全文获取类型
收费全文 | 851篇 |
免费 | 37篇 |
专业分类
电工技术 | 14篇 |
化学工业 | 260篇 |
金属工艺 | 24篇 |
机械仪表 | 17篇 |
建筑科学 | 38篇 |
能源动力 | 29篇 |
轻工业 | 87篇 |
水利工程 | 12篇 |
石油天然气 | 1篇 |
无线电 | 51篇 |
一般工业技术 | 200篇 |
冶金工业 | 33篇 |
原子能技术 | 4篇 |
自动化技术 | 118篇 |
出版年
2024年 | 4篇 |
2023年 | 7篇 |
2022年 | 28篇 |
2021年 | 32篇 |
2020年 | 23篇 |
2019年 | 22篇 |
2018年 | 29篇 |
2017年 | 24篇 |
2016年 | 26篇 |
2015年 | 23篇 |
2014年 | 40篇 |
2013年 | 65篇 |
2012年 | 52篇 |
2011年 | 55篇 |
2010年 | 41篇 |
2009年 | 41篇 |
2008年 | 48篇 |
2007年 | 40篇 |
2006年 | 29篇 |
2005年 | 32篇 |
2004年 | 37篇 |
2003年 | 19篇 |
2002年 | 17篇 |
2001年 | 8篇 |
2000年 | 16篇 |
1999年 | 8篇 |
1998年 | 12篇 |
1997年 | 12篇 |
1996年 | 11篇 |
1995年 | 10篇 |
1994年 | 5篇 |
1993年 | 12篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1987年 | 3篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1971年 | 4篇 |
1968年 | 1篇 |
排序方式: 共有888条查询结果,搜索用时 15 毫秒
831.
This paper summarizes results from an analytical and experimental study of the response to traffic loading of a glued-laminated timber bridge. A numerical model to simulate the passage of a vehicle over a bridge was developed. Calculated modal characteristics of an existing bridge were compared with results of ambient vibration and hammer impact testing. The analysis was used to simulate passages over the bridge of a three-axle vehicle, an empty logging truck, and results were compared with experimental data for such loading. The numerical model was then used to simulate the bridge response to a fully loaded logging truck. Results of these simulations were used to study dynamic amplification factors and to assess dynamic provisions of the new Canadian Highway Bridge Design Code. 相似文献
832.
Filippo Maggi Tomas Bílek Gloria Cristalli Fabrizio Papa Gianni Sagratini Sauro Vittori 《Journal of the science of food and agriculture》2009,89(14):2505-2518
BACKGROUND: Teucrium species (Lamiaceae) are interesting for the food industry since many of them are used in the preparation of flavoured wines and beers, herbal teas, bitters and liqueurs. On this basis, the analysis of the aroma components of Teucrium flavum L. subsp. flavum growing in central Italy was carried out by means of both hydrodistillation (HD) and headspace solid‐phase micro‐extraction (HS‐SPME), coupled with GC/FID and GC/MS. RESULTS: A total of 102 components were identified in the essential oils, representing 99.0‐99.3% of the total oils. Sesquiterpenes hydrocarbons constituted the major fraction (48.5–49.4%), with the apple‐like flavour (Z,E)‐α‐farnesene being the major component. HS‐SPME allowed the analysis of the volatiles not only emitted by specific plant parts, but also by different parts within a single flower: flower calyx afforded the highest contribution, in terms of volatiles, to the aroma of the plant. CONCLUSION: The chemical profile of the volatile fraction obtained by HD and HS‐SPME, demonstrated the plant fruit‐like aroma, confirming the usefulness for flavouring wines, bitters and other kind of beverages, and also suggested other applications, as aroma and taste enhancer in food processing. In particular, SPME resulted in a very useful technique, which permits a choice between the part of the plant which has the highest concentration of a specific fragrance, and therefore establishes the best way of sampling during industrial applications of aromatic plants. Copyright © 2009 Society of Chemical Industry 相似文献
833.
