全文获取类型
收费全文 | 315238篇 |
免费 | 24323篇 |
国内免费 | 15187篇 |
专业分类
电工技术 | 20289篇 |
技术理论 | 60篇 |
综合类 | 43958篇 |
化学工业 | 33189篇 |
金属工艺 | 11785篇 |
机械仪表 | 17341篇 |
建筑科学 | 45863篇 |
矿业工程 | 17656篇 |
能源动力 | 9109篇 |
轻工业 | 17300篇 |
水利工程 | 17122篇 |
石油天然气 | 13402篇 |
武器工业 | 2893篇 |
无线电 | 20622篇 |
一般工业技术 | 21246篇 |
冶金工业 | 19046篇 |
原子能技术 | 2935篇 |
自动化技术 | 40932篇 |
出版年
2024年 | 919篇 |
2023年 | 2840篇 |
2022年 | 5550篇 |
2021年 | 6585篇 |
2020年 | 7011篇 |
2019年 | 5810篇 |
2018年 | 5505篇 |
2017年 | 6832篇 |
2016年 | 8228篇 |
2015年 | 9422篇 |
2014年 | 18378篇 |
2013年 | 15854篇 |
2012年 | 20855篇 |
2011年 | 22370篇 |
2010年 | 17814篇 |
2009年 | 18761篇 |
2008年 | 17552篇 |
2007年 | 22923篇 |
2006年 | 21784篇 |
2005年 | 18910篇 |
2004年 | 15904篇 |
2003年 | 14437篇 |
2002年 | 11840篇 |
2001年 | 9980篇 |
2000年 | 8499篇 |
1999年 | 6857篇 |
1998年 | 5083篇 |
1997年 | 4427篇 |
1996年 | 4085篇 |
1995年 | 3495篇 |
1994年 | 3069篇 |
1993年 | 2296篇 |
1992年 | 2030篇 |
1991年 | 1485篇 |
1990年 | 1321篇 |
1989年 | 1194篇 |
1988年 | 937篇 |
1987年 | 633篇 |
1986年 | 489篇 |
1985年 | 411篇 |
1984年 | 371篇 |
1983年 | 278篇 |
1982年 | 234篇 |
1981年 | 216篇 |
1980年 | 161篇 |
1979年 | 140篇 |
1978年 | 94篇 |
1977年 | 93篇 |
1976年 | 68篇 |
1975年 | 79篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
《International Journal of Hydrogen Energy》2022,47(4):2279-2292
A new catalyst for both water reduction and oxidation, based on an infinite chain, {[Ni(tn)2]3 [Fe(CN)4 (μ-CN)2]2}n, is formed by the reaction of NiCl2, 1,3-propanediamine (tn) and K3 [Fe(CN)6]. {[Ni(tn)2]3 [Fe(CN)4 (μ-CN)2]2}n can electro-catalyze hydrogen evolution from a neutral aqueous buffer (pH 7.0) with a turnover frequency (TOF) of 1561 mol of hydrogen per mole of catalyst per hour (H2/mol catalyst/h) at an overpotential (OP) of 837 mV {[Ni(tn)2]3 [Fe(CN)4 (μ-CN)2]2}n also can electro-catalyze O2 production from water with a TOF of ~45 mol O2 (mol cat)?1s?1 at an OP of 591 mV. Under blue light (λ = 469 nm), together with CdS nanorods (CdS NRs) as a photosensitizer, and ascorbic acid (H2A) as a sacrificial electron donor, {[Ni(tn)2]3 [Fe(CN)4 (μ-CN)2]2}n can photo-catalyze hydrogen generation from an aqueous buffer (pH 4.0) with a turnover number (TON) of 11,450 mol H2 per mole of catalyst (mol of H2 (mol of cat)?1) during 10 h irradiation. The average of apparent quantum yield (AQY) is as high as 40.96% during 10 h irradiation. Studies indicate that {[Ni(tn)2]3 [Fe(CN)4 (μ-CN)2]2}n exists in two forms: a cyano-bridged chain ({[Ni(tn)2]3 [Fe(CN)4 (μ-CN)2]2}n) in solid, and a salt ([Ni(tn)2]3 [Fe(CN)6]2) in aqueous media; Catalytic reaction occurs on the nickel center of [Ni(tn)2]2+, and the introduction of [Fe(CN)6]3- can improve the catalytic efficiency of [Ni(tn)2]2+ for H2 or O2 generation. We hope these findings can afford a new method for the design of catalysts for both water reduction and oxidation. 相似文献
13.
Jean-Claude Malela-Majika Sandile Charles Shongwe Olatunde Adebayo Adeoti 《Quality and Reliability Engineering International》2021,37(8):3314-3322
The sensitivity of a monitoring scheme depends on many factors including the variance of the charting statistic which is very important in the computation of the control limits. This paper discusses the computation of the variance of the recently proposed hybrid homogeneously weighted moving average (HHWMA) scheme which was based on an incorrect assumption. The correct variance is used to evaluate the run-length characteristics of the HHWMA scheme. It is observed that the incorrect variance has a significant impact on the sensitivity (or performance) of the HHWMA scheme. 相似文献
14.
