全文获取类型
收费全文 | 7105篇 |
免费 | 230篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 72篇 |
综合类 | 9篇 |
化学工业 | 1574篇 |
金属工艺 | 73篇 |
机械仪表 | 108篇 |
建筑科学 | 531篇 |
矿业工程 | 33篇 |
能源动力 | 185篇 |
轻工业 | 603篇 |
水利工程 | 72篇 |
石油天然气 | 59篇 |
武器工业 | 1篇 |
无线电 | 434篇 |
一般工业技术 | 1028篇 |
冶金工业 | 1270篇 |
原子能技术 | 35篇 |
自动化技术 | 1253篇 |
出版年
2022年 | 70篇 |
2021年 | 97篇 |
2020年 | 73篇 |
2019年 | 109篇 |
2018年 | 126篇 |
2017年 | 141篇 |
2016年 | 154篇 |
2015年 | 114篇 |
2014年 | 182篇 |
2013年 | 482篇 |
2012年 | 258篇 |
2011年 | 388篇 |
2010年 | 289篇 |
2009年 | 302篇 |
2008年 | 318篇 |
2007年 | 330篇 |
2006年 | 265篇 |
2005年 | 279篇 |
2004年 | 196篇 |
2003年 | 199篇 |
2002年 | 179篇 |
2001年 | 136篇 |
2000年 | 128篇 |
1999年 | 140篇 |
1998年 | 163篇 |
1997年 | 134篇 |
1996年 | 150篇 |
1995年 | 96篇 |
1994年 | 88篇 |
1993年 | 85篇 |
1992年 | 84篇 |
1991年 | 65篇 |
1990年 | 85篇 |
1989年 | 84篇 |
1988年 | 76篇 |
1987年 | 87篇 |
1986年 | 69篇 |
1985年 | 85篇 |
1984年 | 89篇 |
1983年 | 76篇 |
1982年 | 75篇 |
1981年 | 64篇 |
1980年 | 58篇 |
1979年 | 55篇 |
1978年 | 60篇 |
1977年 | 50篇 |
1976年 | 74篇 |
1975年 | 55篇 |
1974年 | 45篇 |
1973年 | 55篇 |
排序方式: 共有7340条查询结果,搜索用时 15 毫秒
991.
Nedos Andronikos Singh Kulpreet Cunningham Raymond Clarke Siobh n 《Mobile Computing, IEEE Transactions on》2009,8(4):544-557
Mobile ad hoc networks rely on the opportunistic interaction of autonomous nodes to form networks without the use of infrastructure. Given the radically decentralized nature of such networks, their potential for autonomous communication is significantly improved when the need for a priori consensus among the nodes is kept to a minimum. This paper addresses an issue within the domain of semantic content discovery, namely, its current reliance on the preexisting agreement between the schema of content providers and consumers. We present OntoMobil, a semantic discovery model for ad hoc networks that removes the assumption of a globally known schema and allows nodes to publish information autonomously. The model relies on the randomized dissemination and replication of metadata through a gossip protocol. Given schemas with partial similarities, the randomized metadata dissemination mechanism facilitates eventual semantic agreement and provides a substrate for the scalable discovery of content. A discovery protocol can then utilize the replicated metadata to identify content within a predictable number of hops using semantic queries. A stochastic analysis of the gossip protocol presents the different trade-offs between discoverability and replication. We evaluate the proposed model by comparing OntoMobil against a broadcast-based protocol and demonstrate that semantic discovery with proactive replication provides good scalability properties, resulting in a high discovery ratio with less overhead than a reactive nonreplicated discovery approach. 相似文献
992.
Chi-Yen Lin You-Ming Chen Hsiao-Fan Chen Fu-Chuan Fang Yu-Cheng Lin Wen-Yi Hung Ken-Tsung Wong Raymond C. Kwong Sean C. Xia 《Organic Electronics》2009,10(1):181-188
This paper describes the synthesis of three triaryldiamine derivatives presenting two thermally polymerizable trifluorovinyl ether groups that can be polymerized through thermal curing to form perfluorocyclobutyl (PFCB) polymers. These PFCB polymers, studied using time-of-flight techniques for the first time, exhibited remarkable non-dispersive hole-transport properties, with values of μh of ca. 10?4 cm2 V?1 s?1. When we employed these thermally polymerized polymers as hole-transport layers (HTLs) in electroluminescence devices containing tris(8-hydroxyquinolate) aluminum (Alq3) as the emission layer, we obtained high current densities (ca. 3400 mA cm?2), impressive brightnesses (5 × 104 cd m?2), and high external quantum efficiencies (EQEs = 1.43%). These devices exhibited the same turn-on voltage, but higher EQEs, relative to those incorporating the vacuum-processed model compound N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine (α-NPD) (EQE = 1.37%) as the HTL under the same device structure. 相似文献
993.
