全文获取类型
收费全文 | 1492篇 |
免费 | 111篇 |
专业分类
电工技术 | 27篇 |
综合类 | 1篇 |
化学工业 | 346篇 |
金属工艺 | 18篇 |
机械仪表 | 18篇 |
建筑科学 | 77篇 |
矿业工程 | 5篇 |
能源动力 | 56篇 |
轻工业 | 129篇 |
水利工程 | 25篇 |
石油天然气 | 4篇 |
无线电 | 161篇 |
一般工业技术 | 282篇 |
冶金工业 | 172篇 |
原子能技术 | 5篇 |
自动化技术 | 277篇 |
出版年
2024年 | 3篇 |
2023年 | 16篇 |
2022年 | 26篇 |
2021年 | 52篇 |
2020年 | 38篇 |
2019年 | 52篇 |
2018年 | 58篇 |
2017年 | 33篇 |
2016年 | 50篇 |
2015年 | 49篇 |
2014年 | 78篇 |
2013年 | 114篇 |
2012年 | 106篇 |
2011年 | 106篇 |
2010年 | 86篇 |
2009年 | 72篇 |
2008年 | 99篇 |
2007年 | 77篇 |
2006年 | 77篇 |
2005年 | 60篇 |
2004年 | 47篇 |
2003年 | 45篇 |
2002年 | 38篇 |
2001年 | 26篇 |
2000年 | 20篇 |
1999年 | 25篇 |
1998年 | 27篇 |
1997年 | 14篇 |
1996年 | 15篇 |
1995年 | 10篇 |
1994年 | 15篇 |
1993年 | 15篇 |
1992年 | 3篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有1603条查询结果,搜索用时 15 毫秒
51.
David J. Fair Rakesh Venkatesh Bruce Boghosian Douglas M. Matson 《Microgravity science and technology》2005,16(1-4):55-58
Certain commercial steel alloys exhibit a two-step phase transformation process during solidification when substantial undercooling of the liquid allows access to the metastable phase. This two-step transformation leads to a desirable microstructure under certain conditions. Electrostatic Levitation (ESL) and Electromagnetic Levitation (EML) are two methods of containerless processing used to study how nucleation and growth kinetics influence the transformation delay between phases. Because the two facilities show substantially different delay results, the test environment differences have been analyzed to determine the root cause of this deviation. In particular, the difference in sample size between ESL and EML is examined and modeling shows that this difference is not the controlling factor in determining transformation delay behavior. 相似文献
52.
Sean MacDonald 《华东电力》2003,32(11):73-76
联合循环机组日益广泛应用于发电厂。与传统的燃煤机组相比 ,联合发电厂的设备及安装成本、发电效率高 ,而且对环境影响小。余热锅炉 ( HRSG)是联合循环机组的一个组成部分。虽然 HRSG的热负荷比传统锅炉低 [1] ,但锅炉水化学却很重要。因此 ,新建 HRSG的化学清洗一直受到关注。传统的新建锅炉中存在油脂 ,氧化皮及焊渣等 ,其化学清洗是为了除去这类杂质以保障机组的正常启动及运行。HRSG系统中存在类似的杂质 ,但 HRSG由两到三个压力不同的蒸汽发生回路所组成 (见图 1 ) ,化学清洗较为复杂。这种锅炉结构一般需要多步或扩大性化学… 相似文献
53.
T. W. Tsuei R. L. Wood C. Khan Malek M. M. Donnelly R. B. Fair 《Microsystem Technologies》1998,4(4):201-204
A method for creating angled structures for use in microvalve devices applicable to control of liquid flow is presented.
This technique utilizes a modified LIGA process with successive angled and rotated exposures into free standing acrylic sheets
to form a tapered valve seat structure. These valve seats are integrated with bulk micromachined silicon diaphragms and tapered
PMMA valve bosses to complete the microvalve. The long term goal of this research effort is to develop a normally-closed,
low power, microfabricated valve for use in an implantable drug delivery system. This paper reports on the design and fabrication
of microvalves using off-axis LIGA exposures. Flow testing and fluid handling characterization results are also presented.
Received: 25 August 1997 Accepted: 22 October 1997 相似文献
54.
Steptoe Andrew; Perkins-Porras Linda; Rink Elisabeth; Hilton Sean; Cappuccio Francesco P. 《Canadian Metallurgical Quarterly》2004,23(6):574
This study assessed psychological and social factors predicting 12-month changes in fruit and vegetable consumption achieved by 271 men and women from a low-income population randomized to brief behavioral and nutrition education counseling. Greater increases in fruit and vegetable intake were achieved in the behavioral than in the nutrition education condition (1.49 vs. 0.87 portions per day, p=.021). Increases were predicted by baseline social support for dietary change but not by baseline psychological measures. However, short-term (8-week) changes in dietary self-efficacy, encouragement, anticipated regret, perceived benefits, and knowledge of recommended intake predicted 12-month changes in fruit and vegetable consumption independently of gender, age, ethnicity, income, and baseline intake. These factors accounted for 51% of the superiority of behavioral counseling over nutrition education. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
55.
