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   805篇
  免费   26篇
  国内免费   2篇
电工技术   33篇
综合类   1篇
化学工业   328篇
金属工艺   20篇
机械仪表   10篇
建筑科学   29篇
能源动力   42篇
轻工业   66篇
水利工程   1篇
无线电   25篇
一般工业技术   158篇
冶金工业   27篇
原子能技术   19篇
自动化技术   74篇
  2023年   8篇
  2022年   11篇
  2021年   16篇
  2020年   14篇
  2019年   18篇
  2018年   11篇
  2017年   15篇
  2016年   28篇
  2015年   7篇
  2014年   17篇
  2013年   43篇
  2012年   31篇
  2011年   54篇
  2010年   32篇
  2009年   44篇
  2008年   42篇
  2007年   38篇
  2006年   40篇
  2005年   27篇
  2004年   25篇
  2003年   34篇
  2002年   26篇
  2001年   12篇
  2000年   21篇
  1999年   19篇
  1998年   13篇
  1997年   14篇
  1996年   14篇
  1995年   20篇
  1994年   14篇
  1993年   7篇
  1992年   9篇
  1991年   7篇
  1990年   9篇
  1989年   8篇
  1988年   11篇
  1987年   11篇
  1986年   10篇
  1985年   5篇
  1984年   3篇
  1983年   5篇
  1981年   5篇
  1980年   6篇
  1979年   3篇
  1978年   2篇
  1977年   10篇
  1976年   3篇
  1975年   4篇
  1974年   3篇
  1973年   2篇
排序方式: 共有833条查询结果,搜索用时 15 毫秒
101.
We propose an algorithm for compensating the phase-shift error of polarization-based parallel two-step phase-shifting digital holography, which is a technique for recording a spatial two-step phase-shifted hologram. Although a polarization-based system of the technique has been experimentally demonstrated, there had been the problem that the phase difference of two phase-shifted holograms had been changed by the extinction ratio of the micropolarizer array attached to the image sensor used in the system. To improve the performance of the system, we established and formulated an algorithm for compensating the phase-shift error. Accurate spatial phase-shifting interferometry in the system can be conducted by the algorithm regardless of phase-shift error due to the extinction ratio. By the numerical simulation, the proposed algorithm was capable of reducing the root mean square errors of the reconstructed image by 1/4 and 1/5 in amplitude and phase, respectively. Also, the algorithm was experimentally demonstrated, and the experimental results showed that the system employing the proposed algorithm suppressed the conjugate image, which slightly appeared in the image reconstructed by the system not employing the algorithm, even when the extinction ratio was 10:1. Thus, the effectiveness of the proposed algorithm was numerically and experimentally verified.  相似文献   
102.
A PCR assay for the detection of acetic acid-tolerant lactic acid bacteria in the genera of Lactobacillus and Pediococcus was developed in this study. Primers targeting the bacterial 16S rRNA gene were newly designed and used in this PCR assay. To determine the specificity of the assay, 56 different bacterial strains (of 33 genera), 2 fungi, 3 animals, and 4 plants were tested. Results were positive for most tested bacterial members of 16S rRNA gene-based phylogenetic groups (classified in the Lactobacillus casei and Pediococcus group), including Lactobacillus fructivorans, Lactobacillus brevis, Lactobacillus buchneri, Lactobacillus plantarum, and Lactobacillus paracasei. For all other bacterial strains and eukaryote tested, results were negative. Bacterial DNA for PCR was prepared with a simple procedure with the use of Chelex 100 resin from culture after growth in deMan Rogosa Sharpe broth (pH 6.0). To test this PCR assay for the monitoring of the acetic acid-tolerant lactic acid bacteria, L. fructivorans was inoculated into several acidic food as an indicator. Before the PCR, the inoculation of 10 to 50 CFU of bacteria per g of food was followed by a 28-h enrichment culture step, and the PCR assay allowed the detection of bacterial cells. Including the enrichment culture step, the entire PCR detection process can be completed within 30 h.  相似文献   
103.
A survey of pesticide residues in 595 imported frozen products on the Tokyo market from April 1989 to March 2008 was carried out. Forty three kinds of pesticides, including organophosphorus, organochlorine, carbamate, pyrethroid and others, were detected between levels of trace (below 0.01 ppm) and 4.6 ppm from 162 samples. Chlorpyrifos, cypermethrin and omethoate were frequently detected in green vegetables (komatsuna leaf and spinach), cypermethrin and methamidophos were detected in pods and seeds (green soybean and string pea), chlorpropham (CIPC) was detected in potato, and captan and carbaryl were detected in berries (blueberry, raspberry and strawberry). The hydrophilic pesticide methamidophos was detected in flesh of lychee. Residue levels of these pesticides were calculated as between less than 0.5% and 30% of their ADI values according to the daily intake of frozen products. Therefore, these frozen products should be safe when they were eaten in customary amounts.  相似文献   
104.
