全文获取类型
收费全文 | 2636篇 |
免费 | 61篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 18篇 |
化学工业 | 473篇 |
金属工艺 | 45篇 |
机械仪表 | 52篇 |
建筑科学 | 108篇 |
矿业工程 | 6篇 |
能源动力 | 58篇 |
轻工业 | 179篇 |
水利工程 | 30篇 |
石油天然气 | 6篇 |
无线电 | 216篇 |
一般工业技术 | 411篇 |
冶金工业 | 752篇 |
原子能技术 | 11篇 |
自动化技术 | 334篇 |
出版年
2021年 | 33篇 |
2020年 | 23篇 |
2019年 | 25篇 |
2018年 | 40篇 |
2017年 | 29篇 |
2016年 | 41篇 |
2015年 | 33篇 |
2014年 | 48篇 |
2013年 | 124篇 |
2012年 | 65篇 |
2011年 | 90篇 |
2010年 | 73篇 |
2009年 | 77篇 |
2008年 | 93篇 |
2007年 | 68篇 |
2006年 | 83篇 |
2005年 | 61篇 |
2004年 | 61篇 |
2003年 | 66篇 |
2002年 | 53篇 |
2001年 | 47篇 |
2000年 | 35篇 |
1999年 | 67篇 |
1998年 | 197篇 |
1997年 | 131篇 |
1996年 | 103篇 |
1995年 | 75篇 |
1994年 | 84篇 |
1993年 | 68篇 |
1992年 | 33篇 |
1991年 | 27篇 |
1990年 | 29篇 |
1989年 | 32篇 |
1988年 | 23篇 |
1987年 | 32篇 |
1986年 | 30篇 |
1985年 | 34篇 |
1984年 | 35篇 |
1983年 | 25篇 |
1982年 | 21篇 |
1981年 | 33篇 |
1980年 | 34篇 |
1979年 | 24篇 |
1978年 | 25篇 |
1977年 | 42篇 |
1976年 | 56篇 |
1975年 | 25篇 |
1974年 | 23篇 |
1973年 | 19篇 |
1971年 | 14篇 |
排序方式: 共有2699条查询结果,搜索用时 15 毫秒
1.
The aim of this work was to establish the important parameters that control the hot compaction behaviour of woven oriented polypropylene. Five commercial woven cloths, based on four different polypropylene polymers, were selected so that the perceived important variables could be studied. These include the mechanical properties of the original oriented tapes or fibres, the geometry of the oriented reinforcement (fibres or tapes), the mechanical properties of the base polymer (which are crucially dependant on the molecular weight and morphology), and the weave style. The five cloths were chosen so as to explore the boundaries of these various parameters, i.e. low and high molecular weight: circular or rectangular reinforcement (fibres or tapes): low or high tape initial orientation: coarse or fine weave.A vital aspect of this study was the realisation that hot compacted polypropylene could be envisaged as a composite, comprising an oriented ‘reinforcement’ bound together by a matrix phase, formed by melting and recrystallisation of the original oriented material. We have established the crucial importance of the properties of the melted and recrystallised matrix phase, especially the level of ductility, in controlling the properties of the hot compacted composite. 相似文献
2.
Kathryn Kromroy Kathleen Ward Paul Castillo Jennifer Juzwik 《Landscape and urban planning》2007,80(4):375-385
Urbanization was associated with loss and transformation of the oak forest in the Twin Cities (Minneapolis and St. Paul) metropolitan area (TCMA) over a recent 7-year interval. Between 1991 and 1998, urbanization increased based on several indicators: population density, area of developed land, and area of impervious surface—total impervious area and area within three classes of increasing degree of imperviousness (protected, affected, and degraded). We quantified relationships between changes in urbanization and changes in several parameters describing the oak forest at the scale of ecological subsection. Increased total and affected impervious area were strongly correlated with decreased area of oak forest when changes of the urbanization indicators and oak were expressed as percentages of the subsection area. Relationships were reversed when changes were expressed as percentages of the 1991 values. Increased population density was strongly correlated with increased loss in numbers and increased isolation of oak patches, but weakly correlated with loss of oak forest area. This is the first study to quantify relationships between changes in urbanization and changes in a specific forest cover type. Our results demonstrate complexities of urbanization impacts on a metropolitan forest resource, and highlight the importance of selected variables, spatial and temporal scales, and expressions of change when quantifying these relationships. 相似文献
3.
Liam Riordan 《电子设计技术》2006,13(9):110-110,112
高速DAC,比如模拟器件(AnalogDevices)公司的AD9776/78/79TxDAC系列,能提供差分输出,但对于低端交流电应用或高精度电平设置应用,配备差分转换电路的单端电流输出DAC提供了一种新颖的方法来生成差分波形控制功能。图1中的基本电路组合了电流输出DAC(即IC1,如8位AD5424D A C)和一个单端至差分运算放大级IC2、IC3A、IC3B——来产生要求的输出。对于双电源应用,可选择DAC的单极工作模式来达到DAC的最优性能。DAC利用单一运算放大器提供了双象限倍增或单极输出电压摆动。DAC的输出需要缓冲器,这是因为对施加到DAC输入端的代… 相似文献
4.
