全文获取类型
收费全文 | 12819篇 |
免费 | 992篇 |
国内免费 | 19篇 |
学科分类
工业技术 | 13830篇 |
出版年
2024年 | 21篇 |
2023年 | 101篇 |
2022年 | 261篇 |
2021年 | 601篇 |
2020年 | 389篇 |
2019年 | 436篇 |
2018年 | 503篇 |
2017年 | 512篇 |
2016年 | 598篇 |
2015年 | 424篇 |
2014年 | 665篇 |
2013年 | 1113篇 |
2012年 | 880篇 |
2011年 | 1078篇 |
2010年 | 766篇 |
2009年 | 810篇 |
2008年 | 744篇 |
2007年 | 630篇 |
2006年 | 499篇 |
2005年 | 388篇 |
2004年 | 339篇 |
2003年 | 289篇 |
2002年 | 299篇 |
2001年 | 168篇 |
2000年 | 128篇 |
1999年 | 120篇 |
1998年 | 162篇 |
1997年 | 102篇 |
1996年 | 95篇 |
1995年 | 93篇 |
1994年 | 74篇 |
1993年 | 69篇 |
1992年 | 49篇 |
1991年 | 36篇 |
1990年 | 40篇 |
1989年 | 37篇 |
1988年 | 29篇 |
1987年 | 26篇 |
1986年 | 26篇 |
1985年 | 31篇 |
1984年 | 37篇 |
1983年 | 19篇 |
1982年 | 29篇 |
1981年 | 12篇 |
1980年 | 22篇 |
1979年 | 13篇 |
1978年 | 12篇 |
1977年 | 14篇 |
1976年 | 9篇 |
1975年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Conductive anodic filament (CAF) formation has been studied for a number of years, but the mechanism of its formation has
not previously been defined. In 2002, Ready identified CAF as atacamite, Cu2(OH)3Cl. Electrochemical studies have shown that both CuCl and CuCl2− participate in the formation of Cu2(OH)3Cl, with the predominating species being CuCl. This paper proposes a mechanism for CAF formation based on x-ray photoelectron
spectroscopy. The data show that CuCl is the precursor to the formation of Cu2(OH)3Cl in the presence of oxygen and water. Earlier, Meeker and Lu Valle had proposed that CAF failure is best represented by
two competing reactions: the formation of a copper chloride corrosion compound (now identified as Cu2(OH)3Cl) and the formation of innocuous trapped chlorine compounds. Since no evidence of any trapped chloride compounds has been
found, we propose that the formation of CAF is best represented by a single nonreversible reaction. 相似文献
992.
The Teleo-Reactive approach designed by N. J. Nilsson offers a high-level programming model for the development of reactive systems such as robotic vehicles. Teleo-Reactive programs are written in a way that allows engineers to define behaviour taking account of goals and changes in the state of the environment. Since Nilsson’s original definition, published in 1994, various researchers have used the Teleo-Reactive paradigm, either applied to a particular domain or extended by adding more capabilities to the original definition. This article provides a systematic literature review of 53 previous Teleo-Reactive-based studies in journals, conference proceedings and the like. The aim of this paper is to identify, appraise, select and synthesize all this high-quality research evidence relating to the use of the Teleo-Reactive paradigm. The literature has been systematically reviewed to offer an overview of the present state of this field of study and identify the principal results that have been obtained thanks to the Teleo-Reactive approach. Finally, this article details the challenges and difficulties that have to be overcome to ensure further advances in the use of this technique. 相似文献
993.
994.
Inaki Gandarias Sara G. Fernández Mohamed El Doukkali Jésus Requies Pedro Luis Arias 《Topics in Catalysis》2013,56(11):995-1007
Glycerol hydrogenolysis to propanediols requires the use of hydrogen as reactant. One interesting option is to directly generate this hydrogen in active sites of the support using hydrogen donors, such as formic acid. The effect that the reacting pressure has on glycerol conversion and product selectivity over a Ni–Cu/Al2O3 catalyst was studied. The negative effect of decreasing the pressure was much more significant when the source of hydrogen was dissolved molecular hydrogen than when it was formic acid. X-ray photoelectron spectroscopy and temperature programmed reduction measurements were performed to understand the effect of Ni–Cu/Al2O3 reduction procedure on the catalytic activity. Semi-batch reactor studies with the Ni–Cu/Al2O3 catalyst were carried out with continuous addition of the hydrogen donor to obtain kinetic data. Langmuir–Hinshelwood type models were developed to describe the direct conversion of glycerol into propanediol, and propanediol further hydrogenolysis to 1-propanol. The model included the competitive adsorption between both glycols. These models were used to obtain valuable data for the optimization of the process. 相似文献
995.
Antonio Luiz dos Santos Filho Francisco Javier Ramirez-Fernandez 《Engineering Applications of Artificial Intelligence》2010,23(2):169-176
This paper traces the development of a software tool, based on a combination of artificial neural networks (ANN) and a few process equations, aiming to serve as a backup operation instrument in the reference generation for real-time controllers of a steel tandem cold mill. By emulating the mathematical model responsible for generating presets under normal operational conditions, the system works as an option to maintain plant operation in the event of a failure in the processing unit that executes the mathematical model. The system, built from the production data collected over six years of plant operation, steered to the replacement of the former backup operation mode (based on a lookup table), which degraded both product quality and plant productivity. The study showed that ANN are appropriated tools for the intended purpose and that by this instrument it is possible to achieve nearly the totality of the presets needed by this kind of process. The text characterizes the problem, relates the investigated options to solve it, justifies the choice of the ANN approach, describes the methodology and system implementation and, finally, shows and discusses the attained results. 相似文献
996.
