全文获取类型
收费全文 | 2575篇 |
免费 | 50篇 |
国内免费 | 32篇 |
专业分类
电工技术 | 48篇 |
综合类 | 43篇 |
化学工业 | 329篇 |
金属工艺 | 107篇 |
机械仪表 | 58篇 |
建筑科学 | 131篇 |
矿业工程 | 3篇 |
能源动力 | 51篇 |
轻工业 | 190篇 |
水利工程 | 19篇 |
石油天然气 | 19篇 |
武器工业 | 2篇 |
无线电 | 178篇 |
一般工业技术 | 249篇 |
冶金工业 | 1036篇 |
原子能技术 | 6篇 |
自动化技术 | 188篇 |
出版年
2023年 | 5篇 |
2022年 | 12篇 |
2021年 | 24篇 |
2020年 | 12篇 |
2019年 | 15篇 |
2018年 | 20篇 |
2017年 | 29篇 |
2016年 | 21篇 |
2015年 | 53篇 |
2014年 | 98篇 |
2013年 | 103篇 |
2012年 | 72篇 |
2011年 | 161篇 |
2010年 | 76篇 |
2009年 | 105篇 |
2008年 | 85篇 |
2007年 | 95篇 |
2006年 | 68篇 |
2005年 | 57篇 |
2004年 | 55篇 |
2003年 | 53篇 |
2002年 | 49篇 |
2001年 | 38篇 |
2000年 | 30篇 |
1999年 | 62篇 |
1998年 | 305篇 |
1997年 | 180篇 |
1996年 | 138篇 |
1995年 | 108篇 |
1994年 | 93篇 |
1993年 | 78篇 |
1992年 | 26篇 |
1991年 | 20篇 |
1990年 | 37篇 |
1989年 | 30篇 |
1988年 | 18篇 |
1987年 | 19篇 |
1986年 | 7篇 |
1985年 | 16篇 |
1984年 | 11篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 11篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1978年 | 11篇 |
1977年 | 30篇 |
1976年 | 59篇 |
1975年 | 7篇 |
1973年 | 5篇 |
排序方式: 共有2657条查询结果,搜索用时 15 毫秒
101.
Infrastructure investment projects and programmes are generally evaluated by comparing project costs with pertinent benefits. In this paper a series of alternative national road investment programmes in Sweden are examined. Each programme is assessed in terms of expected time savings and reduced accident rates. In addition we make use of a general production function with regionally specific accessibility characteristics as arguments. With this approach, improved accessibility implies an increase of the production potential. The paper compares the value of these production effects with the value of time savings and other benefits in a standard CB-calculation. In the comparisons more than 50 alternative national investment programmes are assessed, and their degree of consistency is estimated.An earlier version of this paper was presented at the European RSA-conference in Moscow, August 1993 and has benefitted from comments during the conference. The authors are grateful for suggestions rendered by two anonymous referees. We also wish to thank R. Jonsson, G. Lindberg and L.-G. Mattsson. Supply of data and research funds from the National Road Administration is acknowledged. 相似文献
102.
Henrik Pettersson Tadeusz Gruszecki Lars-Henrik Johansson Per Johander 《Solar Energy Materials & Solar Cells》2003,77(4):6595
A manufacturing technique for monolithic dye-sensitised solar cells is presented. Encapsulated modules designed for indoor low-power applications have been prepared using industrial methods and equipment. Under certain conditions (light intensity <5000 lx, temperature between –10°C and 50°C, and relative humidity of appr. 50%), the modules have performed well and shown excellent long-term stability. Moreover, modules withstand illumination in combination with storage at 100% relative humidity. However, a certain degradation of the module performance takes place at illuminations exceeding 5000 lx and temperatures exceeding 50°C. 相似文献
103.
Abstract Market-based instruments such as fees or tradable permits can be used to simultaneously regulate point and nonpoint sources of pollution discharge into a river. However, sources of pollution discharge often have more information about their own costs of pollution abatement than do regulators. This information asymmetry may lead to strategic behavior, which can lead to different outcomes under different policies. This paper estimates a Nash payoff of a two-period strategic game using econometrically estimated abatement costs for point and nonpoint source phosphorus discharges in the Minnesota River Basin. Results show that when dischargers of pollutants are strategic, discharge permits may yield lower deadweight losses than discharge fees. 相似文献
104.
