全文获取类型
收费全文 | 1147篇 |
免费 | 41篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 42篇 |
化学工业 | 245篇 |
金属工艺 | 49篇 |
机械仪表 | 32篇 |
建筑科学 | 15篇 |
能源动力 | 53篇 |
轻工业 | 39篇 |
石油天然气 | 1篇 |
无线电 | 183篇 |
一般工业技术 | 270篇 |
冶金工业 | 110篇 |
原子能技术 | 13篇 |
自动化技术 | 145篇 |
出版年
2023年 | 10篇 |
2022年 | 36篇 |
2021年 | 51篇 |
2020年 | 27篇 |
2019年 | 30篇 |
2018年 | 34篇 |
2017年 | 33篇 |
2016年 | 27篇 |
2015年 | 22篇 |
2014年 | 34篇 |
2013年 | 58篇 |
2012年 | 49篇 |
2011年 | 49篇 |
2010年 | 43篇 |
2009年 | 45篇 |
2008年 | 52篇 |
2007年 | 49篇 |
2006年 | 47篇 |
2005年 | 37篇 |
2004年 | 22篇 |
2003年 | 27篇 |
2002年 | 27篇 |
2001年 | 19篇 |
2000年 | 13篇 |
1999年 | 23篇 |
1998年 | 49篇 |
1997年 | 28篇 |
1996年 | 24篇 |
1995年 | 21篇 |
1994年 | 12篇 |
1993年 | 21篇 |
1992年 | 9篇 |
1991年 | 14篇 |
1990年 | 15篇 |
1989年 | 13篇 |
1988年 | 13篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1974年 | 5篇 |
1973年 | 7篇 |
排序方式: 共有1197条查询结果,搜索用时 15 毫秒
91.
Salkalachen S. Krishnan N.H. Krishnan S. Satyamurthy H.B. Srinivas K.S. 《Semiconductor Manufacturing, IEEE Transactions on》1990,3(1):12-17
Factors governing long-term stability of silicon power devices are discussed with particular reference to a major failure mechanism observed in a thyristor device. The device failure was due to electrical instability during an electrical and thermal stability storage test, wherein it was observed that the reverse blocking voltage deteriorated under applied bias at the rated maximum junction temperature. The major cause of this failure was identified as lack of exhaust during the edge passivation and curing process due to which excessive chemical deposits are retained in the bevel region of the silicon element. This contributes to surface leakage current and, hence, a rapid degradation of the off-state characteristics. An orthogonal array experiment was employed to optimize the process factors and levels. The manufacturing process was then modified by incorporating an effective exhaust system in the passivant curing oven. This resulted in marked improvements in the electrical stability and manufacturing yield of this device 相似文献
92.
Karthiga Durairaj Barsha Roy Natarajan Chandrasekaran Suresh Palamadai Krishnan Amitava Mukherjee 《IET nanobiotechnology / IET》2020,14(2):161
The production of different size and shape silver nanoparticles (AgNPs) has increased considerably in recent years due to several commercial and biological applications. Here, rod‐shaped AgNPs (SNRs) were prepared using the microwave‐assisted method and characterised by ultraviolet–visible spectroscopy, and transmission electron microscopy analysis. The present study aims to investigate the cyto–genotoxic effect of various concentrations (5, 10, and 15 µM) of SNRs using Allium cepa model. As a result, concentration‐dependent cyto–genotoxic effect of SNRs was observed through a decrease in the mitotic index, and an increase in the chromosomal aberrations such as chromosome break, disturbed metaphase, and anaphase bridge. To check the impact of Ag+ ions, 15 µM silver nitrate (AgNO3) was prepared and tested in all the assays. Furthermore, cell viability and different reactive oxygen species assays were performed to test the cytotoxicity evaluation of SNRs. The authors found that in all the tested assays, SNRs at high concentrations (15 µM) and AgNO3 (15 µM) were observed to cause maximal damage to the roots. Therefore, the current study implies that the cytotoxicity and genotoxicity of SNRs were dependent on the concentration of SNRs.Inspec keywords: ultraviolet spectra, biomedical materials, silver, cellular biophysics, nanorods, toxicology, visible spectra, nanoparticles, nanofabrication, transmission electron microscopy, nanomedicine, aberrations, microwave materials processingOther keywords: biological applications, rod‐shaped AgNPs, microwave‐assisted method, ultraviolet‐visible spectroscopy, transmission electron microscopy, chromosomal aberrations, chromosome break, silver nitrate, reactive oxygen species assays, cytotoxicity, genotoxicity, silver nanorods, oxidative stress, shape silver nanoparticles, concentration‐dependent cyto‐genotoxic effect, Allium cepa model, mitotic index, disturbed metaphase, anaphase bridge, cell viability, cytotoxicity evaluation, Ag 相似文献
93.
Wei B. Silva C. Koutsofios E. Krishnan S. North S. 《Computer Graphics and Applications, IEEE》2000,20(4):50-54
We describe our research at AT&T Infolab on using large displays to interactively analyze and visualize AT&T's communication networks and services 相似文献
94.
The Erlang loss system is a system in which customers arriving in a Poisson stream of arrival rate λ are served by a group of n servers, with a mean service time of 1/μ. Arrivals that find all servers busy are blocked and cleared from the system. The Erlang delay system is a system in which customers who find all servers busy wait in a queue until served by the first available server. Proofs of joint-convexity results in the Erlang delay system and Erlang loss system are presented, using induction on the number of servers and making use of the relation between the Erlang B and the Erlang C functions. The approach leads to a straightforward algebraic analysis of the properties of the performance measures of interest and avoids cumbersome manipulations 相似文献
95.
