全文获取类型
收费全文 | 23232篇 |
免费 | 551篇 |
国内免费 | 24篇 |
专业分类
电工技术 | 219篇 |
综合类 | 18篇 |
化学工业 | 4426篇 |
金属工艺 | 492篇 |
机械仪表 | 365篇 |
建筑科学 | 924篇 |
矿业工程 | 88篇 |
能源动力 | 535篇 |
轻工业 | 1399篇 |
水利工程 | 261篇 |
石油天然气 | 207篇 |
武器工业 | 1篇 |
无线电 | 1426篇 |
一般工业技术 | 3365篇 |
冶金工业 | 6870篇 |
原子能技术 | 167篇 |
自动化技术 | 3044篇 |
出版年
2022年 | 147篇 |
2021年 | 242篇 |
2020年 | 198篇 |
2019年 | 264篇 |
2018年 | 297篇 |
2017年 | 302篇 |
2016年 | 366篇 |
2015年 | 292篇 |
2014年 | 456篇 |
2013年 | 1236篇 |
2012年 | 750篇 |
2011年 | 943篇 |
2010年 | 754篇 |
2009年 | 762篇 |
2008年 | 884篇 |
2007年 | 951篇 |
2006年 | 782篇 |
2005年 | 738篇 |
2004年 | 648篇 |
2003年 | 608篇 |
2002年 | 582篇 |
2001年 | 363篇 |
2000年 | 366篇 |
1999年 | 433篇 |
1998年 | 1133篇 |
1997年 | 786篇 |
1996年 | 620篇 |
1995年 | 500篇 |
1994年 | 452篇 |
1993年 | 506篇 |
1992年 | 343篇 |
1991年 | 259篇 |
1990年 | 313篇 |
1989年 | 345篇 |
1988年 | 303篇 |
1987年 | 287篇 |
1986年 | 308篇 |
1985年 | 321篇 |
1984年 | 297篇 |
1983年 | 294篇 |
1982年 | 242篇 |
1981年 | 271篇 |
1980年 | 271篇 |
1979年 | 253篇 |
1978年 | 234篇 |
1977年 | 283篇 |
1976年 | 318篇 |
1975年 | 196篇 |
1974年 | 174篇 |
1973年 | 179篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
James G. Strathman 《Journal of Urban Affairs》1992,14(1):79-92
ABSTRACT: A ranking of 33 urban studies and urban affairs programs in the US was developed from peer ratings obtained in a program survey and from citation activity reported in the Social Sciences Citation Index over the 1986–1989 period. A breakdown of citations by broadly defined subject areas is presented. The survey revealed a difference between Ph.D. and MUS/MA programs in the perceived relative importance of peer evaluation and citations as rating criteria. The survey results also indicate that the degree of familiarity with other programs is lower than what has been observed in most social science disciplines. 相似文献
22.
George Chryssolouris James E. Pierce Kristian Dicke 《International Journal of Flexible Manufacturing Systems》1992,4(3-4):309-330
This paper introduces a generic decision-making framework for assigning resources of a manufacturing system to production tasks. Resources are broadly defined production units, such as machines, human operators, or material handling vehicles; and tasks are activities performed by resources. In the specific context of FMS, resources correspond to individual machines; tasks correspond to operations to be performed on parts. The framework assumes a hierarchical structure of the system and calls for the execution of four consecutive steps to make a decision for the assignment of a resource to a task. These steps are 1) establishment of decision-making criteria, 2) formation of alternative assignments, 3) estimation of the consequences of the assignments, and 4) selection of the best alternative assignment. This framework has been applied to an existing FMS as an operational policy that decides what task will be executed on which resource of this FMS. Simulation runs provide some initial results of the application of this policy. It is shown that the policy provides flexibility in terms of system performance and computational effort. 相似文献
23.
We derive an effective single-band Hubbard type Hamiltonian for CuO2 planes. The Hamiltonian includes both electron-electron repulsion and electron-phonon coupling to oxygen vibrational modes. We start with first-principles density functional theory parameters and then map onto a single-band model. Unlike previous mappings to a single-band Hamiltonian, ours explicitly preserves the Fermi surface shape and matrix elements of the many-band Hamiltonian. We consider both in-plane oxygen breathing modes as well as out-of-plane tilting modes. The latter modes have a quadratic electron-phonon coupling, and are also highly anharmonic in La2CuO4 based superconductors. The coupling to breathing modes is too small to account for highT
c, while the coupling to quadratic modes is much stronger even though they would be neglected in a standard Migdal-Eliashberg approach to superconductivity. 相似文献
24.