Residential natural gas consumption depends on several factors. Available tools and methods to identify, categorize, and validate effective factors have some limitations, making consumption modeling more complex. Once a comprehensive model of effective consumption factors is developed for residential gas consumers, it can predict consumption. In addition, such a model could be used to verify the accuracy of measuring devices in order to reduce unaccounted for gas (UFG). The key factors affecting residential gas consumption were identified based on previous studies and their mutual effects were analyzed using a fuzzy cognitive mapping (FCM) method. The most significant factors and their effects on natural gas consumption in the residential sector were determined. In this study, for the first time, the expected consumption for each consumer was estimated using a consumption index. Generally, if the estimated consumption is significantly different from the amount recorded by the meter, it could suggest a potential source of UFG. The proposed method was applied to the data collected from the residential gas consumers of a small region in Iran (Dasht-e Arjan region, Fars province), and the results demonstrate the effectiveness of the proposed method. 相似文献
15.
Elli Ntakou Ralph Masiello Farnaz Farzan Shay Bahramirad Aleksi Paaso M.A. Nayeem Maigha Maigha Daniel Kushner 《The Electricity Journal》2019,32(4):45-49
This paper presents part of the work ComEd and Quanta Technology have performed to quantify the locational and temporal value of DER to avoid distribution grid upgrade investments. It focuses on the formulation of a robust and efficient algorithm for DER optimal dispatch on a distribution feeder to mitigate the violation of current and voltage limits using the allocated cost of capacity and locational marginal value of real and reactive DER injection/withdrawal. 相似文献
16.
17.
An electrolyte Equation of State is presented by combining the Cubic Plus Association Equation of State,Mean Spherical Approximation and the Born equation.This new model uses experimental relative static permittivity,intend to predict well the activity coefficients of individual ions (ACI) and liquid densities of aqueous solutions.This new model is applied to model water + NaCl binary system and water + gas +NaCl ternary systems.The cation/anion-water interaction parameters of are obtained by fitting the exper-imental data of ACI,mean ionic activity coefficients (MIAC) and liquid densities of water + NaCl binary system.The cation/anion-gas interaction parameters are obtained by fitting the experimental data of gas solubilities in aqueous NaCl solutions.The modeling results show that this new model can correlate well with the phase equilibrium and volumetric properties.Without gas,predictions for ACI,MIAC,and liquid densities present relative average deviations of 1.3%,3.6% and 1.4% compared to experimental ref-erence values.For most gas-containing systems,predictions for gas solubilities present relative average deviations lower than 7.0%.Further,the contributions of ACI,and salting effects of NaCl on gases are ana-lyzed and discussed. 相似文献
18.
The effect of the emergency perception of bystanders of cyberbullying victims on helping behaviors is often neglected in research on cyberbullying. In this study, we explored the influence of this cognitive factor on cyber-bystanders’ helping tendencies as well as elucidated possible underlying processes. The results of two studies were reported. In Study 1, 150 undergraduates read a true case of a girl experiencing cyberbullying. The results indicated that when the participants perceived the victim’s situation to be more critical (i.e., higher emergency perception), their helping tendencies were stronger, partly through increased state empathy followed by feelings of responsibility to help. In Study 2, we randomly assigned 300 undergraduates to two groups. The low emergency group read the same cyberbullying case as Study 1, whereas the cyberbullying case read by the high emergency group contained additional emergency information of the victim. The results indicated that the high emergency group expressed stronger helping tendencies than did the low emergency group. This effect was caused by a stronger perception that the victim was in an emergency situation, which not only strengthened the participants’ helping tendencies directly but also indirectly through increasing their state empathy and feelings of responsibility to help. 相似文献
19.
20.
Zachary Zander Deirdre Newton Heather Scaglione Averie Reiber Parminder Agarwal 《Polymer Engineering and Science》2021,61(12):3029-3036
The incursion of microbial growth on polymeric products can deteriorate their performance and lead to the development of undesirable staining and odors. A growing trend in the industry has aimed to reduce microbial populations on high-touch surfaces via the use of antimicrobials to protect material aesthetics and durability or to prevent the spread of pathogenic microorganisms. In this study, a variety of plastic substrates (30 unique polymer compounds), including poly(acrylonitrile-co-butadiene-co-styrene), poly(butylene terephthalate), poly(etherimide), various thermoplastic elastomers (TPEs), poly(carbonates), and poly(amides), were screened for susceptibility to microbial attack using American Society for Testing and Materials (ASTM) G21 (fungi susceptibility), Japanese Industrial Standard (JIS) Z2801, and modified ASTM E1428-15a (bacterial susceptibility) test standards. TPEs were determined to be most susceptible to microbial attack under the appropriate environmental conditions. Subsequent studies assessed the use of an antimicrobial additive, zinc pyrithione (ZPT), for potential efficacy in a variety of TPE blends for diverse target market applications. ZPT proved to be very effective in protecting TPEs, reducing Staphylococcus aureus and Escherichia coli populations by 99.9% or more in JIS Z2801 testing and inhibiting fungal growth (rating = 0) according to the ASTM G21 standard. 相似文献