Kao TJ Saulnier GJ Isaacson D Szabo TL Newell JC 《IEEE transactions on bio-medical engineering》2008,55(11):2601-2607
834.
Henrik Pettersson Tadeusz Gruszecki Roman Bernhard Leif Hggman Mikhail Gorlov Gerrit Boschloo Tomas Edvinsson Lars Kloo Anders Hagfeldt 《Progress in Photovoltaics: Research and Applications》2007,15(2):113-121
A multicell is presented as a tool for testing material components in encapsulated dye‐sensitized solar cells. The multicell is based on a four‐layer monolithic cell structure and an industrial process technology. Each multicell plate includes 24 individual well‐encapsulated cells. A sulfur lamp corrected to the solar spectrum has been used to characterize the cells. Efficiencies up to 6·8% at a light‐intensity of 1000 W/msu2 (up to 7·5% at 250 W/m2) have been obtained with an electrolyte solution based on γ‐butyrolactone. Additionally, a promising long‐term stability at cell efficiencies close to 5% at 1000 W/m2 has been obtained with an electrolyte based on glutaronitrile. The reproducibility of the cell performance before and after exposure to accelerated testing has been high. This means that the multicell can be used as an efficient tool for comparative performance and stability tests. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
835.
Tomas Kohoutek Jiri Orava Tomas Wagner Martin Hrdlicka Milan Vlcek Miloslav Frumar 《Journal of Materials Science: Materials in Electronics》2009,20(Z1):346-350
We describe the preparation and optical properties of the 15-layer chalcogenide dielectric mirrors with the first order stop
bands in near infrared range. The high refractive index Sb–Se and low refractive index Ge–S layers were deposited on silicon
and glass substrates using thermal evaporation method. To centre the stop bands of the prepared chalcogenide mirrors at 1.55 μm,
the layer thicknesses, d(Sb–Se) = 117 and d(Ge–S) = 183 nm, were calculated from the quarter wave stack condition. The optical
reflectivity measurements revealed the total reflection from the 15-layer chalcogenide mirrors in the range of 1,400–1,600 nm
for the unpolarized light with normal incidence. The effect of annealing on the optical properties of the prepared chalcogenide
mirrors was studied as well. Using spectral ellipsometry, we examined the angular dependence of the multilayers reflectivity
for the light with s- and p-polarization. The preparation of the dielectric mirrors for near infrared region from chalcogenide
films seems to be possible exploiting good optical quality of chalcogenide films and their simple deposition. 相似文献
836.
Sandberg T Carlsson J Karlsson Ott M 《Journal of materials science. Materials in medicine》2009,20(2):621-631
Recently, we showed microscopically that bovine (BSM), porcine (PGM) and human (MG1) mucin coatings could suppress the adhesion
of neutrophils to a polyethylene terephthalate-based model biomaterial (Thermanox). Here, using the release of reactive oxygen
species (ROS) as a marker of material-induced neutrophil activation, the strong surface-passivating effects of these mucin
coatings were corroborated. Under optimal adsorption conditions, all mucin species performed equally well, thus indicating
a high degree of functional homology between the mucins. Cell adhesion and morphology correlated well with the release of
ROS. Quartz crystal microbalance (QCM-D) analysis linked low neutrophil activation to efficient mucin surface-shielding. Interestingly,
the shielding power appeared equal for thick expanded and thin compact mucin coatings. Combined mucin-serum coatings were
found to be highly surface-passivating. Particularly, since our data suggested partly synergistic mucin-serum action, we highlight
the possibility that pre-adsorbed mucins could provide favorable support for adsorbing host components. 相似文献
837.
