全文获取类型
收费全文 | 7170篇 |
免费 | 394篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 97篇 |
综合类 | 5篇 |
化学工业 | 2069篇 |
金属工艺 | 85篇 |
机械仪表 | 169篇 |
建筑科学 | 285篇 |
矿业工程 | 7篇 |
能源动力 | 277篇 |
轻工业 | 1025篇 |
水利工程 | 64篇 |
石油天然气 | 65篇 |
无线电 | 533篇 |
一般工业技术 | 1092篇 |
冶金工业 | 308篇 |
原子能技术 | 37篇 |
自动化技术 | 1463篇 |
出版年
2024年 | 18篇 |
2023年 | 93篇 |
2022年 | 222篇 |
2021年 | 312篇 |
2020年 | 186篇 |
2019年 | 252篇 |
2018年 | 264篇 |
2017年 | 227篇 |
2016年 | 331篇 |
2015年 | 210篇 |
2014年 | 374篇 |
2013年 | 621篇 |
2012年 | 504篇 |
2011年 | 597篇 |
2010年 | 405篇 |
2009年 | 431篇 |
2008年 | 355篇 |
2007年 | 317篇 |
2006年 | 244篇 |
2005年 | 181篇 |
2004年 | 185篇 |
2003年 | 138篇 |
2002年 | 153篇 |
2001年 | 82篇 |
2000年 | 73篇 |
1999年 | 81篇 |
1998年 | 87篇 |
1997年 | 76篇 |
1996年 | 59篇 |
1995年 | 54篇 |
1994年 | 48篇 |
1993年 | 42篇 |
1992年 | 41篇 |
1991年 | 31篇 |
1990年 | 30篇 |
1989年 | 42篇 |
1988年 | 30篇 |
1987年 | 25篇 |
1986年 | 20篇 |
1985年 | 21篇 |
1984年 | 26篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1981年 | 14篇 |
1980年 | 15篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 9篇 |
1976年 | 7篇 |
1975年 | 3篇 |
排序方式: 共有7581条查询结果,搜索用时 0 毫秒
1.
2.
The thermal and mechanical properties and the morphologies of blends of poly(propylene) (PP) and an ethylene–(vinyl alcohol) copolymer (EVOH) and of blends of PP/EVOH/ethylene–(methacrylic acid)–Zn2+ ionomer were studied to establish the influence of the ionomer addition on the compatibilization of PP/EVOH blends and on their properties. The oxygen transmission rate (O2TR) values of the blends were measured as well. PP and EVOH are initially incompatible as was determined by tensile tests and scanning electronic microscopy. Addition of the ionomer Zn2+ led to good compatibility and mechanical behaviour was improved in all blends. The mechanical properties on extruded films were studied for 90/10 and 80/20 w/w PP/EVOH blends compatibilized with 10 % of ionomer Zn2+. These experiments have shown that the tensile properties are better than in the injection‐moulded samples. The stretching during the extrusion improved the compatibility of the blends, diminishing the size of EVOH domains and enhancing their distribution in the PP matrix. As was to be expected, the EVOH improved the oxygen permeation of the films, even in compatibilized blends. Copyright © 2004 Society of Chemical Industry 相似文献
3.
Fernando J. Muzzio Marcos Llusa Christopher L. Goodridge Nhat-Hang Duong Elizabeth Shen 《Powder Technology》2008,186(3):247-254
This paper investigates the effects of processing and equipment parameters of a ribbon blender (i.e. loading method of lubricant, fill level, blade speed and blade design) on magnesium stearate homogeneity. A core sampling technique is used to obtain at least one hundred samples per sampling event, which are extracted throughout the blender and yield a thorough characterization of the entire bed. The results presented here can be used as a guideline to develop appropriate blending processes and characterization protocols for ribbon blenders. 相似文献
4.
