全文获取类型
收费全文 | 116439篇 |
免费 | 9957篇 |
国内免费 | 7265篇 |
专业分类
电工技术 | 10828篇 |
技术理论 | 4篇 |
综合类 | 8978篇 |
化学工业 | 20163篇 |
金属工艺 | 6345篇 |
机械仪表 | 8998篇 |
建筑科学 | 4604篇 |
矿业工程 | 2315篇 |
能源动力 | 3785篇 |
轻工业 | 6520篇 |
水利工程 | 1604篇 |
石油天然气 | 4880篇 |
武器工业 | 1782篇 |
无线电 | 16353篇 |
一般工业技术 | 11453篇 |
冶金工业 | 2635篇 |
原子能技术 | 1230篇 |
自动化技术 | 21184篇 |
出版年
2024年 | 194篇 |
2023年 | 1530篇 |
2022年 | 2095篇 |
2021年 | 3156篇 |
2020年 | 2983篇 |
2019年 | 2874篇 |
2018年 | 2612篇 |
2017年 | 3378篇 |
2016年 | 3733篇 |
2015年 | 3976篇 |
2014年 | 5863篇 |
2013年 | 6596篇 |
2012年 | 7268篇 |
2011年 | 8472篇 |
2010年 | 7127篇 |
2009年 | 8029篇 |
2008年 | 7632篇 |
2007年 | 8385篇 |
2006年 | 7987篇 |
2005年 | 6526篇 |
2004年 | 5636篇 |
2003年 | 5270篇 |
2002年 | 4203篇 |
2001年 | 3330篇 |
2000年 | 2872篇 |
1999年 | 2175篇 |
1998年 | 1529篇 |
1997年 | 1269篇 |
1996年 | 1221篇 |
1995年 | 1220篇 |
1994年 | 1026篇 |
1993年 | 868篇 |
1992年 | 679篇 |
1991年 | 420篇 |
1990年 | 274篇 |
1989年 | 271篇 |
1988年 | 188篇 |
1987年 | 117篇 |
1986年 | 119篇 |
1985年 | 90篇 |
1984年 | 80篇 |
1983年 | 53篇 |
1982年 | 58篇 |
1981年 | 58篇 |
1980年 | 36篇 |
1979年 | 23篇 |
1978年 | 24篇 |
1977年 | 22篇 |
1976年 | 27篇 |
1975年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
采用Ni-P复合改性HZSM-5催化剂催化木质素降解制备高附加值的单酚类化学品,探讨了催化剂种类、金属负载量、反应温度、反应时间以及溶剂种类对木质素催化降解制备酚类化合物的影响。同时采用X射线衍射仪(XRD)、比表面积和孔径分析仪(BET)、化学吸附仪(NH3-TPD)、热重分析仪(TG)以及气相色谱质谱联用仪(GC/MS)对催化剂以及液相产物进行分析表征,同时探讨其催化失活以及再生机制。结果表明:Ni、P高度分散在HZSM-5催化剂的表面,Ni的添加有效地弱化了C-C键,致使β-O-4和α-O-4发生断裂,有效地提高了木质素加氢解聚的活性,减少了焦炭的生成,但催化剂的再生水热稳定性较差,重复使用性较低。当采用甲醇为供氢试剂,在反应温度为220℃,氢气压力为2MPa,反应时间为8h,催化剂负载量为10%,NaOH为共催化剂时,其木质素的转化率为98.6%,酚类化合物的含量达到74.97%。产物以苯酚、愈创木酚和紫丁香酚为主,低温促进了紫丁香酚的产生。 相似文献
92.
In an environment where robots coexist with humans, mobile robots should be human-aware and comply with humans' behavioural norms so as to not disturb humans' personal space and activities. In this work, we propose an inverse reinforcement learning-based time-dependent A* planner for human-aware robot navigation with local vision. In this method, the planning process of time-dependent A* is regarded as a Markov decision process and the cost function of the time-dependent A* is learned using the inverse reinforcement learning via capturing humans' demonstration trajectories. With this method, a robot can plan a path that complies with humans' behaviour patterns and the robot's kinematics. When constructing feature vectors of the cost function, considering the local vision characteristics, we propose a visual coverage feature for enabling robots to learn from how humans move in a limited visual field. The effectiveness of the proposed method has been validated by experiments in real-world scenarios: using this approach robots can effectively mimic human motion patterns when avoiding pedestrians; furthermore, in a limited visual field, robots can learn to choose a path that enables them to have the larger visual coverage which shows a better navigation performance. 相似文献
93.