We have used a variety of methods to characterize the genome of the archaeon Methanosarcina thermophila TM-1. Pulsed-field gel analysis indicates a genome size of 2.8 Mb. We have constructed a bacterial artificial chromosome (BAC) library of M. thermophila and have used it to generate physical maps for this organism. The library is made up of 384 clones with an average insert size of 58 kb representing 8.0 genome equivalents. The utility of the library for low-resolution physical mapping was shown by identifying NotI linking clones and using these to order the NotI macrorestriction fragments of M. thermophila into a 2.8 Mb map. Hybridization of nine single copy genes and a 16S rRNA sequence to these macrorestriction fragments forms the basis for the first genetic map in this organism. High-resolution physical maps, consisting of overlapping clones, have been created using HindIII fingerprints of BAC clones. In this way, we identified a minimal path of five clones that span a 270 kb NotI fragment. The ease of manipulating BAC clones makes the BAC system an excellent choice for the construction of low-resolution and high-resolution physical and genetic maps of archaeal genomes. It also provides a substrate for future genome-sequencing efforts. 相似文献
5.
James A. Ward 《Information Systems Management》1997,14(1):62-65
The road to employee empowerment runs between true commitment on the one side and enforced compliance and chaos on the other. By following this column's guidelines, IS managers can steer their organizations to success and help free employees to be more creative in terms of both quality and productivity. 相似文献
6.
Accuracy of patient recall of opportunistic smoking cessation advice in general practice 总被引:6,自引:1,他引:5 下载免费PDF全文
OBJECTIVE: To determine the accuracy of patient recall of a question about smoking in a specified consultation in general practice; the accuracy of smokers' recall of advice to stop smoking; and predictors of accurate recall. DESIGN: Analysis of 1075 audiotapes was compared blind with matching patient questionnaires administered after the consultation to calculate sensitivity and specificity for patient recall as a dichotomous variable. Predictors of recall were determined by logistic regression. SETTING: General practitioner training practices, New South Wales, Australia. SUBJECTS: Thirty-four trainees and consecutive samples of their patients 16-65 years of age. RESULTS: Patient recall of a question about smoking had a high false positive rate of 21% but a sensitivity of 93%. Smokers over-reported advice to stop smoking (specificity 82%; sensitivity 92%). Predictors of accuracy of a question about smoking included patient sex (women 1.58 times more likely than men to be accurate); smoking status (smokers 1.7 times as likely as non-smokers to be accurate); and interval since consultation (those who completed their questionnaires within a week were 1.84 times more likely to be accurate). CONCLUSIONS: Patient recall is systematically biased towards over-reporting of a question about smoking status and, among smokers, of advice to quit. Although we recommend its continued application in health services evaluation, findings should be interpreted with caution, particularly if subjects are male or the interval between recall of smoking cessation advice and the occasion of service in which it might have occurred is considerably delayed.
相似文献
相似文献
7.
Danil Van Nieuwenhove Ward van der Tempel Riemer Grootjans Johan Stiens Maarten Kuijk 《IEEE sensors journal》2007,7(3):317-318
A current assisted photonic demodulator for use as a pixel in a 3-D time-of-flight imager shows nearly 100% static demodulator contrast and is operable beyond 30 MHz. An integrated tunable sensitivity control is also presented for increasing the distance measurement range and avoiding unwanted saturation during integration periods. This is achieved by application of a voltage on a dedicated drain tap showing a quenching of sensor sensitivity to below 1% 相似文献
8.
9.
Fundamental frequency techniques are used to analyze the series-parallel resonant converter under heavy load conditions, both with a continuous, but distorted parallel capacitor voltage waveform, and with a discontinuous capacitor voltage waveform. The analysis is validated with results from an experimental prototype. The application of the technique to the parallel-loaded L-C resonant converter is also considered. 相似文献
10.
CE Alpers CC Tsai KL Hudkins Y Cui L Kuller RE Benveniste JM Ward WR Morton 《Canadian Metallurgical Quarterly》1997,13(5):413-424
Focal and segmental glomerulosclerosis (FSG) with endothelial tubuloreticular inclusions (TRIs) is the typical lesion of human HIV-associated glomerulopathy. Autopsy studies showed the presence of FSG in 3 of 15 macaques dying 15-120 weeks after experimental infection with a simian immunodeficiency virus (SIVMne). Ultrastructural studies generally revealed numerous endothelial TRIs (also present in normals), mesangial expansion, and evidence of mesangial cell injury. One additional animal had a small-vessel polyarteritis with a proliferative and focally crescentic glomerulonephritis; seven animals had mild, multifocal interstitial nephritis. All animals had documented viremia after infection; 14 of 15 developed antibodies to SIV postinoculation. Additional postmortem findings included severe enterocolitis, encephalitis, and opportunistic infections. In contrast, autopsy studies of macaques infected with a type D simian retrovirus (SAIDS-D/Washington, SRV-2) for similar periods of time (n = 40) showed no evidence of FSG. One SRV-infected animal had a mild proliferative glomerulonephritis. These studies indicate SIV-infected primates may provide a relevant model for study of human HIV-associated nephropathy. They also indicate the variable pathology that can be seen in primate infections of distinct retrovirus types, each of which produces a simian immunodeficiency state that resembles human AIDS. 相似文献