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   2341篇
  免费   205篇
电工技术   21篇
综合类   29篇
化学工业   960篇
金属工艺   25篇
机械仪表   42篇
建筑科学   98篇
矿业工程   6篇
能源动力   56篇
轻工业   379篇
水利工程   41篇
石油天然气   4篇
无线电   83篇
一般工业技术   374篇
冶金工业   124篇
原子能技术   7篇
自动化技术   297篇
  2024年   15篇
  2023年   28篇
  2022年   174篇
  2021年   177篇
  2020年   96篇
  2019年   85篇
  2018年   89篇
  2017年   93篇
  2016年   109篇
  2015年   92篇
  2014年   124篇
  2013年   171篇
  2012年   141篇
  2011年   203篇
  2010年   120篇
  2009年   117篇
  2008年   126篇
  2007年   96篇
  2006年   70篇
  2005年   49篇
  2004年   46篇
  2003年   49篇
  2002年   41篇
  2001年   25篇
  2000年   28篇
  1999年   28篇
  1998年   28篇
  1997年   14篇
  1996年   10篇
  1995年   15篇
  1994年   16篇
  1993年   13篇
  1992年   7篇
  1991年   9篇
  1990年   3篇
  1989年   4篇
  1987年   4篇
  1986年   4篇
  1985年   2篇
  1983年   1篇
  1982年   2篇
  1981年   3篇
  1980年   2篇
  1979年   5篇
  1978年   2篇
  1977年   3篇
  1976年   1篇
  1975年   2篇
  1974年   1篇
  1964年   1篇
排序方式: 共有2546条查询结果,搜索用时 15 毫秒
61.
We calculate the signal-to-noise ratio in a dc SQUID system as a function of source impedance, taking into account the effects of current and voltage noise sources in the SQUID. The optimization of both tuned and untuned voltmeters and magnetometers is discussed and typical sensitivities are predicted using calculated noise spectra. The calculations are based on an ideal symmetric dc SQUID with % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4baFfea0dXde9vqpa0lb9% cq0dXdb9IqFHe9FjuP0-iq0dXdbba9pe0lb9hs0dXda91qaq-xfr-x% fj-hmeGabaqaciGacaGaaeqabaWaaeaaeaaakeaacqaHYoGycqGH9a% qpcaaIYaacbaGaa8htaiaa-LeadaWgaaWcbaacbiGaa4hmaaqabaGc% caGGVaGaeuOPdy0aaSbaaSqaaiaa+bdaaeqaaOGaeyypa0JaaGymaa% aa!3D23!\[\beta = 2LI_0 /\Phi _0 = 1\] and moderate noise rounding % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4baFfea0dXde9vqpa0lb9% cq0dXdb9IqFHe9FjuP0-iq0dXdbba9pe0lb9hs0dXda91qaq-xfr-x% fj-hmeGabaqaciGacaGaaeqabaWaaeaaeaaakeaaiiGacqWFOaakcq% WFtoWrcqWF9aqpcqWFYaGmcqaHapaCcaWGRbWaaSbaaSqaaiaadkea% aeqaaGqaaOGaa4hvaiaac+cacaGFjbWaaSbaaSqaaerbbjxAHXgaiu% GacaqFWaaabeaakiab-z6agnaaBaaaleaacaqGGaacbiGaaWhmaaqa% baGccqGH9aqpcaaIWaGaaiOlaiaaicdacaaI1aGaaiykaaaa!471A!\[(\Gamma = 2\pi k_B T/I_0 \Phi _{{\rm{ }}0} = 0.05)\], where 0 is the flux quantum, T is the temperature, L is the SQUID inductance, and I 0 is the critical current of each junction. The optimum noise temperatures of tuned and untuned voltmeters are found to be 2.8(L/R)T and 8(L/R)T (1 + 1.52 + 0.74)1/2/2 respectively, where /2 is the signal frequency, assumed to be much less than the Josephson frequency, and is the coupling coefficient between the SQUID and its input coil. It is found that tuned and untuned magnetometers can be characterized by optimum effective signal energies given by (16k B TLE/2 R)[1 + (1 + 1.52 + 0.72)1/2 + 0.752] and 2kB T iRiB/2 L p respectively, where B is the bandwidth, R i is the resistance representing the losses in the tuned circuit at temperature T i and L p is the inductance of the pickup coil.This work was supported by the Division of Materials Sciences, Office of Basic Energy Sciences, U.S. Department of Energy, and by the U.S. Office of Naval Research.Guggenheim Fellow.  相似文献   
62.
