
收费全文 | 1001篇 |
免费 | 47篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 9篇 |
化学工业 | 169篇 |
金属工艺 | 28篇 |
机械仪表 | 19篇 |
建筑科学 | 49篇 |
矿业工程 | 1篇 |
能源动力 | 58篇 |
轻工业 | 84篇 |
水利工程 | 3篇 |
石油天然气 | 2篇 |
无线电 | 62篇 |
一般工业技术 | 192篇 |
冶金工业 | 168篇 |
原子能技术 | 6篇 |
自动化技术 | 200篇 |
出版年
2023年 | 12篇 |
2022年 | 16篇 |
2021年 | 49篇 |
2020年 | 30篇 |
2019年 | 26篇 |
2018年 | 25篇 |
2017年 | 36篇 |
2016年 | 17篇 |
2015年 | 27篇 |
2014年 | 44篇 |
2013年 | 53篇 |
2012年 | 50篇 |
2011年 | 64篇 |
2010年 | 36篇 |
2009年 | 52篇 |
2008年 | 41篇 |
2007年 | 35篇 |
2006年 | 38篇 |
2005年 | 17篇 |
2004年 | 24篇 |
2003年 | 21篇 |
2002年 | 20篇 |
2001年 | 12篇 |
2000年 | 11篇 |
1999年 | 15篇 |
1998年 | 39篇 |
1997年 | 20篇 |
1996年 | 12篇 |
1995年 | 15篇 |
1994年 | 20篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1983年 | 10篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1976年 | 11篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1964年 | 3篇 |
排序方式: 共有1050条查询结果,搜索用时 15 毫秒
101.
Isaac Seoane Gerson Rodríguez de los Santos José Alberto Hernández Manuel Urueña Ricardo Romeral Ángel Cuevas David Larrabeiti 《Photonic Network Communications》2011,21(3):278-287
In Tunable-Transmitter Fixed-Receiver (TT-FR)-based Wavelength Division Multiplexed (WDM) ring topologies, each node is provided
with a dedicated wavelength (home channel) for reception, which must be shared by the upstream nodes willing to communicate
with it. Thus, to avoid channel collisions, it is necessary to define a Medium Access Control (MAC) mechanism that arbitrates
access to a given destination wavelength. This work proposes and analyses a simple MAC mechanism that avoids channel collisions
by recirculating traffic on the upstream ring segment where congestion was detected. Essentially, whenever a given node has
got any traffic to transmit, it must first block access to in-transit traffic, which is reflected back to the upstream node
over a second optical fibre. Such blocked traffic is given a second chance to pass through the congested node after a round
segment delay, thus making use of the ring topology as buffering units. This work analyses the performance operation of such
a MAC protocol under two policies applied to recirculated traffic: (1) recirculation bypass and (2) recirculation store-and-forward. 相似文献
102.
Sudip Misra P. Venkata Krishna Kiran Isaac Abraham 《Wireless Personal Communications》2011,56(1):55-72
Providing effective medium access for wireless networks is a challenging task. Most of the existing protocols of IEEE 802.11
Medium Access Control (MAC) work towards the goal of achieving effective channel access by developing various backoff procedures.
In this paper, we make an attempt to develop a new medium access protocol named Learning Automata (LA) based Wireless Channel
Reservation (LAWCR). We use an LA approach to implement reservation for channel access for single hop wireless networks. Also,
sequence procedure is used to improve the reservation mechanism. The performance of the proposed LAWCR scheme show significant
improvements over the legacy DCF protocol with respect to important criteria such as the average time spent in the buffer
and the throughput. 相似文献
103.
Probability and convexity concepts are not antagonistic 总被引:1,自引:0,他引:1
104.
An assessment of the sewage occurrence and biodegradability of seven parabens and three halogenated derivatives of methyl paraben (MeP) is presented. Several wastewater samples were collected at three different wastewater treatment plants (WWTPs) during April and May 2010, concentrated by solid-phase extraction (SPE) and analysed by liquid chromatography-electrospray-quadrupole-time-of-flight mass spectrometry (LC-QTOF-MS). The performance of the QTOF system proved to be comparable to triple-quadrupole instruments in terms of quantitative capabilities, with good linearity (R2 > 0.99 in the 5-500 ng mL−1 range), repeatability (RSD < 5.6%) and LODs (0.3-4.0 ng L−1 after SPE). MeP and n-propyl paraben (n-PrP) were the most frequently detected and the most abundant analytes in raw wastewater (0.3-10 μg L−1), in accordance with the data displayed in the bibliography and reflecting their wider use in cosmetic formulations. Samples were also evaluated in search for potential halogenated by-products of parabens, formed as a result of their reaction with residual chlorine contained in tap water. Monochloro- and dichloro-methyl paraben (ClMeP and Cl2MeP) were found and quantified in raw wastewater at levels between 0.01 and 0.1 μg L−1. Halogenated derivatives of n-PrP could not be quantified due to the lack of standards; nevertheless, the monochlorinated species (ClPrP) was identified in several samples from its accurate precursor and product ions mass/charge ratios (m/z). Removal efficiencies of parabens and MeP chlorinated by-products in WWTPs exceeded 90%, with the lowest percentages corresponding to the latter species. This trend was confirmed by an activated sludge biodegradation batch test, where non-halogenated parabens had half-lives lower than 4 days, whereas halogenated derivatives of MeP turned out to be more persistent, with up to 10 days of half-life in the case of dihalogenated derivatives. A further stability test performed with raw wastewater also showed that parabens degrade rapidly in real sewage, with half-lives lower than 10 h for n-butyl-paraben, while dihalogenated species again turned out to be more stable, with half-lives longer than a week. 相似文献
105.
