全文获取类型
收费全文 | 401篇 |
免费 | 4篇 |
专业分类
电工技术 | 7篇 |
化学工业 | 56篇 |
金属工艺 | 7篇 |
机械仪表 | 20篇 |
建筑科学 | 20篇 |
能源动力 | 20篇 |
轻工业 | 34篇 |
石油天然气 | 2篇 |
无线电 | 15篇 |
一般工业技术 | 64篇 |
冶金工业 | 77篇 |
原子能技术 | 4篇 |
自动化技术 | 79篇 |
出版年
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 5篇 |
2017年 | 5篇 |
2016年 | 3篇 |
2015年 | 6篇 |
2014年 | 11篇 |
2013年 | 13篇 |
2012年 | 16篇 |
2011年 | 19篇 |
2010年 | 17篇 |
2009年 | 18篇 |
2008年 | 19篇 |
2007年 | 19篇 |
2006年 | 15篇 |
2005年 | 9篇 |
2004年 | 15篇 |
2003年 | 8篇 |
2002年 | 15篇 |
2001年 | 7篇 |
2000年 | 9篇 |
1999年 | 12篇 |
1998年 | 31篇 |
1997年 | 11篇 |
1996年 | 16篇 |
1995年 | 9篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 2篇 |
排序方式: 共有405条查询结果,搜索用时 31 毫秒
121.
Evaluation of an ultrasonic echo-tracking method for measurements of arterial wall movements in two dimensions 总被引:2,自引:0,他引:2
Cinthio M Ahlgren AR Jansson T Eriksson A Persson HW Lindström K 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2005,52(8):1300-1311
The longitudinal movement of blood vessel walls has so far gained little or no attention, as it has been presumed that these movements are of a negligible magnitude. However, modern high-resolution ultrasound scanners can demonstrate that the inner layers of the arterial wall exhibit considerable movements in the longitudinal direction. This paper evaluates a new, noninvasive, echo-tracking technique, which simultaneously can track both the radial and the longitudinal movements of the arterial wall with high resolution in vivo. Initially, the method is evaluated in vitro using a specially designed ultrasound phantom, which is attached to and moved by an X-Y system, the movement of which was compared with two high-resolution triangulation lasers. The results show an inaccuracy of 2.5% full scale deflection (fsd), reproducibility of 12 microm and a resolution of 5 microm, which should be more than sufficient for in vivo studies. The ability of the method is also demonstrated in a limited in vivo study in which a preselected part of the inner vessel wall of the right common carotid artery of a healthy volunteer is tracked in two dimensions over many cardiac cycles. The results show well reproducible x-y movement loops in which the recorded radial and longitudinal movements both are of the magnitude millimetre. 相似文献
122.
Describes a set of attitudes linked to the temporary closing of a major university. Data came from 434 students who completed questionnaires sent to their homes prior to the reopening of the university. Results indicate that the average student was concerned, yet moderate in his views. A minority of students, however, (from 19-44%) gave answers to key questions which seemed to represent a "change at any price" syndrome: drastic educational change, overturn of the administration, and violence. A final portion of the questionnaire elicited attitudes presumed to be held by significant others. Students believed that parents, relatives, and friends agreed with them about most issues other than the justification of the student actions. Specific changes in student attitudes during the 10-day closing are enumerated and thought to result from the interaction between students and significant others. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
123.
124.
Balogh I Ørbaek P Ohlsson K Nordander C Unge J Winkel J Hansson GA;Malmö Shoulder/Neck Study Group 《Applied ergonomics》2004,35(1):49-56
This study compares questionnaire assessed physical activity with direct technical measurements among cleaners and office workers, stratified regarding age, gender and self-reported neck/shoulder complaints. During two full working days number of steps was recorded by a pedometer, sitting/standing positions by a posimeter and heart rate by a Sport-Tester. In addition the subjects kept a work task diary for 10 days. There were high intra-individual variations in exposure between the days. Subjects with complaints rated their exposure higher than those without, although they in fact showed lower direct measured exposure. This may imply underestimation of exposure-effect relationships. Rate of perceived exertion showed low correlation with heart rate ratio within the two occupational groups, but high, 0.64 when the two groups were combined. Age and complaints explained 31% of the variance for the cleaners. 相似文献
125.
Sophie von Kraemer Kjell Wikander Göran Lindbergh Anders Lundblad Anders E.C. Palmqvist 《Journal of power sources》2008
Anatase TiO2 is evaluated as catalyst support material in authentic Pt-TiO2/C composite gas diffusion electrodes (GDEs), as a different approach in the context of improving the proton exchange membrane fuel cell (PEMFC) cathode stability. A thermal stability study shows high carbon stability as Pt nanoparticles are supported on TiO2 instead of carbon in the Pt-TiO2/C composite material, presumably due to a reduced direct contact between Pt and C. The performance of Pt-TiO2/C cathodes is investigated electrochemically in assembled membrane-electrode assemblies (MEAs) considering the added carbon fraction and Pt concentration deposited on TiO2. The O2 reduction current for the Pt-TiO2 alone is expectedly low due to the low electronic conductivity in bulk TiO2. However, the Pt-TiO2/C composite cathodes show enhanced fuel cell cathode performance with growing carbon fraction and increasing Pt concentration deposited on TiO2. The proposed reasons for these observations are improved macroscopic and local electronic conductivity, respectively. Electron micrographs of fuel cell tested Pt-TiO2/C composite cathodes illustrate only a minor Pt migration in the Pt-TiO2/C structure, in which anatase TiO2 is used as Pt support. On the whole, the study demonstrates a stable Pt-TiO2/C composite material possessing a performance comparable to conventional Pt–C materials when incorporated in a PEMFC cathode. 相似文献
126.
