全文获取类型
收费全文 | 226篇 |
免费 | 6篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 32篇 |
化学工业 | 46篇 |
金属工艺 | 8篇 |
机械仪表 | 4篇 |
能源动力 | 4篇 |
轻工业 | 13篇 |
无线电 | 22篇 |
一般工业技术 | 48篇 |
冶金工业 | 31篇 |
自动化技术 | 25篇 |
出版年
2022年 | 3篇 |
2021年 | 7篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 2篇 |
2014年 | 4篇 |
2013年 | 19篇 |
2012年 | 13篇 |
2011年 | 14篇 |
2010年 | 7篇 |
2009年 | 8篇 |
2008年 | 4篇 |
2007年 | 11篇 |
2006年 | 11篇 |
2005年 | 9篇 |
2004年 | 11篇 |
2003年 | 7篇 |
2002年 | 9篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 7篇 |
1998年 | 12篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有233条查询结果,搜索用时 31 毫秒
21.
Fear reactions of rats given bilateral lesions to the septum, hippocampus, or amygdala were compared with those of rats given sham lesions, in 2 animal models of anxiety: the shock-probe burying test and the elevated plus-maze test. Septal lesions produced anxiolytic effects in both tests (i.e., an increase in open-arm activity and a decrease in burying), whereas hippocampal and amygdaloid lesions produced neither of these effects. On the other hand, hippocampal and amygdaloid lesions impaired rats' passive avoidance of the electrified shock-probe, whereas septal lesions did not. These dissociations suggest that limbic structures such as the septum, amygdala, and hippocampus exert parallel but distinct control over different fear reactions. 相似文献
22.
Stability of a fracture toughness testing geometry is important to determine the crack trajectory and R-curve behavior of the specimen. Few configurations provide for inherent geometric stability, especially when the specimen being tested is brittle. We propose a new geometrical construction called the single edge notched clamped bend specimen (SENCB), a modified form of three point bending, yielding stable cracking under load control. It is shown to be particularly suitable for small-scale structures which cannot be made free-standing, (e.g., thin films, coatings). The SENCB is elastically clamped at the two ends to its parent material. A notch is inserted at the bottom center and loaded in bending, to fracture. Numerical simulations are carried out through extended finite element method to derive the geometrical factor f(a/W) and \(\hbox {K}_{\mathrm{I}}\) for different beam dimensions. Experimental corroborations of the FEM results are carried out on both micro-scale and macro-scale brittle specimens. A plot of \(\hbox {K}_{\mathrm{I}}\) vs a/W, is shown to rise initially and fall off, beyond a critical a/W ratio. The difference between conventional SENB and SENCB is highlighted in terms of \(\hbox {K}_{\mathrm{I}}\) and FEM simulated stress contours across the beam cross-section. The \(\hbox {K}_{\mathrm{IC}}\) ’s of bulk NiAl and Si determined experimentally are shown to match closely with literature values. Crack stability and R-curve effect is demonstrated in a PtNiAl bond coat sample and compared with predicted crack trajectories from the simulations. The stability of SENCB is shown for a critical range of a/W ratios, proving that it can be used to get controlled crack growth even in brittle samples under load control. 相似文献
23.
The site-specific DNA recombinase Flp shows two types of RNA cleavage activities on hybrid DNA-RNA substrates. One targets the phosphodiester position involved in DNA recombination and follows a related mechanistic path. In this two-step reaction, first-strand scission is mediated by a nucleophilic attack of the scissile phosphodiester bond by the active site tyrosine of Flp. The resultant 3'-O-phosphoryl tyrosine bond is then attacked by the adjacent 2'-hydroxyl group. The second activity targets the immediately adjacent phosphodiester bond to the 3' side using a distinct mechanism. In this reaction, the vicinal 2'-hydroxyl directly attacks the phosphate group in a manner that is reminiscent of the pancreatic RNase mechanism. The Flp protein can also be shown to possess a topoisomerase-like activity. 相似文献
24.
Oscar Rodríguez-González Markus Walkling-Ribeiro Shesha Jayaram Mansel W. Griffiths 《International Dairy Journal》2011,21(12):953-962
The effect of exposure of Escherichia coli O157:H7 to prior stress on the effectiveness of pulsed electric field (PEF) treatment of milk was studied. Cells were exposed to a variety of temperatures (7–45 °C), pH (4.0–7.0), osmotic conditions (0–10% NaCl), starvation (100 h at 25 °C), and cold shock (5 °C for 250 h). Stress responses were explained by the Gompertz and Weibull models with similar goodness-of-fit. Using these models, conditions that induced adequate stress were identified and used to pre-condition E. coli O157:H7 cells. The inactivation of the bacterial cells in milk by PEF was characterized by downward concavity with differences in mean time of resistance between cells exposed to temperature, acid or osmotic stress. Application of the Weibullian–Log-Logistic model indicated that, at higher field strengths, inactivation occurred at lower onset temperatures, and this was related to an increase in heat dissipation. 相似文献
25.
