全文获取类型
收费全文 | 1780篇 |
免费 | 138篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 35篇 |
化学工业 | 467篇 |
金属工艺 | 45篇 |
机械仪表 | 69篇 |
建筑科学 | 49篇 |
矿业工程 | 3篇 |
能源动力 | 79篇 |
轻工业 | 327篇 |
水利工程 | 19篇 |
石油天然气 | 7篇 |
无线电 | 134篇 |
一般工业技术 | 311篇 |
冶金工业 | 154篇 |
原子能技术 | 14篇 |
自动化技术 | 208篇 |
出版年
2024年 | 5篇 |
2023年 | 18篇 |
2022年 | 70篇 |
2021年 | 105篇 |
2020年 | 63篇 |
2019年 | 56篇 |
2018年 | 81篇 |
2017年 | 89篇 |
2016年 | 71篇 |
2015年 | 61篇 |
2014年 | 89篇 |
2013年 | 128篇 |
2012年 | 130篇 |
2011年 | 123篇 |
2010年 | 92篇 |
2009年 | 90篇 |
2008年 | 84篇 |
2007年 | 70篇 |
2006年 | 80篇 |
2005年 | 47篇 |
2004年 | 41篇 |
2003年 | 29篇 |
2002年 | 30篇 |
2001年 | 16篇 |
2000年 | 11篇 |
1999年 | 20篇 |
1998年 | 42篇 |
1997年 | 35篇 |
1996年 | 30篇 |
1995年 | 17篇 |
1994年 | 17篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 13篇 |
1990年 | 14篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1974年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1921条查询结果,搜索用时 31 毫秒
61.
This paper focuses on the design of time-homogeneous fully observed Markov decision processes (MDPs), with finite state and action spaces. The main objective is to obtain policies that generate the maximal set of recurrent states, subject to convex constraints on the set of invariant probability mass functions. We propose a design method that relies on a finitely parametrized convex program inspired on principles of entropy maximization. A numerical example is provided to illustrate these ideas. 相似文献
62.
Lucas Oliveira Rodrigues Marcos Martins Gouvêa Flávia Ferreira de Carvalho Marques Samanta Cardozo Mourão 《Scientometrics》2017,110(3):1157-1171
In Brazil, the National Council for Scientific and Technological Development (CNPq) distributes productivity fellowships in research (RS) as a recognition to individuals with outstanding productivity levels in their areas. The aim of this study is to evaluate the scientific production of the Brazilian Pharmacy area, one division of the Health Sciences Great Area of CNPq, considering the profile and productivity levels of RS fellows. The results showed that most of the 156 active RS fellows in 2015 were female, with doctorate completed in the Southeast region (mainly in University of São Paulo) and with research activities developed in the South and Southeast regions. Most of their work was published in journals classified as B1 and B2 Qualis in Pharmacy by the Coordination for the Improvement of Higher Education Personnel (CAPES), with high prevalence of publications in local journals and/or specialized on medicinal plants. Besides, they featured much dependence on advising and productivity indexes related to the category and level of RS fellowship. The evolution of such data must be continually evaluated to determine the influence of CNPq productivity fellowships on performance and stratification of researchers in the Pharmacy area in Brazil. 相似文献
63.
Joana V. Barbosa Fernanda Oliveira Jorge Moniz Fern?o D. Magalh?es Margarida M. S. M. Bastos 《Journal of the American Oil Chemists' Society》2012,89(12):2215-2226
This work evaluated the use of allyl fatty acid esters derived from vegetable oil (palmitic acid, soybean and sunflower oils) as reactive coalescing agents in a waterborne latex system. Allyl fatty acid derivatives (AFAD) from vegetable oils were synthesized by two different processes. The synthesis was monitored by IR-spectroscopy and the final product characterized by FT-IR, GC–MS, 1H and 13C NMR. The presence of conjugated double bonds in the aliphatic chain was confirmed, which is a determinant for the proposed autoxidative latexes drying mechanism. Each of the AFAD were subsequently added to a standard acrylic emulsion, in order to study its potential as reactive coalescing agent. The minimum film-forming temperature (MFT), glass transition temperature (T g), drying time and rubbing resistance to solvents were evaluated. The results showed that, when added to water-borne acrylic resins, an AFAD acts as a non-volatile plasticizer capable of autoxidative crosslinking with itself. 相似文献
64.
Long‐term expansion of human induced pluripotent stem cells in a microcarrier‐based dynamic system
下载免费PDF全文
![点击此处可从《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
65.
Oscar L. Ramos Ricardo N. Pereira Artur Martins Rui Rodrigues Clara Fuciños José A. Teixeira 《Critical reviews in food science and nutrition》2017,57(7):1377-1393
Whey proteins are widely used as nutritional and functional ingredients in formulated foods because they are relatively inexpensive, generally recognized as safe (GRAS) ingredient, and possess important biological, physical, and chemical functionalities. Denaturation and aggregation behavior of these proteins is of particular relevance toward manufacture of novel nanostructures with a number of potential uses. When these processes are properly engineered and controlled, whey proteins may be formed into nanohydrogels, nanofibrils, or nanotubes and be used as carrier of bioactive compounds. This review intends to discuss the latest understandings of nanoscale phenomena of whey protein denaturation and aggregation that may contribute for the design of protein nanostructures. Whey protein aggregation and gelation pathways under different processing and environmental conditions such as microwave heating, high voltage, and moderate electrical fields, high pressure, temperature, pH, and ionic strength were critically assessed. Moreover, several potential applications of nanohydrogels, nanofibrils, and nanotubes for controlled release of nutraceutical compounds (e.g. probiotics, vitamins, antioxidants, and peptides) were also included. Controlling the size of protein networks at nanoscale through application of different processing and environmental conditions can open perspectives for development of nanostructures with new or improved functionalities for incorporation and release of nutraceuticals in food matrices. 相似文献
66.
