全文获取类型
收费全文 | 2646篇 |
免费 | 120篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 28篇 |
综合类 | 12篇 |
化学工业 | 602篇 |
金属工艺 | 132篇 |
机械仪表 | 46篇 |
建筑科学 | 45篇 |
矿业工程 | 7篇 |
能源动力 | 197篇 |
轻工业 | 171篇 |
水利工程 | 34篇 |
石油天然气 | 23篇 |
无线电 | 324篇 |
一般工业技术 | 596篇 |
冶金工业 | 302篇 |
原子能技术 | 32篇 |
自动化技术 | 224篇 |
出版年
2024年 | 13篇 |
2023年 | 47篇 |
2022年 | 79篇 |
2021年 | 118篇 |
2020年 | 89篇 |
2019年 | 105篇 |
2018年 | 126篇 |
2017年 | 109篇 |
2016年 | 108篇 |
2015年 | 60篇 |
2014年 | 111篇 |
2013年 | 248篇 |
2012年 | 130篇 |
2011年 | 178篇 |
2010年 | 105篇 |
2009年 | 122篇 |
2008年 | 126篇 |
2007年 | 75篇 |
2006年 | 63篇 |
2005年 | 55篇 |
2004年 | 48篇 |
2003年 | 48篇 |
2002年 | 39篇 |
2001年 | 30篇 |
2000年 | 37篇 |
1999年 | 31篇 |
1998年 | 49篇 |
1997年 | 38篇 |
1996年 | 38篇 |
1995年 | 35篇 |
1994年 | 34篇 |
1993年 | 30篇 |
1992年 | 27篇 |
1991年 | 20篇 |
1990年 | 19篇 |
1989年 | 16篇 |
1988年 | 25篇 |
1987年 | 20篇 |
1986年 | 15篇 |
1985年 | 17篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1976年 | 8篇 |
1975年 | 4篇 |
1973年 | 3篇 |
排序方式: 共有2775条查询结果,搜索用时 15 毫秒
41.
Nishant Doshi Saru Kumari Dheerendra Mishra Xiong Li Kim-Kwang Raymond Choo Arun Kumar Sangaiah 《Multimedia Tools and Applications》2017,76(24):25893-25918
In this digital era, where Internet of Things (IoT) is increasing day by day, use of resource constrained devices is also increasing. Indeed, the features such as low cost, less maintenance, more adaptive to hostile environment, etc. make the wireless multimedia devices to be the best choice as the resource constrained devices. For the security, the end user device requires to establish the session key with the server before transferring the data. Mobile is one of the device having more and more usage as wireless multimedia device in recent years. In 2013, Li et al. proposed an efficient scheme for the wireless mobile communications and claimed it to be secure against various attacks. Recently, Shen et al. claimed that the scheme of Li et al. is still vulnerable to the privileged insider attack, the stolen verifier attack and finally proposed a scheme to withstand the mentioned and other attacks. However, in this paper we claim that the scheme of Shen et al. is still susceptible to the user anonymity, the session specific temporary information attack and the replay attack. In addition, Shen et al.’s scheme requires more time due to many operations. Further, we propose an efficient scheme that is secure against various known attacks and due to reduced time complexity our scheme is a preferred choice for the wireless mobile networks and hence for wireless multimedia systems. 相似文献
42.
Semantic web reasoners and languages 总被引:1,自引:0,他引:1
Semantic web reasoners and languages enable the semantic web to function. Some of the latest reasoning models developed in
the last few years are: DLP, FaCT, RACER, Pellet, MSPASS, CEL, Cerebra Engine, QuOnto, KAON2, HermiT and others. Some software
tools such as Protégé, Jena and others also have been developed, which provide inferencing as well as ontology development
and management environments. These reasoners usually differ in their inference procedures, supporting logic, completeness
of reasoning, expressiveness and implementation languages. Various semantic web languages with increasing expressive power
continue to be developed for describing web services. We survey the some of the more recent languages like OWL-S (Ontology
Web Language-Schema), WSML (Web Service Modeling Language), SWRL (Semantic Web Rule Language) and others that have been tested
in early use. We also survey semantic web reasoners and their relationship to these languages. 相似文献
43.
Creep fracture behaviour of pure aluminium-matrix composites with 10–30 vol% SiC particulates at 623 K is reported. A comparison of tensile and compression creep data shows the existence of a transition stress. Above this transition stress no steady state creep is observed in tension. This transition stress is related to a transition from intergranular to transgranular fracture. The origin of transition stress is perhaps associated with the diffusional relaxation of stress concentration at the matrix/particle interface by lattice diffusion. The intergranular creep fracture of composites appears to be similar to that of unreinforced aluminium and it is power-law creep controlled. The transgranular creep fracture occurs by void nucleation and growth. The nucleation strain for voids is quite small and hence the tertiary stage starts before the end of the primary stage. The ductile fracture models overestimate the strain to fracture and do not predict the observed stress dependence of strain to fracture. 相似文献
44.
Delayed settling of the ash particles and poor drainage of water from the pond ash are the major problems faced during the hydraulic stowing of pond ash. In this study the effect of polymeric flocculant on settling of the ash particles and drainage of water during pond ash stowing are investigated. In addition, the parameters, viz. drainage and absorption of water during pond ash stowing are quantified by stowing a mine goaf model with pond ash slurries of five different concentrations added with and without flocculant. The study revealed that addition of only 5 × 10?6 of Sodium Carboxymethyl Cellulose (Na-CMC) flocculant with the pond ash slurries during stowing offers best result in terms of quicker settling of the ash particles and enhanced water drainage from the hydraulically stowed pond ash. Besides, it resulted in drainage of more than 85% of the total water used in the initial 45 min of stowing. The improvement in drainage is caused due to coagulation and flocculation of the pond ash particles because of charge neutralization and particle–particle bridging. This study may provide a basis for estimating the drainage and absorption of water during the real pond ash stowing operation in underground mines. 相似文献
45.
