全文获取类型
收费全文 | 10194篇 |
免费 | 763篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 48篇 |
综合类 | 2篇 |
化学工业 | 2690篇 |
金属工艺 | 122篇 |
机械仪表 | 190篇 |
建筑科学 | 341篇 |
矿业工程 | 16篇 |
能源动力 | 217篇 |
轻工业 | 2613篇 |
水利工程 | 109篇 |
石油天然气 | 51篇 |
无线电 | 393篇 |
一般工业技术 | 1399篇 |
冶金工业 | 1521篇 |
原子能技术 | 21篇 |
自动化技术 | 1231篇 |
出版年
2024年 | 23篇 |
2023年 | 124篇 |
2022年 | 373篇 |
2021年 | 472篇 |
2020年 | 290篇 |
2019年 | 326篇 |
2018年 | 400篇 |
2017年 | 401篇 |
2016年 | 460篇 |
2015年 | 346篇 |
2014年 | 484篇 |
2013年 | 825篇 |
2012年 | 693篇 |
2011年 | 716篇 |
2010年 | 535篇 |
2009年 | 532篇 |
2008年 | 475篇 |
2007年 | 438篇 |
2006年 | 273篇 |
2005年 | 225篇 |
2004年 | 221篇 |
2003年 | 170篇 |
2002年 | 175篇 |
2001年 | 114篇 |
2000年 | 107篇 |
1999年 | 125篇 |
1998年 | 562篇 |
1997年 | 312篇 |
1996年 | 209篇 |
1995年 | 107篇 |
1994年 | 91篇 |
1993年 | 85篇 |
1992年 | 23篇 |
1991年 | 15篇 |
1990年 | 15篇 |
1989年 | 27篇 |
1988年 | 28篇 |
1987年 | 23篇 |
1986年 | 16篇 |
1985年 | 25篇 |
1984年 | 13篇 |
1983年 | 4篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1979年 | 2篇 |
1978年 | 6篇 |
1977年 | 20篇 |
1976年 | 29篇 |
1970年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Andrés García Higuera Javier de las Morenas 《Journal of Intelligent Manufacturing》2014,25(5):1197-1206
Traditional management and control models can benefit from added levels of intelligence to increase their capability to adapt to the continuous changes in global markets. After reviewing the classical definition of intelligence and its levels, this paper provides a new approach to help increase the responsiveness of management and control to changes and disturbances in the manufacturing supply chain. The ancient concept of the “Tertium Quid” has inspired a three-level community of agents (MAS-TRIO) that is proposed to improve the coordination of all actors involved. The proposed model combines Multi-Agent Systems (MAS) with Radio-Frequency Identification (RFID) to make possible a certain level of Autonomous Intelligence in the decision-taking process. This paper analyses how these levels of intelligence can be applied to management and control, and the performance of the proposed model has been tested at low and mid-levels on an experimental platform representing the facilities of a distribution centre controlled by a network of programmable logic controllers (PLCs). 相似文献
92.
Tracy Q. Gardner Ana I. Flores Richard D. Noble John L. Falconer 《American Institute of Chemical Engineers》2002,48(6):1155-1167
A transient permeation method presented here not only determines the adsorption and diffusion properties of the pores that are the transport pathways through zeolite membranes, but nondestructively estimates the effective thickness of the membrane. Transient responses of the permeate concentration to step changes in the feed were measured on two H-ZSM-5 tubular membranes and modeled assuming Maxwell-Stefan diffusion and Langmuir adsorption. The adsorption isotherms determined from these transient measurements at 298 K of N2 and CO2 were nearly identical to those measured by calorimetry on H-ZSM-5 powders. The CH4 isotherm at 298 K was similar to isotherms measured by calorimetry and gravimetric techniques on Na-ZSM-5 and silicalite powders. The similarity of the isotherms indicates that transport of these light gases occurs mainly through zeolite pores. The Maxwell-Stefan diffusion coefficients DMS depended on concentration and were higher for higher feed partial pressures. Average DMS values for the two membranes were 7.5, 5 and 1.5×10−10 m2/s for N2, CH4, and CO2, respectively; these are in the same range and order as diffusion coefficients measured in zeolite crystals. 相似文献
93.
