首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   425篇
  免费   47篇
电工技术   9篇
化学工业   88篇
金属工艺   4篇
机械仪表   17篇
建筑科学   31篇
能源动力   62篇
轻工业   29篇
水利工程   1篇
无线电   33篇
一般工业技术   94篇
冶金工业   24篇
原子能技术   11篇
自动化技术   69篇
  2024年   1篇
  2023年   13篇
  2022年   11篇
  2021年   18篇
  2020年   15篇
  2019年   11篇
  2018年   15篇
  2017年   15篇
  2016年   22篇
  2015年   11篇
  2014年   22篇
  2013年   34篇
  2012年   29篇
  2011年   44篇
  2010年   27篇
  2009年   27篇
  2008年   38篇
  2007年   23篇
  2006年   15篇
  2005年   11篇
  2004年   9篇
  2003年   12篇
  2002年   5篇
  2001年   5篇
  2000年   5篇
  1999年   2篇
  1998年   4篇
  1997年   1篇
  1996年   1篇
  1995年   1篇
  1994年   2篇
  1993年   1篇
  1992年   1篇
  1991年   3篇
  1989年   2篇
  1988年   1篇
  1987年   2篇
  1986年   4篇
  1984年   1篇
  1983年   1篇
  1982年   2篇
  1981年   2篇
  1977年   2篇
  1976年   1篇
排序方式: 共有472条查询结果,搜索用时 15 毫秒
101.
102.
For electrical machines, accurate position estimations at low speed can be obtained from current responses on high-frequency voltage test pulses. Nevertheless, to apply these voltage test pulses the current controller is often interrupted. In this paper, a modified test pulse sequence is discussed for which the current can be controlled without interruption. To generate the modified test pulse sequence, an asymmetric pulse-width modulator is required. The improvement in the dynamic behaviour of the sensorless drive is discussed by simulations including a salient-pole permanent-magnet synchronous machine, the current control loop, the pulse-width modulator and the position estimator.  相似文献   
103.
104.
105.
Small molecule organic solar cells were studied with respect to water and oxygen induced degradation by mapping the spatial distribution of reaction products in order to elucidate the degradation patterns and failure mechanisms. The active layers consist of a 30 nm bulk heterojunction formed by the donor material zinc-phthalocyanine (ZnPc) and the acceptor material Buckminsterfullerene (C60) followed by 30 nm C60 for additional absorption. The active layers are sandwiched between 6 nm 4,7-diphenyl-1,10-phenanthroline (Bphen) and 30 nm N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine p-doped with C60F36 (MeO-TPD:C60F36), which acted as hole transporting layer. Indium-tin-oxide (ITO) and aluminum served as hole and electron collecting electrode, respectively. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS) in conjunction with isotopic labeling using H218O and 18O2 provided information on where and to what extent the atmosphere had reacted with the device. A comparison was made between the use of a humid (oxygen free) atmosphere, a dry oxygen atmosphere, and a dry (oxygen free) nitrogen atmosphere during testing of devices that were kept in the dark and devices that were subjected to illumination under simulated sunlight. It was found that water significantly causes the device to degrade. The two most significant degradation mechanisms are diffusion of water through the aluminum electrode resulting in massive formation of aluminum oxide at the BPhen/Al interface, and diffusion of water into the ZnPc:C60 layer where ZnPc becomes oxidized. Finally, diffusion from the electrodes was found to have no or a negligible effect on the device lifetime.  相似文献   
106.
Bimodal cellular poly(methyl methacrylate) with micro‐ and nano‐sized (300–500 nm) cells with up to 5 wt% of sepiolite nanoparticles and porosity from 50% to 75% are produced by solid‐state foaming. Uniaxial compression tests are performed to measure the effect of sepiolite concentration on the elastic modulus and the yield strength of the solid and cellular nanocomposites. Single edge notch bend tests are conducted to relate the fracture toughness of the solid and cellular nanocomposites to sepiolite concentration. The relative modulus is independent of sepiolite content to within material scatter when considering the complete porosity range. In contrast, a mild enhancement of the relative modulus is observed by the addition of sepiolite particles for the foamed nanocomposites with a porosity close to 50%. The relative compressive strength of the cellular nanocomposites mildly decreases as a function of sepiolite concentration. A strong enhancement of the relative fracture toughness by the addition of sepiolites is observed. The enhancement of the relative fracture toughness and the relative modulus (at 50% porosity) can be attributed to an improved dispersion of the particles due to foaming and the migration of micro‐sized aggregates from the solid phase to the microcellular pores during foaming.  相似文献   
107.
A technique has been developed for the autoradiographic localization of steroids in testes at the light and possibly electron microscope level. During processing of the tissue there is no contact of tissue with water up to the moment of photographic development of the autoradiographs. Tritium labelled steroids have been introduced into the testis through perfusion of the isolated organ. Small tissue samples were rapidly frozen, freeze dried and fixed with osmium vapour. The fixed tissue was embedded in Epon and thin sections could be cut from this material on an ultra-cryotome without the aid of floatation liquids. Results with light microscopic autoradiography indicate the potential of this technique. This procedure which avoids any contact of the tissue with water offers good prospects for autoradiography of steroids and other soluble compounds at the electron microscope level. A comparison is made with other proposed techniques for steroid autoradiography.  相似文献   
108.
