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   1283篇
  免费   87篇
  国内免费   1篇
电工技术   18篇
综合类   2篇
化学工业   205篇
金属工艺   28篇
机械仪表   94篇
建筑科学   47篇
矿业工程   3篇
能源动力   40篇
轻工业   120篇
水利工程   7篇
石油天然气   2篇
无线电   169篇
一般工业技术   216篇
冶金工业   202篇
原子能技术   7篇
自动化技术   211篇
  2024年   2篇
  2023年   16篇
  2022年   30篇
  2021年   50篇
  2020年   22篇
  2019年   39篇
  2018年   44篇
  2017年   39篇
  2016年   66篇
  2015年   41篇
  2014年   53篇
  2013年   99篇
  2012年   58篇
  2011年   73篇
  2010年   49篇
  2009年   74篇
  2008年   49篇
  2007年   42篇
  2006年   53篇
  2005年   56篇
  2004年   41篇
  2003年   28篇
  2002年   28篇
  2001年   21篇
  2000年   14篇
  1999年   21篇
  1998年   76篇
  1997年   47篇
  1996年   37篇
  1995年   13篇
  1994年   9篇
  1993年   25篇
  1992年   8篇
  1991年   4篇
  1990年   2篇
  1988年   3篇
  1987年   4篇
  1986年   4篇
  1985年   4篇
  1983年   2篇
  1982年   2篇
  1979年   3篇
  1976年   5篇
  1975年   2篇
  1974年   2篇
  1973年   1篇
  1972年   2篇
  1971年   1篇
  1965年   1篇
  1939年   1篇
排序方式: 共有1371条查询结果,搜索用时 15 毫秒
981.
Branched chain fatty acids (BCFA) have recently been shown to be a major component of the normal human newborn gastrointestinal tract and have long been known to be a component of human milk. Ruminant food products are major sources of fat in the American diet, but there are no studies of milkfat BCFA content in retail milk. We report here the profile and concentrations of BCFA in a representative sampling of retail milk in the 48 contiguous United States (US), and their estimated intake in the American diet. Conventionally produced whole fluid milk samples were obtained from 56 processing plants across the contiguous 48 states. Retail milk samples contain exclusively iso- and anteiso-BCFA with 14–18 carbons. BCFA were 2.05 ± 0.14%, w/w of milkfat fatty acids (mean ± SD), and anteiso-BCFA comprised more than half this total. Based on these data and USDA food availability data, the average per capita BCFA intake of Americans is estimated to be about 220 mg/d from dairy; if current dietary recommendations were followed, BCFA intake would be about 400 mg/d. Adding intake from beef consumption, these estimates rise to approximately 400 and 575 mg/d, respectively. These results indicate that BCFA intake is a substantial fraction of daily fat intake, in amounts exceeding those of many bioactive fatty acids.  相似文献   
982.
A fast sodium ion conductor, NASICON (Na3Zr2Si2PO12), has been widely used for gas sensor applications. In this study, we demonstrate that a device combining NASICON with an oxygen-ion conductor of BiCuVOx (Bi2Cu0.1V0.9O5.35) can electrochemically detect volatile organic compounds (VOCs), such as ethanol, formaldehyde, and toluene. The sensing electrode made of BiCuVOx was attached onto a sintered NASICON disk at high temperature to produce an interfacial layer that had a different morphology and composition from those of NASICON and BiCuVOx, as observed by scanning electron microscopy-energy dispersive X-ray spectroscopy analysis. The device in which NASICON was fitted with the BiCuVOx-based electrode was found to efficiently detect VOCs in ppm concentrations. The sensor signal (electromotive force) exceeded 100 mV in response to 10 ppm HCOH at 400 °C, demonstrating the high sensitivity of the device. It also exhibited a relatively quick response, reproducible and stable sensor signals, and high selectivity to VOCs. The sensor responses followed behavior typical for mixed-potential-type gas sensors based on oxygen-ion conductors. It was thus suggested that the electrochemical oxidation of VOCs with oxide ions took place at the interfacial oxygen ion-conductive layer that was formed by the reaction of NASICON with BiCuVOx.  相似文献   
983.
This article presents the predictions of the rotordynamic performance of oil-free turbochargers (TCs) for various lobed gas foil bearings (GFBs) with the first-generation bump-type configuration and compares these predictions to the measured test data reported earlier. The three-lobed GFBs used for the simulations have increased bearing clearances and mechanical preloads with a fixed minimum bearing clearance, thus yielding larger average bearing clearances and higher wedge effects at the same time. The engine-induced TC housing excitation is found to have no influence on the critical speeds and damping ratios of the rotor rigid modes. The synchronous and asynchronous GFB analyses imply decreases in destabilizing forces for the highly lobed GFBs. The predicted critical speed and damping ratio of the TC rotor supported on the lobed GFBs demonstrate increasing system natural frequency and enhanced rotordynamic stability with increasing mechanical preload. The rotordynamic and bearing analyses of the lobed GFBs validate the beneficial effects of the mechanical preload on the rotordynamic stability of GFBs even with an increased average bearing clearance, which leads to a decreased bearing friction torque as well.  相似文献   
984.