Two-stage quasi-class-E power amplifier in GaN HEMT technology 总被引:2,自引:0,他引:2
Gao S. Hongtao Xu Heikman S. Mishra U.K. York R.A. 《Microwave and Wireless Components Letters, IEEE》2006,16(1):28-30
This letter presents a two-stage quasi-class-E monolithic microwave integrated circuit power amplifier at 2.0GHz, which is based on field-plated GaN high electron mobility transistor technology. It consists of a driver stage and a power stage. The circuit schematic is described. The amplifier achieves an output power of 37.5dBm into a 50-/spl Omega/ load, a power added efficiency (PAE) of 50%, and a gain of 18.2dB. A power density of 5.6W/mm is achieved. 相似文献
46.
This paper describes the design, implementation, and evaluation of interagent communication and synchronization models in the DaAgent mobile-agent based computing system. Based on the requirements of some sample Internet computing applications, eight system-level models of interagent communication and synchronization are proposed. A new synchronization mechanism called location synchronization that is relevant for interacting mobile agents is also proposed. This paper evaluates the eight models based on their utility, performance, level of communication and synchronization support, and applicability in the Internet computing environment. A prototype implementation and detailed performance evaluation of these models based on two interacting, multiagent applications are also presented. 相似文献
47.
Ti-Al intermetallics have been produced using mechanical alloying technique. A composition of Ti-48Al-2Nb at % powders was mechanically alloyed for various durations of 20, 40, 60, 80 and 100 h. At the early stages of milling, a Ti (Al) solid solution is formed, on further milling the formation of amorphous phase occurs. Traces of TiAl and Ti3Al were formed with major Ti and Al phases after milling at 40 h and beyond. When further milled, phases of intermetallic compounds like TiAl and Ti3Al were formed after 80 hours of milling and they also found in 100 h milled powders. The powders milled for different durations were sintered at 785°C in vacuum. The mechanically alloyed powders as well as the sintered compacts were characterized by XRD, FESEM and DTA to determine the phases, crystallite size, microstructures and the influence of sintering over mechanical alloying. 相似文献
48.
In the present study,corrosion behavior of diffusion bonded joints formed between micro-duplex stainless steel(MDSS) and Ti6AI4V alloy(TiA)(at 900 ℃ for 60 min under 4 MPa uniaxial pressure in vacuum) was investigated in 1 mol/L HCI and 1 mol/L NaOH solutions using various electrochemical measurements such as open circuit potential(OCP),electrochemical impedance spectroscopy(EIS) and potentiodynamic polarization(PD).For comparison,corrosion behavior of base metals(MDSS and TiA) was also evaluated.Bonded joint was characterized by light optical microscopy and scanning electron microscopy using backscattered electron mode.The layer wise σ phase and λ + FeTi phase mixture has been observed at the bond interface and the bond tensile strength and shear strength were ~556.4 MPa and ~420.2 MPa,respectively. 相似文献
49.
Rami T. ElAfandy Ayman F. AbuElela Pawan Mishra Bilal Janjua Hassan M. Oubei Ulrich Büttner Mohammed A. Majid Tien Khee Ng Jasmeen S. Merzaban Boon S. Ooi 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(7)
Knowledge of materials' thermal‐transport properties, conductivity and diffusivity, is crucial for several applications within areas of biology, material science and engineering. Specifically, a microsized, flexible, biologically integrated thermal transport sensor is beneficial to a plethora of applications, ranging across plants physiological ecology and thermal imaging and treatment of cancerous cells, to thermal dissipation in flexible semiconductors and thermoelectrics. Living cells pose extra challenges, due to their small volumes and irregular curvilinear shapes. Here a novel approach of simultaneously measuring thermal conductivity and diffusivity of different materials and its applicability to single cells is demonstrated. This technique is based on increasing phonon‐boundary‐scattering rate in nanomembranes, having extremely low flexural rigidities, to induce a considerable spectral dependence of the bandgap‐emission over excitation‐laser intensity. It is demonstrated that once in contact with organic or inorganic materials, the nanomembranes' emission spectrally shift based on the material's thermal diffusivity and conductivity. This NM‐based technique is further applied to differentiate between different types and subtypes of cancer cells, based on their thermal‐transport properties. It is anticipated that this novel technique to enable an efficient single‐cell thermal targeting, allow better modeling of cellular thermal distribution and enable novel diagnostic techniques based on variations of single‐cell thermal‐transport properties. 相似文献
50.
The steady state creep behaviour of the two-phase Ti3Al-based alloy, Ti-24Al-11Nb, has been examined as a function of microstructure at temperatures ranging from 798 to 998 K and stress levels ranging from 30 to 400 MPa. Three microstructural conditions corresponding to 90% equiaxed 2, 40% equiaxed 2, and 100% lath 2 structures have been studied. A low-stress Coble creep regime has been identified, with the lath 2 structure showing the greates creep resistance in this regime. The lath 2 structure is also stronger in the dislocation creep regime. The creep strength of this ordered alloy is shown to derive from frequency factors for diffusion, which are about two to three orders of magnitude lower than those for disordered alloys. Activation energies for creep in both the diffusional and dislocation creep domains are similar to values obtained in disordered alloys. 相似文献