全文获取类型
收费全文 | 241214篇 |
免费 | 18474篇 |
国内免费 | 9891篇 |
专业分类
电工技术 | 13213篇 |
技术理论 | 24篇 |
综合类 | 15081篇 |
化学工业 | 40623篇 |
金属工艺 | 13757篇 |
机械仪表 | 15243篇 |
建筑科学 | 18715篇 |
矿业工程 | 7861篇 |
能源动力 | 6829篇 |
轻工业 | 14325篇 |
水利工程 | 3772篇 |
石油天然气 | 17217篇 |
武器工业 | 1725篇 |
无线电 | 26502篇 |
一般工业技术 | 28556篇 |
冶金工业 | 13397篇 |
原子能技术 | 2507篇 |
自动化技术 | 30232篇 |
出版年
2024年 | 1066篇 |
2023年 | 4005篇 |
2022年 | 6814篇 |
2021年 | 9553篇 |
2020年 | 7450篇 |
2019年 | 6293篇 |
2018年 | 7059篇 |
2017年 | 7923篇 |
2016年 | 7085篇 |
2015年 | 9343篇 |
2014年 | 11868篇 |
2013年 | 13951篇 |
2012年 | 14934篇 |
2011年 | 16287篇 |
2010年 | 14176篇 |
2009年 | 13404篇 |
2008年 | 13054篇 |
2007年 | 12566篇 |
2006年 | 13092篇 |
2005年 | 11390篇 |
2004年 | 7701篇 |
2003年 | 6587篇 |
2002年 | 5857篇 |
2001年 | 5236篇 |
2000年 | 5808篇 |
1999年 | 6785篇 |
1998年 | 5693篇 |
1997年 | 4678篇 |
1996年 | 4394篇 |
1995年 | 3654篇 |
1994年 | 2949篇 |
1993年 | 2052篇 |
1992年 | 1610篇 |
1991年 | 1301篇 |
1990年 | 970篇 |
1989年 | 782篇 |
1988年 | 566篇 |
1987年 | 352篇 |
1986年 | 305篇 |
1985年 | 207篇 |
1984年 | 148篇 |
1983年 | 124篇 |
1982年 | 131篇 |
1981年 | 104篇 |
1980年 | 74篇 |
1979年 | 37篇 |
1978年 | 28篇 |
1977年 | 20篇 |
1976年 | 37篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
羟基烷基磺酸镀液电镀Sn—Pb合金的研究 总被引:2,自引:0,他引:2
我国自行研制生产的羟基烷基磺酸电镀Sn-Pb合金镀液已经在部分厂家投产使用.生产实践证明,该镀液能获得不同铅含量的、可焊性优良且镀层结晶细致而光亮的Sn-Pb合金镀层.本研究重点测定了该镀液的电化学性能,如阴极电流效率、分散能力及深镀能力.并对添加剂的作用进行了研究探讨. 相似文献
942.
Pengbao Lian Qiang Liu Lizhen Chen Cai Cao Jiaxiang Zhao Jianlong Wang 《中国化学工程学报》1982,28(10):2634-2639
In this paper, the solubility of 4-nitroimidazole in twelve pure solvents (toluene, benzene, 1,4-dioxane, acetonitrile, ethyl acetate, acetone, GBL, ethanol, methanol, n-butanol, DMF and NMP) were determined by using the laser monitoring system from 278.15 K to 323.15 K under 101.1 kPa, which are 0.00018-0.00070, 0.00021-0.00073, 0.00034-0.00092, 0.00038-0.00142, 0.00047-0.00120, 0.00126-0.00303, 0.00225-0.00517, 0.00310-0.00724, 0.00467-0.00982, 0.00453-0.01940, 0.01947-0.04652, and 0.04670-0.07452, respectively. At constant temperature, the mole fraction solubility of 4-nitroimidazole were increased as the following order: toluene < benzene < 1,4-dioxane < (ethyl acetate or acetonitrile) < acetone < GBL < ethanol < (methanol or nbutanol) < DMF < NMP, and the solubility of 4-nitroimidazole in (ethyl acetate, acetonitrile) and (methanol, n-butanol) had an intersection point at 297.55 K and 281.85 K, respectively. The solubility of 4-nitroimidazole could be increased with increasing temperature in twelve pure solvents. The ideal model, modified Apelblat equation, polynomial empirical equation, and λh equation were used to correlate the experimental values. The experimental solubility values were employed to calculate the standard dissolution enthalpy, standard dissolution entropy and Gibbs energy. The dissolution of 4-nitroimidazole could be an endothermic process in twelve pure solvents. The determination and fitting solubility of 4-nitroimidazole have important guiding significance for the purification and crystallization of its preparation process. 相似文献
943.