26.
Nithyanantham Thangamani Ashutosh S. Gandhi Vikram Jayaram Atul H. Chokshi 《Journal of the American Ceramic Society》2005,88(10):2696-2701
This study examined pressure consolidation of amorphous Al2 O3 –15 mol% Y2 O3 powders prepared by co-precipitation and spray pyrolysis. The two amorphous powders had similar true densities and crystallization sequences. Uniaxial hot pressing was carried out at 450°–600°C with a moderate pressure of 750 MPa. The co-precipitated powder could be hot pressed to a maximum relative density of 98% and remained amorphous. Pressure adversely affected the densification of the spray-pyrolyzed powder by favoring an early crystallization of γ-Al2 O3 phase at 580°C. Plastic deformation of the amorphous phase is believed to be responsible for the large densification of the amorphous powders. 相似文献
27.
Lingappa Rangaraj Siriyara J. Suresha Canchi Divakar Vikram Jayaram 《Metallurgical and Materials Transactions A》2008,39(7):1496-1505
Dense ZrB2-ZrC and ZrB2-ZrC
x∼0.67 composites have been produced by reactive hot pressing (RHP) of stoichiometric and nonstoichiometric mixtures of Zr and B4C powders at 40 MPa and temperatures up to 1600 °C for 30 minutes. The role of Ni addition on reaction kinetics and densification
of the composites has been studied. Composites of ∼97 pct relative density (RD) have been produced with the stoichiometric
mixture at 1600 °C, while the composite with ∼99 pct RD has been obtained with excess Zr at 1200 °C, suggesting the formation
of carbon deficient ZrC
x
that significantly aids densification by plastic flow and vacancy diffusion mechanism. Stoichiometric and nonstoichiometric
composites have a hardness of ∼20 GPa. The grain sizes of ZrB2 and ZrC
x∼0.67 are ∼0.6 and 0.4 μm, respectively, which are finer than those reported in the literature.
This article is based on a presentation given in the symposium entitled “Materials Behavior: Far from Equilibrium” as part
of the Golden Jubilee Celebration of Bhabha Atomic Research Centre, which occurred during December 15–16, 2006 in Mumbai,
India. 相似文献
28.
Proton exchange membrane fuel cell (PEMFC) performance degrades when impurities are present in the anode fuel gas, referred to as catalyst poisoning. This paper investigates the effect of carbon dioxide and ammonia as impurities in the anode gas of the PEMFC, and found that the presence of CO2 decreases the performance of the fuel cell by up to 10%. The performance loss depends on the CO2 concentration and the exposure time. The voltage loss is recoverable on passing pure hydrogen gas, indicating that a permanent poisoning of the catalyst layer has not taken place. Exposure of the fuel cell to ammonia beyond 20 ppm, even for a short duration, causes permanent PEMFC failure, probably due to the deterioration of the membrane. 相似文献
29.
El-Hag A. H. Dadarwal R. Gonzalez O. R. Jayaram S. H. Griffiths M. W. 《Industry Applications, IEEE Transactions on》2010,46(1):9-15
30.
The increasing demand in the diverse device applications of transparent conducting oxides(TCOs) requires synthesis of new TCOs of n- or p-type conductivity.This article is about materials engineering of ZnO—SnO2—ln2O3—Ga2O3 to synthesize powders of the quaternary compound Zn2-xSn1-xJnxGaxO4-δ in the stoichiometry of x = 0.2,0.3,and 0.4 by solid state reaction at 1275℃.Lattice parameters were determined by X-ray diffraction(XRD) technique and solubility of ln3+ and Ga3+ in spinel Zn2SnO4 was found at 1275℃.The solubility limit of ln3+ and Ga3+ in Zn2SnO4 is found at below x = 0.4.The optical transmittance approximated by the UV—Vis reflectance spectra showed excellent characteristics while optical band gap was consistent across 3.2 eV with slight decrease along increasing x value.Carrier mobility of the species was considerably higher than the older versions of zinc stannate spinel co-substitutions whereas the carrier concentrations were moderate. 相似文献