There is an implicit assumption in electronic commerce that induces the buyers to believe that their deals will be handled appropriately. However, after a seller has already committed to a buyer, he may be tempted by several requests though he will not be able to supply them all. We analyze markets in which a finite set of automated buyers interacts repeatedly with a finite set of automated sellers. These sellers can satisfy one buyer at a time, and they can be tempted to break a commitment they already have. We have found the perfect equilibria that exist in markets with a finite horizon, and with an unrestricted horizon. A significant result stemming from our study reveals that sellers are almost always tempted to breach their commitments. However, we also show that if markets' designers implement an external mechanism that restricts the automated buyers actions, then sellers will keep their commitments.  相似文献   
63.
Nos observations au secondaire et au collégial et les travaux menés sur la transition secondaire postsecondaire en mathématiques ont permis de documenter un ensemble de ruptures dans le passage d'un ordre à l'autre, soulignant l'importance de s'attarder à l'articulation entre ces deux ordres. C'est afin de mieux comprendre ces articulations possibles qu'une recherche collaborative a été menée avec des enseignants des deux ordres. L'analyse, puisant ses fondements en ethnométhodologie, fait apparaître l'utilisation du symbolisme comme un thème central de cette articulation interordres, et permet de retracer une trajectoire d'harmonisation qui se développe durant les rencontres en lien avec cette utilisation.  相似文献   
64.
Cognition, Technology & Work - This paper presents an approach to human–machine interactions based on the concept of teamwork and the psychological theory of object relations. We envision...  相似文献   
65.
This article reports an extraction–purification of napins from an industrial rapeseed meal and the assessment of their antimicrobial activity against Fusarium langsethiae. The best extraction conditions are observed at pH 2, 12% (w/w) of rapeseed meal after 15 min of extraction in water at room temperature. Under these conditions the extraction is highly selective, allowing a simple purification process (ammonium sulfate precipitation followed by desalting size exclusion chromatography) to get purified napins. These napins possessed significant anti-Fusarium activity (IC50 = 70 μM) and a compact secondary structure rich in α-helix, which may explain this bioactivity.  相似文献   
66.
67.
68.
69.
The oxidation-reduction potential (ORP) is an important factor in H2 production via dark fermentation however its effect over microbial diversity in an acidogenic sludge has not, been well studied. This work studies the effect of ORP controlled by hydrogen peroxide and potassium ferricyanide on continuous hydrogen production and microbial diversity in an acidogenic sludge fed (HRT 12 h and pH 5.5) with glycerol. Results show that the more oxidizing ORP control environment (?540 mV) improves H2 yield by 50–70% (0.31–0.51 molH2/mol glycerol) over non-ORP control conditions. Oxidizing ORP values were shown to enrich microorganisms of the genus Clostridium, which have been linked to high H2 yields. Therefore, controlling ORP in an acidogenic sludge was shown to directly modify microbial diversity at the genus level, and could likely to indirectly regulate metabolic function. Additionally, metabolic pathways were regulated by the kind of agent used.  相似文献   
70.
Flow curves of aqueous dispersions of tragacanth gum (T) with sucrose and glucose at different temperatures were determined using a controlled‐stress rheometer. The effect of sodium chloride without or with sucrose (at the highest content) on the rheology of T dispersions was evaluated. The presence of sucrose and glucose promoted a noticeable enhancement impact on the apparent viscosity of aqueous T dispersions, which depended on sugar type/content, shear rate and temperature. In all cases, the glucose addition led to the largest enhanced viscosities at low shear rates (<10 s?1) and temperature. The joint action of sugar and salt exhibited a notable effect on apparent viscosity at low shear rates, softening the strong shear‐thinning behaviour of T samples. Flow curves of T in the presence of sugars were satisfactorily described by the Cross‐Williamson model, being semi‐empirical correlations of the model parameters with ingredients content and temperature stablished.  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