DC Madsen 《Canadian Metallurgical Quarterly》1993,218(2):219; author reply 219-219; author reply 220
25.
Oxygen Tracer Diffusion in Vitreous Silica 总被引:2,自引:0,他引:2
Joseph D. Kalen Rethia S. Boyce James D. Cawley 《Journal of the American Ceramic Society》1991,74(1):203-209
Oxygen diffusion in vitreous silica glass is studied using the gas exchange technique. The tracer concentration profiles are consistent with a model based on two mechanisms, one network and the other interstitial. These processes are coupled through limited network–interstitial exchange. Nuclear reaction analysis and secondary ion mass spectrometry techniques are performed and compared. These results are compared to experiments on transport in thin silica films grown on single-crystal silicon. 相似文献
26.
Several types of ink are used in web offset printing. However, heatset inks predominate in general commercial work. In these inks, the vehicle consists of resin dissolved in a solvent, and drying takes place mainly by evaporation. In heatset web offset printing, the printed web is passed through dryers, which raise the temperature of the web enough to cause evaporation of the solvent. leaving only the resin to bind the pigment into a film and to the paper.
Since the solvents used in the heatset inks vary in boiling range from approximately 232° C to 316° C, and the solvent selected depends on the printing conditions, it is necessary to determine the vapor pressure values of heatset inks versus web temperatures for drying calculations. The isoteniscope method is limited to only the vapor pressure measurement of liquids. It cannot be used for materials such as heatset inks. To overcome this difficulty, an apparatus was designed and con- structed by TEC Systems for directly measuring the vapor pressure versus temperature of heatset inks from approximately 21°C to 316°C. In this paper, TEC's apparatus, test procedure developed, and typical test results for pure solvents and heatset inks will be described. 相似文献
Since the solvents used in the heatset inks vary in boiling range from approximately 232° C to 316° C, and the solvent selected depends on the printing conditions, it is necessary to determine the vapor pressure values of heatset inks versus web temperatures for drying calculations. The isoteniscope method is limited to only the vapor pressure measurement of liquids. It cannot be used for materials such as heatset inks. To overcome this difficulty, an apparatus was designed and con- structed by TEC Systems for directly measuring the vapor pressure versus temperature of heatset inks from approximately 21°C to 316°C. In this paper, TEC's apparatus, test procedure developed, and typical test results for pure solvents and heatset inks will be described. 相似文献
27.
Everyday memory performance was examined longitudinally in 2 groups of Ss meeting the diagnostic criteria for age-associated memory impairment (AAMI). One group of 157 participants in a drug trial for reversing memory loss in AAMI was tested over multiple sessions. The other group of 75 persons did not participate in a drug trial and thus was tested only twice. Both groups were retested for longitudinal follow-up about 4 yrs after initial session. Follow-up test performance remained fairly stable relative to initial performance in both groups. The drug study group showed large practice effects during the course of the drug studies, but these effects subsided after the drug studies' end. Implications regarding memory decline in the normal elderly and neuropsychological measurement issues are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
28.
29.
Summary Styrene polymerization was initiated by methylaluminoxane in the presence of haloalkane. The propagating species are shown by trapping experiments and electron paramagnetic resonance to be both radicals and cations. 相似文献
30.
Crook Thomas H.; Youngjohn James R.; Larrabee Glenn J.; Salama Maurice 《Canadian Metallurgical Quarterly》1992,6(2):123
Performance on computer-simulated, everyday memory tasks was found to deteriorate with age in 434 Belgian (aged 14–88 yrs) and 434 American Ss matched on gender and age. This age-related memory decline was reasonably consistent across samples. Difficulties in cross-cultural research and the advantages of ecologically valid measurement instruments are discussed. Instruments included a grocery list selective reminding test, the Wechsler Memory Scale, the Benton Visual Retention Test, and the Wechsler Adult Intelligence Scale (WAIS). (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献