全文获取类型
收费全文 | 2232篇 |
免费 | 63篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 23篇 |
化学工业 | 232篇 |
金属工艺 | 25篇 |
机械仪表 | 55篇 |
建筑科学 | 25篇 |
矿业工程 | 6篇 |
能源动力 | 32篇 |
轻工业 | 106篇 |
水利工程 | 5篇 |
石油天然气 | 15篇 |
无线电 | 73篇 |
一般工业技术 | 135篇 |
冶金工业 | 1468篇 |
原子能技术 | 8篇 |
自动化技术 | 92篇 |
出版年
2023年 | 8篇 |
2022年 | 17篇 |
2021年 | 33篇 |
2020年 | 27篇 |
2019年 | 31篇 |
2018年 | 30篇 |
2017年 | 42篇 |
2016年 | 35篇 |
2015年 | 24篇 |
2014年 | 31篇 |
2013年 | 81篇 |
2012年 | 44篇 |
2011年 | 40篇 |
2010年 | 52篇 |
2009年 | 57篇 |
2008年 | 39篇 |
2007年 | 28篇 |
2006年 | 33篇 |
2005年 | 26篇 |
2004年 | 23篇 |
2003年 | 15篇 |
2002年 | 21篇 |
2001年 | 12篇 |
2000年 | 12篇 |
1999年 | 48篇 |
1998年 | 419篇 |
1997年 | 251篇 |
1996年 | 187篇 |
1995年 | 88篇 |
1994年 | 82篇 |
1993年 | 76篇 |
1992年 | 27篇 |
1991年 | 30篇 |
1990年 | 25篇 |
1989年 | 12篇 |
1988年 | 18篇 |
1987年 | 24篇 |
1986年 | 17篇 |
1985年 | 15篇 |
1984年 | 1篇 |
1983年 | 8篇 |
1982年 | 14篇 |
1981年 | 15篇 |
1980年 | 13篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 52篇 |
1976年 | 110篇 |
1975年 | 2篇 |
1965年 | 1篇 |
排序方式: 共有2300条查询结果,搜索用时 812 毫秒
51.
E. Di Todaro C. T. O. F. Ruckert M. T. Milan W. W. Bose Filho J. R. Tarpani D. Spinelli 《Journal of Materials Engineering and Performance》2006,15(5):608-613
The main goal of this work was to evaluate the effectiveness of Walker’s equation in collapsing the fatigue crack propagation
data of a SAE AMS 7475-T7351 aluminum alloy loaded either longitudinally (L-T) or transversely (T-L) to the rolling direction.
T-L orientation testpieces presented lower ductility and fracture toughness values than L-T orientation. As a consequence,
during the fatigue crack propagation tests, T-L testpieces exhibited a stronger influence of monotonic modes of fracture,
resulting in higher Paris exponent values,m. Walker’s model was able to collapse fatigue crack propagation data of L-T test pieces at different applied stress ratios,R. However, for the T-L orientation, due to theR ratio dependency onm andC, simply averaging ofm values for the calculations of Walker’s exponent proved to be inefficient. A simple analytical procedure was proposed by
the authors to modify Walker’s model to take into account such effect. For T-L test pieces, when Walker’s model is modified
by considering both Paris’s exponent as well the coefficient as a function of theR ratio, the fatigue crack growth data collapses within a narrow band, thus allowing predictions to be made satisfactorily.
The collapsed band is even narrower if the empirical relationm=a+blogC is used instead of simple polynomial equations due to a better correlation coefficient. 相似文献
52.