Five different indium‐tin‐oxide free (ITO‐free) polymer solar cell architectures provided by four participating research institutions that all presented a laboratory cell performance sufficient for use in mobile and information and communication technology (ICT) were evaluated based on photovoltaic performance and lifetime tests according to the ISOS protocols. The comparison of the different device architectures was performed using the same active material (P3HT: PCBM) and tested against an ITO‐based reference device. The active area was 1 cm2 and rigid glass or flexible polyester substrates were employed. The performance results were corroborated by use of a round robin methodology between the four participating laboratories (DTU/DK, ECN/NL, Frauenhofer ISE/DE, and the Holst Centre/NL), while the lifetime testing experiments were carried out in only one location (DTU). Five different lifetime testing experiments were carried out for a minimum of 1000 h: (1) shelf life (according to ISOS‐D‐1); (2–3) stability under continuous 1 sun illumination (1000 Wm?2, AM1.5G) at low (37 ± 3°C) and high (80 ± 5°C) temperatures (according to ISOS‐L‐1 and ISOS‐L‐2); (4) stability under continuous low‐light conditions at 0.1 sun (100 Wm?2, AM1.5G, 32°C) (according to ISOS‐LL); (5) continuous illumination (670 Wm?2, AM1.5G) at high temperature (65°C) and high humidity (50% RH) (according to ISOS‐L‐3). Finally, the upscaling compatibility of these device architectures based on the device photovoltaic behavior, stability and scalability were identified and we confirm that an architecture that presents a high score in only one aspect of the solar cell performance is not sufficient to justify an investment in upscaling. Many will require further technical development. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 944‐954, 2013  相似文献   
109.
Ozonation of natural surface water increases the concentration of oxygen-containing low molecular weight compounds. Many of these compounds support microbiological growth and as such are termed assimilable organic carbon (AOC). Phytoplankton can contribute substantially to the organic carbon load when surface water is used as source for drinking water treatment. We have investigated dissolved organic carbon (DOC) formation from the ozonation of a pure culture of Scenedesmus vacuolatus under defined laboratory conditions, using a combination of DOC fractionation, analysis of selected organic acids, aldehydes and ketones, and an AOC bioassay. Ozonation of algae caused a substantial increase in the concentration of DOC and AOC, notably nearly instantaneously upon exposure to ozone. As a result of ozone exposure the algal cells shrunk, without disintegrating entirely, suggesting that DOC from the cell cytoplasm leaked through compromised cell membranes. We have further illustrated that the specific composition of newly formed AOC (as concentration of organic acids, aldehydes and ketones) in ozonated lake water differed in the presence and absence of additional algal biomass. It is therefore conceivable that strategies for the removal of phytoplankton before pre-ozonation should be considered during the design of drinking water treatment installations, particularly when surface water is used.  相似文献   
110.
The nutrition labeling compositional data (NLCD) required for fat‐containing food products consists of the percentages of saturated, cis‐monounsaturated, and cis‐polyunsaturated fat as well as trans content. The capability of 1H NMR spectroscopy to determine the NLCD components in oils that do not contain significant levels of trans isomers has already been established in the literature, but not its capability to differentiate between cis‐ and trans‐unsaturation. In the present study, the determination of all four NLCD components in fats and oils has been demonstrated for the first time. A preliminary analysis of the intensity‐normalized 1H NMR spectra of defined mixtures of pure triacylglycerols (TAG) by partial least squares (PLS) regression revealed that the (mono)allylic proton resonances of cis and trans bonds were sufficiently well separated to allow for accurate quantitation of trans content by simple peak integration. This chemometric approach also served to facilitate the identification of optimal integration limits for these cis‐ and trans‐allylic resonances. Fixed integration limits were also set for the other resonances employed in the determination of the four NLCD components, and a standardized spectral preprocessing procedure was established. The 1H NMR NLCD data obtained for the TAG mixtures by this methodology was a good match to the actual values, calculated from the known molar composition of these gravimetrically prepared mixtures. A procedure for the conversion of the NMR mol% NLCD to units of wt%, previously developed for 13C NMR, was adapted for 1H NMR and shown to be effective in compensating for the overestimation of wt% saturates and underestimation of wt% unsaturates by 1H NMR if this conversion is not made. The 1H NMR methodology for NLCD determination was validated by analyzing AOCS Laboratory Proficiency Program GC samples as well as samples taken from a hydrogenator over time and analyzed for trans content by GC and IR spectroscopy. Comparison of the 1H NMR mol% and wt% NLCD obtained for these validation samples with the data obtained from the reference methods indicated that 1H NMR can deliver high‐quality, accurate NLCD, much like 13C NMR, but in a much shorter time frame. Thus, 1H NMR provides a more rapid and cost‐effective means of obtaining NLCD than 13C NMR and can replace GC as a primary reference method for the calibration of simpler and automatable instrumental methods such as Fourier transform infrared (FTIR) spectroscopy.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号