全文获取类型
收费全文 | 959篇 |
免费 | 5篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 10篇 |
综合类 | 2篇 |
化学工业 | 169篇 |
金属工艺 | 28篇 |
机械仪表 | 18篇 |
建筑科学 | 28篇 |
能源动力 | 28篇 |
轻工业 | 101篇 |
水利工程 | 4篇 |
石油天然气 | 2篇 |
无线电 | 77篇 |
一般工业技术 | 195篇 |
冶金工业 | 154篇 |
原子能技术 | 8篇 |
自动化技术 | 147篇 |
出版年
2023年 | 5篇 |
2022年 | 17篇 |
2021年 | 16篇 |
2020年 | 11篇 |
2019年 | 9篇 |
2018年 | 9篇 |
2017年 | 14篇 |
2016年 | 23篇 |
2015年 | 12篇 |
2014年 | 34篇 |
2013年 | 32篇 |
2012年 | 49篇 |
2011年 | 76篇 |
2010年 | 56篇 |
2009年 | 49篇 |
2008年 | 53篇 |
2007年 | 54篇 |
2006年 | 45篇 |
2005年 | 23篇 |
2004年 | 32篇 |
2003年 | 33篇 |
2002年 | 20篇 |
2001年 | 16篇 |
2000年 | 19篇 |
1999年 | 22篇 |
1998年 | 39篇 |
1997年 | 40篇 |
1996年 | 25篇 |
1995年 | 17篇 |
1994年 | 15篇 |
1993年 | 14篇 |
1992年 | 13篇 |
1991年 | 9篇 |
1990年 | 4篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1976年 | 6篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 2篇 |
1967年 | 1篇 |
排序方式: 共有971条查询结果,搜索用时 15 毫秒
1.
Analysis of electrocardiograms during atrial fibrillation 总被引:1,自引:0,他引:1
Vincent Jacquemet Adriaan van Oosterom Jean-Marc Vesin Lukas Kappenberger 《IEEE engineering in medicine and biology magazine》2006,25(6):79-88
The research discussed in this article is motivated by the search for an optimal classification of the different types of atrial fibrillation (AF) on the basis of recorded atrial signals. This would facilitate the selection of an optimal therapy. This article focuses on the biophysical models of the genesis of ECG waveforms during AF. The model of the electric activity of the atria was found to have sufficient realism to be used to describe the electric sources during AF. The inclusion of the volume conduction model resulted in electrocardiographic signals that are in all aspects similar to those observed clinically. The model is currently applied to solve various problems related to optimal signal preprocessing and extraction of features in AF signals for the classification of AF abnormalities. The biophysical model of the atrial activity is an essential element in this research, since it is capable of describing the electric source specifications derived from different hypotheses relating to the etiology of AF 相似文献
2.
3.
R Faccio M Grano S Colucci AZ Zallone V Quaranta AJ Pelletier 《Canadian Metallurgical Quarterly》1998,249(2):522-525
Integrins mediate cell adhesion and can induce different cellular responses, including changes in intracellular pH, changes and oscillation in intracellular free calcium, and protein phosphorylation on tyrosine. During bone resorption, the integrin alphav beta3 regulates adhesion of osteoclasts to bone extracellular matrix proteins, such us osteopontin (Opn). Adhesion via alphav beta3 is followed by osteoclast polarization onto the bone surface and by the onset of bone resorption. To characterize these events at the molecular level, we investigated the state of activation of alphav beta3 on the human osteoclast-like cell line GCT23 using the monoclonal antibody AP5 which binds to and can induce, under low calcium conditions, activated alphav beta3. By flow cytometry, approximately 50% of alphav beta3 on the surface of the osteoclast-like cell line GCT23 was reactive with AP5 and was therefore in the activated state. Incubation with AP5 in the presence of low calcium concentrations increased activated alphav beta3 to 90-100%. Activation of alphav beta3 increased the efficiency of GCT23 adhesion to Opn by 2-fold. Furthermore, haptotactic migration on Opn was also enhanced about 40% compared to control. We propose that changes in the activation state of alphav beta3 may be a regulation point for osteoclasts during bone resorption. 相似文献
4.
B. Van de Moortéle 《材料科学技术学报》2003,19(6)
The homogeneous plastic flow of fully amorphous and partially crystallized Zr(41.2)Ti(13.8)Cu(12.5)Ni(10)Be(22.5) bulk metallic glass (Vitl) has been investigated by compression tests at high temperatures in supercooled liquid region. Experimental results show that at sufficiently low strain rates, the supercooled liquid of the fully amorphous alloy reveals Newtonian flow with a linear relationship between the flow stress and strain rate. As the strain rate is increased, a transition from linear Newtonian to nonlinear flow is detected, which can be explained by the transition state theory. Over the entire strain rate interval investigated, however, only nonlinear flow is present in the partially crystallized alloy, and the flow stress for each strain rate is much higher. It is found that the strain rate-stress relationship for the partially crystaltized alloy at the given temperature of 646 K also obeys the sinh law derived from the transition state theory, similar to that of the initial homogeneous amo 相似文献
5.
6.
