全文获取类型
收费全文 | 2940篇 |
免费 | 104篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 39篇 |
综合类 | 10篇 |
化学工业 | 686篇 |
金属工艺 | 102篇 |
机械仪表 | 94篇 |
建筑科学 | 51篇 |
矿业工程 | 9篇 |
能源动力 | 186篇 |
轻工业 | 329篇 |
水利工程 | 17篇 |
石油天然气 | 4篇 |
无线电 | 250篇 |
一般工业技术 | 622篇 |
冶金工业 | 268篇 |
原子能技术 | 26篇 |
自动化技术 | 361篇 |
出版年
2024年 | 12篇 |
2023年 | 38篇 |
2022年 | 120篇 |
2021年 | 129篇 |
2020年 | 99篇 |
2019年 | 110篇 |
2018年 | 144篇 |
2017年 | 136篇 |
2016年 | 113篇 |
2015年 | 56篇 |
2014年 | 130篇 |
2013年 | 234篇 |
2012年 | 125篇 |
2011年 | 173篇 |
2010年 | 139篇 |
2009年 | 121篇 |
2008年 | 122篇 |
2007年 | 106篇 |
2006年 | 66篇 |
2005年 | 63篇 |
2004年 | 44篇 |
2003年 | 49篇 |
2002年 | 55篇 |
2001年 | 29篇 |
2000年 | 29篇 |
1999年 | 32篇 |
1998年 | 65篇 |
1997年 | 63篇 |
1996年 | 40篇 |
1995年 | 27篇 |
1994年 | 20篇 |
1993年 | 29篇 |
1992年 | 21篇 |
1991年 | 27篇 |
1990年 | 23篇 |
1989年 | 29篇 |
1988年 | 23篇 |
1987年 | 25篇 |
1986年 | 20篇 |
1985年 | 18篇 |
1984年 | 11篇 |
1983年 | 13篇 |
1981年 | 13篇 |
1980年 | 13篇 |
1979年 | 16篇 |
1978年 | 8篇 |
1977年 | 14篇 |
1976年 | 17篇 |
1974年 | 10篇 |
1973年 | 10篇 |
排序方式: 共有3054条查询结果,搜索用时 0 毫秒
991.
Use of the Finite-Difference Time-Domain Method in Calculating EM Absorption in Human Tissues 总被引:1,自引:0,他引:1
Sullivan Dennis M. Borup David T. Gandhi Om P. 《IEEE transactions on bio-medical engineering》1987,(2):148-157
Although there are acceptable methods for calculating whole body electromagnetic absorption, no completely acceptable method for calculating the local specific absorption rate (SAR) at points within the body has been developed. Frequency domain methods, such as the method of moments (MoM) have achieved some success; however, MoM requires computer storage on the order of (3N) 2 and computation time on the order of (3N) 3 where N is the number of cells. The finite-difference time-domain (FDTD) method has been employed extensively in calculating the scattering of metallic objects, and recently is seeing some use in calculating the interaction of EM fields with complex, lossy dielectric bodies. Since the FDTD method has storage and time requirements proportional to N, it presents an attractive alternative to calculating SAR distribution in large bodies. This paper describes the FDTD method and evaluates it by comparing its results to analytic solutions in two and three dimensions. The utility of the FDTD method is demonstrated by a 3D scan of the human torso. The results obtained demonstrate that the FDTD method is capable of calculating internal SAR distribution with acceptable accuracy. With the availability of supercomputers, such as the CRAY II, the calculation of SAR distribution in a man model of 50 000 cells (1.27 cm per cell) appears to be feasible. 相似文献
992.
Two smectite samples having different layer charges were pillared using hydroxy aluminium oligomers at a OH/Al ratio of 2.5 and at pH 4.3 to 4.6. Pillaring was carried out at different conditions such as ageing, temperature and base addition time of the pillaring solution, and also in the presence of nonionic surfactant polyoxyethylene sorbitanmonooleate (Tween-80). The primary objective of preparing at different conditions was to introduce varied quantities of aluminium oligomer between the layers and to study its effect on the properties of the pillared products. A simple method has been followed to estimate the amount of interlayer aluminium. A quantity called pillar density number (PDN) based on the ratio of interlayer Al adsorbed to CEC of the parent clay has been effectively used to evaluate the nature of the resulting pillared product. PDN, for a given clay, was found to correlate well with the sharpness of the d(0001) peaks for the air dried samples. The calculated number of pillars, varied from 3.00 × 1018 to 5.32 × 1018 per meq charge. The present study shows that a higher value of PDN is indicative of better thermal stability. Pillar density number may be conveniently used as a measure of the thermal stability of pillared samples. 相似文献
993.
