全文获取类型
收费全文 | 40107篇 |
免费 | 4935篇 |
国内免费 | 1996篇 |
专业分类
电工技术 | 1259篇 |
技术理论 | 8篇 |
综合类 | 2364篇 |
化学工业 | 14881篇 |
金属工艺 | 2839篇 |
机械仪表 | 974篇 |
建筑科学 | 2363篇 |
矿业工程 | 863篇 |
能源动力 | 2566篇 |
轻工业 | 2142篇 |
水利工程 | 306篇 |
石油天然气 | 2193篇 |
武器工业 | 155篇 |
无线电 | 1992篇 |
一般工业技术 | 8297篇 |
冶金工业 | 2817篇 |
原子能技术 | 375篇 |
自动化技术 | 644篇 |
出版年
2024年 | 247篇 |
2023年 | 1013篇 |
2022年 | 1452篇 |
2021年 | 1515篇 |
2020年 | 1617篇 |
2019年 | 1505篇 |
2018年 | 1383篇 |
2017年 | 1562篇 |
2016年 | 1669篇 |
2015年 | 1542篇 |
2014年 | 2314篇 |
2013年 | 2454篇 |
2012年 | 2940篇 |
2011年 | 3176篇 |
2010年 | 2351篇 |
2009年 | 2397篇 |
2008年 | 1884篇 |
2007年 | 2362篇 |
2006年 | 2325篇 |
2005年 | 1951篇 |
2004年 | 1634篇 |
2003年 | 1481篇 |
2002年 | 1171篇 |
2001年 | 885篇 |
2000年 | 813篇 |
1999年 | 616篇 |
1998年 | 541篇 |
1997年 | 382篇 |
1996年 | 341篇 |
1995年 | 281篇 |
1994年 | 253篇 |
1993年 | 184篇 |
1992年 | 152篇 |
1991年 | 118篇 |
1990年 | 107篇 |
1989年 | 64篇 |
1988年 | 44篇 |
1987年 | 48篇 |
1986年 | 34篇 |
1985年 | 57篇 |
1984年 | 46篇 |
1983年 | 45篇 |
1982年 | 26篇 |
1981年 | 4篇 |
1980年 | 13篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1963年 | 1篇 |
1959年 | 6篇 |
1951年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
We have grown thin carbon films by pulsed laser deposition and have investigated the extent to which the properties of such
films, as well as the processes responsible for these properties, are laser wavelength dependent. Films were grown by ablating
material from a graphite target onto room temperature Si(100) substrates with 1064 and 248 nm laser radiation. The films were
analyzed byin situ electron energy loss spectroscopy and byex situ Raman spectroscopy. The results indicated that films grown with 1064 nm ablation were graphitic, while those grown with 248
nm radiation were diamond-like. We have also examined the mass and kinetic energy distributions of the particles ejected from
graphite by the two laser wavelengths. The results indicated that irradiation of graphite with 1064 nm laser radiation results
in the ejection of a series of carbon cluster ions C
n
+
(1 ≤ n ≤ 30) with mean kinetic energies less than 5 eV. Ablation of graphite with 248 nm radiation results in the ejection
of primarily C
2
+
and C
3
+
with mean kinetic energies of 60 and 18 eV, respectively. These results suggest that large, low energy clusters produce graphitic
films, while small, high energy clusters produce films of diamond-like carbon. 相似文献
52.
D. E. Wetzler P. F. Aramendía M. L. Japas R. Fernández-Prini 《International Journal of Thermophysics》1998,19(1):27-42
Thermal diffusivities of supercritical CO2 and C2H6 were determined over a wide density range with a photothermal technique. The thermal lens, formed by the degradation of the absorbed light energy as heat by the sample, allows the employment of a nonequilibrium method in the critical region. Controlling the refractive-index gradient, i.e., a density gradient, perturbations can be maintained at levels where convection is negligible. An easy-to-operate setup allowed us to measure thermal diffusivities in the density ranges 5 to 20 mol·dm–3 for CO2 at 308 and 313 K and 2 to 12 mol·dm–3 for C2H6 at 308 K with a standard precision of 15%. 相似文献
53.