Joo Batista A. Silva Regina C. M. de Paula Judith P. A. Feitosa Eduardo Diogo Gurgel‐Filho Claudio Maniglia‐Ferreira Francisco Jose de Souza Filho 《应用聚合物科学杂志》2006,100(5):4082-4088
Gutta‐percha cone is the most widely used material for root canal filling. The in vivo aging of this cone focus on the degradation of its main organic component, trans‐1,4‐polyisoprene, was studied. Aged cones (25 samples) from 2 to 30 years of root canal filling were extracted from different patients in the occasion of retreatment by mechanical way. The information about the aging time was given by the patients. Gel‐permeation chromatography (GPC) and infrared spectroscopy (FTIR) were the analytical techniques used. Polyisoprene degrades with time of aging, but in a slow process. Decrease in polymer molar mass from 5.7 × 105 to 1.7 × 105 g/mol was observed in polyisoprene from cone after 30 years of root canal filling and inside a noninfected tooth. In tooth with caries and periodontal infection, the decrease in molar mass is higher (4.6 × 104 g/mol in cone with 10 years of aging). The production of carbonyl and hydroxyl groups in the aged material indicates that the process is oxidative, even in closed teeth. In these cases, the oxygen could be provided from tissue fluid. The degradation mechanism is complex and depends on many factors, besides time of root canal filling. The dental problem caused by the aging could be the production and migration of cytotoxic substances to periodontal ligament and the reduction on the canal sealing property due to the polymer weight loss. Both of them could contribute to the root canal treatment failure. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100:4082–4088, 2006 相似文献
53.
We present implementations of the numerical integration of systems with long-range interactions on graphic processing units for three N-body models with long-range interactions of general interest: the Hamiltonian Mean Field, Ring and two-dimensional self-gravitating models. We discuss the algorithms, speedups and errors using one and two GPU units. Speedups can be as high as 140 compared to a serial code, and the overall relative error in the total energy is of the same order of magnitude as for the CPU code. The number of particles used in the tests range from 10,000 to 50,000,000 depending on the model. 相似文献
54.
Sorption and diffusion of dichloromethane vapor were measured in atactic polystyrene films, obtained with different cooling conditions and after controlled aging times at different temperatures. The diffusional behavior is characterized by three zones, depending on temperature and penetrant activity. In Zone I, at low activity, the diffusion coefficient is independent of vapor concentration; Zone II is characterized by concentration-dependent diffusion, whereas in Zone III structural transformations are possible. The study of diffusion at three temperatures allowed building of a temperature-penetrant concentration diagram, which is very useful to visualize the different zones of behavior. The aging at room temperature has no effect on the curve of sorption as a function of vapor activity, whereas it determines two effects on the diffusion: a decrease of the zero concentration diffusion coefficient and a more and more anomalous behavior with the aging time. The aging at 70°C produces the same effects on the diffusion behavior as the aging at room temperature; in addition, a decrease sorption is observed at low penetrant activity. The possible presence of ordered domains, impermeable to the vapor, in the samples stored at 70°C, was suggested on the basis of sorption results. 相似文献
55.
Guimes Rodrigues Filho Leandra Cardoso Toledo Daniel Alves Cerqueira Rosana Maria Nascimento de Assunção Carla da Silva Meireles Harumi Otaguro Sizue Ota Rogero Ademar Benévolo Lugão 《Polymer Bulletin》2007,59(1):73-81
Summary In this article, cellulose acetate produced through the homogeneous acetylation of sugar cane bagasse cellulose was used to
produce membranes, using poly(ethyleneglycol) 600 (PEG 600) as an admixture. The membranes were characterized using water
flux measurements (Payne’s cup), differential scanning calorimetry (DSC) and neutral red uptake (cytotoxicity). The results
showed that PEG 600 acts as a crystallinity inductor and/or pore former in the cellulose acetate matrix. The induction of
crystallinity is important for this system since it had not been reported on the literature yet. The results also demonstrated
that the studied membranes present a nontoxic behavior. 相似文献
56.
The mathematical optimisation of a batch cooling crystallization process is considered in this work. The objective is to minimize the standard deviation of the final crystal size distribution (CSD), which is an important feature in many industrial processes. The results with the problem written as a nonlinear programming and solved with the successive quadratic programming (SQP) coupled with the discretization of the control variable are compared with those obtained when SQP coupled with the parameterisation of the control variable is applied. Also it is proposed the implementation of the genetic algorithm (GA) coupled with parameterisation of the control variable. Extensive evaluations show that the SQP method is sensitive both to the parameterisation formulation and to the initial estimate. The solution with GA provided the control variable profile that leads to the minimum standard deviation of the final CSD. Nevertheless, it is a very time-consuming technique, which hampers its utilization in real time applications. However, its feature of global searching suggests its suitability in solving offline problems, in order to provide initial setup profiles. Bearing this in mind, it is proposed an algorithm which allows for the implementation of GA solution in a real time fashion, taking advantage of its robustness to find out the optimal solution. 相似文献
57.
