全文获取类型
收费全文 | 1005篇 |
免费 | 22篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 25篇 |
综合类 | 2篇 |
化学工业 | 193篇 |
金属工艺 | 31篇 |
机械仪表 | 17篇 |
建筑科学 | 19篇 |
矿业工程 | 1篇 |
能源动力 | 56篇 |
轻工业 | 58篇 |
水利工程 | 4篇 |
石油天然气 | 5篇 |
无线电 | 149篇 |
一般工业技术 | 195篇 |
冶金工业 | 93篇 |
原子能技术 | 10篇 |
自动化技术 | 170篇 |
出版年
2023年 | 9篇 |
2022年 | 12篇 |
2021年 | 25篇 |
2020年 | 20篇 |
2019年 | 24篇 |
2018年 | 30篇 |
2017年 | 20篇 |
2016年 | 24篇 |
2015年 | 20篇 |
2014年 | 26篇 |
2013年 | 82篇 |
2012年 | 45篇 |
2011年 | 58篇 |
2010年 | 45篇 |
2009年 | 55篇 |
2008年 | 30篇 |
2007年 | 41篇 |
2006年 | 39篇 |
2005年 | 36篇 |
2004年 | 21篇 |
2003年 | 19篇 |
2002年 | 24篇 |
2001年 | 9篇 |
2000年 | 12篇 |
1999年 | 20篇 |
1998年 | 25篇 |
1997年 | 22篇 |
1996年 | 24篇 |
1995年 | 14篇 |
1994年 | 20篇 |
1993年 | 12篇 |
1992年 | 14篇 |
1991年 | 14篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1976年 | 12篇 |
1971年 | 5篇 |
1970年 | 4篇 |
排序方式: 共有1028条查询结果,搜索用时 15 毫秒
101.
Sujoy Saha Subrata Nandi Rohit Verma Satadal Sengupta Kartikeya Singh Vivek Sinha Sajal K. Das 《Wireless Networks》2018,24(1):173-194
Delay tolerant networks (DTNs) are characterized by delay and intermittent connectivity. Satisfactory network functioning in a DTN relies heavily on co-ordination among participating nodes. However, in practice, such co-ordination cannot be taken for granted due to possible misbehaviour by relay nodes. Routing in a DTN is, therefore, vulnerable to various attacks, which adversely affect network performance. Several strategies have been proposed in the literature to alleviate such vulnerabilities—they vary widely in terms of throughput, detection time, overhead etc. One key challenge is to arrive at a tradeoff between detection time and overhead. We observe that the existing table-based reactive strategies to combat Denial-of-service (DoS) attacks in DTN suffer from two major drawbacks: high overhead and slow detection. In this paper, we propose three secure, light-weight and time-efficient routing algorithms for detecting DoS attacks (Blackhole and Grey-hole attacks) in the Spray & Focus routing protocol. The proposed algorithms are based on use of a small fraction of privileged (trusted) nodes. The first strategy, called TN, outperforms the existing table-based strategy with 20–30 % lesser detection time, 20–25 % higher malicious node detection and negligible overhead. The other two strategies, CTN_MI and CTN_RF explore the novel idea that trusted nodes are able to utilize each others’ information/experience using their long range connectivity as and when available. Simulations performed using an enhanced ONE simulator reveals that investing in enabling connectivity among trusted nodes (as in CTN_RF) can have significant performance benefits. 相似文献
102.
103.
A general packet assembly function in which the bundle is completed whenever any one of a number of conditions is satisfied is analyzed. These conditions subsume those most commonly found in practice. The analysis yields the distribution of bundle size. In several useful cases, closed form expressions for the mean bundle size is obtained 相似文献
104.
105.
K. Sengupta 《International Journal of Heat and Mass Transfer》2005,48(15):3035-3046
This paper presents a collection of numerical simulation data which provides a reference for the assessment of various statistical/stochastic models in incompressible homogeneous particle-laden turbulent flows. Four different homogeneous flow configurations are studied, namely, homogeneous shear flow, homogeneous plane strain flow, homogeneous axisymmetric expansion and contraction. An Eulerian-Lagrangian formulation is used for the two-phase flow simulation. A Fourier pseudospectral method is used for the solution of the Eulerian carrier-phase equations without resorting to any turbulence model. The Lagrangian equations for the dispersed phase are integrated using a modified Stokes drag. For the shear flow, both monodispersed and polydispersed particles have been considered. In this paper, only the results that are relevant for assessment of various statistical models for both the fluid and dispersed phases are presented. 相似文献
106.