94.
Sawarot Phetsuk Robert Molloy Kanarat Nalampang Puttinan Meepowpan Paul D Topham Brian J Tighe Winita Punyodom 《Polymer International》2020,69(3):248-256
Understanding the underlying role of microstructural design in polymers allows for the manipulation and control of properties for a wide range of specific applications. As such, this work focuses on the study of microstructure–property relationships in l‐ lactide/?‐caprolactone (LL/CL) copolymers. One‐step and two‐step bulk ring‐opening polymerization (ROP) procedures were employed to synthesize LL/CL copolymers of various compositions and chain microstructures. In the one‐step procedure, LL and CL were simultaneously copolymerized to yield P(LL‐stat‐CL) statistical copolymers. In the two‐step procedure, poly(l‐ lactide) (PLL) and poly(?‐caprolactone) (PCL) prepolymers were synthesized in the first step before CL and LL respectively were added in the second step to yield P[LL‐b‐(CL‐stat‐LL)‐b‐LL] and P[CL‐b‐(LL‐stat‐CL)‐b‐CL] block copolymers as the final products. The findings reveal that, in addition to the copolymerization procedure employed, the length and type of the prepolymer play important roles in determining the chain microstructure and thereby the overall properties of the final copolymer. Moreover, control over the degree of crystallinity and the type of crystalline domains, which is controlled during the polymer chemistry process, heavily influences the physical and mechanical properties of the final polymer. In summary, this work describes an interesting approach to the microstructural design of biodegradable copolymers of LL and CL for potential use in biomedical applications. © 2019 Society of Chemical Industry 相似文献
95.
不同含量低污染水对人工湿地中细菌的影响研究 总被引:1,自引:0,他引:1
探究水平流人工湿地(HFCW)系统处理低污染水过程中,相同COD/ρ(TN)下不同碳氮含量对细菌群落结构的影响。结果表明,进水为较高碳氮含量的HFCW(HF1)和进水为较低碳氮含量的HFCW(HF2)对COD和TN的去除效率具有一定的差异,HF1和HF2对COD的去除效率分别为48.26%和28.89%,对TN的去除率分别为79.06%和81.87%。HF1中细菌的丰富度和多样性均高于HF2,HF1中富集的优势细菌为Chloroflexaceae、Comamonadaceae和Rhodocyclaceae,均具有异养反硝化功能,HF2中富集的优势细菌为Xanthomonadaceae和Rhodocyclaceae,其中Xanthomonadaceae具有自养反硝化功能。COD、NH4^+-N和NO3^--N对HF1中细菌群落的影响大于对HF2中细菌群落的影响,HF1中COD对细菌群落的影响大于NH4^+-N和NO3^--N。 相似文献
96.
采用酸处理方法对CoPd/TiO2催化剂进行改性,并将酸改性催化剂用于温和条件下CH4-CO2梯阶转化直接合成C2含氧化合物(乙酸和乙醇)的反应。在150~300℃考察了浸酸方式和不同种类酸处理对催化剂活性和选择性的影响。采用X射线衍射(XRD)、X射线光电子能谱(XPS)、NH3程序升温脱附(NH3-TPD)和N2吸附对催化剂进行了表征。结果表明,酸改性明显提高了CoPd/TiO2上C2含氧化合物的生成速率和选择性。浸酸方式对催化剂性能和结构有显著影响,先用酸浸渍载体然后再浸渍活性金属所得催化剂具有更高的活性。在H3PO4、HNO3和HCl中,H3PO4浸渍的催化剂活性最佳,在150℃时C2含氧化合物(乙酸和乙醇)的生成速率为3365 μg/(g·h),选择性达到91%。 相似文献
97.
