全文获取类型
收费全文 | 1949篇 |
免费 | 125篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 27篇 |
综合类 | 7篇 |
化学工业 | 314篇 |
金属工艺 | 57篇 |
机械仪表 | 43篇 |
建筑科学 | 35篇 |
矿业工程 | 5篇 |
能源动力 | 31篇 |
轻工业 | 177篇 |
水利工程 | 12篇 |
石油天然气 | 1篇 |
无线电 | 147篇 |
一般工业技术 | 408篇 |
冶金工业 | 533篇 |
原子能技术 | 5篇 |
自动化技术 | 273篇 |
出版年
2023年 | 25篇 |
2022年 | 5篇 |
2021年 | 39篇 |
2020年 | 47篇 |
2019年 | 35篇 |
2018年 | 64篇 |
2017年 | 49篇 |
2016年 | 65篇 |
2015年 | 43篇 |
2014年 | 69篇 |
2013年 | 105篇 |
2012年 | 97篇 |
2011年 | 110篇 |
2010年 | 69篇 |
2009年 | 83篇 |
2008年 | 80篇 |
2007年 | 80篇 |
2006年 | 55篇 |
2005年 | 37篇 |
2004年 | 44篇 |
2003年 | 36篇 |
2002年 | 20篇 |
2001年 | 42篇 |
2000年 | 18篇 |
1999年 | 46篇 |
1998年 | 154篇 |
1997年 | 100篇 |
1996年 | 69篇 |
1995年 | 40篇 |
1994年 | 32篇 |
1993年 | 35篇 |
1992年 | 9篇 |
1991年 | 20篇 |
1990年 | 13篇 |
1989年 | 19篇 |
1988年 | 14篇 |
1987年 | 17篇 |
1986年 | 7篇 |
1985年 | 20篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 11篇 |
1976年 | 35篇 |
1959年 | 4篇 |
1932年 | 4篇 |
排序方式: 共有2075条查询结果,搜索用时 109 毫秒
81.
Listeriosis is a foodborne disease caused by the bacterium Listeria monocytogenes. The food industry and government agencies devote considerable resources to reducing contamination of ready-to-eat foods with L. monocytogenes. Because inactivation treatments can effectively eliminate L. monocytogenes present on raw materials, postprocessing cross-contamination from the processing plant environment appears to be responsible for most L. monocytogenes food contamination events. An improved understanding of cross-contamination pathways is critical to preventing L. monocytogenes contamination. Therefore, a plant-specific mathematical model of L. monocytogenes cross-contamination was developed, which described the transmission of L. monocytogenes contamination among food, food contact surfaces, employees' gloves, and the environment. A smoked fish processing plant was used as a model system. The model estimated that 10.7% (5th and 95th percentile, 0.05% and 22.3%, respectively) of food products in a lot are likely to be contaminated with L. monocytogenes. Sensitivity analysis identified the most significant input parameters as the frequency with which employees' gloves contact food and food contact surfaces, and the frequency of changing gloves. Scenario analysis indicated that the greatest reduction of the within-lot prevalence of contaminated food products can be achieved if the raw material entering the plant is free of contamination. Zero contamination of food products in a lot was possible but rare. This model could be used in a risk assessment to quantify the potential public health benefits of in-plant control strategies to reduce cross-contamination. 相似文献
82.
Produktschonende Betriebs‐ und Designparameter von Wärmeübertragern für temperaturempfindliche Prozessströme
下载免费PDF全文
![点击此处可从《化学,工程师,技术》网站下载免费的PDF全文](/ch/ext_images/free.gif)
To allow the calculation of product degradation rates as extension to the currently used thermotechnical design calculations for heat exchangers, a volume‐related, reaction‐kinetic approach was developed. Therefore, a model system was selected and the product protection design parameters were determined for a lab‐scale heat exchanger with the help of simulations. The validation was demonstrated in an experiment. Additionally, the product‐protecting operating parameters for the heat exchanger were calculated with a technically relevant set of compounds. 相似文献
83.
B. Svecova P. Nekvindova A. Mackova J. Oswald J. Vacik R. Grötzschel J. Spirkova 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2009,267(8-9):1332-1335
Erbium-doped lithium niobate (Er:LiNbO3) is a prospective photonics component, operating at 1.5 μm, which could find its use chiefly as an optical amplifier or waveguide laser. In this study, we have focused on the properties of the optically active Er:LiNbO3 layers, which are fabricated by medium energy ion implantation under various experimental conditions. Erbium ions were implanted at energies of 330 and 500 keV with fluences of 1.0 × 1015, 2.5 × 1015 and 1.0 × 1016 cm?2 into LiNbO3 single-crystalline cuts of various orientations. The as-implanted samples were annealed in air at 350 °C for 5 h. The depth distribution and diffusion profiles of the implanted Er were measured by Rutherford Backscattering Spectroscopy (RBS) using 2 MeV He+ ions. The projected range RP and projected range straggling ΔRP were calculated employing the SRIM code. The damage distribution and structural changes were described using the RBS/channelling method. Changes of the lithium concentration depth distribution were studied by Neutron Depth Profiling (NDP). The photoluminescence spectra of the samples were measured to determine whether the emission was in the desired region of 1.5 μm. The obtained data made it possible to reveal the relations between the structural changes of erbium-implanted lithium niobate and its luminescence properties important for photonics applications. 相似文献
84.