Because of the prominence of vinylidene chloride/methyl acrylate copolymers in barrier plastic packing applications, the degradation of these materials continues to be the focus of much interest. The prominent degradation process at moderate temperature (<200°C) is dehydrochlorination. This reaction is a typical radical chain process with distinct initiation, propagation, and termination phases. A principal defect structure responsible for the initiation of degradation is unsaturation along the polymer backbone. Although most stabilization packages for these polymers contain basic components to absorb hydrogen chloride as it is generated, materials sufficiently basic to abstract hydrogen chloride might actually enhance the rate of degradation by introducing double bonds into the polymer structure. That this is the case has been established by the thermogravimetric examination of the degradation of a methyl acrylate (5 mol%)/ vinylidene chloride copolymer in the presence of amines of varying base strengths. In general, the initiation rate constant, kt, for the degradation process is enhanced in the presence of amine. 相似文献
944.
1991—1992国外工程塑料进展 总被引:1,自引:0,他引:1
介绍了1991~1992年国外工程塑料研究和生产概况。论述了通用工程塑料、特种工程塑料和聚合物合金的研究开发、改性和应用方面的进展。且指出工程塑料发展趋势和特点;对复合材料技术进展作了较详尽的分析与阐述。 相似文献
945.
为制备强韧的共混材料,利用熔融接枝法研制了含有两种接技单体的新型聚丙烯接枝物,讨论了第二单体在接枝过程中的作用,并将其应用于尼龙6/聚丙烯(PA6/PP)共混体系,获得了使分散相粒径更细小、界面更模糊的增容效果。 相似文献
946.
947.
Phase transitions of canola oil sediment 总被引:3,自引:0,他引:3
H. Liu C. G. Biliaderis R. Przybylski N. A. M. Eskin 《Journal of the American Oil Chemists' Society》1993,70(5):441-448
Canola sediment was obtained from an industrial filter cake by solvent extraction. When heated in the differential scanning
calorimeter (DSC) (5–100°C), the sediment exhibited a single narrow melting peak at around 74.8°C. No solid-state polymorphic
transformation of the material could be detected over this temperature range. The X-ray powder diffraction pattern of canola
sediment resembled waxes from other sources with an orthorhombic unit cell. The phase transition behavior of canola sediment
in oil was studied by both DSC and polarizing microscopy. With increasing ratio of oil/sediment, a reduction in both melting
temperature and transition enthalpy was observed. The shape of the supercooling curve resembled that of the melting curve.
The induction time was determined by spectrophotometry and was used to calculate the interfacial free energyσ between sediment and oil; σ=4.71 erg/cm2. The effect of temperature and sediment concentration on the clouding time of canola oil was studied; the clouding time was
the shortest at 5°C. 相似文献
948.
949.
This paper is concerned with the state estimation problem for the complex networked systems with randomly occurring nonlinearities and randomly missing measurements. The nonlinearities are included to describe the phenomena of nonlinear disturbances which exist in the network and may occur in a probabilistic way. Considering the fact that probabilistic data missing may occur in the process of information transmission, we introduce the randomly data missing into the sensor measurements. The aim of this paper is to design a state estimator to estimate the true states of the considered complex network through the available output measurements. By using a Lyapunov functional and some stochastic analysis techniques, sufficient criteria are obtained in the form of linear matrix inequalities under which the estimation error dynamics is globally asymptotically stable in the mean square. Furthermore, the state estimator gain is also obtained. Finally, a numerical example is employed to illustrate the effectiveness of the proposed state estimation conditions. 相似文献
950.
Yulian Jiang Jianchang Liu Shubin Tan Pingsong Ming 《International journal of systems science》2014,45(9):1869-1879
In this paper, a robust consensus algorithm is developed and sufficient conditions for convergence to consensus are proposed for a multi-agent system (MAS) with exogenous disturbances subject to partial information. By utilizing H∞ robust control, differential game theory and a design-based approach, the consensus problem of the MAS with exogenous bounded interference is resolved and the disturbances are restrained, simultaneously. Attention is focused on designing an H∞ robust controller (the robust consensus algorithm) based on minimisation of our proposed rational and individual cost functions according to goals of the MAS. Furthermore, sufficient conditions for convergence of the robust consensus algorithm are given. An example is employed to demonstrate that our results are effective and more capable to restrain exogenous disturbances than the existing literature. 相似文献