Three beams of rectangular cross-section and having same cross-sectional dimensions were tested in two-point bending, over
an effective span of 4.2 m. All three beams contained steel only in the tension zone and the tension steel was distributed
in three different ways. A deterministic analysis of strains, crack spacings and crack widths for all three beams is carried
out and the results are compared with the respective experimental values. A probabilistic analysis of strains, crack spacings
and crack widths is performed for all the three beams at different stages of loading. 相似文献
994.
995.
996.
Graft copolymerization of ethylmethacrylate (EMA) onto Himachali wool fiber has been investigated in aqueous medium by mutual gamma irradiation from a Co60 source in air and in nitrogen atmosphere. Percentage of grafting has been evaluated as a function of (i) total dose, (ii) concentration of monomer, and (iii) effect of concentration of different acids such as hydrochloric acid, sulfuric acid, nitric acid, perchloric acid, and acetic acid. Maximum percentage of grafting has been obtained in the presence of sulfuric acid. Following reactivity order of different acids towards grafting has been observed: H2SO4 > HCI > HNO3 > HCIO4 > CH3COOH. A plausible mechanism to explain the effect of acids on percentage of grafting of EMA has been suggested. 相似文献
997.
998.
André Nieuwland Jeffrey Kang Om Prakash Gangwal Ramanathan Sethuraman Natalino Busá Kees Goossens Rafael Peset Llopis Paul Lippens 《Design Automation for Embedded Systems》2002,7(3):233-270
The key issue in the design of Systems-on-a-Chip (SoC) is to trade-off efficiency against flexibility, and time to market versus cost. Current deep submicron processing technologiesenable integration of multiple software programmable processors (e.g., CPUs,DSPs) and dedicated hardware components into a single cost-efficient IC. Ourtop-down design methodology with various abstraction levels helps designingthese ICs in a reasonable amount of time. This methodology starts with a high-levelexecutable specification, and converges towards a silicon implementation.A major task in the design process is to ensure that all components (hardwareand software) communicate with each other correctly. In this article, we tacklethis problem in the context of the signal processing domain in two ways: wepropose a modular, flexible, and scalable heterogeneous multi-processor architecturetemplate based on distributed shared memory, and we present an efficient andtransparent protocol for communication and (re)configuration. The protocolimplementations have been incorporated in libraries, which allows quick traversalof the various abstraction levels, so enabling incremental design. The designdecisions to be taken at each abstraction level are evaluated by means of(co-)simulation. Prototyping is used too, to verify the system's functionalcorrectness. The effectiveness of our approach is illustrated by a designcase of a multi-standard video and image codec.He currently works with Magma Design Automation. E-mail: 相似文献
999.
1000.
Efforts made over the last three decades to understand the fracture behaviour of structural materials in elastic and elasto-plastic
fracture mechanics are numerous, whereas investigations related to fracture behaviour of materials in thin sheets or general
yielding fracture regimes are limited in number. Engineering simulative tests are being used to characterize formability and
drawability of sheet metals. However, these tests do not assure consistency in quality of sheet metal products. The prevention
of failure in stressed structural components currently requires fracture mechanics based design parameters like critical load,
critical crack-tip opening displacement or fracture toughness. The present attempt would aim to fulfill this gap and generate
more information thereby increased understanding on fracture behaviour of sheet metals. In the present investigation, using
a recently developed technique for determining fracture criteria in sheet metals, results are generated on critical CTOD and
fracture toughness. Finite element analysis was performed to support the results on various fracture parameters. The differences
are within 1 to 4%. At the end it is concluded that magnitude of critical CTOD and/or critical load can be used as a fracture
criterion for thin sheets. 相似文献