全文获取类型
收费全文 | 368篇 |
免费 | 11篇 |
专业分类
电工技术 | 3篇 |
综合类 | 2篇 |
化学工业 | 90篇 |
金属工艺 | 9篇 |
机械仪表 | 14篇 |
建筑科学 | 7篇 |
矿业工程 | 2篇 |
能源动力 | 7篇 |
轻工业 | 12篇 |
水利工程 | 1篇 |
无线电 | 55篇 |
一般工业技术 | 87篇 |
冶金工业 | 34篇 |
原子能技术 | 5篇 |
自动化技术 | 51篇 |
出版年
2024年 | 2篇 |
2023年 | 4篇 |
2022年 | 11篇 |
2021年 | 8篇 |
2020年 | 6篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 13篇 |
2015年 | 10篇 |
2014年 | 13篇 |
2013年 | 23篇 |
2012年 | 30篇 |
2011年 | 30篇 |
2010年 | 20篇 |
2009年 | 26篇 |
2008年 | 26篇 |
2007年 | 17篇 |
2006年 | 15篇 |
2005年 | 8篇 |
2004年 | 6篇 |
2003年 | 11篇 |
2002年 | 11篇 |
2001年 | 7篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1977年 | 5篇 |
1976年 | 1篇 |
1974年 | 2篇 |
排序方式: 共有379条查询结果,搜索用时 171 毫秒
41.
The temperature dependences of electrical conductivity, σ, and Seebeck coefficient, S, for some new pyridium monoquaternary salts derivatives, 1-(p-R-phenacyl)-4-{[(1′-ethylcarboxylate)-(3′-p-R′-phenacyl)]-7′-indolizinyl}pyridinium bromides have been studied.The film samples (d = 0.08-0.28 μm) have been deposited onto glass by an immersion technique (dimethylformamide was used as a solvent).The investigated compounds behave as typical p-type polycrystalline semiconductors. The activation energy of electrical conduction ranged between 0.65 and 1.72 eV, while the ratio of charge carrier mobilities laid in the range (0.60-0.83).The model based on band gap representation is suitable in explaining the electronic transport in present compounds in the higher temperature range (385-500 K). 相似文献
42.
Foods are complex multi-component systems which are composed of volatile and non-volatile substances. The flavour profile of a food is an important criterion for the selection of our foodstuffs. The main objective of this study was the clarification of the complex relationships of the flavour release as a function of the composition of the food matrix at molecular level. Therefore the influence of matrix effects onto the odorants partition coefficients in oil–water model systems and a custard sample were investigated. The studies included a series of lactones, ester and alcohols (γ- and δ-octalactone, γ- and δ-nonalactone, γ- and δ-decalactone, ethyl hexanoate, 3-methyl-1-butanol and 2-phenylethanol). The partition coefficients were determined using static headspace gas chromatography (SH-GC). The results indicated that the custard/air partition coefficients of selected odorants are located between the water/air- and miglyol/air partition coefficients. Furthermore the mass transfer rates of selected odorants were investigated in custard- and milk powder–water samples. The values of the mass transfer rate were found higher in milk powder/water systems than in custard model. Nevertheless the results indicated that the viscosity of the matrix did not significantly influence the values of mass transfer rate of selected flavour compounds. 相似文献
43.
44.
Assaf Gal Vlad Brumfeld Steve Weiner Lia Addadi Dan Oron 《Advanced materials (Deerfield Beach, Fla.)》2012,24(10):OP77-OP83
Cystoliths are amorphous calcium carbonate bodies that form in the leaves of some plant families. Cystoliths are regularly distributed in the epidermis and protrude into the photosynthetic tissue, the mesophyll. The photosynthetic pigments generate a steep light gradient in the leaf. Under most illumination regimes the outer mesophyll is light saturated, thus the photosynthetic apparatus is kinetically unable to use the excess light for photochemistry. Here we use micro‐scale modulated fluorometry to demonstrate that light scattered by the cystoliths is distributed from the photosynthetically inefficient upper tissue to the efficient, but light deprived, lower tissue. The results prove that the presence of light scatterers reduces the steep light gradient, thus enabling the leaf to use the incoming light flux more efficiently. MicroCT and electron microscopy confirm that the spatial distribution of the minerals is compatible with their optical function. During the study we encountered large calcium oxalate druses in the same anatomical location as the cystoliths. These druses proved to have similar light scattering functions as the cystoliths. This study shows that certain minerals in the leaves of different plants distribute the light flux more evenly inside the leaf. 相似文献
45.