106.
Isaac Fried 《International journal for numerical methods in engineering》2016,106(9):760-770
A universal, practical, a priori, numerical procedure is presented by which to realistically bind the spectral condition number of the global stiffness matrix generated by the finite element least‐squares method. The procedure is then applied to second and fourth‐order problems in one and two dimensions to show that the condition of the global stiffness matrix thus generated is, in all instances, proportional to but the diameter of the element squared. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
107.
RA Barton IR Storch VP Adiga R Sakakibara BR Cipriany B Ilic SP Wang P Ong PL McEuen JM Parpia HG Craighead 《Nano letters》2012,12(9):4681-4686
By virtue of their low mass and stiffness, atomically thin mechanical resonators are attractive candidates for use in optomechanics. Here, we demonstrate photothermal back-action in a graphene mechanical resonator comprising one end of a Fabry-Perot cavity. As a demonstration of the utility of this effect, we show that a continuous wave laser can be used to cool a graphene vibrational mode or to power a graphene-based tunable frequency oscillator. Owing to graphene's high thermal conductivity and optical absorption, photothermal optomechanics is efficient in graphene and could ultimately enable laser cooling to the quantum ground state or applications such as photonic signal processing. 相似文献
108.
Direct evaluation of stress intensity factors for curved cracks using Irwin's integral and XFEM with high‐order enrichment functions 下载免费PDF全文
Yongxiang Wang Haim Waisman Isaac Harari 《International journal for numerical methods in engineering》2017,112(7):629-654
This paper presents a comprehensive study on the use of Irwin's crack closure integral for direct evaluation of mixed‐mode stress intensity factors (SIFs) in curved crack problems, within the extended finite element method. The approach employs high‐order enrichment functions derived from the standard Williams asymptotic solution, and SIFs are computed in closed form without any special post‐processing requirements. Linear triangular elements are used to discretize the domain, and the crack curvature within an element is represented explicitly. An improved quadrature scheme using high‐order isoparametric mapping together with a generalized Duffy transformation is proposed to integrate singular fields in tip elements with curved cracks. Furthermore, because the Williams asymptotic solution is derived for straight cracks, an appropriate definition of the angle in the enrichment functions is presented and discussed. This contribution is an important extension of our previous work on straight cracks and illustrates the applicability of the SIF extraction method to curved cracks. The performance of the method is studied on several circular and parabolic arc crack benchmark examples. With two layers of elements enriched in the vicinity of the crack tip, striking accuracy, even on relatively coarse meshes, is obtained, and the method converges to the reference SIFs for the circular arc crack problem with mesh refinement. Furthermore, while the popular interaction integral (a variant of the J‐integral method) requires special auxiliary fields for curved cracks and also needs cracks to be sufficiently apart from each other in multicracks systems, the proposed approach shows none of those limitations. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
109.
Anand Embar John Dolbow Isaac Harari 《International journal for numerical methods in engineering》2010,83(7):877-898
A key challenge while employing non‐interpolatory basis functions in finite‐element methods is the robust imposition of Dirichlet boundary conditions. The current work studies the weak enforcement of such conditions for B‐spline basis functions, with application to both second‐ and fourth‐order problems. This is achieved using concepts borrowed from Nitsche's method, which is a stabilized method for imposing constraints on surfaces. Conditions for the stability of the system of equations are derived for each class of problem. Stability parameters in the Nitsche weak form are then evaluated by solving a local generalized eigenvalue problem at the Dirichlet boundary. The approach is designed to work equally well when the grid used to build the splines conforms to the physical boundary of interest as well as to the more general case when it does not. Through several numerical examples, the approach is shown to yield optimal rates of convergence. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
110.
Isaac Vaghefi Liette Lapointe Camille Boudreau‐Pinsonneault 《Information Systems Journal》2017,27(2):125-169
To date, information systems (IS) research mainly has provided a monolithic view of information technology (IT) use, considering it to be a desired behaviour with positive outcomes. However, given the dramatic increase in the use of technology during the last few years, susceptibility to IT addiction is increasingly becoming an important issue for technology users and IS researchers. In this paper, we report the results of a study that focuses on identifying variations in user liability to IT addiction, which reflects the susceptibility of individual users to develop IT addiction. First, a review of the literature in different disciplines (e.g. health, psychology and IS) allows us to better understand the concepts of IT addiction and liability to addiction. The literature review also provides an overview of the antecedents and consequences associated with IT addiction. Then, building on the analysis of 15 in‐depth interviews and 182 exploratory open‐ended surveys collected from smartphone users, we apply the concept of liability to addiction in the IT use context and propose a typological theory of user liability to IT addiction. Our typology reveals five ideal types; each can be associated to a user profile (addict, fanatic, highly engaged, regular and thoughtful ). Building upon both the extant literature and our results, we put forth propositions to extend the theoretical contributions of the study. We finally discuss the contributions and implications of our paper for research and practice. 相似文献