Circulating tumor cells (CTCs), though exceedingly rare in the blood, are nonetheless becoming increasingly important in cancer diagnostics. Despite this keen interest and the growing number of potential clinical applications, there has been limited success in developing a CTC isolation platform that simultaneously optimizes recovery rates, purity, and cell compatibility. Herein, a novel tracheal carina‐inspired bifurcated (TRAB) microfilter system is reported, which uses an optimal filter gap size satisfying both 100% theoretical recovery rate and purity, as determined by biomechanical analysis and fluid–structure interaction (FSI) simulations. Biomechanical properties are also used to clearly discriminate between cancer cells and leukocytes, whereby cancer cells are selectively bound to melamine microbeads, which increase the size and stiffness of these cells. Nanoindentation experiments are conducted to measure the stiffness of leukocytes as compared to the microbead‐conjugated cancer cells, with these parameters then being used in FSI analyses to optimize the filter gap size. The simulation results show that given a flow rate of 100 μL min?1, an 8 μm filter gap optimizes the recovery rate and purity. MCF‐7 breast cancer cells with solid microbeads are spiked into 3 mL of whole blood and, by using this flow rate along with the optimized microfilter dimensions, the cell mixture passes through the TRAB filter, which achieves a recovery rate of 93% and purity of 59%. Regarding cell compatibility, it is verified that the isolation procedure does not adversely affect cell viability, thus also confirming that the re‐collected cancer cells can be cultured for up to 8 days. This work demonstrates a CTC isolation technology platform that optimizes high recovery rates and cell purity while also providing a framework for functional cell studies, potentially enabling even more sensitive and specific cancer diagnostics.  相似文献   
985.
986.
The adhesive properties have been investigated in blends of mono‐carboxyl‐terminated poly(2‐ethylhexyl acrylate‐co‐methyl methacrylate) with diglycidyl ether of bisphenol A and three different aliphatic amine epoxy hardener. The adhesives properties are evaluated in steel alloy substrate using single‐lap shear test. The copolymers are initially miscible in the stoichiometric blends of epoxy resin and hardener at room temperature. Phase separation is noted in the course of the polymerization reaction. Different morphologies are obtained according to the amine epoxy hardener. The most effective adhesive for steel–steel joints in single‐lap shear test is the blends using 1‐(2‐aminoethyl)piperazine (AEP) as hardener. This system shows the biggest lap shear strength. However, the modified adhesives show a reduction in the mechanical resistance. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010  相似文献   
987.
The bubble characteristics have been investigated in an air–water bubble column with shallow bed heights. The effect of bed height, location and the presence of solids on the bubble size, bubble rise velocity and overall and sectional gas holdup are studied over a range of superficial gas velocities. Optimal shallow bed operation relies on the combined entrance and exit effects at the distributor and the liquid bed surface. The gas holdup is found to decrease with an increase in H/D ratio but the effect is diminishing at high H/D ratios. A H/D ratio of 2–4 is found to be suitable for shallow bed operation. The presence of solids causes the formation of larger bubbles at the distributor and the effect is diminishing as the gas velocity is increased.  相似文献   
988.
Analytical data on fatty acid, amino acid and mineral content of defatted melon seed and fluted pumpkin seed are presented and discussed. Also discussed are experimental data on availability of amino acids and minerals in these meals. Defatted melon seed and fluted pumpkin seed have protein contents of 66.20% and 66.54%, respectively, with an excellent pattern of amino acids, containing higher levels of most essential amino acids (except lysine) than soya bean meal. Amino acid availability is high (melon seed 95.30%, pumpkin seed 93.12%) and similar to the level in soya bean meal (94.31%). Mineral availability is significantly lower in melon seed (53.63%) and soya bean meal (54.94%) than in pumpkin seed (58.84%). The potential for increased dietary utilisation of melon and fluted pumpkin meals and flours to meet the dietary needs of monogastric animals as well as human subjects is discussed.  相似文献   
989.
Porous semiconducting (Ba, Sr)TiO3 ceramics were fabricated by the addition of potato-starch to the (Ba, Sr)TiO3 powders. The effects of potato-starch on the microstructure and PTCR characteristics of the porous (Ba, Sr)TiO3 ceramics have been investigated. The porosity largely increased and the grain size slightly decreased with increasing potato-starch content. The crystalline structure of (Ba, Sr)TiO3 ceramics was independent of the potato-starch content. The (Ba, Sr)TiO3 ceramics containing potato-starch showed higher PTCR (106) characteristics than that of the (Ba, Sr)TiO3 ceramics without potato-starch. It was found that the development of PTCR characteristic in the porous (Ba, Sr)TiO3 ceramics containing various amounts of potato-starch, in the same way as normal BaTiO3 ceramics without potato-starch, is associated with grain boundaries, from the impedance analysis.  相似文献   
990.
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