β-Fur-2-yl-α-halogenacrylonitriles. V. Preparation of β-(5-Nitro-fur-2-yl)-α-azidoacrylonitrile and β-(5-Nitro-fur-2-yl)-α-aminoacrylonitrile β-(5-Nitro-fur-2-yl)-α-chloroacrylonitrile ( 1 ) reacts with sodium azide to yield β-(5-nitro-fur-2-yl)-α-azidoacrylonitrile ( 2 ). By Staudinger-reaction β-(5-nitro-fur-2-yl)-α-aminoacrylonitrile ( 5 ) is formed. The 1H- and 13C-n.m.r. spectra of E/Z isomers are discussed. 相似文献
85.
Ute Förster Katharina Lommel Daniel Sauter Christian Grünewald Joachim W. Engels Prof. Dr. Josef Wachtveitl Prof. Dr. 《Chembiochem : a European journal of chemical biology》2010,11(5):664-672
A series of short RNA duplexes containing one or two 1‐ethynylpyrene‐modified adenine bases was synthesised. The melting behaviour of these duplexes was examined by monitoring temperature‐dependent pyrene fluorescence. In the singly modified RNA duplexes, the bases flanking the ethynylpyrene‐rA were varied to examine the sequence specificity of the fluorescence change of pyrene upon RNA hybridisation. Because an increase in pyrene fluorescence upon melting of the duplex can be correlated with intercalation of pyrene, and a decrease is usually associated with the position of pyrene outside the strand, a relationship between the flanking bases and the tendency of the dye to intercalate has been established. It was found that pyrene intercalation is less likely to take place if the modified base is flanked only by A–U base pairs. Flanking G–C base pairs, even only in the 5′‐direction of the modified base, will favour intercalation. In addition, we examined a doubly modified compound that had a pyrene located on each strand. The spectra indicated that the two pyrenes were close enough for interaction. Upon melting of the strand, a fluorescence blue shift corresponding to the dissociation of the pyrene–pyrene complex could be observed in addition to the intensity effect already known from the singly modified compounds. Two melting curves based on the different properties of the fluorophore could be extracted, leading to different melting points corresponding to the global duplex melting and to the change of local pyrene environment, respectively. 相似文献
86.
J. M. N. Silva J. F. C. L. Cadima J. M. C. Pereira J.-M. Grégoire 《International journal of remote sensing》2013,34(22):4889-4913
The possibility of using the Syst@me Probatoire de l'Observation de la Terre (SPOT)-VEGETATION (VGT) data for global burned area mapping with a single algorithm was investigated. Using VGT images from south-eastern Africa, the Iberian Peninsula and south-eastern Siberia/north-eastern China, we analysed the variability of the spectral signature of burned areas and its relationship with land cover, and performed the selection of the best variables for burned area mapping. The results show that in grasslands and croplands, near-infrared (NIR) and short-wave infrared (SWIR) reflectance always decreases as a result of fire. In forests and woodlands, there may occur a simultaneous decrease of SWIR and NIR or an increase of SWIR and a decrease of NIR. Burning of green vegetation (high values of the Normalized Difference Vegetation Index (NDVI)) tends to result in an increase of the SWIR. The best variables for burned area mapping are different in each region. Only the NIR allows a good discrimination of burned areas in all study areas. We derived a logistic regression model for multi-temporal burned area mapping in tropical, temperate and boreal regions, which handles the spectral variability of burned areas dependent on the type of vegetation. The results underline the feasibility of a single model for global burned area mapping. 相似文献
87.
David Conciatori Étienne Grégoire Éric Samson Jacques Marchand Luc Chouinard 《Materials and Structures》2014,47(1-2):89-103
Results of a statistical analysis of transport properties measurements carried out on a number of concrete mixtures are presented. Migration and drying experiments were performed to evaluate the ionic diffusion coefficients and permeability of concrete mixtures. Seven concrete mixtures were tested. The mixtures were either batched under laboratory conditions or sampled from construction sites. For each mixture, approximately eighty concrete samples from a single batch were tested. Ionic diffusion coefficients were calculated by analyzing the evolution of the electrical current passing through concrete samples during the migration tests. Calculations took into account the volume of permeable pores of the materials and the pore solution chemistry. Permeability was calculated from mass loss measured during drying tests. The study indicates that the coefficient of variation of ionic diffusion coefficients is 11.1 % on average, with a maximum of 23.5 %, and that the coefficient of variation of permeability is 20.6 % on average, with a maximum of 37.3 %. 相似文献
88.
Salvatore Ventre Flavio Calvano Grégoire Pichenot Pierre Calmon Antonello Tamburrino 《NDT & E International》2011,44(4):376-386
This paper is focused on the Eddy Current Testing (ECT) method applied to important industrial applications such as the inspection of tubes in nuclear power plants and the inspection of planar surface from aeronautical industry. Specifically, we consider the prediction of the signatures produced by small defects through two fully three-dimensional numerical models developed for ECT. In particular we consider the responses to small defects described in two experimental benchmarks from nuclear power industry and one experimental benchmark from aeronautical applications. Despite of the small size of the defects that, in some cases, is of the order of few millimetres, the numerical models reproduce correctly the experimental responses provided in the benchmarks, including the challenging case of a defect (in a tube) close to the support plate. 相似文献
89.
90.