The high computation requirements of global optimization algorithms, when used to solve real optimization problems, have caused the appearance of different parallelization strategies using several parallel computing architectures. In this work, the Universal Evolutionary Global Optimizer is implemented in CUDA to be run on GPU architectures (GPuEGO). This parallelization of the referred evolutionary multimodal optimization algorithm is rather different from other previous parallel implementations designed to be executed into shared or distributed memory processors. In this case, due to the special characteristics of a GPU architecture, the original data structures are not valid and it has been necessary to redefine them and all the functions that operate with them. When this approach is applied the acceleration factors achieved by GPuEGO range from \({\times }\) 6.33 to \({\times }\) 23.20 depending on the test function. 相似文献
94.
Male rats maintained at 24 C and then shifted to 5 C for 5 days increased food intake and decreased in growth rate and food
conversion. No modification was observed in Δ6 desaturase activity, while Δ9 desaturase activity decreased after this period
of time. These results were confirmed by liver microsomal and mitochondrial fatty acid composition. The phospholipid composition
of liver microsomes was unaltered, whereas in mitochondria, phosphatidylcholine and sphingomyelin decreased and phosphatidylethanolamine
increased due to the cold environment. The influence of food intake and weight changes on fatty acid metabolism was studied
using (i) rats maintained at 5 C with restricted food intake to match the food intake of those kept at 24 C with food ad libitum
and (ii) rats maintained at 24 C whose food intake was also restricted so that their growth rate would be the same as that
of rats maintained at 5 C with food ad libitum, respectively. These results indicate that the negative metabolic balance state
of these cold conditions is not an active factor modifier of Δ6 desaturase activity, whereas it decreases Δ9 desaturase activity,
reflecting the lipogenic characteristics of the latter enzyme. 相似文献
95.
Lisbeth M Ottosen Ana T Lima Anne J Pedersen Alexandra B Ribeiro 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2006,81(4):553-559
The possibility of using fly ash from municipal solid waste incineration (MSWI) in, for example, concrete is considered. MSWI fly ash, however, has too high a concentration of heavy metals, which may cause leaching problems during use or problems with waste handling at the end of the lifetime of the concrete. The Cl content in MSWI fly ash is also too high and will cause corrosion problems in reinforced concrete. The possibility of removing some of the unwanted heavy metals (Cu and Pb) together with Cl from an MSWI fly ash suspended in water using an electrodialytic separation method was investigated. The removal of Pb and Cu was found to be highly pH dependent and the highest contents removed were 41 and 90%, respectively. The Cu concentration of the ash decreased from 2200 to 860 mg kg?1 but the Pb concentration increased from 8560 to 16 800 mg kg?1, showing that Pb is mainly found in the ash fraction that is least soluble. Hence electrodialytic treatment of the ash suspended in water is not a solution to improve the ash quality in terms of Pb. The water‐soluble Cl content per unit weight of the original ash was 12.4%. The removal of water‐soluble Cl was efficient and >98% of Cl was removed (calculated on the basis of mean initial and final concentrations). This result indicates that electrodialytic extraction may be a method that can be used for the removal of Cl from ash prior to its utilization in concrete. Copyright © 2006 Society of Chemical Industry 相似文献
96.