Emiliane Andrade Araújo Nélio José de Andrade Luis Henrique Mendes da Silva Antônio Fernandes de Carvalho Cleuber Antônio de Sá Silva Afonso Mota Ramos 《Food and Bioprocess Technology》2010,3(3):321-332
Bacteria and other microorganisms have a natural tendency to adhere to surfaces as a survival mechanism. This can occur in
many environments, including the living host, industrial systems, and natural waters. The general outcome of bacterial colonization
of a surface is biofilm formation, which consists of microorganisms immobilized in a variety of polymeric compounds generally
referred to as extracellular polymeric substances. Bacterial adhesion to a solid surface is a crucial step in the biofilm
process. This step is dependent upon van der Waals, electrostatic, and acid–base interactions. These interactions are influenced
by physicochemical properties of the substratum and the bacterial surface, such as hydrophobicity, surface charge, and electron
donor–electron acceptor properties. In addition, the roughness of the substratum and the microbiological characteristics of
the cell surface, such as cellular appendages and production of exopolysaccharides, can affect the adherence process. To date,
many strategies have been developed to decrease the adherence of bacteria to surfaces. Surface modification with the addition
of the suitable compounds makes surfaces less attractive for microorganisms and therefore prevents bacterial adherence and
biofilm formation. 相似文献
997.
Arantzazu Eiguren-Fernandez Edward L. Avol Suresh Thurairatnam Mahnaz Hakami John R. Froines Antonio H. Miguel 《Aerosol science and technology》2013,47(4):438-446
Ambient concentrations of 15 vapor-and particle-phase (PM 2.5 ) polycyclic aromatic hydrocarbons (PAHs), listed by the US EPA as priority pollutants, were measured between July 2002 and November 2003 in six Southern California communities participating in a multi-year chronic respiratory health study of schoolchildren. The communities were geographically distributed over two hundred kilometers, extending from Long Beach in coastal Los Angeles, to high mountain areas to the north and west of the Los Angeles basin, and south into Eastern San Diego County. Seasonal and spatial variation in the atmospheric concentrations of PAHs is of interest because this class of compounds includes potent mutagens, carcinogens, and species capable of generating reactive oxygen species (ROS) that may lead to oxidative stress. Naphthalene accounted for 95% of the total PAH mass; annual averages ranged from 89 to 142 ng m ? 3 . Benzo[ghi]perylene (BGP) and the pro-carcinogen benzo[a]pyrene (BAP), present almost exclusively in the particle-phase, ranged respectively from 38 to 231 pg m ?3 and 75 and 111 pg m ? 3 , with the highest values observed in Long Beach, a community with a high volume of seaport-related activities, and Lancaster, a commuter dormitory community. A considerable increase in the particle-phase PAH concentration, relative to the vapor-phase, was observed as ambient temperature decreased. Cold/hot season ratios for PAHs in PM 2.5 averaged 5.7, reaching 54 at Long Beach. The presented data underscore the importance of seasonal variations on atmospheric PAH concentrations. These observations are relevant to future interpretation and analysis of community-scale human health effects research. 相似文献
998.
Antonio H. Miguel Aarantzazu Eiguren-Fernandez Constantinos Sioutas Philip M. Fine Michael Geller Paul R. Mayo 《Aerosol science and technology》2013,47(5):415-418
Particle size distribution measurements of twelve USEPA priority pollutant polycyclic aromatic hydrocarbons (PAHs)—collected in Riverside, California, down to 10 nm aerodynamic diameter (Dp)—observed on integrated nocturnal samples (7:00 p.m.-6:30 a.m.) revealed that between 46 and 100% of the mass of particles in the Aitken size range was found in the 10–18 nm size bin. Particles in this size range have high alveolar deposition efficiency. 相似文献
999.
The present article studies the spatial and temporal behavior of the solutions to the initial boundary value problems associated with the linear theory of thermoelastic materials with voids. The spatial behavior is described by spatial estimates of Saint-Venant type (for bounded bodies) and Phragmén-Lindelöf type (for unbounded bodies) with time-dependent and time-independent rates. Some appropriate time-weighted integral measures are used. The temporal behavior is studied using the Cesaro means of various parts of the total energy. The relations describing the asymptotic behavior of the Cesaro means are established. 相似文献
1000.
Giorgio Schileo Luke Luisman Antonio Feteira Marco Deluca Klaus Reichmann 《Journal of the European Ceramic Society》2013,33(8):1457-1468
Ba1?xBixTi1?xYbx/2Fex/2O3 ceramics were fabricated by the solid state reaction method. X-ray diffraction analyses show 0 ≤ x ≤ 0.04 ceramics to have an average crystal structure described by the non-centrosymmetric tetragonal P4 mm space group, whereas x ≥ 0.08 ceramics are consistent with a centrosymmetric cubic perovskite (space group Pm-3 m). Coexistence of both tetragonal and cubic symmetries is observed for x = 0.06. Raman spectroscopy analysis corroborate a change in average structure with increasing x, but also show the local crystal symmetry for x ≥ 0.08 ceramics to deviate from the idealized cubic perovskite structure. Dielectric data show a ferroelectric-to-relaxor crossover, which occurs in conjunction with the change in both the average and local crystal symmetry as indicated by X-ray and Raman data. For x ≥ 0.08, ceramics exhibit relaxor behavior, which is also accompanied by a shift of the permittivity maxima towards higher temperatures with increasing x. 相似文献