全文获取类型
收费全文 | 398140篇 |
免费 | 34188篇 |
国内免费 | 24145篇 |
专业分类
电工技术 | 59895篇 |
技术理论 | 28篇 |
综合类 | 40460篇 |
化学工业 | 29527篇 |
金属工艺 | 16243篇 |
机械仪表 | 32231篇 |
建筑科学 | 35469篇 |
矿业工程 | 15097篇 |
能源动力 | 15467篇 |
轻工业 | 10757篇 |
水利工程 | 11458篇 |
石油天然气 | 13029篇 |
武器工业 | 6384篇 |
无线电 | 35730篇 |
一般工业技术 | 24643篇 |
冶金工业 | 14926篇 |
原子能技术 | 3832篇 |
自动化技术 | 91297篇 |
出版年
2024年 | 1560篇 |
2023年 | 4361篇 |
2022年 | 7665篇 |
2021年 | 9683篇 |
2020年 | 10833篇 |
2019年 | 8419篇 |
2018年 | 7669篇 |
2017年 | 10761篇 |
2016年 | 12125篇 |
2015年 | 13700篇 |
2014年 | 25416篇 |
2013年 | 22516篇 |
2012年 | 28878篇 |
2011年 | 30837篇 |
2010年 | 23286篇 |
2009年 | 23703篇 |
2008年 | 23708篇 |
2007年 | 29699篇 |
2006年 | 26841篇 |
2005年 | 23457篇 |
2004年 | 19464篇 |
2003年 | 17289篇 |
2002年 | 13702篇 |
2001年 | 11442篇 |
2000年 | 9646篇 |
1999年 | 7732篇 |
1998年 | 5948篇 |
1997年 | 5100篇 |
1996年 | 4287篇 |
1995年 | 3543篇 |
1994年 | 2928篇 |
1993年 | 2096篇 |
1992年 | 1768篇 |
1991年 | 1340篇 |
1990年 | 1068篇 |
1989年 | 907篇 |
1988年 | 655篇 |
1987年 | 390篇 |
1986年 | 273篇 |
1985年 | 284篇 |
1984年 | 293篇 |
1983年 | 240篇 |
1982年 | 215篇 |
1981年 | 146篇 |
1980年 | 109篇 |
1979年 | 96篇 |
1978年 | 71篇 |
1977年 | 68篇 |
1976年 | 29篇 |
1959年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
The effects of parameter uncertainty on optimal policy have been a matter of interest for academics, and even for some policymakers,
for a long time. Two lines of literature have developed analytical results on this matter. The first line uses static models
and the second dynamic models. In this dynamic line most of the results are confined to models with a single state and a single
control variable.
In this paper we want to encourage the analysis of more general dynamic cases. To do so, the results in the dynamic line are
extended from one-state and one-control finite horizon models to models with a pair of control variables. We then discuss
some of the hurdles which must be surmounted for the results to be made more general and suggests some lines for further research.
JEL classification: C61; E61 相似文献
32.
33.
34.
针对有线电视系统工程建设的特点,依照《招标投标法》的规定和程序,对有线电视系统工程招标的种类、招标方式、招标工程必备的条件、标底的编制及审定、开标、评标和中标的原则进行详细介绍,对招标文件的编制进行具体说明。 相似文献
35.
人工智能的原理及应用 总被引:7,自引:0,他引:7
介绍了人工智能的发展,并对改进的神经网络专家系统的优越性做了介绍,指出了神经网络专家系统广阔的应用前景及实现。 相似文献
37.
38.
实验室质量体系的建立与运行 总被引:2,自引:0,他引:2
详细论述了质量和质量体系的基本概念、建立质量体系的必要性、质量体系的构成和建立过程、质量体系文件的编制、质量体系的运行和持续改进以及中国实验室国家认可委员会的有关政策。 相似文献
39.
The problem of operating freeze drying of pharmaceutical products in vials placed in trays of a freeze dryer to remove free water (in frozen state) at a minimum time was formulated as an optimal control problem. Two different types of freeze dryer designs were considered. In type I freeze dryer design, upper and lower plate temperatures were controlled together, while in type II freeze dryer design, upper and lower plate temperatures were controlled independently. The heat input to the material being dried and the drying chamber pressure were considered as control variables. Constraints were placed on the system state variables by the melting and scorch temperatures during primary drying stage. Necessary conditions of optimality for the primary drying stage of freeze drying process in vials are derived and presented. Furthermore, an approach for constructing the optimal control policies that would minimize the drying time for the primary drying stage was given. In order to analyze optimal control policy for the primary drying stage of the freeze-drying process in vials, a rigorous multi-dimensional unsteady state mathematical model was used. The theoretical approach presented in this work was applied in the freeze drying of skim milk. Significant reductions in the drying times of primary drying stage of freeze drying process in vials were obtained, as compared to the drying times obtained from conventional operational policies. 相似文献
40.
Scheduling Algorithms for Packet-Oriented MAC Protocols in Wireless Multimedia Systems 总被引:1,自引:1,他引:0
Romano Fantacci Giovanni Giambene Francesco Petiti 《Wireless Personal Communications》2003,24(3):363-388
Future generation wireless multimediacommunications will require efficient Medium AccessControl (MAC) protocols able to guarantee suitable Qualityof Service (QoS) levels for different traffic classes whileachieving a high utilization of radio resources. This paperproposes a new scheduling technique to be adopted at the MAClevel in wireless access systems, named Dynamic Scheduling-Time DivisionDuplexing (DS-TDD), that efficiently managesvideo, voice, Web and background traffics. A theoretical approachis proposed in this paper to evaluate the DS-TDD performance withvoice and Web traffics. Simulation results have permitted tohighlight the following promising characteristics of the DS-TDDscheme: (i) a high capacity of real-time traffics isattained with a QoS insensitive to Web and background trafficloads; (ii) a high throughput can be guaranteed whilepreserving the QoS levels of the different traffic classes;(iii) heavier downlink traffic loads do not modify the QoSof uplink traffics. Finally, extensive comparisons with differentscheduling schemes proposed in the literature have permitted tohighlight the better performanceof DS-TDD. 相似文献