The use of Neural Networks for the estimation of oceanic constituents based on the MERIS instrument 总被引:1,自引:0,他引:1
Daniel Buckton Eon O'Mongain Sean Danaher 《International journal of remote sensing》2013,34(9):1841-1851
Artificial Neural Networks (NNs) are used in estimations of oceanic constituents from simulated data for the Mechron Resolution Imaging Spectrometer (MERIS) instrument system for Case II water applications. The simulation includes the effects of oceanic substances such as algal related chlorophyll, non-chlorophyllous suspended matter and DOM (dissolved organic matter). It is shown here that NNs can be used to estimate oceanic constituents based on simulated data which include the effects of realistic noise and variability models. The advantage of NNs is that they not only achieve higher retrieval accuracy than more traditional techniques such as band ratio algorithms, but they also allow the inclusion of usually superfluous or unused information, such as geometric parameters and atmospheric visibility. 相似文献
56.
The electricity industry is rapidly changing: costs are increasingly dominated by capital and technology is turning loads into resources. This is similar to the early days of the Internet. Building on rate-structures used in the communications industry, utilities of the future should offer customers a portfolio of service contract options that provide a signal to the utility regarding the type and amount of infrastructure that should be deployed. 相似文献
57.
Andrew T. Sensenig Kimberly A. Lorentz Sean P. Kelly Todd A. Blackledge 《Journal of the Royal Society Interface》2012,9(73):1880-1891
The kinetic energy of flying insect prey is a formidable challenge for orb-weaving spiders. These spiders construct two-dimensional, round webs from a combination of stiff, strong radial silk and highly elastic, glue-coated capture spirals. Orb webs must first stop the flight of insect prey and then retain those insects long enough to be subdued by the spiders. Consequently, spider silks rank among the toughest known biomaterials. The large number of silk threads composing a web suggests that aerodynamic dissipation may also play an important role in stopping prey. Here, we quantify energy dissipation in orb webs spun by diverse species of spiders using data derived from high-speed videos of web deformation under prey impact. By integrating video data with material testing of silks, we compare the relative contributions of radial silk, the capture spiral and aerodynamic dissipation. Radial silk dominated energy absorption in all webs, with the potential to account for approximately 100 per cent of the work of stopping prey in larger webs. The most generous estimates for the roles of capture spirals and aerodynamic dissipation show that they rarely contribute more than 30 per cent and 10 per cent of the total work of stopping prey, respectively, and then only for smaller orb webs. The reliance of spider orb webs upon internal energy absorption by radial threads for prey capture suggests that the material properties of the capture spirals are largely unconstrained by the selective pressures of stopping prey and can instead evolve freely in response to alternative functional constraints such as adhering to prey. 相似文献
58.
59.
Patrick J. Gray Sean D. Conklin Todor I. Todorov Sasha M. Kasko 《Food additives & contaminants. Part A, Chemistry, analysis, control, exposure & risk assessment》2016,33(1):78-85
This paper reports the effects of rinsing rice and cooking it in variable amounts of water on total arsenic, inorganic arsenic, iron, cadmium, manganese, folate, thiamin and niacin in the cooked grain. We prepared multiple rice varietals both rinsed and unrinsed and with varying amounts of cooking water. Rinsing rice before cooking has a minimal effect on the arsenic (As) content of the cooked grain, but washes enriched iron, folate, thiamin and niacin from polished and parboiled rice. Cooking rice in excess water efficiently reduces the amount of As in the cooked grain. Excess water cooking reduces average inorganic As by 40% from long grain polished, 60% from parboiled and 50% from brown rice. Iron, folate, niacin and thiamin are reduced by 50–70% for enriched polished and parboiled rice, but significantly less so for brown rice, which is not enriched. 相似文献
60.
Dorian A. H. Hanaor Mohammed H. N. Assadi Sean Li Aibing Yu Charles C. Sorrell 《Computational Mechanics》2012,50(2):185-194
Ab initio density functional theory calculations of the relative stability of the anatase and rutile polymorphs of TiO2 were carried out using all-electron atomic orbitals methods with local density approximation. The rutile phase exhibited a moderate margin of stability of ~ 3 meV relative to the anatase phase in pristine material. From computational analysis of the formation energies of Si, Al, Fe and F dopants of various charge states across different Fermi level energies in anatase and in rutile, it was found that the cationic dopants are most stable in Ti substitutional lattice positions while formation energy is minimised for F? doping in interstitial positions. All dopants were found to considerably stabilise anatase relative to the rutile phase, suggesting the anatase to rutile phase transformation is inhibited in such systems with the dopants ranked F?>?Si?>?Fe?>?Al in order of anatase stabilisation strength. Al and Fe dopants were found to act as shallow acceptors with charge compensation achieved through the formation of mobile carriers rather than the formation of anion vacancies. 相似文献