全文获取类型
收费全文 | 41926篇 |
免费 | 5408篇 |
国内免费 | 2920篇 |
专业分类
电工技术 | 3993篇 |
技术理论 | 1篇 |
综合类 | 3149篇 |
化学工业 | 10677篇 |
金属工艺 | 4501篇 |
机械仪表 | 1616篇 |
建筑科学 | 838篇 |
矿业工程 | 601篇 |
能源动力 | 1539篇 |
轻工业 | 3094篇 |
水利工程 | 295篇 |
石油天然气 | 1930篇 |
武器工业 | 396篇 |
无线电 | 6538篇 |
一般工业技术 | 5875篇 |
冶金工业 | 2446篇 |
原子能技术 | 481篇 |
自动化技术 | 2284篇 |
出版年
2024年 | 209篇 |
2023年 | 829篇 |
2022年 | 1157篇 |
2021年 | 1457篇 |
2020年 | 1580篇 |
2019年 | 1512篇 |
2018年 | 1397篇 |
2017年 | 1672篇 |
2016年 | 1651篇 |
2015年 | 1658篇 |
2014年 | 2283篇 |
2013年 | 2611篇 |
2012年 | 2784篇 |
2011年 | 2750篇 |
2010年 | 1949篇 |
2009年 | 2230篇 |
2008年 | 2069篇 |
2007年 | 2559篇 |
2006年 | 2441篇 |
2005年 | 2037篇 |
2004年 | 1681篇 |
2003年 | 1687篇 |
2002年 | 1422篇 |
2001年 | 1316篇 |
2000年 | 1207篇 |
1999年 | 921篇 |
1998年 | 838篇 |
1997年 | 747篇 |
1996年 | 597篇 |
1995年 | 567篇 |
1994年 | 500篇 |
1993年 | 344篇 |
1992年 | 357篇 |
1991年 | 263篇 |
1990年 | 230篇 |
1989年 | 225篇 |
1988年 | 107篇 |
1987年 | 69篇 |
1986年 | 58篇 |
1985年 | 52篇 |
1984年 | 54篇 |
1983年 | 35篇 |
1982年 | 37篇 |
1981年 | 25篇 |
1980年 | 28篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1975年 | 7篇 |
1951年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
To confirm the reliability of the theory of phase equibria of multicomponent polymer 1/multicomponent polymer 2 systems (i.e. quasi-binary systems) and the method of computer experiment based on this theory (Brit. Polym. J., 23 (1990)285; 23 (1990)299; Polym. Int., 29 (1992)219), could point curves (CPC), two-phase volume ratios ( R ) and critical solution points (CSP) have been determined experimentally for the quasi-binary mixtures of poly(ethylene oxide) (M¯w = 647, M¯w/M¯n = 1.15; M¯w and M¯n, the weight-average and numberaverage molecular weights, respectively) and poly(propylene oxide) (M¯w = 2028, M¯w/M¯n = 1.08; and Mw = 2987, Mw/Mn = 1.13). The hydroxyl end groups of both polymers were methoxylated in advance by the Cooper & Booth method (Polymer, 18 (1977)164). The thermodynamic interaction parameter between both polymers, χ12, and the concentration dependence parameters for the above quasi-binary systems were determined by the method proposed in a previous paper (Brit. Polym. J., 23 (1990)299). CPC, R and CSP values calculated on the basis of the theory are in good agreement with the values determined experimentally. 相似文献
102.
103.
104.
本文综述了氟化物玻璃中的分相研究。在前人研究基础上应用透射电镜,X射线能谱,电子能量损失谱及X射线衍射,差热分析等研究了锆钡镧铝氟化物玻璃中的液-液分相,发现此种现象普遍存在于该类玻璃之中。对玻璃成分与分相形貌及微观结构之间的关系、对析出晶相种类及分相与析晶的相互影响进行了研究。提出欲降低氟化物玻璃的光损耗,分相与析晶一样是不容忽视的因素。 相似文献
105.
不用专门相移装置的三维面形测量 总被引:1,自引:1,他引:0
提出一种不需要专用相移装置实现相移,主要利用数字图像处理技术实现三维面形测量的方法,研究结果表明,用原干涉图像及1幅以上的移值条纹图主可能实现物体三维面形的测量。 相似文献
106.
