全文获取类型
收费全文 | 108829篇 |
免费 | 11507篇 |
国内免费 | 5165篇 |
专业分类
电工技术 | 4771篇 |
技术理论 | 1篇 |
综合类 | 5640篇 |
化学工业 | 33952篇 |
金属工艺 | 13642篇 |
机械仪表 | 3167篇 |
建筑科学 | 5643篇 |
矿业工程 | 1579篇 |
能源动力 | 5270篇 |
轻工业 | 11554篇 |
水利工程 | 817篇 |
石油天然气 | 2717篇 |
武器工业 | 1036篇 |
无线电 | 6070篇 |
一般工业技术 | 22270篇 |
冶金工业 | 4727篇 |
原子能技术 | 955篇 |
自动化技术 | 1690篇 |
出版年
2024年 | 714篇 |
2023年 | 2469篇 |
2022年 | 3574篇 |
2021年 | 4512篇 |
2020年 | 4611篇 |
2019年 | 3945篇 |
2018年 | 4091篇 |
2017年 | 4748篇 |
2016年 | 4796篇 |
2015年 | 4911篇 |
2014年 | 6231篇 |
2013年 | 7648篇 |
2012年 | 7071篇 |
2011年 | 8246篇 |
2010年 | 5733篇 |
2009年 | 6159篇 |
2008年 | 5128篇 |
2007年 | 6040篇 |
2006年 | 5788篇 |
2005年 | 4505篇 |
2004年 | 4157篇 |
2003年 | 3472篇 |
2002年 | 2999篇 |
2001年 | 2278篇 |
2000年 | 2034篇 |
1999年 | 1572篇 |
1998年 | 1380篇 |
1997年 | 1226篇 |
1996年 | 945篇 |
1995年 | 795篇 |
1994年 | 595篇 |
1993年 | 477篇 |
1992年 | 471篇 |
1991年 | 400篇 |
1990年 | 408篇 |
1989年 | 372篇 |
1988年 | 189篇 |
1987年 | 118篇 |
1986年 | 116篇 |
1985年 | 129篇 |
1984年 | 118篇 |
1983年 | 74篇 |
1982年 | 95篇 |
1981年 | 31篇 |
1980年 | 49篇 |
1979年 | 11篇 |
1975年 | 10篇 |
1974年 | 8篇 |
1959年 | 8篇 |
1951年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Preparation of polyimide-epoxy composites 总被引:2,自引:0,他引:2
Kevin Gaw Mitsutoshi Kikei Masa-aki Kakimoto Yoshio Imai 《Reactive and Functional Polymers》1996,30(1-3):85-91
The formation of a three dimensional network of crosslinked epoxy leads all unmodified epoxies to have inherent brittleness and relatively low degradation temperatures. Polyimides, on the other hand, are widely used for applications that require high degrees of flexibility and thermal resistance. Here, we have focused on the preparation of epoxy systems cured with polyamic acids instead of traditional amino-group-containing hardening agents. The cure behavior and potential reaction mechanisms of EPON 828 resin and polyamic acid mixtures were evaluated by DSC and TGA. Thermal analysis showed a complex reaction sequence taking place in the mixture and also determined the extent of reaction of the polyamic acid with itself and the competitive reaction of the polyamic acid with the epoxy. The compositions of the mixtures were varied to see the dependence of the cure behavior on component concentrations. Solutions of the two components did not phase separate and also phase separation was not apparent either optically or microscopically in the cured samples. This phase behavior was attributed to a unique in situ reaction. A novel solvent system for the polyamic acid precursor was also used. 相似文献
82.
R. C. Pennefather D. H. Boone 《International Journal of Pressure Vessels and Piping》1996,66(1-3):351-358
Cyclic oxidation tests were performed on a large variety of commercially available overlay coatings. The results of cyclic oxidation tests confirmed that the composition of the coating as well as the processing method of the coating can affect the life of the system. Coating life was determined by the time to coating penetration and initiation of substrate attack. As this work was part of a effort to evaluate the relative protectiveness of available coating systems for Industrial Gas Turbine applications at relatively high temperature, an extensive testing programme was undertaken. The different coatings were tested to visual failure. The results presented in this paper concentrate on the surface instability of the coating. Apart from usual oxidation of the coating an additional degradation mechanism was observed. A mechanical effect caused by the instability of the coating as a result of the difference in the thermal coefficient of expansion and mechanical properties between the substrate and coating. This effect, the so-called “rumpling” effect, resulted in a significant reduction in time to penetration and was in some systems the life controlling factor. 相似文献
83.