Aggregates of carbon black (CB) in a polymer matrix have a tendency to form a CB network. The dynamic mechanical properties of binary systems of chlorinated polyethylene (CPE) and CB or 3,9‐bis{1,1‐dimethyl‐2[β‐(3‐tert‐butyl‐4‐hydroxy‐5‐methylphenyl)propionyloxy]ethyl}‐2,4,8,10‐tetraoxaspiro[5,5]‐undecane (AO‐80) and their ternary systems were investigated. It was found that the dynamic mechanical properties of those systems depend on the colloidal properties, surface oxides, and surface modification of CB. For binary systems of CPE and CB, oxidized CB gives a high modulus at low strain amplitude and a large Payne effect compared with untreated CB. In contrast, the reverse effect was observed for their ternary systems. Consequently, a good micro‐dispersion is obtainable by surface modification due to physical adsorption of AO‐80 on oxidized CB particles via hydrogen bonds. © 2003 Society of Chemical Industry 相似文献
54.
简要介绍了国内少有的干气催化部分氧化转化制氢工艺,重点讨论了转化水碳比的控制条件,对降低水碳比操作进行了有益地探讨。 相似文献
55.
56.
Works of adhesion at the carbon fiber-liquid interface determined using a modified wetting technique
Works of adhesion WSL between aqueous solutions with pH values in the range from 1 to 14 and carbon fibers from different sources, which were additionally treated in an inert atmosphere or in oxygen, were measured by use of a microbalance. These works of adhesion WSL were found to show distinct stepwise dependencies on the pH value. The works of adhesion WSL are attributed to dispersion interactions WSL1 and various acid-base interactions wslab—in the latter case between the acidic and basic surface groups of carbon and the various basic and acidic aqueous solutions. 相似文献
57.
活性炭单柱提取肌苷新技术研究 总被引:1,自引:0,他引:1
活性炭单柱提取肌苷新技术研究李永泉,张进,姚恕,郑莲英,俞峰(杭州大学生物系杭州310028)(浙江大学化工系杭州310027)关键词:肌苷,提取技术,活性炭单柱1前言目前,国内肌苷发酵后处理工艺落后,在分离提取工序中肌苷损失严重,收率一般只有50%... 相似文献
58.
Asbestos fibres, of the chrysotile variety, and chopped carbon fibres were pretreated by an in-situ polycondensation technique eventually resulting in a polyamide coating on the fibre surface. Ionomer based composites containing either carbon or asbestos fibres in random in plane fibre orientation were prepared, and the influence of this coating process on the tensile properties was investigated. It was found that for the asbestos-filled composites the presence of the nylon 6,6 interlayer improves the tensile performance, especially at moderate polyamide depositions. This is not the case with the pretreated carbon-filled composites for which carbon fibres with higher polyamide contents are preferred. Combinations of the treated asbestos fibres with carbon and/or aramid fibres may be used to reduce the asbestos content in asbestos-only based engineering plastics. 相似文献
59.
The effect of heat treatment on microstructure of a plain-weave carbon fabric reinforced carbon-carbon composite with phenolformaldehyde-derived carbon matrix was investigated by X-ray diffraction. The diffraction patterns were analysed by the least-square fitting program Carbonxs. After heat treatment from 1000 to 2800 °C the interplanar distance of (002) planes decreased from 3.488 to 3.420 Å and the lattice parameter in basal plane increased from 2.440 to 2.464 Å, respectively. Simultaneously, the coherent block size in the basal plane directions increased from 18 to 54 Å, which was accompanied by an increase of the fraction of organised carbon atoms from 0.50 to 0.85. The 002 diffraction profile of the composite was much narrower than the sum of peaks of the matrix and fabric alone. This can probably be caused by a better crystallographic ordering (or by a partial graphitisation) of the matrix in the composite. On the other hand, the composite Young’s modulus slightly decreased with the treatment temperature increasing from 2200 to 2800 °C in spite of the established strong improvement of fibre crystallinity and, therefore, fibre modulus. The mechanisms diminishing the modulus of composite (e.g. partial matrix graphitisation at the fibre/matrix interface and decreasing fibre/matrix contact area) probably prevailed over the increasing contribution of the fibre modulus. 相似文献
60.