127.
Marie Austdal Line H. Tanger?s Ragnhild B. Skr?stad Kjell ?. Salvesen Rigmor Austgulen Ann-Charlotte Iversen Tone F. Bathen 《International journal of molecular sciences》2015,16(9):21520-21538
Hypertensive disorders of pregnancy, including preeclampsia, are major contributors to maternal morbidity. The goal of this study was to evaluate the potential of metabolomics to predict preeclampsia and gestational hypertension from urine and serum samples in early pregnancy, and elucidate the metabolic changes related to the diseases. Metabolic profiles were obtained by nuclear magnetic resonance spectroscopy of serum and urine samples from 599 women at medium to high risk of preeclampsia (nulliparous or previous preeclampsia/gestational hypertension). Preeclampsia developed in 26 (4.3%) and gestational hypertension in 21 (3.5%) women. Multivariate analyses of the metabolic profiles were performed to establish prediction models for the hypertensive disorders individually and combined. Urinary metabolomic profiles predicted preeclampsia and gestational hypertension at 51.3% and 40% sensitivity, respectively, at 10% false positive rate, with hippurate as the most important metabolite for the prediction. Serum metabolomic profiles predicted preeclampsia and gestational hypertension at 15% and 33% sensitivity, respectively, with increased lipid levels and an atherogenic lipid profile as most important for the prediction. Combining maternal characteristics with the urinary hippurate/creatinine level improved the prediction rates of preeclampsia in a logistic regression model. The study indicates a potential future role of clinical importance for metabolomic analysis of urine in prediction of preeclampsia. 相似文献
128.
Improved Heat Spreading Performance of Functionalized Graphene in Microelectronic Device Application
下载免费PDF全文
![点击此处可从《Advanced functional materials》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Yong Zhang Haoxue Han Nan Wang Pengtu Zhang Yifeng Fu Murali Murugesan Michael Edwards Kjell Jeppson Sebastian Volz Johan Liu 《Advanced functional materials》2015,25(28):4430-4435
It is demonstrated that a graphene‐based film (GBF) functionalized with silane molecules strongly enhances thermal performance. The resistance temperature detector results show that the inclusion of silane molecules doubles the heat spreading ability. Furthermore, molecular dynamics simulations show that the thermal conductivity (κ) of the GBF increased by 15%–56% with respect to the number density of molecules compared to that with the nonfunctionalized graphene substrate. This increase in κ is attributed to the enhanced in‐plane heat conduction of the GBF, resulting from the simultaneous increase of the thermal resistance between the GBF and the functionalized substrate limiting cross‐plane phonon scattering. Enhancement of the thermal performance by inserting silane‐functionalized molecules is important for the development of next‐generation electronic devices and proposed application of GBFs for thermal management. 相似文献
129.
Nikhil H. Jalani Manikandan Ramani Kristina Ohlsson Steve Buelte Greg Pacifico Richard Pollard Rhonda Staudt Ravindra Datta 《Journal of power sources》2006,160(2):1096-1103
Polarization curves, i.e., dc performance, and impedance spectral signatures of polybenzimidazole (PBI)–phosphoric acid (H3PO4) membrane fuel cells are obtained in the temperature range of 160–180 °C, in an effort to investigate the effect of temperature, anode humidification, various cathode stoichs, and use of oxygen versus air. Thus, in situ electrochemical impedance spectroscopy (EIS) was used to obtain various resistances, ohmic as well as charge-transfer resistances, under these conditions. The results obtained show that PBI–H3PO4 gel membrane fuel cells exhibit very good performance in the temperature range of 160–180 °C with an ohmic resistance similar to Nafion. Mass transfer limitations were determined by comparing performance polarization curves with air and oxygen along with EIS. Further EIS was also used to obtain signatures during fuel starvation, and electrical shorting across the cell. 相似文献
130.
Peter Lindblad Kjell Christensson Pia Lindberg Alexander Fedorov Fernando Pinto Anatoly Tsygankov 《International Journal of Hydrogen Energy》2002,27(11-12)
We have analyzed the filamentous cyanobacterium Anabaena PCC 7120 (wildtype) containing one nitrogenase, one uptake hydrogenase and one bidirectional hydrogenase and its hydrogen uptake deficient mutant AMC 414 for their H2 production capacities. Anabaena PCC 7120 and AMC 414 had similar growth rates in turbidostat mode with increased growth rates at higher light intensity. Rates of C2H2 reduction were similar for both strains. In contrast to the wildtype, AMC 414 produced H2 in a PhotoBioReactor (PhBR) using air as the lifting gas. The rate of H2 production increased with light intensity and was not even saturated at 456 μEm−2 s−1. H2 production increased significantly when replacing the air with argon. The maximal H2 production during outdoor conditions was recorded using AMC 414 with a peak at 14.9 ml H2 h−1 l−1. Despite the relatively high production, maximal efficiency of solar energy to H2 conversion was only 0.042%. A molecular method was developed to analyze the relative abundancies of weight and mutant in competition experiments in the PhBR. 相似文献