V. B. Martins T. P. Nagasima L. T. F. Eleno C. G. Schön 《Journal of Phase Equilibria and Diffusion》2017,38(3):195-200
The Pb–Bi (Lead–Bismuth) binary system has gained some prominence in recent years due to the possible use of eutectic alloys as primary-circuit coolant in generation IV nuclear reactors. Apart from the terminal solid solutions A1-Pb and A7-Bi, the system presents also one intermetallic phase with the hexagonal close-packed structure (A3), usually denoted ε phase. Due to the low temperatures involved in this system, attainment of equilibrium is difficult, and in addition, the proximity of x-ray scattering factors for both elements raises questions about a possible polymorphic transition. In the present work, three samples with compositions Pb–29 wt.%Bi, Pb–31 wt.%Bi and Pb–33 wt.%Bi were prepared and characterized by x-ray diffraction. The lattice parameters of ε are consistent with those reported in the literature, and their dependence on Bi content was determined as well. Only the hexagonal phase was identified in the 29 wt.%Bi sample, although the currently assessed Pb–Bi phase diagram predicts the presence of the Pb-rich A1 terminal solid solution in this composition. A 2-year annealing at room temperature was performed and the XRD characterization results for these samples are compared with the original data. 相似文献
67.
A. J. Cavaleiro A. S. Ramos R. M. S. Martins C. Baetz M. T. Vieira F. M. Braz Fernandes 《Journal of Materials Engineering and Performance》2014,23(7):2446-2449
Joining shape-memory alloys (SMA) to other materials is strongly required in order to enlarge their fields of application. Fusion welding induces strong compositional and microstructural changes that significantly affect the shape-memory effect and the superelastic behavior of these alloys. The exothermic and in some cases self-propagating character of some nano-multilayer reactions is explored in this study as an alternative for joining SMA. To follow these very fast reactions, high brilliance sources, such as synchrotron radiation, are required. In situ high-resolution x-ray diffraction data, giving the phase evolution sequence with temperature of the Ni/Ti multilayer thin films under study, are presented. A correlation between the multilayer design and the tendency for the sequence of phase formation is established. 相似文献
68.
Alessandro C. Martins Lais BukmanAlexandro M.M. Vargas Érica O. BarizãoJuliana C.G. Moraes Jesuí V. VisentainerVitor C. Almeida 《Food chemistry》2013
This study proposes a FRAP assay adapted to FIA system with a merging zones configuration. The FIA system conditions were optimised with the response surface methodology using the central composite rotatable design. The optimisation parameters studied were: the carrier flow rate, the lengths of the sample and reagent loops, and reactor length. The conditions selected in accordance with the results were: carrier flow rate of 1.00 ml/min, length of the loops 18.2 cm and length of the reaction coil 210.1 cm. The detection and quantification limits were, respectively, 28.6 and 86.8 μmol/l Fe2+, and the precision was 1.27%. The proposed method had an analytical frequency of 30 samples/h and about 95% less volume of FRAP reagent was consumed. The FRAP assay adapted to the FIA system under the optimised conditions was utilised to determine the antioxidant activity of tea samples. 相似文献
69.
Rejane Martins Fernandes Canha Kenneth de Borja Jaguaribe Ana Lúcia Homce de Cresce El Debs Mounir Khalil El Debs 《Engineering Structures》2009,31(3):788-798
This paper presents a theoretical and experimental analysis of socket base connections of precast concrete structures with regard to the behavior of transverse walls. The experimental program included seven specimens, for which the type of interface in contact with cast-in-place concrete, the load eccentricities and the embedded lengths were all varied. A design model was proposed to calculate the reinforcements of the transverse walls. Based on the obtained results, some conclusions can be drawn: (a) The top of the transverse wall on the compression side of the smooth connections and the top of the two transverse walls of the rough connections are submitted to a bending-tension and this tension prevails on the bending; (b) The design model proposed for the calculation of the reinforcement of the transverse wall on the compression side provides the best prediction of the experimental results for all specimens when compared to the current design models; (c) For rough interfaces, the top of the transverse wall on the tension side is more requested than the top of transverse wall on the compression side; (d) The results of the proposed design model for the reinforcement of the transverse wall on the tension side of rough connections were in close agreement with the experimental results. 相似文献
70.
Simulated annealing (SA) is an optimization technique that can process cost functions with degrees of nonlinearities, discontinuities and stochasticity. It can process arbitrary boundary conditions and constraints imposed on these cost functions. The SA technique is applied to the problem of robot path planning. Three situations are considered here: the path is represented as a polyline; as a Bézier curve; and as a spline interpolated curve. In the proposed SA algorithm, the sensitivity of each continuous parameter is evaluated at each iteration increasing the number of accepted solutions. The sensitivity of each parameter is associated to its probability distribution in the definition of the next candidate. 相似文献