J. Sengupta S. L. Cockcroft D. M. Maijer M. A. Wells A. Larouche 《Metallurgical and Materials Transactions B》2004,35(3):523-540
The control of the heat transfer during the start-up phase of the direct-chill (DC) casting process for aluminum sheet ingots
is critical from the standpoint of defect formation. Process control is difficult because of the various inter-related phenomena
occurring during the cast start-up. First, the transport of heat to the mold is altered as the ingot base deforms and the
sides are pulled inward during the start-up phase. Second, the range of temperatures and water flow conditions occurring on
the ingot surface as it emerges from the mold results in the full range of boiling-water heat-transfer conditions—e.g., film boiling, transition boiling, nucleate boiling, and convection—making the rate of transport highly variable. For example,
points on the ingot surface below the point of water impingement can experience film boiling, resulting in the water being
ejected from the surface, causing a dramatic decrease in heat transfer below the point of ejection. Finally, the water flowing
down the ingot sides may enter the gap formed between the ingot base and the bottom block due to butt curl. This process alters
the heat transfer from the base of the ingot and, in turn, affects the surface temperature on the ingot faces, due to the
transport of heat within the ingot in the vertical direction. A comprehensive mathematical model has been developed to describe
heat transfer during the start-up phase of the DC casting process. The model, based on the commercial finite-element package
ABAQUS, includes primary cooling via the mold, secondary cooling via the chill water, and ingot-base cooling. The algorithm used to account for secondary cooling to the water includes boiling
curves that are a function of ingot-surface temperature, water flow rate, impingement-point temperature, and position relative
to the point of water impingement. In addition, a secondary cooling algorithm accounts for water ejection, which can occur
at low water flow rates (low heat-extraction rates). The algorithm used to describe ingot-base cooling includes both the drop
in contact heat transfer due to gap formation between the ingot base and bottom block (arising from butt curl) as well as
the increase in heat transfer due to water incursion within the gap. The model has been validated against temperature measurements
obtained from two 711×1680 mm AA5182 ingots, cast under different start-up conditions (nontypical “cold” practice and nontypical
“hot” practice). Temperature measurements were taken at various locations on the ingot rolling and narrow faces, ingot base,
and top surface of the bottom block. Ingot-based deflection data were also obtained for the two test conditions. Comparison
of the model predictions with the data collected from the cast/embedded thermocouples indicates that the model accounts for
the processes of water ejection and water incursion and is capable of describing the flow of heat in the early stages of the
casting process satisfactorily. 相似文献
107.
BACKGROUND: This study aimed to compare efficacy and cost of key informants and survey for ascertainment of childhood epilepsy within a treatment context in rural India. METHODS: The study was set in a non-governmental, community programme for the functional and socioeconomic rehabilitation of children with disabilities in rural West Bengal, India. Ascertainment was by two methods: house-to-house survey of 15000 households and also by 430 key informants including village leaders, health workers and 670 schoolchildren. Methods were compared for positive predictive value, and sensitivity by capture-recapture technique. Ninety four children were enrolled into treatment. Predictors of treatment success were determined by multiple logistic regression analysis, giving adjusted odds ratios for remission. The costs of identifying one case and one treatment success were measured by costing personnel, materials and overheads. RESULTS: The survey was four times as sensitive as key informants although the positive predictive values were similar (36%, 40%). The survey had an absolute sensitivity of only 59%. Identification by key informants strongly predicted successful treatment outcome (odds ratio [OR] = 4.74, 95% confidence interval [CI] : 1.19-18.85). The cost of finding one case was US$11 and US$14, and of finding one successful treatment outcome US$35 and US$67 for informants and survey respectively. Key informants were essential in attaining longer term programme objectives. CONCLUSIONS: In the context of a treatment programme, key informants were the more cost-effective method, but community involvement was traded against low sensitivity in the short term. Overall ascertainment costs were significant in the context of primary health care in India. 相似文献
108.
In this paper we give sharp bounds on the reliability of discrete IFR, IFRA, NBU, DFR, DFRA and NWU classes, based on one known moment. Subsequently the discrete analogues of several continuous-time results related to maintained systems are also presented. 相似文献
109.
This work presents an exact piezothermoelastic solution of a finite transversely isotropic piezoelectric cylindrical shell under axisymmetric thermal, pressure and electrostatic excitation. The general solution of the governing equations is obtained in terms of potential functions which satisfy the boundary conditions at the ends. The axisymmetric loadings are expanded as a Fourier series in the axial coordinate. The coefficients in the infinite set of potential functions are obtained by solving sets of six algebraic equations resulting from the satisfaction of boundary conditions at the inner and outer surfaces of the shell for each Fourier component. The inverse problem of inferring the applied temperature and pressure fields from the given measured distribution of electrical potential difference between the inner and outer surfaces of the shell has also been solved. Numerical results are presented for typical pressure, thermal and electrostatic loadings. 相似文献
110.
Secure routing in mobile wireless ad hoc networks 总被引:3,自引:0,他引:3
We discuss several well known contemporary protocols aimed at securing routing in mobile wireless ad hoc networks. We analyze each of these protocols against requirements of ad hoc routing and in some cases identify fallibilities and make recommendations to overcome these problems so as to improve the overall efficacy of these protocols in securing ad hoc routing, without adding any significant computational or communication overhead. 相似文献