V. Kalliyana Krishnan A. Jayakrishnan J. D. Francis 《Journal of materials science. Materials in medicine》1991,2(1):56-61
Medical grade poly(vinyl chloride) (PVC) sheets were surface modified by grafting a combination of 2-hydroxyethyl methacrylate (HEMA) and N-vinyl pyrrolidone (NVP) or NVP alone using gamma radiation in an effort to retard the migration of the plasticizer from the PVC matrix. Presence of cupric ions at a concentration of 0.005m was found to be optimal in not only preventing the homopolymerization of the monomers but also producing the highest graft yield at all monomer concentrations used for grafting. The grafted PVC was characterized for its water absorption properties. Surface morphology of the grafted surface was examined using scanning electron microscopy (SEM). PVC sheets grafted on both sides as well as on one side were characterized for their physical and mechanical properties in order to assess their suitability in biomedical applications. While the tensile strength and percentage elongation values of PVC sheets grafted on both sides showed a downward trend with increasing graft yield, these properties were not drastically affected by surface modification on one side only at graft yields pertinent to prevent the migration of the plasticizer. Measurement of Shore A hardness and optical transparency of the migration resistant sheetings showed that such properties were not seriously affected by surface modification thus rendering them suitable for their intended applications. 相似文献
96.
97.
Abdulaziz T. Almaktoom Krishna K. Krishnan Pingfeng Wang Samir Alsobhi 《The International Journal of Advanced Manufacturing Technology》2014,74(1-4):445-460
Despite studies that consider service level rates of individual factories in a supply chain system, the interactions between connected factories and the impact of these interactions on the overall supply chain service level rate have been rarely studied. Moreover, due to uncertainties induced by various sources such as transportation delay and manufacturing processes variability, ensuring the robustness of system service level rate while considering these uncertainties in individual factories is a highly complex task. This paper studies uncertainty effect introduced by factory service level rates on the robustness of overall supply chain network performance, and presents a novel robust design optimization methodology to derive designs of factory service level rates in order to satisfy the service level rate requirement of the system and ensure its robustness. A case study with a multi-level multiple factories supply chain network is used to demonstrate the efficacy of the proposed methodology. 相似文献
98.
The heat transfer effectiveness of nanofluids is adversely affected by the delay in convection onset. The lesser effectiveness, when compared to that of base fluid, is observed in a range of nanofluid layer thickness. The heat transfer coefficient of water–Al2O3 nanofluid can be enhanced by sustaining the equilibrium between Rayleigh number, temperature, particle volume fraction, and enclosure aspect ratio. In this paper, the specific correlation of fluid layer thickness and the onset of convection, which can significantly dominate the heat transfer characteristics of nanofluids are investigated using the concept of critical Rayleigh number. The water layer thickness for convection onset is first experimentally assessed for different real-life heat flux densities. It is then performed for Al2O3–water nanofluid for varying volume fractions. With the increase in volume fraction even though thermal conductivity increases, the overall heat transfer enhancement of the nanofluid is reduced. Temperature involved (heat flux density), the volume fraction of the nanofluid used, nanofluid layer thickness (space availability for the cooling system), and mass of the nanoparticle influence heat transfer enhancement. A higher volume fraction may not always result in enhancement of heat transfer as far as nanofluids are concerned. 相似文献
99.
Asphalt exhibits Newtonian, non-Newtonian and viscoelastic behavior as the temperature is varied. This investigation reports the temperature at which asphalt exhibits non-Newtonian to Newtonian transition. Air blown, blended asphalt and petroleum pitch were tested at different aging conditions. The temperature at which the material exhibited shear rate independent viscosity was taken as the transition temperature. The transition temperature varied with processing method and aging conditions. It was seen that blended asphalt exhibited greater increase in apparent viscosity during aging when compared to air blown asphalt, whereas air blown asphalt showed greater shift in transition temperature for the same aging conditions. 相似文献
100.
In the single rent-to-buy decision problem, without a priori knowledge of the amount of time a resource will be used we need
to decide when to buy the resource, given that we can rent the resource for $1 per unit time or buy it once and for all for
$c . In this paper we study algorithms that make a sequence of single rent-to-buy decisions, using the assumption that the resource
use times are independently drawn from an unknown probability distribution. Our study of this rent-to-buy problem is motivated
by important systems applications, specifically, problems arising from deciding when to spindown disks to conserve energy
in mobile computers [4], [13], [15], thread blocking decisions during lock acquisition in multiprocessor applications [7],
and virtual circuit holding times in IP-over-ATM networks [11], [19].
We develop a provably optimal and computationally efficient algorithm for the rent-to-buy problem. Our algorithm uses time and space, and its expected cost for the t th resource use converges to optimal as , for any bounded probability distribution on the resource use times. Alternatively, using O(1) time and space, the algorithm almost converges to optimal.
We describe the experimental results for the application of our algorithm to one of the motivating systems problems: the
question of when to spindown a disk to save power in a mobile computer. Simulations using disk access traces obtained from
an HP workstation environment suggest that our algorithm yields significantly improved power/ response time performance over the nonadaptive 2-competitive algorithm which is optimal in the worst-case competitive analysis
model.
Received October 22, 1996; revised September 25, 1997. 相似文献