R.D. Toledo Filho J.P. Gonçalves E.M.R. Fairbairn 《Cement and Concrete Research》2007,37(9):1357-1365
The Brazilian ceramic industry generates large amounts of calcined-clay waste. This paper examines the factors that influence its potential for use as a partial replacement of Portland cement. Superplasticized mortars of equal workability containing ground crushed waste calcined-clay brick (GCWCCB) in the proportions of 10, 20, 30 and 40% as a cement replacement were analyzed through mechanical tests, pore structure characterization and durability tests. The results indicated the optimal percentages of substitution lies between 10% to 20%. The potential reduction of CO2 emissions could be as high as 10% of current Brazilian cement industry emissions if this approach were to be fully implemented, and it could be eligible for “Clean Development Mechanism” credits under Kyoto protocol. 相似文献
58.
Delba N.C. Melo Eduardo C. Vasco De Toledo Marcela M. Santos Salah D.M. Hasan Maria Regina Wolf Maciel Rubens Maciel Filho 《Computers & Chemical Engineering》2005,29(11-12):2485
In order to develop and test the integration procedure, in this paper a real time process integration involving the optimization and control of the process is presented, in this case, with the two-layer approach. The used optimization algorithms were Levenberg–Marquardt and SQP that solve a non-linear least square problem subject to bounds on the variables. The two-layer approach is a hierarchical control structure where an optimization layer calculates the set points and manipulated variables to the advanced controller, which is based on the dynamic matrix control with constraints (QDMC). The non-isothermal dynamic model of the three-phase slurry catalytic reactor with appropriate solution procedure was utilized in this work (Vasco de Toledo, E. C., Santana, P. L., Maciel, M. R. W., & Maciel Filho, R. (2001). Dynamic modeling of a three-phase catalytic slurry reactor. Chemical Engineering Science, 56, 6055–6061). The model consists on mass and heat balance equations for the catalyst particles as well as for the bulk phases of gas and liquid. The model was used to describe the dynamic behavior of hydrogenation reaction of o-cresol to obtain 2-methil-cyclohexanol, in the presence of a catalyst Ni/SiO2. 相似文献
59.
Cláudio de Almeida Filho 《Carbon》2006,44(14):2869-2876
Disordered carbon materials with high porosity were prepared through the pyrolysis of TiO2/poly(furfuryl alcohol) composites, obtained by the sol-gel method. The composites were prepared starting from titanium tetra-isopropoxide (TTIP) and furfuryl alcohol (FA) as precursors. Two different synthetic procedures for our composites were carried out, based on the addition of furfuryl alcohol (FA) before or after the TiO2 nanoparticles formation. Also, different TTIP/FA ratio was tested. The hybrid materials obtained by both synthetic routes were pyrolyzed, under argon flow, at 900 °C producing novel TiO2/carbon composites. All samples were characterized by XRD, FT-IR, DR-FTIR, Raman spectroscopy and TEM. Results indicated the effective FA polymerization on TiO2 (anatase) nanoparticles, and polymer conversion to disordered carbon after the pyrolysis, simultaneously with TiO2 anatase-rutile phase transition. The resulting TiO2/carbon composites were treated with HF solution aiming the oxide dissolution, yielding an extremely porous carbon material as insoluble fraction. The morphology of these porous carbon materials is strongly dependent on the synthetic route adopted for the composite precursor, varying from carbon foam to highly ordered hollow microspheres. 相似文献
60.
In this paper we study the unconfined potential steady flow through a porous media with semipermeable bottom. We propose a
model that leads to a free boundary-value-problem with complementarities conditions on the bottom. The shape of a part of
the domain boundary, called free boundary, is one of the unknown of the problem. The pressure of the flow as well as the flow
velocity on the another part of the boundary, that is a one way permeable bottom, are also unknowns and satisfy a complementarity
condition. We present the numerical implementation of the model based on an optimization approach. Performing a boundary-element
discretization we get a nonlinear mathematical programming problem with complementarities conditions. To solve it we use Herskovits’s
interior point algorithm. Numerical examples are presented. 相似文献