Gerlinde Rusu Nicolas Joly Geza Bandur Ionel Manoviciu Patrick Martin Lucian Rusnac 《Journal of Polymer Research》2011,18(6):2495-2504
New inulin-based materials were obtained by graft-copolymerization of inulin (poly-β(1 → 2)-fructoside) with 2-ethyl-hexyl
acrylate. Inulin mixed esters were first synthesized by acylation using methacryloyl and palmitoyl chlorides. Further, these
esters were copolymerized with 2-ethyl-hexyl acrylate in order to obtain bio-based crosslinked materials that could be used
as commodity plastics and that would have biodegradable properties. The obtained products were characterized using FT-IR and
1H NMR spectroscopies, thermogravimetry; differential scanning calorimetry, and activation energy for the degradation processes
(using Kissinger method) was calculated. These biomaterials were also subjected to density measurement, tensile and torsion
tests to evaluate their mechanical properties. 相似文献
46.
Bei der Ermittlung von kontinuierlichen ZTU-Schaubildern unter dem Einfluß einer Warmverformung von rund 50% wurde festgestellt, daß die Wechselbeziehungen zwischen der verformungs- und legierungsbedingten Realstruktur des Austenits und den Umwandlungsvorgängen bei der anschließenden Abkühlung sich stark auf die Kinetik der γ/α-Umwandlung auswirkt. Änderungen im Löslichkeitsverhalten und in der Diffusionskinetik der Legierungselemente sowie in der Selbstdiffusion des Eisens als Folge der durch die bei der Umformung eingebrachten Gitterfehler im Austenit beeinflussen sowohl die Keimbildung als auch das Wachstum der verschiedenen Umwandlungsphasen. Die Ergebnisse von Versuchen an mehreren niedriglegierten Kohlenstoffstählen zeigen auf, daß die Austenitumwandlung zu Ferrit und Perlit durch eine erhöhte Konzentration an Gitterleerstellen infolge der Warmumformung beschleunigt wird. Die martensitische Umwandlung wird ebenso von der Defektstellenkonzentration im verformten Austenit in dem Sinne beeinflußt, daß die Martensit-Starttemperatur Ms im Vergleich zum unverformten Zustand zu etwa 30 bis 40°C niedrigeren Werten verschoben wird. Es liegen Beweise vor, daß die Erniedrigung der Ms-Temperatur zusätzlich mit der Entstehung einer starken {123} ?412?-Austenittextur verknüpft ist. Bei umwandlungsträgen Stahlsorten wurden beim kontinuierlichen Abkühlen umwandlungsfreie Bereiche zwischen der Ferrit/Perlit- und Bainitstufe als Folge der Warmumformung festgestellt. Teilweise wird die bainitische Umwandlung völlig unterdrückt. Die Ausbildung einer starken Textur im Austenit vor der Bainitumwandlung führt zu einer Senkung der Bainit-Starttemperatur von bis zu 100°C bei höheren Abkühlraten. 相似文献
47.
Vlad Ionescu 《Systems & Control Letters》1992,18(5)
This paper deals with the l2-problem for time-varying discrete systems. The problem considered is a deterministic counterpart of the well-known LQG problem. An adequate l2-seminorm for linear bounded input-output operators is introduced in order to express the optimality criterion. The solution is obtained by successively reducing the original problem to simpler ones putting in evidence the Separation Principle of the optimal controller. 相似文献
48.
O. Újsághy K. Vladár G. Zaránd A. Zawadowski 《Journal of Low Temperature Physics》2002,126(3-4):1221-1231
In studying the different Kondo problems it is generally assumed that breaking the electron-hole symmetry does not affect the perturbative infrared divergencies. It is shown here that, in contrast, breaking that symmetry may in some cases lead to observable modifications while in other cases it does not. 相似文献
49.
A.M. Ionescu A. Chovet A.E. Popescu A. Rusu D. Steriu 《Microelectronics Reliability》1998,38(5):753-758
A new extraction method for source series resistance and mobility reduction coefficient with transverse field, based on the MOSFET transconductance modeling in the saturation region, is reported. The simple associated transconductance model also appears to be extremely useful for optimal parameter extraction. The proposed method is validated on partially depleted SIMOX MOSFETs. 相似文献
50.
M. Rusu M. BärD. Fuertes Marrón S. LehmannTh. Schedel-Niedrig M.Ch. Lux-Steiner 《Thin solid films》2011,519(21):7304-7307
The transport properties of thin-film solar cells based on wide-gap CuGaSe2 absorbers have been investigated as a function of the bulk [Ga]/[Cu] ratio ranging from 1.01 to 1.33. We find that (i) the recombination processes in devices prepared from absorbers with a composition close to stoichiometry ([Ga]/[Cu] = 1.01) are strongly tunnelling assisted resulting in low recombination activation energies (Ea) of approx. 0.95 eV in the dark and 1.36 eV under illumination. (ii) With an increasing [Ga]/[Cu] ratio, the transport mechanism changes to be dominated by thermally activated Shockley-Read-Hall recombination with similar Ea values of approx. 1.52-1.57 eV for bulk [Ga]/[Cu] ratios of 1.12-1.33. The dominant recombination processes take place at the interface between CdS buffer and CuGaSe2 absorber independently from the absorber composition. The increase of Ea with the [Ga]/[Cu] ratio correlates with the open circuit voltage and explains the better performance of corresponding solar cells. 相似文献