M Carrier TK Leung BC Solymoss R Cartier Y Leclerc LC Pelletier 《Canadian Metallurgical Quarterly》1996,61(5):1310-4; discussion 1314-5
BACKGROUND: A prospective, randomized clinical study involving 34 patients undergoing heart transplantation compared myocardial preservation of donor hearts maintained with continuous reperfusion with retrograde warm blood cardioplegia during surgical implantation versus the standard cold topical irrigation. METHODS: Hearts in both groups were arrested with a standard crystalloid solution and maintained in a cold saline solution during transportation. In the retrograde group, cardioplegia was administered through a catheter in the coronary sinus during surgical implantation. An average of 471 +/- 30 mL of hyperkalemic crystalloid solution diluted 1:4 in warm blood from the oxygenator was infused. In the standard group, the heart was kept cold by topical irrigation of cold saline solution and was reperfused only when the ascending aorta was unclamped. RESULTS: Preoperative characteristics of donors and recipients were similar in the two cohorts. Ischemic time average 139 +/- 12 minutes in the retrograde group compared with 130 +/- 11 minutes in the standard group (p = 0.57). Cardiopulmonary bypass time averaged 89 +/- 4 minutes in the retrograde group and 110 +/- 12 minutes in the standard group (p = 0.12). Defibrillation at reperfusion was performed in 4 patients (4/17, 24%) in the retrograde group and 12 patients (12/18, 67%) in the standard group (p = 0.01). There were no deaths in the retrograde group (0/17), whereas in the standard group, 3 patients (3/17) died of early graft failure (p = 0.11). Four early graft failures occurred in the standard group (p = 0.06). Two patients (2/17, 12%) were weaned from bypass with ventricular assist devices in the standard group. The number of subendocardial necrotic cells in the first two weekly endomyocardial biopsy specimens averaged 2.7 +/- 0.8 cells/mm2 in the retrograde group and 5.9 +/- 2.4 cells/mm2 in the standard group (p = 0.12). CONCLUSIONS: Retrograde warm blood reperfusion appears to improve the initial recovery of transplanted hearts. The technique is easy to use and may be a useful approach to graft protection during surgical implantation. 相似文献
7.
We measure the refractive index of thin films of TiO2 and SiO2 for given deposition parameters. Two complementary methods are used. The first is a postdeposition technique which uses the measurements of reflectance and transmittance in air. The second, in contrast, makes use of in situ measurements (under vacuum and during the actual deposition of the layer). The differences between the values deduced from the two methods can be explained by the amount of atmospheric moisture adsorbed by films. One tries to minimize these shifts for the two materials by choosing deposition parameters. The difficulties come from the absorption losses which must be as small as possible. We use the measured refractive indices of individual layers to give good numerical prediction of the wavelength shift (observed during the admittance of air after deposition in the vacuum chamber) of the transmittance peak of multidielectric Fabry-Perot filters. 相似文献
8.
Quinkal Isabelle; Davasse Valerie; Gaillard Jacques; Moulis Jean-Marc 《Protein engineering, design & selection : PEDS》1994,7(5):681-687
The widespread occurrence of Pro residues adjacent to Cys ligandsin the sequences of [4Fe-4S] electron transfer proteins hasnot yet found a functional basis. The two such Pro of Clostridiumpasteurianum 2[4Fe-4S] ferredoxin have been probed by site-directedmutagenesis. Any one of them, but not both simultaneously, canbe substituted without impairing the proper folding of the protein.The reduction potentials of the ferredoxin variants fall ina narrow range of <20 mV above the potential of the nativeprotein. The biological activities with C.pasteurianum hydrogenaseand pyruvate-ferredoxin oxidoreductase do not change significantly,except when Lys replaces Pro. In these cases, the data suggestthat the two clusters of 2[4Fe-4S] ferredoxin may not alwaysbe equivalent in the interaction with the redox partners. Destabilizationof the structure has been observed as the consequence of theProl9 or Pro48 substitutions. Using 2-D NMR, this effect hasbeen associated with perturbations of both the hydrogen bondnetwork and one amino acid side chain around the [4Fe-4S] clusters.Thus, the conserved Pro found in the binding motif of [4Fe-4S]clusters in proteins strongly stabilizes the active site butdoes not play an essential role in the mechanism of electrontransfer. 相似文献
9.
Jean-Marc Tulliani Laura MontanaroAlfredo Negro Mario Collepardi 《Cement and Concrete Research》2002,32(6):843-849
A case history of a severe degradation of concrete foundation plinths and piers of an about-35-year-old building located in Northern Italy is described. Significant amounts of gypsum, near ettringite and/or thaumasite were detected by X-ray diffraction analyses performed on ground concrete samples. Large gypsum crystals were mainly located at the interface between the cement paste and aggregates, as observed by scanning electron microscopy coupled to energy-dispersive spectroscopy microanalysis. The degradation effects increased with decreasing the distance of concrete structures from an absorbing well located in the courtyard of the building. The well was recognized as the sulfate source due to the microorganism metabolism of sulfur compounds present in the sewage. Consequences of this attack were a very poor bond strength between cement paste and aggregates and a severe cracking of the concrete cover of the steel reinforcement. 相似文献
10.
The damage induced in 3C-SiC epilayers on a silicon wafer by 2.3-MeV Si ion irradiation for fluences of 1014, 1015, and 1016 cm−2, was studied by conventional and high-resolution transmission electron microscopy (TEM/HRTEM). The evolution of extended defects and lattice disorder is followed in both the 3C-SiC film and Si substrate as a function of ion fluence, with reference to previous FTIR spectroscopy data. The likelihood of athermal unfaulting of native stacking faults by point defect migration to the native stacking faults is discussed in relation to damage recovery. Threshold energy densities and irradiation doses for dislocation loop formation and amorphous phase transformation are deduced from the damage depth profile by nuclear collisions. The role of electronic excitations on the damage recovery at high fluence is also addressed for both SiC and Si. 相似文献