Characterization of multiporous structure and oxygen transfer inside aerobic granules with the percolation model 总被引:1,自引:0,他引:1
Liu L Sheng GP Liu ZF Li WW Zeng RJ Lee DJ Liu JX Yu HQ 《Environmental science & technology》2010,44(22):8535-8540
The characteristics of aerobic granules for wastewater treatment are greatly related to their complex internal structure. However, due to the limitation of characterizing methods, information about the granule internal morphology and structure is very sparse, and mechanism of mass transfer process is yet unclear. In this work, the internal structure of aerobic granules was explored using nitrogen adsorption method and confocal laser scanning microscopy technique. It was found that aerobic granules had multiporous structure with cross-linked gel matrix structure. With a consideration of the hydrodynamic regime and the porous structure of granules, a two-dimensional percolation model was established to describe the mass transfer in granules. With the approaches, interesting and useful results regarding the pore distribution and mass transfer in aerobic granules have been obtained. The results demonstrate that the intragranule convection could enhance mass transfer, hence ensure an efficient and stable operation of aerobic-granule-based reactors. Such approaches might also be applicable to characterizing the multiporous structure and mass transfer of other microbial aggregates for wastewater treatment. 相似文献
994.
Josette M. Landry D. Gerrard Marangoni Deborah A. Arden Ian J. MacLennan Jan C. T. Kwak 《Journal of surfactants and detergents》2009,12(2):155-164
NMR chemical shifts and linewidth measurements were examined for mixtures of sodium 10-phenyldecanoate (Na ω-PhDec) in deuterated
aqueous solutions in the presence of varying compositions of poly(ethylene oxide) (PEO) polymers of 2000 and 4000 molecular
weight. In addition, variable temperature NMR spectra and NMR spin lattice relaxation times (T
1) were obtained for the PEO-4000/Na ω-PhDec system as a function of varying polymer concentrations. As expected, the polymer/surfactant
systems exhibit the behaviour typical of that of an anionic surfactant/neutral polymer system with well defined critical aggregation
concentrations (CMC) corresponding to the formation of polymer/surfactant complexes below the CMC of the free surfactant.
The 1H-NMR linewidths acquired for the Na ω-PhDec/PEO-4000 system before and after the CMC region of the surfactant indicate that
the maximum in the linewidth of the PEO proton peak is reached at approximately twice the CMC of the free surfactant. 2D-NMR
NOESY measurements on this system exhibit cross peaks between the PEO protons and the protons on the surfactant backbone,
consistent with the location of the phenyl group in the micellar interior. All these NMR experiments are interpreted in terms
of the structure of the polymer/surfactant complexes as a function of the system composition.
相似文献
Jan C. T. Kwak (Corresponding author)Email: |
995.
The objective of this research is to explore the fundamental characteristics of how particles in wastewater respond to ultrasound, with an aim to improve wastewater disinfection. Particles of a predetermined size fraction and concentration were treated with varying doses of ultrasound at 20.3 kHz. Ultrasonic power transfer to the fluid was measured using calorimetry or acoustical measurements. Image analysis particle counting was used to measure the size distribution of particles before and after ultrasound treatment. The influence of three parameters: particle origin (raw wastewater or from the aeration basin of the activated sludge process), particle concentration, and particle size on the percentage of particle breakage after ultrasound treatment was compared. It was found that raw wastewater and aeration basin particles of the same size fraction (90-106 μm) responded to ultrasound in a similar way. Particle breakage was not affected by changes in particle concentration from 100 to 400 particles per mL. Larger wastewater particles (90-250 μm) were more susceptible to breakage than smaller ones (38-63 μm diameter). The percentage of particle breakage increased linearly with a logarithmic increase in the ultrasound energy density, that is the ultrasound energy delivered per unit volume of the sample (R2 = 0.48-0.91). An expression that predicts the percent of particles broken as a function of ultrasound energy density is provided. 相似文献
996.
Stephen Patterson Dr. Deuan C. Jones Dr. Emma J. Shanks Dr. Julie A. Frearson Prof. Ian H. Gilbert Prof. Paul G. Wyatt Prof. Alan H. Fairlamb Prof. 《ChemMedChem》2009,4(8):1341-1353
Thirty two analogues of phencyclidine were synthesised and tested as inhibitors of trypanothione reductase (TryR), a potential drug target in trypanosome and leishmania parasites. The lead compound BTCP ( 1 , 1‐(1‐benzo[b]thiophen‐2‐yl‐cyclohexyl) piperidine) was found to be a competitive inhibitor of the enzyme (Ki=1 μM ) and biologically active against bloodstream T. brucei (EC50=10 μM ), but with poor selectivity against mammalian MRC5 cells (EC50=29 μM ). Analogues with improved enzymatic and biological activity were obtained. The structure–activity relationships of this novel series are discussed. 相似文献
997.
