首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   46420篇
  免费   3849篇
  国内免费   2087篇
电工技术   2402篇
综合类   3133篇
化学工业   7734篇
金属工艺   2414篇
机械仪表   2720篇
建筑科学   4018篇
矿业工程   997篇
能源动力   1461篇
轻工业   2893篇
水利工程   747篇
石油天然气   2453篇
武器工业   407篇
无线电   5760篇
一般工业技术   5668篇
冶金工业   2365篇
原子能技术   541篇
自动化技术   6643篇
  2024年   177篇
  2023年   620篇
  2022年   1119篇
  2021年   1550篇
  2020年   1197篇
  2019年   1075篇
  2018年   1157篇
  2017年   1342篇
  2016年   1234篇
  2015年   1641篇
  2014年   2063篇
  2013年   2601篇
  2012年   2753篇
  2011年   2976篇
  2010年   2653篇
  2009年   2592篇
  2008年   2588篇
  2007年   2528篇
  2006年   2520篇
  2005年   2203篇
  2004年   1708篇
  2003年   1744篇
  2002年   1992篇
  2001年   1617篇
  2000年   1280篇
  1999年   1214篇
  1998年   1060篇
  1997年   889篇
  1996年   861篇
  1995年   700篇
  1994年   551篇
  1993年   496篇
  1992年   336篇
  1991年   256篇
  1990年   253篇
  1989年   167篇
  1988年   144篇
  1987年   99篇
  1986年   84篇
  1985年   59篇
  1984年   50篇
  1983年   36篇
  1982年   34篇
  1981年   22篇
  1980年   22篇
  1979年   14篇
  1977年   10篇
  1976年   12篇
  1973年   9篇
  1970年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Malignant melanoma is a highly aggressive tumor resistant to chemotherapy. Therefore, the development of new highly effective therapeutic agents for the treatment of malignant melanoma is highly desirable. In this study, a new class of polymeric photothermal agents based on poly(N‐phenylglycine) (PNPG) suitable for use in near‐infrared (NIR) phototherapy of malignant melanoma is designed and developed. PNPG is obtained via polymerization of N‐phenylglycine (NPG). Carboxylate functionality of NPG allows building multifunctional systems using covalent bonding. This approach avoids complicated issues typically associated with preparation of polymeric photothermal agents. Moreover, PNPG skeleton exhibits pH‐responsive NIR absorption and an ability to generate reactive oxygen species, which makes its derivatives attractive photothermal therapy (PTT)/photodynamic therapy (PDT) dual‐modal agents with pH‐responsive features. PNPG is modified using hyaluronic acid (HA) and polyethylene glycol diamine (PEG‐diamine) acting as the coupling agent. The resultant HA‐modified PNPG (PNPG‐PEG‐HA) shows negligible cytotoxicity and effectively targets CD44‐overexpressing cancer cells. Furthermore, the results of in vitro and in vivo experiments reveal that PNPG‐PEG‐HA selectively kills B16 cells and suppresses malignant melanoma tumor growth upon exposure to NIR light (808 nm), indicating that PNPG‐PEG‐HA can serve as a very promising nanoplatform for targeted dual‐modality PTT/PDT of melanoma.  相似文献   
982.
983.
In this paper, a modified teaching–learning-based optimisation (mTLBO) algorithm is proposed to solve the re-entrant hybrid flowshop scheduling problem (RHFSP) with the makespan and the total tardiness criteria. Based on the simple job-based representation, a novel decoding method named equivalent due date-based permutation schedule is proposed to transfer an individual to a feasible schedule. At each generation, a number of superior individuals are selected as the teachers by the Pareto-based ranking phase. To enhance the exploitation ability in the promising area, the insertion-based local search is embedded in the search framework as the training phase for the TLBO. Due to the characteristics of the permutation-based discrete optimisation, the linear order crossover operator and the swap operator are adopted to imitate the interactions among the individuals in both the teaching phase and the learning phase. To store the non-dominated solutions explored during the search process, an external archive is used and updated when necessary. The influence of the parameter setting on the mTLBO in solving the RHFSP is investigated, and numerical tests with some benchmarking instances are carried out. The comparative results show that the proposed mTLBO outperforms the existing algorithms significantly.  相似文献   
984.
In this paper, we consider quality improvement efforts coordination in a two-stage decentralised supply chain with a partial cost allocation contract. The supply chain consists of one supplier and one manufacturer, both of which produce defective products. Two kinds of failure cost occur within the supply chain: internal and external. The supplier and the manufacturer determine their individual quality levels to maximise their own profits. We propose a partial cost allocation contract, under which the external failure cost is allocated between the manufacturer and the supplier at different rates based on information derived from failure root cause analysis. If the quality levels of the supplier and the manufacturer are observable, we show that the partial cost allocation contract coordinates the supply chain, provided that the failure root cause analysis does not erroneously identify the manufacturer’s fault as the supplier’s, and the supplier does not take responsibility for the manufacture’s fault. In the single moral hazard model, where only the quality level of the supplier is unobservable, the optimal share rates require the supplier to take some responsibility for the manufacture’s fault. However, in the double moral hazard model, where quality levels of the supplier and the manufacturer are unobservable to each other, the optimal share rates require the supplier not to take responsibility for the manufacturer’s fault. It is noted that the root cause analysis conducted by the manufacturer may have its disadvantage in attributing the fault to the supplier when both sides are at fault. We also propose a contract based on the dual root cause analysis to reduce the supplier’s penalty cost. Numerical results illustrate that the partial cost allocation contract satisfies the fairness criterion compared with the traditional cost allocation contract.  相似文献   
985.
986.
987.
988.
This paper presents a reliability analysis method on repairable system with standby structure based on goal oriented (GO) methodology. Firstly, a new combination of GO operator, which is composed of a new logical GO operator named Type 18A operator and a new auxiliary GO operator named Type 20 operator, is created to represent standby mode. The availability formula of standby equipment with translation exception is deduced based on Markov process theory. Then, the application method of combination of GO operator for standby mode and the analysis process of repairable system with standby structure based on GO method are proposed. Thirdly, this new combination of GO operator is applied in availability analysis of the hydraulic oil supply system of power‐shift steering transmission. Finally, the results obtained by the new GO method are compared with the results of fault tree analysis, Monte Carlo simulation, GO methods using Type 2 operator and Type 18 operator to represent the standby mode, respectively. And the comparison results show that this new GO method is applicable and reasonable for reliability analysis of repairable system with standby structure. All in all, this paper provides guidance for reliability analysis of repairable systems with standby structure. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
989.
Organic afterglow materials, developed recently by breaking through the difficulties in modulating ultrafast‐decayed excited states, exhibit ultralong‐lived emission for persistent luminescence with lifetimes of several orders of magnitude longer than traditional fluorescent and phosphorescent emissions at room temperature. Their exceptional properties, namely ultralong luminescent lifetime, large Stokes shifts, facile excited state transformation, and environmentally sensitive emission, have led to a diverse range of advanced optoelectronic applications. Here, the organic afterglow is reviewed from the perspective of fundamental concepts on both phenomenon and mechanism, examining the technical challenges in relation to excited state tuning and lifetime elongation. In particular, the advances in material design strategies that afford a large variety of organic afterglow materials for a broad utility in optoelectronics including lighting and displays, anti‐counterfeiting, optical recording, chemical sensors and bio‐imaging are highlighted.  相似文献   
990.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号