The authors have proposed a new concept of a distribution system “Flexible, Reliable and Intelligent ENergy Delivery System (FRIENDS)” with intent to solve imminent operating problems faced by utilities in providing their customers with reliable supply of power at several levels of quality. The main idea of FRIENDS is to introduce new facilities, so‐called Quality Control Centers (QCCs), which are installed very close to the customers for the purpose of implementing multiple functions, such as Customized Power Quality Service. In addition, these QCCs form a network for energy and information transmission at a level below distribution substations. QCCs make it possible to frequently change configuration of the network depending on the system and load conditions. These frequent reconfigurations of the network require fast and reliable Transfer Switching in the QCCs to ease an effect on customers. The reconfiguration for the purpose of fault area isolation also requires a fast Fault Detection feature. This paper presents a new method for controlling Transfer Switching and a method of Fault Detection in order to realize a fast and reliable reconfiguration of QCC network in a normal state, as well as under fault conditions. This paper also analyzes the methods in terms of instantaneous values calculated by PSCAD/EMTDC. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(3): 25–35, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10298  相似文献   
105.
In an attempt to clarify the mechanism of lipid accumulation inMortierella ramanniana var.angulispora, diacylglycerol acyltransferase (DGAT) in the membrane fraction from this fungus was characterized. The enzyme had an optimum pH of 7.0–7.5, and enzyme activity was blocked by SH-reagents. Metal ions were not essential for maintaining DGAT activity.n-Octyl-β-d-glucoside, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate and Tween 80 were found to preserve activity, while Triton X-100 and sucrose monolaurate inhibited it. As the inhibition of DGAT activity by Triton X-100 was overcome by the addition of diacylglycerol (DG), the dependency of DGAT activity on exogenous DG was determined in the presence of 0.1% Triton X-100. DGAT activity in the membrane fraction was traced in fungi cultured for different time periods or in media at different carbon to nitrogen (C/N) ratios. Although the increase in total lipid content with culture time was accompanied by an increase in DGAT activity, total lipid changes related to changes in C/N ratio did not correlate with DGAT activity. Factors other than DGAT activity in the membrane fraction would appear to be involved in the regulation of total lipid content in this fungus.  相似文献   
106.
For the liquid-phase partial hydrogenation of benzene at 483 K, the selectivity toward cyclohexene was greatly improved upon treating rare earth nitride with ammonia. For YbN obtained by thermal decomposition of Yb(NH2)2 at 1173 K, the selectivity of the NH3-treated YbN was 75%, in contrast to nil for the untreated YbN.  相似文献   
107.
We developed a new in-situ process for preparing functional ceramic fibers with a gradient surface layer by means of precursor methods using a polycarbosilane. After incorporation of selected low-molecular-mass additives into the precursor polymer from which the ceramic forms, thermal treatment of the resulting bodies leads to controlled phase separation ("bleed out") of the additives. Subsequent calcination stabilizes the compositionally changed surface region, generating a functional surface layer. Using this technology, we developed a strong photocatalytic fiber (TiO2-covered SiO2 fiber), which effectively decomposed many types of organic chemicals and bacteria into CO2and water by irradiation with UV light. Furthermore, we performed some field tests using a circulation purifier with a module composed of the cone-shaped felt material of our new fiber.  相似文献   
108.
The effect of addition of In and Pb on the reduction of N2O by CO was studied over SiO2 supported Pd catalysts, using a closed gas circulation system as well as in-situ infrared spectroscopy. Formation of intermetallic compounds such as Pd0.48In0.52, Pd3Pb and Pd3Pb2 was observed which caused a drastic enhancement of the rate of N2 formation. The infrared spectroscopic analyses revealed a weakening of the adsorption strength of CO on Pd metal by the formation of intermetallic compounds, which is likely the main reason for the enhancement of the reaction rate. From a kinetic investigation as well as in situ FT-IR observation during the N2O-CO reaction, a redox mechanism was proposed involving the oxidation of the surface by N2O followed by its reduction by CO. Over Pd/SiO2, the former process seems to be the rate limiting step because of the inhibition of N2O activation by strongly adsorbed CO. By adding In or Pb, the rate limiting step shifted to the latter process, which resulted in a large enhancement in the rate of N2 formation.  相似文献   
109.
Industrial production of L ‐lactic acid, which in polymerized form as poly‐lactic acid is widely used as a biodegradable plastic, has been attracting world‐wide attention. By genetic engineering we constructed a strain of the Crabtree‐negative yeast Candida boidinii that efficiently produced a large amount of L ‐lactic acid. The alcohol fermentation pathway of C. boidinii was altered by disruption of the PDC1 gene encoding pyruvate decarboxylase, resulting in an ethanol production that was reduced to 17% of the wild‐type strain. The alcohol fermentation pathway of the PDC1 deletion strain was then successfully utilized for the synthesis of L ‐lactic acid by placing the bovine L ‐lactate dehydrogenase‐encoding gene under the control of the PDC1 promoter by targeted integration. Optimizing the conditions for batch culture in a 5 l jar‐fermenter resulted in an L ‐lactic acid production reaching 85.9 g/l within 48 h. This productivity (1.79 g/l/h) is the highest thus far reported for L ‐lactic acid‐producing yeasts. DDBJ/EMBL/GenBank nucleotide database with Accession Nos. AB440630 and AB440631. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   
110.
One of the important factors for designing solar house is to examine the most economic combination what is called optimum design between solar collector area and storage volume for the required energy demand. The result of experimentation gives the fundamental data for completing the computer simulation program that is effectively usable for designing solar house.  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