B. Wilthan G. Pottlacher 《稀有金属(英文版)》2006,25(5):592-596
1. Introduction Metal working industry needs accurate thermo- physical properties of liquid metals and alloys as input data for different simulation routines to im- prove the performance of their products. Within this paper we continue the systematic investigation of the dependence of emissivity of binary alloys on the relative concentration of the constituent elements (for a previous paper see [1]). 2. Experimental method A fast ohmic pulse heating technique is applied to heat metallic wire-s… 相似文献
107.
A series of new o‐phenylenediamine (OPD)/o‐phenetidine (PHT) copolymers with partly phenazine‐like structures has been successfully synthesized at three polymerization temperatures by chemically oxidative polymerization in four different polymerization media. The molecular structures and properties of the resulting OPD/PHT polymers were investigated by IR, UV–vis and high‐resolution 1H NMR spectroscopies, and DSC, in order to ascertain the effect of reaction temperature, comonomer ratio and acid medium. The copolymerization mechanism of OPD with PHT monomers has been proposed. It is found that the statistical OPD/PHT copolymer obtained at a temperature of 118 °C has a higher degree of polymerization than that obtained at 12–17 °C. The OPD content in the copolymers calculated from NMR spectroscopic analysis is higher than that in the feed OPD content, whereas the OPD content calculated from element analysis is slightly lower than the feed OPD content. It can be predicted that denitrogenation takes place in the OPD units during the polymerization process at OPD/PHT molar ratios of 90/10 and 100/0. These OPD/PHT copolymers exhibit a much better solubility than the OPD homopolymer, hence suggesting an incorporation of PHT units into the phenazine structure of the homopolymer. The thermal behavior of the copolymers was also studied. Copyright © 2004 Society of Chemical Industry 相似文献
108.
Low carbon steel was oxidized over the temperature range 1000‐1250°C in O2‐CO2‐H2O‐N2, O2‐H2O‐N2, and O2‐CO2‐N2 gas mixtures. Oxidation times were 12‐120 min. and the scales were 50‐2000 μm thick. The variations of these parameters were chosen to elucidate the phase composition of oxide scales under conditions similar to those of reheating furnaces in hot strip mills, using either thin slab casting or conventional casting and rolling technology. Two types of scales have been observed which are influenced by the furnace atmosphere, oxidation time, and temperature. The first type is a crystalline scale with an irregular outer surface, composed mostly of wustite (FeO), and a negligible amount of magnetite (Fe3O4). The second type is the classical three‐layer scale, composed of wustite (FeO), magnetite (Fe3O4), and hematite (Fe2O3). In general, the experiments showed that an increase in oxidation time decreased the percentage of wustite while the percentages of magnetite and hematite increased. A rise in oxygen concentration in the gas mixture increased the percentages of magnetite and hematite, confirming earlier experimental findings. In water vapour‐free atmospheres O2‐CO2‐N2, the oxide scales had a low percentage of wustite, and high percentage of magnetite and hematite. Carbon dioxide showed a small influence at 1100°C, and a negligible one at 1250°C. 相似文献
109.
The free energies of mixing of two networks in the interpenetrating polymer network based on crosslinked polyurethane and poly(ester acrylate) have been determined by the vapour sorption method. It was established that the constituent networks in the IPN are not miscible. The introduction of fillers of different chemical nature increases the compatibility. The thermodynamic affinity of the fillers to the individual networks and IPN was estimated. It was established that when the free energy of interaction of one or both components of the IPN with the filler is negative, reinforcement leads to the formation of a compatible and equilibrium system. For fillers having no affinity to the polymers, compatibilization is observed, which is connected with slowing down of phase separation in the system in the presence of filler. 相似文献
110.
Undoped and Te-doped gallium antimonide (GaSb) layers have been grown on GaSb bulk substrates by the liquid phase epitaxial
technique from Ga-rich and Sb-rich melts. The nucleation morphology of the grown layers has been studied as a function of
growth temperature and substrate orientation. MOS structures have been fabricated on the epilayers to evaluate the native
defect content in the grown layers from theC-V characteristics. Layers grown from antimony rich melts always exhibitp-type conductivity. In contrast, a type conversion fromp- ton- was observed in layers grown from gallium rich melts below 400 C. The electron mobility of undopedn-type layers grown from Ga-rich melts and tellurium doped layers grown from Sb- and Ga-rich solutions has been evaluated.
Paper presented at the poster session of MRSI AGM VI. Kharagpur. 1995 相似文献