In this paper, we examine methods of characterizing somatosensory evoked potentials (SEP's) in both the time and frequency domains. We have found that the truncated impulse response (TIR) method produced an accurate time domain model of the SEP signals at model orders greatly reduced from the original state space matrix. The TIR method was valuable for smoothing signals that were slightly corrupted by noise. In this case, the simulated data sequence was close to the original data sequence in the mean squared error sense. For signals that were greatly corrupted by noise, the TIR method was not able to perform as well. Therefore, the TIR method was not a feature extraction method but was valuable for data simulation. In the frequency domain, we have used the autoregressive moving average model (ARMA) to parameterize the SEP signal. An overdetermined set of Yule-Walker equations was created to determine the autoregressive (AR) parameters of the original data with the model order established by the singular value decomposition. From these AR parameters, a residual time series was generated which was used to find the moving average parameters. The resulting ARMA model was used to produce a simulated data sequence. The frequency domain characteristics of the simulated sequence and the corresponding power spectral density of the ARMA filter were very close to the periodogram of the original data sequence. Accurate parameterization was achieved for the SEP waveforms at low filter lengths. 相似文献
5.
6.
7.
Fernando J Beltrn F Javier Rivas Olga Gimeno 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(9):973-984
Photocatalytic ozonation (1O3 + VUV + TiO2), ozonation (O3), catalytic ozonation (O3 + TiO2), ozone photolysis (O3 + VUV), photocatalysis (TiO2 + VUV) and photolysis (VUV) have been compared in terms of formation of intermediates, extent of, mineralization (TOC, COD, chloride, nitrate) and kinetics in the aqueous treatment of three phenols (phenol, p‐chlorophenol and p‐nitrophenol). In all cases, photocatalytic ozonation led to lower degradation times for chemical oxygen demand and total organic carbon removal. Intermediates formed were similar in the different oxidation systems with some exceptions. They can be classified into three different types: polyphenols (resorcinol, catechol, hydroquinone), unsaturated carboxylic acids (maleic and fumaric acids) and saturated carboxylic acids (glyoxylic, formic and oxalic acids). First order kinetic equations have been checked for the oxidation processes studied in the case of the parent compound. Rate constants of these systems have also been calculated. Copyright © 2005 Society of Chemical Industry 相似文献
8.
Gyrotron coaxial resonators with a longitudinally slotted inner cylinder are examined analytically using a surface impedance model, from which expressions for the electromagnetic field, ohmic quality (Q) factor, and characteristic equation of the transverse eigenvalues χ m,p are obtained. The major attributes of such resonators are expressed by the dependence of χm,p on the parameter C-defined as the ratio of the outer to inner radii of the coaxial structure. In that connection, the effect of the corrugation parameters on χm,p is particularly investigated on the basis of an expression derived for the slope function dχm,p,p/dC. It is shown that the χm,p(C) curve may either exhibit oscillatory behavior or present a flat portion over a wide range of C depending on the corrugation parameters chosen. The theory is checked against experiment in which resonant frequencies and total Q factors were measured for TE modes operating in the range of 8-16 GHz in a coaxial cavity with 40 slots. Good agreement is found in that the magnitude of the relative error in frequency is less than 0.5%. Corrugated coaxial resonators prove to be relevant to megawatt gyrotrons where highly selective cavities are required to ensure high conversion efficiency 相似文献
9.
10.
ChenluSONG WenjianWENG KuiCHENG HaiboQU PiyiDU GeSHEN GaorongHAN JuanYANC JoseM.F.Ferreira 《材料科学技术学报》2003,19(5):495-499
Fluorapatite/hydroxyapatite solid solution has better biological properties than other apatites, especially used as films or coatings. In this work, sol-gel preparation and in vitro behavior of fluorapatite/hydroxyapatite solid solution films on titanium alloy were investigated. Ca(NO3)2-4H20 and PO(OH)x(OEt)3-x were selected as precursors, and hexafluorophosphoric acid (HPFo) was used as a fluorine containing reagent. The Ca and P precursors were mixed with HPFo to keep the Ca/P molar ratio 1.67. The mixtures refluxed for 12 h were used as dipping sols for the preparation of the films. The phase of the films obtained at 600℃ was apatite. The F contents in the films increased with the concentrations of HPF6 in the dipping sols. The solid solution films were shown to have better stability than hydroxyapatite films, and a reasonably good bioactivity in the in vitro evaluation. 相似文献