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   872篇
  免费   1篇
化学工业   14篇
建筑科学   5篇
能源动力   4篇
轻工业   12篇
无线电   9篇
一般工业技术   28篇
冶金工业   761篇
原子能技术   2篇
自动化技术   38篇
  2019年   2篇
  2017年   2篇
  2016年   2篇
  2015年   1篇
  2014年   3篇
  2013年   25篇
  2012年   3篇
  2011年   3篇
  2009年   3篇
  2008年   1篇
  2006年   2篇
  2004年   2篇
  2003年   3篇
  2002年   3篇
  2001年   2篇
  2000年   3篇
  1999年   20篇
  1998年   241篇
  1997年   112篇
  1996年   78篇
  1995年   54篇
  1994年   48篇
  1993年   41篇
  1992年   8篇
  1991年   13篇
  1990年   17篇
  1989年   13篇
  1988年   15篇
  1987年   12篇
  1986年   11篇
  1985年   12篇
  1984年   3篇
  1983年   3篇
  1982年   3篇
  1981年   5篇
  1980年   8篇
  1979年   1篇
  1978年   5篇
  1977年   16篇
  1976年   64篇
  1975年   1篇
  1974年   1篇
  1973年   1篇
  1972年   1篇
  1971年   2篇
  1970年   2篇
  1965年   1篇
  1955年   1篇
排序方式: 共有873条查询结果,搜索用时 78 毫秒
1.
This paper provides a perspective on the contemporary debate over the production of social housing. Its main focus is on the issue that geographic patterns of service levels may be related to the type of supply program in place. The paper describes the social housing programs in Ontario, Canada over the post‐war period. Two main approaches have been taken: public housing, an essentially centralized program; and locally sponsored, third sector housing provided through non‐profit corporations and co‐operatives. The programs operated in different time periods and the analysis suggests they do have distinctive geographic distributions. The distribution of public housing shows strong correlations with need as defined by the incidence of poor housing conditions and mother‐led families. Provision under the localized program is also strongly correlated with the incidence of mother‐led families; however, the most consistent associations are with measures of socio‐economic status. These results may be partly understood in terms of the changing concept of housing need over the temporal span of the study. Program influences may be that the centralized nature of the public housing program enabled the direction of allocations to high need areas; whereas under the localized program the distribution is more closely related to the social differentiation of leadership roles in service provision under a third sector delivery model. As this approach becomes more prevalent it may be important to examine its potential impacts on service provision.  相似文献   
2.
Phase‐change alloys are the functional materials at the heart of an emerging digital‐storage technology. The GeTe‐Sb2Te3 pseudo‐binary systems, in particular the composition Ge2Sb2Te5 (GST), are one of a handful of materials which meet the unique requirements of a stable amorphous phase, rapid amorphous‐to‐crystalline phase transition, and significant contrasts in optical and electrical properties between material states. The properties of GST can be optimized by doping with p‐block elements, of which Bi has interesting effects on the crystallization kinetics and electrical properties. A comprehensive simulational study of Bi‐doped GST is carried out, looking at trends in behavior and properties as a function of dopant concentration. The results reveal how Bi integrates into the host matrix, and provide insight into its enhancement of the crystallization speed. A straightforward explanation is proposed for the reversal of the charge‐carrier sign beyond a critical doping threshold. The effect of Bi on the optical properties of GST is also investigated. The microscopic insight from this study may assist in the future selection of dopants to optimize the phase‐change properties of GST, and also of other PCMs, and the general methods employed in this work should be applicable to the study of related materials, for example, doped chalcogenide glasses.  相似文献   
3.
J. Skelton 《纺织学会志》2013,104(11):533-556
A theoretical investigation of the tensile, flexural and torsional behaviour of crimped filaments has been made; the relationships describing the filament behaviour are presented in graphical and in analytical form, and are verified experimentally. Two results are of particular importance in routine textile testing: it is shown that the Young's modulus of staple fibres measured with a tensile-testing machine is not subject to significant error caused by crimp; and a new expression is proposed which enables the optimum tension for the routine yarn-crimp test to be calculated.  相似文献   
4.