Meiling He Yinzi Cheng Linli Shen Huiling Zhang Chenyang Shen Weidong Xiang Xiaojuan Liang 《Journal of the American Ceramic Society》2019,102(3):1090-1100
CsPbX3 (X = Cl, Br, I) perovskite quantum dots (QDs) represent bright and tunable photoluminescence, it is regrettable that the air instability and poor water resistant properties prevent their application in optoelectronic devices. At the same time, the toxicity of lead is also a major factor restricting its development. As a consequence, we demonstrate the partial replacement of Pb with Mn through conventional melt-quenching and heat-treatment method preparation of Mn-doped CsPb(Cl/Br)3 QD glass. Mn-doped CsPb(Cl/Br)3 QD glass exhibits high luminescent intensity like QDs. It is important that Mn-doped CsPb(Cl/Br)3 QD glass with Dual-Color maintained the same lattice structure like Mn-doped CsPb(Cl/Br)3 QDs, and highly homogeneous spectral characteristics of Mn luminescence. The intensity and position of this Mn-related emission are also tunable by altering the experimental parameters, such as the Pb-to-Mn feed ratio, annealing temperature. More importantly, the as-prepared orange Mn-doped CsPb(Cl/Br)3 QD glass was employed to fabricate white LEDs combined with a commercial Ce3+:Y3Al5O12 phosphor-in-glass (Ce-PiG) on top of a InGaN blue chip. And the constructed WLEDs generate a warm white with an optimal luminous efficacy (LE) of 67.00 lm/W, a high CRI of 81.4, and a low CCT of 4902 K. 相似文献
98.
通过制备不同晶相结构〔单斜相(m-ZrO_2)、四方相(t-ZrO_2)和无定型(a-ZrO_2)〕ZrO_2载体,再通过沉积沉淀法制得Cu/m-ZrO_2、Cu/t-ZrO_2和Cu/a-ZrO_2催化剂,分别用于催化二乙醇胺脱氢合成亚氨基二乙酸反应。采用XRD、氮气物理吸附脱附、XPS、H_2-TPR、CO_2-TPD对催化剂的结构进行了表征。结果表明,Cu/m-ZrO_2催化剂界面更加有利于Cu~+/Cu~0稳定存在,具有更多的碱性位点,且抗氧化性较好。在二乙醇胺脱氢反应中,Cu/m-ZrO_2催化剂性能最好,反应时间为2.5 h,亚氨基二乙酸收率为97.64%。 相似文献
99.
Fateme Marandi 《国际生产研究杂志》2019,57(3):722-748
This paper introduces a new integrated multi-factory production and distribution scheduling problem in supply chain management. This supply chain consists of a number of factories joined together in a network configuration. The factories produce intermediate or finished products and supply them to other factories or to end customers that are distributed in various geographical zones. The problem consists of finding a production schedule together with a vehicle routing solution simultaneously to minimise the sum of tardiness cost and transportation cost. A mixed-integer programming model is developed to tackle the small-sized problems using CPLEX, optimally. Due to the NP-hardness, to deal with medium- and large-sized instances, this paper develops a novel Improved Imperialist Competitive Algorithm (IICA) employing a local search based on simulated annealing algorithm. Performance of the proposed IICA is compared with the optimal solution and also with four variants of population-based metaheuristics: Imperialist Competitive Algorithm, Genetic Algorithm, Particle Swarm Optimisation (PSO), and Improved PSO. Based on the computational results, it is statistically shown that quality of the IICA’s solutions is the same as optimal ones solving small problems. It also outperforms other algorithms in finding near-optimal solutions dealing with medium and large instances in a reasonably short running time. 相似文献
100.
Wei Zhou Qun Li Yi‐fan Zhu Hua He 《International Journal of Satellite Communications and Networking》2019,37(6):561-570
This study is extended to construct the network model, the node model, and the link model of complex communication network for satellite navigation system (CCN‐SNS) based on the hierarchical architecture. Firstly, a method called snapshots was proposed to describe the dynamic topology for CCN‐SNS; secondly, another method was put forward to model the different nodes of the CCN‐SNS; thirdly, the different links between every two different nodes were modeled. Therefore, based on the OPNET tools, a simulation for the CCN‐SNS, which contains the models that proposed earlier used to analyze the navigation accuracy and network transmission performance, was performed. 相似文献