Sofía Tomas Dols Francisco Javier Álvarez González Noelia Llorens Aleixandre Antonio Vidal-Infer María José Torrijo Rodrigo Juan Carlos Valderrama-Zurián 《Accident; analysis and prevention》2010,42(6):2024-2029
Background
Driving under the influence of alcohol and drugs has been identified as a risk factor for road traffic crashes. We have assessed the prevalence and predictor factors for driving after alcohol and drug use by adolescents.Methods
A cross-sectional survey involving 11,239 students aged 14–18 years from 252 private and public schools in the Valencia region of Spain was conducted. The prevalence and predictors of driving after alcohol use, alcohol and drug use, or drug use during the previous 6 months were measured.Results
Of the students who reported driving (20%), 45.1% indicated driving after alcohol and drug use. The consumption of various drugs was higher among students who drove a vehicle compared with those who did not. The likelihood of driving after consuming alcohol, or alcohol and drugs, increased in line with the number of standard drink units per week, reports of any lifetime alcohol- or drug-related problems, and poor family relationship. In addition, masculine gender and early alcohol use increased the likelihood of driving after consuming alcohol.Conclusions
Driving after alcohol and drug use is quite prevalent among adolescents in the Valencia region of Spain. There is a need for implementation of targeted policies for adolescents. This should focus on education and information on alcohol/drug use and driving. 相似文献838.
Roman Sotner Zdenek Hrubos Norbert Herencsar Jan Jerabek Tomas Dostal Kamil Vrba 《Circuits, Systems, and Signal Processing》2014,33(1):1-35
A new oscillator suitable for quadrature and multiphase signal generation is introduced in this contribution. A novel active element, called the controlled gain-buffered current and voltage amplifier (CG-BCVA) with electronic possibilities for current and voltage gain adjustment is implemented together with a controlled gain-current follower differential output buffered amplifier (CG-CFDOBA) for linear adjustment of the oscillation frequency and precise control of the oscillation condition in order to ensure a stable level of generated voltages and sufficient total harmonic distortion. The parameters of the oscillator are directly controllable electronically. Simultaneous changes of two current gains allow linear adjusting of the oscillation frequency, and a controllable voltage gain is intended to control the oscillation condition. A detailed comparison of the proposed circuits with recently developed and discovered solutions employing the same type of electronic control is provided and shows the useful features of the proposed oscillator and utilized methods of electronic control. Behavioral models based on commercially available ICs have been used for experimental purposes. CMOS implementation of active elements was introduced and utilized for additional simulations and studies. Non-ideal analysis, Monte Carlo statistical evaluations of simulated models, and further analyses were performed for the exact determination of the expected results. Laboratory experiments confirmed the workability and estimated behavior of the proposed circuit as well. 相似文献
839.
High-speed, high-resolution LC separations, using a poly(styrene-divinylbenzene) monolithic column, have been coupled to MALDI MS and MS/MS through an off-line continuous deposition interface. The LC eluent was mixed with alpha-cyano-4-hydroxycinnamic acid matrix solution and deposited on a MALDI plate that had been precoated with nitrocellulose. Deposition at subatmospheric pressure (80 Torr) formed a 250-microm-wide serpentine trace with uniform width and microcrystalline morphology. The deposited trace was then analyzed in the MS mode using a MALDI-TOF/TOF MS instrument. Continuous deposition allowed interrogation of the separation with a high data sampling rate in the chromatographic dimensions, thus preserving the high resolution of narrow peaks (3-5-s peak width at half-height) of the fast monolithic LC. No extracolumn band broadening due to the deposition process was observed. Over 2000 components were resolved in a 10-min linear gradient separation of the model sample, and 386 unique peptides were identified in the subsequent MS/MS analysis. The continuous deposition interface allows the coupling of high-resolution separations to MALDI MS without degradation in separation efficiency, thus enabling high-throughput proteome analysis. 相似文献
840.
Single aerosol particles of ethylene glycol and oleic acid are vaporized on a heater at temperatures between 500 and 700 K, and the resulting vapor plume is ionized by a 10.5-eV vacuum ultraviolet (VUV) laser. The mass spectra are compared to those obtained by CO2 laser vaporization followed by VUV laser ionization. The relative intensities of the parent and fragment ion peaks are remarkably similar for the two modes of vaporization. A Maxwell-Boltzmann distribution of speeds accurately describes the dependence of the signal as a function of the VUV laser pulse timing. The signal levels obtained with this design are sufficient to obtain good-quality mass spectra. 相似文献