Aranzazu García M Victoria Ruiz-Méndez Concepción Romero Manuel Brenes 《Journal of the American Oil Chemists' Society》2006,83(2):159-164
By definition, virgin olive oil is consumed unrefined, although a great proportion of the olive oil produced has to be refined
to render it edible. Phenolic compounds are among the substances eliminated during the refining process; in the present work
these were characterized by HPLC, and their evolution during the different refining steps was studied. The complete refining
process removed most polyphenols from oils, but the behavior of individual compounds at each step also was observed. o-Diphenols
(hydroxytyrosol, catechol, and hydroxytyrosol acetate) and flavonoids (luteolin and apigenin) were eliminated first during
the alkaline treatment. Tyrosol and 4-ethylphenol remained in the oil until the deodorization step. A large amount of phenolic
compounds was discovered in the refining by-products such as soapstocks and deodorization distillates. In the latter streams,
the concentrations of tyrosol and 4-ethylphenol reached up to 149 and 3720 mg/kg by-product, respectively. This high level
of 4-ethylphenol and its well-known strong off-odor can interfere during further processing of the deodorization distillates,
and this must be taken into account when deciding what is to become of them. Similarly, the results of this work open the
possibility of recovering phenolic compounds from the “second centrifugation olive oils” by adding a new washing step prior
to the refining process. By including this new step, the most polar polyphenols, hydroxytyrosol and tyrosol, will diffuse
from oil to water and a concentration of up to 1400 mg/L of hydroxytyrosol may be achieved. 相似文献
97.
J. Linares-Pérez R. Caballero-Águila I. García-Garrido 《International journal of systems science》2014,45(7):1548-1562
This paper addresses the optimal least-squares linear estimation problem for a class of discrete-time stochastic systems with random parameter matrices and correlated additive noises. The system presents the following main features: (1) one-step correlated and cross-correlated random parameter matrices in the observation equation are assumed; (2) the process and measurement noises are one-step autocorrelated and two-step cross-correlated. Using an innovation approach and these correlation assumptions, a recursive algorithm with a simple computational procedure is derived for the optimal linear filter. As a significant application of the proposed results, the optimal recursive filtering problem in multi-sensor systems with missing measurements and random delays can be addressed. Numerical simulation examples are used to demonstrate the feasibility of the proposed filtering algorithm, which is also compared with other filters that have been proposed. 相似文献
98.
99.
The polymerization of α-methylstyrene (αMeSty) initiated by HI/I2 or HI in the presence of liquid sulfur dioxide has been investigated. The number-average molecular weight increased with
the monomer concentration for reactions initiated by the HI/I2 system. I2 also participates in the initiation process, increasing the number-average polymer chain at higher monomer concentration.
HI alone is also able to initiate the polymerization of αMeSty in the presence of SO2. With this initiator, transfer reaction can be minimized in systems containing low amount of SO2.
Received: 19 December 1996/Revised: 27 January 1997/Accepted 29 January 1997 相似文献
100.
M. Perez-Luna J.A. Toledo-Antonio F. Hernandez-Beltrán H. Armendariz A. García Borquez 《Catalysis Letters》2002,83(3-4):201-207
The effect of alumina and nickel in sulfated ZrO2 as a catalyst for n-butane isomerization was investigated. Samples were synthesized by supporting nickel sulfated zirconia on boehmite and then calcining the material. The crystalline structure of ZrO2 was studied by X-ray powder diffraction and refined by the Rietveld method. Surface areas were determined by N2 adsorption and BET analysis, while the acid properties were studied by NH3 adsorption. The chemical reaction was carried out in a fixed-bed microreactor at 338 K under atmospheric (78 kPa) or 245 kPa total pressure. Results showed that either nickel or alumina improved the catalytic activity, but a synergic effect was observed when both components assisted. The catalytic activity was related to the relative content of tetragonal zirconia and acid site density. Alumina stabilized tetragonal zirconia increased the acid site density and presumably led to a better dispersion of nickel oxide. The catalytic activity could be related to both oxidation and acid sites produced by nickel. A bimolecular reaction mechanism helps explain the observed trends. The increase in the reaction rate would be explained by the increase in the rate of the initial step of dehydrogenation either caused by a better dispersion of nickel or higher operating pressure. 相似文献