Laurent Picot Rozenn Ravallec Martine Fouchereau‐Péron Laurent Vandanjon Pascal Jaouen Maryse Chaplain‐Derouiniot Fabienne Guérard Aurélie Chabeaud Yves LeGal Oscar Martinez Alvarez Jean‐Pascal Bergé Jean‐Marie Piot Irineu Batista Carla Pires Gudjon Thorkelsson Charles Delannoy Greta Jakobsen Inez Johansson Patrick Bourseau 《Journal of the science of food and agriculture》2010,90(11):1819-1826
BACKGROUND: Numerous studies have demonstrated that in vitro controlled enzymatic hydrolysis of fish and shellfish proteins leads to bioactive peptides. Ultrafiltration (UF) and/or nanofiltration (NF) can be used to refine hydrolysates and also to fractionate them in order to obtain a peptide population enriched in selected sizes. This study was designed to highlight the impact of controlled UF and NF on the stability of biological activities of an industrial fish protein hydrolysate (FPH) and to understand whether fractionation could improve its content in bioactive peptides. RESULTS: The starting fish protein hydrolysate exhibited a balanced amino acid composition, a reproducible molecular weight (MW) profile, and a low sodium chloride content, allowing the study of its biological activity. Successive fractionation on UF and NF membranes allowed concentration of peptides of selected sizes, without, however, carrying out sharp separations, some MW classes being found in several fractions. Peptides containing Pro, Hyp, Asp and Glu were concentrated in the UF and NF retentates compared to the unfractionated hydrolysate and UF permeate, respectively. Gastrin/cholecystokinin‐like peptides were present in the starting FPH, UF and NF fractions, but fractionation did not increase their concentration. In contrast, quantification of calcitonin gene‐related peptide (CGRP)‐like peptides demonstrated an increase in CGRP‐like activities in the UF permeate, relative to the starting FPH. The starting hydrolysate also showed a potent antioxidant and radical scavenging activity, and a moderate angiotensin‐converting enzyme (ACE)‐1 inhibitory activity, which were not increased by UF and NF fractionation. CONCLUSION: Fractionation of an FPH using membrane separation, with a molecular weight cut‐off adapted to the peptide composition, may provide an effective means to concentrate CGRP‐like peptides and peptides enriched in selected amino acids. The peptide size distribution observed after UF and NF fractionation demonstrates that it is misleading to characterize the fractions obtained by membrane filtration according to the MW cut‐off of the membrane only, as is currently done in the literature. Copyright © 2010 Society of Chemical Industry 相似文献
105.
Consumer and sensory investigations in relation to physical/chemical aspects of cooked pork in Scandinavia 总被引:1,自引:0,他引:1
Bryhni EA Byrne DV Rødbotten M Møller S Claudi-Magnussen C Karlsson A Agerhem H Johansson M Martens M 《Meat science》2003,65(2):737-748
The present study addresses sensory quality and liking for pork (eight samples) varying in quality due to adrenaline injection resulting in elevated ultimate pH post-slaughter (24h), meat ageing, cooking temperature and warmed-over flavour (WOF) among consumers (n=288) in Scandinavia. The consumers preferred meat with higher pH (pH(24h)=6.0), cooked to the lowest temperature (65?°C versus 80?°C). Consumers least preferred samples with WOF described as metallic, acidic and off-flavour by a trained panel. "Elevated pH(24h) meat" cooked to 65?°C resulted in a more sweet and tender meat. Juiciness, tenderness and the absence of off-flavour were the most important characteristics for consumers' liking of pork. Consumption frequency and liking of pork were positively related. The consumers that were most satisfied with pork quality reported highest consumption frequency. Elderly people and males expressed the highest liking score and consumption frequency, respectively. 相似文献
106.
大型单盘浮顶的钢板薄、焊缝密度高、焊接工作量大、焊缝交叉点较多.很难控制焊接变形.不仅影响浮顶单盘焊后的外观质量.而且影响浮顶单盘的排水能力。结合大型储罐单盘浮顶的施工.分析了施工工艺的特点与不足.创新性地总结出了大型储罐单盘浮顶施工的新工艺。新工艺采用CO2气体保护焊+手工焊焊接方法、更利于均匀释放焊接应力的焊接顺序以及更合理的浮顶临时架台搭设方法等,能有效节约施工成本,缩短工期,解决单盘浮顶焊接变形等问题。文章对该工艺的施工特点、适用范围、工艺原理、工艺流程及操作要点等进行了详细的介绍。 相似文献
107.
108.
The potential of colour measurement for strength prediction of thermally treated wood 总被引:2,自引:2,他引:2
This paper investigates the effects of thermal treatment of birch with respect to colour and strength. Birch wood was treated at 175 °C and 200 °C for 0 h, 1 h, 3 h and 10 h. In bending-strength experiments, treatment was also performed at 185 °C for 2 h. Both static bending strength and impact bending strength were investigated using multivariate statistics (PLS) for correlation to process parameters, density, EMC, position in board, modulus of elasticity (only in static bending), colour and dimensions of samples. In static bending, two PLS models were designed, one based on process parameters and the other based on colour and EMC. From these models it was concluded that colour is not a useful parameter for prediction of strength. In impacted bending, the correlation was too small to give useful results. One test of static bending strength with matched samples was performed, and it showed a strength reduction of 43% when treatment was conducted at 200 °C for 3 h. Measurement of colour homogeneity of the treated boards showed that the colour is not homogeneous. 相似文献
109.
Bai Yu-chuan Institute for Sedimentation on River Coast Engineering Tianjin University Tianjing China Ng Chiu-On Department of Mechanical Engineering The University of Hongkong Hongkong China 《水动力学研究与进展(B辑)》2002,14(4)
1 . INTRODUCTIONShearflowspastwavy likeboundarieshaveat tractedconsiderableattentioninrecentyearsbe causeofthecentralrolethey playinseveralin triguing phenomena ,suchasthe generationofwindwavesonwater ,theformationofsedimenta ryripplesanddunesindesertsandri… 相似文献
110.