K Umakantham K Chandramouli G Nageswara Rao A Bhanumathi 《Bulletin of Materials Science》1996,19(2):345-355
Rare-earth doped strontium barium niobates were synthesized using usual ceramic technique. The dopants are La, Ce, Gd, Sm
and Nd. The materials were characterized by XRD and density measurements. The grain sizes were determined from SEM analysis.
Lattice parameters changed uniformly with rare-earth dopants in unfilled structures. Density measurements and SEM analysis
confirmed only minute changes in the densities of the ceramics. 相似文献
84.
85.
The dye-sensitized TiO2 complex films were prepared by the dye coat onto TiO2 surfaces,and the sensitizing mechanism and adsorption properties of the dye-sensitized TiO2 complex films were inverstigated.The influence of the application conditions of dye adsorbed on TiO2 films on the amount of dye adsorption was discussed.Experimental results show that the concentration,the temperature of dye solutions and the dipping time of TiO2 films in the dye solutions have a significant influence on the amount of dye adsorption.Cell test indicates that the conversion efficiency of light to electricity increases with the amount of dye adsorption. 相似文献
86.
液相添加剂对PTCR陶瓷电性能的影响 总被引:3,自引:2,他引:1
液相添加剂AST(Al2O3+SiO2+TiO2)对BaTiO3陶瓷材料电性能的影响很大,随着Al2O3含量的增加,材料的电性能降低;SiO2、TiO2的物理特性对材料电性能影响较大;过量TiO2对材料PTC效应有重要影响,适当过量TiO2含量,可得到性能优良的PTCR陶瓷。 相似文献
87.
氮化硅的性能及其聚合物材料 总被引:1,自引:0,他引:1
陈继兰 《高分子材料科学与工程》1996,12(6):144-147
叙述了氮化硅(Si3N4)的性能并制备了含Si3N4的聚合物材料,这种材料在医学上具有重要价值,对改变医学方面的概念、和对促进人类健康长寿具有重要意义。 相似文献
88.
彩色PDP用玻璃基板 总被引:4,自引:0,他引:4
本文讨论了彩色PDP现用钠钙玻璃的热稳定性,指出由于这种玻璃在热处理过程中易变形和收缩,因而不适合作大面积彩色PDP基板材料,介绍了彩色PDP基板玻璃的制造方法和特点。最后介绍了日本旭硝子公司和美国康宁公司各自为彩色PDP新开发的玻璃基板材料PD200和CS25。 相似文献
89.
César I. Beristain Ebner Azuara Hugo S. Garcia & Eduardo J. Vernon-Carter 《International Journal of Food Science & Technology》1996,31(5):379-386
The water and oil uptake of mesquite and arabic gums in powdered form was studied at temperatures of 23, 35 and 45°C. A previously proposed equation to predict osmotic equilibrium was tested using the experimental data with both gums and a good statistical fit was obtained. Mesquite gum showed the highest water and oil absorption at all temperatures studied. Temperature dependence of the reciprocal of the S1 and WL∞ were determined using an Arrhenius equation. The activation energy for water and oil absorption for gum arabic was 21.98 and 39.57 kJ mol−1 , compared to that of mesquite gum having values of 15.79 and 46.16 kJ mol−1 , respectively. A second order kinetic model was obtained for water and oil absorption for both gums. 相似文献
90.
《稀有金属材料与工程》2004,21(6):19-21
采用步进轧制工艺制备了Ti-6-22-22S合金Ф50mm棒材,对加工、热处理、组织与性能的关系进行了分析。结果表明:在两相区上部温度960℃轧制获得细网篮组织,棒材性能较好且数据均匀;热处理后,得到双态组织,强度.塑性达到优良组合,而片层状组织强度较高,但塑性稍低。 相似文献