John L. Richardson Dr. Isabelle R. E. Nett Dr. Deuan C. Jones Dr. Mohamed H. Abdille Ian H. Gilbert Prof. Alan H. Fairlamb Prof. 《ChemMedChem》2009,4(8):1333-1340
Trypanothione reductase (TryR) is a key validated enzyme in the trypanothione‐based redox metabolism of pathogenic trypanosomes and leishmania parasites. This system is absent in humans, being replaced with glutathione and glutathione reductase, and as such offers a target for selective inhibition. As part of a program to discover antiparasitic drugs, the LOPAC1280 library of 1266 compounds was screened against TryR and the top hits evaluated against glutathione reductase and T. brucei parasites. The top hits included a number of known tricyclic neuroleptic drugs along with other new scaffolds for TryR. Three novel druglike hits were identified and SAR studies on one of these using information from the tricyclic neuroleptic agents led to the discovery of a competitive inhibitor (Ki=330 nM ) with an improved potency against T. brucei (EC50=775 nM ). 相似文献
998.
Assessment of the In Vivo Toxicity of Gold Nanoparticles 总被引:1,自引:0,他引:1
The environmental impact of nanoparticles is evident; however, their toxicity due to their nanosize is rarely discussed. Gold
nanoparticles (GNPs) may serve as a promising model to address the size-dependent biological response to nanoparticles because
they show good biocompatibility and their size can be controlled with great precision during their chemical synthesis. Naked
GNPs ranging from 3 to 100 nm were injected intraperitoneally into BALB/C mice at a dose of 8 mg/kg/week. GNPs of 3, 5, 50,
and 100 nm did not show harmful effects; however, GNPs ranging from 8 to 37 nm induced severe sickness in mice. Mice injected
with GNPs in this range showed fatigue, loss of appetite, change of fur color, and weight loss. Starting from day 14, mice
in this group exhibited a camel-like back and crooked spine. The majority of mice in these groups died within 21 days. Injection
of 5 and 3 nm GNPs, however, did not induce sickness or lethality in mice. Pathological examination of the major organs of
the mice in the diseased groups indicated an increase of Kupffer cells in the liver, loss of structural integrity in the lungs,
and diffusion of white pulp in the spleen. The pathological abnormality was associated with the presence of gold particles
at the diseased sites, which were verified by ex vivo Coherent anti-Stoke Raman scattering microscopy. Modifying the surface
of the GNPs by incorporating immunogenic peptides ameliorated their toxicity. This reduction in the toxicity is associated
with an increase in the ability to induce antibody response. The toxicity of GNPs may be a fundamental determinant of the
environmental toxicity of nanoparticles. 相似文献
999.
The behaviour of composite cellular floor beams is becoming important as such members are increasingly used in multistorey
buildings. In the event of fire, this issue becomes increasingly critical, particularly for exposed steelwork. In a fire situation,
a composite beam has a much higher perimeter area exposed to fire in its lower web-flange section than in the upper web-flange
section, and so the temperature distribution across a composite beam is usually non-uniform. The reduction in fire of the
strength and stiffness of the material properties of the perforated steel beam, as well as differential thermal expansion,
therefore becomes an important influence on the overall behaviour of the composite beam. The objective of this research is
to enhance the level of understanding of the generic behaviour of composite cellular floor beams in fire conditions. In this
paper, three-dimensional nonlinear finite element models of composite cellular floor beams have been developed, taking into
consideration the influence of the changes in material properties with temperature. Experimental data from furnace tests on
cellular composite floor beams obtained from previous research work has been used to validate the FE models. An analytical
model based on existing design guides is also presented in this paper. It is concluded that finite element analysis results
are in good agreement with the experimental data, and all the failure modes have been accurately predicted. The proposed simplified
analytical methods show reasonable agreement with the test and FE results, and are always conservative. 相似文献
1000.
Component modelling of flexible end-plate connections in fire 总被引:2,自引:2,他引:0
This paper describes a component-based model for simulating the behaviour of flexible end-plate connections between beams and columns in steel framed structures in fire conditions. In this method, a simple steel connection was split into a number of active components for which mechanical properties are represented by non-linear springs. The behaviour of a steel connection is then determined by assembling the individual behaviour for each active component into a spring model. The component model presented in this paper is capable of predicting the behaviour of steel connections under varied loading conditions. It is also capable of predicting the tying resistance and critical components of failure for steel connections in fire. Compared with experimental test data, a good correlation with the simplified model has been achieved and this method, combined with finite element modelling, may be used to examine the performance of simple steel connections in fire conditions. 相似文献