Health care providers and purchasers of health services have an opportunity to improve patient care and potentially save costs through the wise purchase of interactive health communication applications for patients and employees. Purchasing decisions based on evaluation and evidence should drive the design and development of new systems. The cycle of evaluation includes a needs assessment before system development, usability testing during development, and studies of use and outcomes in natural settings. This type of evidence is critical to our understanding of how best to provide health information and decision assistance to patients, employees, and others.  相似文献   
5.
Dense multichannel recordings of scalp electroencephalogram (EEG) were obtained in the vicinity of primary somatosensory cortex, time-locked to repetitive vibrotactile stimulation of sites on the right index finger of a single human subject. Frequency-domain analysis of cross-trial averages revealed prominent 'driving' responses in the EEG at the frequency of stimulation, which under specific stimulus conditions displayed pronounced changes in amplitude and topographic organization over brief (4 s) durations of stimulus exposure. The changes were systematic and physiologically coherent, evolving toward driving-response topographies observed in the same subject in conjunction with periodic microstimulation of single mechanoreceptive afferents whose receptive fields occupied corresponding positions on the digit. This dynamic process was orderly and reproducible, and could be controlled by manipulating factors such as the amplitude, frequency, and temporal spacing of the stimuli. The results are tentatively interpreted in light of a previously proposed neurophysiological model of stimulus-driven response plasticity in mammalian somatosensory cortex.  相似文献   
6.
7.
8.
Instrument precision is characterized by its signal-to-noise ratio, employing a new noise model. In this paper, this measure of precision of each instrument is used to characterize instrumentation, and an integration is achieved by jointly optimizing the feedback control law and the instrument signal-to-noise ratios to meet control system performance requirements. Iterative algorithms are proposed to find locally optimal solutions. Assuming that the signal-to-noise ratio is directly related to the instrumentation cost, this integration provides a systematic procedure to design a low cost control system. More importantly, this procedure identifies the performance-limiting components of a control system, identifies where to spend money on a system, and generates component design requirements from closed loop system performance criteria.  相似文献   
9.
The authors compared the extent of development of the germ cells of the human fetus ovaries developing in the organ culture and of control ovaries obtained of fetuses of "equivalent" age. The capacity to enter the meiosis prophase under conditions of the organ culture was expressed by the germ cells of fetuses of 8-9 week of gestation, and older; only individual oocytes reached the leptotene stage in the explants of the ovaries of 7-8 week fetuses. The oocytes at the leptotene, zygotene and pachitene stage appeared in the culture at the same periods as in the organism. However, the percentage of cells of these stages in the explant was as a rule lower than in control ovaries. In case of pulse administration of thymidine-3H into the culture labeled oocytes at the zygotene stage appeared in 4, and at the pachitene stage - in 14 days.  相似文献   
10.
Synthetic human C-peptide bearing a Tyrosine group at its amino end is labelled with 125iodine using chloramin T or hydrogen peroxide and lactoperoxidase. The results are compared applying both methods. Antiserum to synthetic human C-peptide (without Tyrosine) which was partially compared to rabbit albumin, is raised in guinea pigs and goats. Goats show to be superior to guinea pigs concerning antibody production. The so-called "hook effect" phenomenon is observed in setting up the standard curves for the radioimmunoassay. Monotonically decreasing standard curves are obtained on dilution of antiserum with a high antibody titer which was produced by repeated immunization in goats. Free C-peptide and C-peptide bound to antiserum are separated with the anxion exchange resin Amberlite. Using this separation technique we excluded unspecific binding of labelled C-peptide to protein fractions in serum of diabetics. The sensitivity of our radioimmunoassay is approx. 0.3 ng C-peptide/ml serum. Intra- and interassay variability are below 10%. Human proinsulin is the only substance found to crossreact with the antiserum.  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